Anxiolytic-like Effects and Quantitative EEG Profile of Palmitone Induces Responses Like Buspirone Rather Than Diazepam as Clinical Drugs.

Anxiety is a mental disorder with a growing worldwide incidence due to the SARS-CoV-2 virus pandemic. Pharmacological therapy includes drugs such as benzodiazepines (BDZs) or azapirones like buspirone (BUSP) or analogs, which unfortunately produce severe adverse effects or no immediate response, respectively. Medicinal plants or their bioactive metabolites are a shared global alternative to treat anxiety. Palmitone is one active compound isolated from Annona species due to its tranquilizing activity. However, its influence on neural activity and possible mechanism of action are unknown. In this study, an electroencephalographic (EEG) spectral power analysis was used to corroborate its depressant activity in comparison with the anxiolytic-like effects of reference drugs such as diazepam (DZP, 1 mg/kg) and BUSP (4 mg/kg) or 8-OH-DPAT (1 mg/kg), alone or in the presence of the GABAA (picrotoxin, PTX, 1 mg/kg) or serotonin 5-HT1A receptor antagonists (WAY100634, WAY, 1 mg/kg). The anxiolytic-like activity was assayed using the behavioral response of mice employing open-field, hole-board, and plus-maze tests. EEG activity was registered in both the frontal and parietal cortex, performing a 10 min baseline and 30 min recording after the treatments. As a result, anxiety-like behavior was significantly decreased in mice administered with palmitone, DZP, BUSP, or 8-OH-DPAT. The effect of palmitone was equivalent to that produced by 5-HT1A receptor agonists but 50% less effective than DZP. The presence of PTX and WAY prevented the anxiolytic-like response of DZP and 8-OH-DPAT, respectively. Whereas only the antagonist of the 5-HT1A receptor (WAY) inhibited the palmitone effects. Palmitone and BUSP exhibited similar changes in the relative power bands after the spectral power analysis. This response was different to the changes induced by DZP. In conclusion, brain electrical activity was associated with the anxiolytic-like effects of palmitone implying a serotoninergic rather than a GABAergic mechanism of action.

Role of 5-HT1A Receptor in the Anxiolytic-Relaxant Effects of Bergamot Essential Oil in Rodent.

The essential oil obtained by the fresh fruit of Citrus bergamia Risso et Poiteau is used worldwide in aromatherapy to reduce pain, facilitate sleep induction, and/or minimize the effects of stress-induced anxiety. Preclinical pharmacological data demonstrate that bergamot essential oil (BEO) modulates specific neurotransmissions and shows an anxiolytic-relaxant effect not superimposable to that of the benzodiazepine diazepam, suggesting that neurotransmissions, other than GABAergic, could be involved. Several studies on essential oils indicate a role for serotonergic (5-HT) neurotransmission in anxiety. Interestingly, among serotonergic receptors, the 5-HT1A subtype seems to play a key role in the control of anxiety. Here, we report that modulation of the 5-HT1A receptor by selective agonist ((±)8-OH-DPAT) or antagonist (WAY-100635) may influence some of the anxiolytic-relaxant effects of BEO in Open Field and Elevated Plus Maze tests.

5-HT1A receptor-mediated activation of neuroendocrine responses and multiple protein kinase pathways in the peripubertal rat hypothalamus.

Increasing evidence suggests that multiple factors can produce effects on the immature brain that are distinct and more long-lasting than those produced in adults. The hypothalamic paraventricular nucleus (PVN) is a region integral to the hypothalamic-pituitary-adrenal axis and is affected by anxiety, depression, and drugs used to treat these disorders, yet receptor signaling mechanisms operative in hypothalamus prior to maturation remain to be elucidated. In peripubertal male rats, systemic injection of the selective serotonin 1A (5-HT1A) receptor agonist (+)8-OH-DPAT (0.2 mg/kg) markedly elevated plasma levels of oxytocin and adrenocorticotropic hormone (ACTH) at 5 and 15 min post-injection. The 5-HT1A receptor selectivity was demonstrated by the ability of the 5-HT1A receptor selective antagonist WAY100635 to completely block both oxytocin and ACTH responses at 5 min, with some recovery of the ACTH response at 15 min. At 15 min post-injection, (+)8-OH-DPAT also increased levels of phosphorylated extracellular signal-regulated kinase (pERK) and phosphorylated protein kinase B (pAkt) in the PVN. As previously observed in adults, (+)8-OH-DPAT reduced levels of pERK in hippocampus. WAY100635 also completely blocked (+)8-OH-DPAT-mediated elevations in hypothalamic pERK and pAkt and the reductions in hippocampal pERK, demonstrating 5-HT1A receptor selectivity of both kinase responses. This study provides the first demonstration of functional 5-HT1A receptor-mediated ERK and Akt signaling pathways in the immature hypothalamus, activated by a dose of (+)8-OH-DPAT that concomitantly stimulates neuroendocrine responses. This information is fundamental to identifying potential signaling pathways targeted by biased agonists in the development of safe and effective treatment strategies in children and adolescents.

The GABAergic Gudden's dorsal tegmental nucleus: A new relay for serotonergic regulation of sleep-wake behavior in the mouse.

Serotonin (5-HT) neurons are involved in wake promotion and exert a strong inhibitory influence on rapid eye movement (REM) sleep. Such effects have been ascribed, at least in part to the action of 5-HT at post-synaptic 5-HT1A receptors (5-HT1AR) in the brainstem, a major wake/REM sleep regulatory center. However, the neuroanatomical substrate through which 5-HT1AR influence sleep remains elusive. We therefore investigated whether a brainstem structure containing a high density of 5-HT1AR mRNA, the GABAergic Gudden's dorsal tegmental nucleus (DTg), may contribute to 5-HT-mediated regulatory mechanisms of sleep-wake stages. We first found that bilateral lesions of the DTg promote wake at the expense of sleep. In addition, using local microinjections into the DTg in freely moving mice, we showed that local activation of 5-HT1AR by the prototypical agonist 8-OH-DPAT enhances wake and reduces deeply REM sleep duration. The specific involvement of 5-HT1AR in the latter effects was further demonstrated by ex vivo extracellular recordings showing that the selective 5-HT1AR antagonist WAY 100635 prevented DTg neuron inhibition by 8-OH-DPAT. We next found that GABAergic neurons of the ventral DTg exclusively targets glutamatergic neurons of the lateral mammillary nucleus (LM) in the posterior hypothalamus by means of anterograde and retrograde tracing techniques using cre driver mouse lines and a modified rabies virus. Altogether, our findings strongly support the idea that 5-HT-driven enhancement of wake results from 5-HT1AR-mediated inhibition of DTg GABAergic neurons that would in turn disinhibit glutamatergic neurons in the mammillary bodies. We therefore propose a Raphe→DTg→LM pathway as a novel regulatory circuit underlying 5-HT modulation of arousal.

Estradiol suppresses ingestive response evoked by activation of 5-HT1A receptors in the lateral hypothalamus of ovariectomized rats.

The present study investigated the effects of estradiol (E2) on ingestive behavior after activation of 5-HT1A receptors in the lateral hypothalamus (LH) of female rats habituated to eat a wet mash diet. Ovariectomized rats treated with corn oil (OVX) or estradiol cypionate (OVX+E) received local injections into the LH of vehicle or an agonist of 5-HT1A receptors, 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT; at a dose of 6 nmol). To determine the involvement of these receptors in food intake, some animals were pretreated with N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane carboxamide maleate (WAY-100635, a 5-HT1A receptor full antagonist, at a dose of 0.37 nmol), followed by the injection of the agonist 8-OH-DPAT or its vehicle. The results showed that the injection of 8-OH-DPAT into the LH of OVX rats significantly increased food intake, and the duration and frequency of this behavior. The pretreatment with E2 suppressed the hyperphagic response induced by 8-OH-DPAT in OVX animals. The inhibition of 5-HT1A receptors after pretreatment with WAY-100635 blocked the hyperphagic effects evoked by 8-OH-DPAT in OVX. These results indicate that the activity of LH 5-HT1A receptors could be affected by blood E2 levels.

Chronic BMY7378 treatment alters behavioral circadian rhythms.

The mammalian circadian clock is synchronized to the day : night cycle by light. Serotonin modulates the circadian effects of light, with agonists inhibiting response to light and antagonists enhancing responses to light. A special class of serotonergic compounds, the mixed 5-HT1A agonist/antagonists, potentiates light-induced phase advances by up to 400% when administered acutely. In this study, we examine the effects of one of these mixed 5-HT1A agonist/antagonists, BMY7378, when administered chronically. Thirty adult male hamsters were administered either vehicle or BMY7378 via surgically implanted osmotic mini pumps over a period of 28 days. In a light : dark cycle, chronic BMY7378 advanced the phase angle of entrainment, prolonged the duration of the active phase and attenuated the amplitude of the wheel-running rhythm during the early night. In constant darkness, chronic treatment with BMY7378 significantly attenuated light-induced phase advances, but had no significant effect on light-induced phase delays. Non-photic phase shifts to daytime administration of a 5-HT1A/7 agonist were also attenuated by chronic BMY7378 treatment. qRT-PCR analysis revealed that chronic BMY7378 treatment upregulated mRNA for 5-HT1A and 5-HT1B receptors in the hypothalamus and downregulated mRNA for 5-HT1A and monoamine oxidase-A in the brainstem. These results highlight adaptive changes of serotonin receptors in the brain to chronic treatment with BMY7378 and link such up- and downregulation to changes in important circadian parameters. Such long-term changes to the circadian system should be considered when patients are treated chronically with drugs that alter serotonergic function.

µ-Opioid and 5-HT1A receptors in the dorsomedial hypothalamus interact for the regulation of panic-related defensive responses.

The dorsomedial hypothalamus (DMH) and the dorsal periaqueductal gray (DPAG) have been implicated in the genesis and regulation of panic-related defensive behaviors, such as escape. Previous results point to an interaction between serotonergic and opioidergic systems within the DPAG to inhibit escape, involving µ-opioid and 5-HT1A receptors (5-HT1AR). In the present study we explore this interaction in the DMH, using escape elicited by electrical stimulation of this area as a panic attack index. The obtained results show that intra-DMH administration of the non-selective opioid receptor antagonist naloxone (0.5 nmol) prevented the panicolytic-like effect of a local injection of serotonin (20 nmol). Pretreatment with the selective µ-opioid receptor (MOR) antagonist CTOP (1 nmol) blocked the panicolytic-like effect of the 5-HT1AR agonist 8-OHDPAT (8 nmol). Intra-DMH injection of the selective MOR agonist DAMGO (0.3 nmol) also inhibited escape behavior, and a previous injection of the 5-HT1AR antagonist WAY-100635 (0.37 nmol) counteracted this panicolytic-like effect. These results offer the first evidence that serotonergic and opioidergic systems work together within the DMH to inhibit panic-like behavior through an interaction between µ-opioid and 5-HT1A receptors, as previously described in the DPAG.

Activation of 5-HT1A receptors in the rat dorsomedial hypothalamus inhibits stress-induced activation of the hypothalamic-pituitary-adrenal axis.

Acute activation of the hypothalamic-pituitary-adrenal (HPA) axis, leading to the release of corticosteroid hormones into the circulation, is an adaptive response to perceived threats. Persistent activation of the HPA axis can lead to impaired physiological or behavioral function with maladaptive consequences. Thus, efficient control and termination of stress responses is essential for well-being. However, inhibitory control mechanisms governing the HPA axis are poorly understood. Previous studies suggest that serotonergic systems, acting within the medial hypothalamus, play an important role in inhibitory control of stress-induced HPA axis activity. To test this hypothesis, we surgically implanted chronic jugular cannulae in adult male rats and conducted bilateral microinjection of vehicle or the 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino) tetralin hydrobromide (8-OH-DPAT; 8 nmol, 0.2 µL, 0.1 µL/min, per side) into the dorsomedial hypothalamus (DMH) immediately prior to a 40 min period of restraint stress. Repeated blood sampling was conducted using an automated blood sampling system and plasma corticosterone concentrations were determined using enzyme-linked immunosorbent assay. Bilateral intra-DMH microinjections of 8-OH-DPAT suppressed stress-induced increases in plasma corticosterone within 10 min of the onset of handling prior to restraint and, as measured by area-under-the-curve analysis of plasma corticosterone concentrations, during the 40 min period of restraint. These data support an inhibitory role for serotonergic systems, acting within the DMH, on stress-induced activation of the HPA axis. Lay summary: Inhibitory control of the hypothalamic-pituitary-adrenal (HPA) stress hormone response is important for well-being. One neurochemical implicated in inhibitory control of the HPA axis is serotonin. In this study we show that activation of serotonin receptors, specifically inhibitory 5-HT1A receptors in the dorsomedial hypothalamus, is sufficient to inhibit stress-induced HPA axis activity in rats.

Serotonin and arginine-vasopressin mediate sex differences in the regulation of dominance and aggression by the social brain.

There are profound sex differences in the incidence of many psychiatric disorders. Although these disorders are frequently linked to social stress and to deficits in social engagement, little is known about sex differences in the neural mechanisms that underlie these phenomena. Phenotypes characterized by dominance, competitive aggression, and active coping strategies appear to be more resilient to psychiatric disorders such as posttraumatic stress disorder (PTSD) compared with those characterized by subordinate status and the lack of aggressiveness. Here, we report that serotonin (5-HT) and arginine-vasopressin (AVP) act in opposite ways in the hypothalamus to regulate dominance and aggression in females and males. Hypothalamic injection of a 5-HT1a agonist stimulated aggression in female hamsters and inhibited aggression in males, whereas injection of AVP inhibited aggression in females and stimulated aggression in males. Striking sex differences were also identified in the neural mechanisms regulating dominance. Acquisition of dominance was associated with activation of 5-HT neurons within the dorsal raphe in females and activation of hypothalamic AVP neurons in males. These data strongly indicate that there are fundamental sex differences in the neural regulation of dominance and aggression. Further, because systemically administered fluoxetine increased aggression in females and substantially reduced aggression in males, there may be substantial gender differences in the clinical efficacy of commonly prescribed 5-HT-active drugs such as selective 5-HT reuptake inhibitors. These data suggest that the treatment of psychiatric disorders such as PTSD may be more effective with the use of 5-HT-targeted drugs in females and AVP-targeted drugs in males.

Neurotoxic Effects of 5-MeO-DIPT: A Psychoactive Tryptamine Derivative in Rats.

5-Methoxy-N,N-diisopropyltryptamine (5-MeO-DIPT, 'foxy') is one of the most popular tryptamine hallucinogens in the illicit drug market. It produces serious adverse effects, but its pharmacological profile is not well recognized. In vitro data have shown that 5-MeO-DIPT acts as a potent serotonin transporter (SERT) inhibitor and displays high affinity at serotonin 5-HT1A, 5-HT2A, and 5-HT2C receptors. In this study, using microdialysis in freely moving rats, we examined the effect of 5-MeO-DIPT on dopamine (DA), serotonin (5-HT), and glutamate release in the rat striatum, nucleus accumbens, and frontal cortex. In search of a possible neurotoxic effect of 5-MeO-DIPT, we measured DA and 5-HT tissue content in the above rat brain regions and also determined the oxidative DNA damage with the comet assay. Moreover, we tested drug-elicited head-twitch response and a forepaw treading induced by 8-OH-DPAT. 5-MeO-DIPT at doses of 5, 10, and 20 mg/kg increased extracellular DA, 5-HT, and glutamate level but the differences in the potency were found between brain regions. 5-MeO-DIPT increased 5-HT and decreased 5-HIAA tissue content which seems to result from SERT inhibition. On the other hand, a decrease in DA, DOPAC, and HVA tissue contents suggests possible adaptive changes in DA turnover or damage of DA terminals by 5-MeO-DIPT. DNA single and double-strand breaks persisted up to 60 days after the treatment, indicating marked neurotoxicity of 5-MeO-DIPT. The induction of head-twitch response and potentiation of forepaw treading induced by 8-OH-DPAT indicate that hallucinogenic activity seems to be mediated through the stimulation of 5-HT2A and 5-HT1A receptors by 5-MeO-DIPT.

Food intake inhibition in rainbow trout induced by activation of serotonin 5-HT2C receptors is associated with increases in POMC, CART and CRF mRNA abundance in hypothalamus.

In rainbow trout, the food intake inhibition induced by serotonin occurs through 5-HT2C and 5-HT1A receptors, though the mechanisms involved are still unknown. Therefore, we assessed if a direct stimulation of 5-HT2C and 5-HT1A serotonin receptors (resulting in decreased food intake in rainbow trout), affects gene expression of neuropeptides involved in the control of food intake, such as pro-opiomelanocortin (POMC), cocaine- and amphetamine-regulated transcript (CART), corticotrophin releasing factor (CRF), and agouti-related peptide (AgRP). In a first set of experiments, the injection of the 5-HT2C receptor agonists MK212 (60 µg kg(-1) icv) and WAY 161503 (1 mg kg(-1) ip), and of the 5-HT1A receptor agonist 8-OH-DPAT (1 mg kg(-1) ip and 30 µg kg(-1) icv) induced food intake inhibition. In a second set of experiments, we observed that the injection of MK212 or WAY 161503 (1 and 3 mg kg(-1)) significantly increased hypothalamic POMC mRNA abundance. CART mRNA abundance in hypothalamus was enhanced by treatment with MK212 and unaffected by WAY 161503. The administration of the 5-HT1A receptor agonist 8-OH-DPAT did not induce any significant variation in the hypothalamic POMC or CART mRNA levels. CRF mRNA abundance was only affected by MK212 that increased hypothalamic values. Finally, hypothalamic AgRP mRNA abundance was only evaluated with the agonist 5-HT2C MK212 resulting in no significant effects. The results show that the reduction in food intake mediated by 5-HT2C receptors is associated with increases in hypothalamic POMC, CART and CRF mRNA abundance.

Distribution of serotonin 5-HT1A-binding sites in the brainstem and the hypothalamus, and their roles in 5-HT-induced sleep and ingestive behaviors in rock pigeons (Columba livia).

Serotonin 1A receptors (5-HT1ARs), which are widely distributed in the mammalian brain, participate in cognitive and emotional functions. In birds, 5-HT1ARs are expressed in prosencephalic areas involved in visual and cognitive functions. Diverse evidence supports 5-HT1AR-mediated 5-HT-induced ingestive and sleep behaviors in birds. Here, we describe the distribution of 5-HT1ARs in the hypothalamus and brainstem of birds, analyze their potential roles in sleep and ingestive behaviors, and attempt to determine the involvement of auto-/hetero-5-HT1ARs in these behaviors. In 6 pigeons, the anatomical distribution of [(3)H]8-OH-DPAT binding in the rostral brainstem and hypothalamus was examined. Ingestive/sleep behaviors were recorded (1h) in 16 pigeons pretreated with MM77 (a heterosynaptic 5-HT1AR antagonist; 23 or 69 nmol) for 20 min, followed by intracerebroventricular ICV injection of 5-HT (N:8; 150 nmol), 8-OH-DPAT (DPAT, a 5-HT1A,7R agonist, 30 nmol N:8) or vehicle. 5-HT- and DPAT-induced sleep and ingestive behaviors, brainstem 5-HT neuronal density and brain 5-HT content were examined in 12 pigeons, pretreated by ICV with the 5-HT neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) or vehicle (N:6/group). The distribution of brainstem and diencephalic c-Fos immunoreactivity after ICV injection of 5-HT, DPAT or vehicle (N:5/group) into birds provided with or denied access to water is also described. 5-HT1ARs are concentrated in the brainstem 5-HTergic areas and throughout the periventricular hypothalamus, preoptic nuclei and circumventricular organs. 5-HT and DPAT produced a complex c-Fos expression pattern in the 5-HT1AR-enriched preoptic hypothalamus and the circumventricular organs, which are related to drinking and sleep regulation, but modestly affected c-Fos expression in 5-HTergic neurons. The 5-HT-induced ingestivebehaviors and the 5-HT- and DPAT-induced sleep behaviors were reduced by MM77 pretreatment. 5,7-DHT increased sleep per se, decreased tryptophan hydroxylase expression in the raphe nuclei and decreased prosencephalic 5-HT release but failed to affect 5-HT- or DPAT-induced drinking or sleep behavior. 5-HT- and DPAT-induced ingestive and sleep behaviors in pigeons appear to be mediated by heterosynaptic and/or non-somatodendritic presynaptic 5-HT1ARs localized to periventricular diencephalic circuits.

5-Hydroxytryptamine 1A (5HT1A) receptors mediate increases in plasma glucose independent of corticosterone.

Hypothalamic 5HT1A receptors play an important role in the regulation of satiety, glycemia and endocrine status. In the present study, 8-OH-DP administered centrally and peripherally to C57/Bl6 mice and plasma glucose insulin and corticosterone were evaluated. In these studies, dose and time dependent increases in glucose and corticosterone were observed while no alterations in insulin were seen. The increases in plasma corticosterone were prevented by prior central or peripheral administration of LY426965, a specific 5HT1A antagonist. Intracerebroventricular coadministration of a 5HT1A antagonist with 8-OH-DPAT prevented the increase in plasma glucose establishing this response as a centrally mediated response in mice. Given that increases in plasma corticosterone are associated with increases in plasma glucose, we conducted experiments to determine if increased plasma corticosterone was the mechanism by which 8-OH-DPAT increased plasma glucose. Prior administration of the glucocorticoid antagonist mifepristone did not affect the increase in plasma glucose produced by 8-OH-DPAT. Prior administration of the glucocorticoid synthesis inhibitor, metyrapone, reduced basal corticosterone and the concentrations of corticosterone associated with 8-OH-DPAT administration. However, metyrapone administration did not affect the increases in plasma glucose. Therefore, 5HT1A receptors regulate glucose through brain mechanisms, but not through regulation of the hypophyseal-pituitary axis. Antagonism of brain 5HT1A receptors may enable discovery of novel antidiabetic agents.

The effects of serotonin1A receptor on female mice body weight and food intake are associated with the differential expression of hypothalamic neuropeptides and the GABAA receptor.

Both common eating disorders anorexia nervosa and bulimia nervosa are characteristically diseases of women. To characterize the role of the 5-HT1A receptor (5-HT1A-R) in these eating disorders in females, we investigated the effect of saline or 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) treatment on feeding behavior and body weight in adult WT female mice and in adult 5-HT1A-R knockout (KO) female mice. Our results showed that KO female mice have lower food intake and body weight than WT female mice. Administration of 8-OH-DPAT decreased food intake but not body weight in WT female mice. Furthermore, qRT-PCR was employed to analyze the expression levels of neuropeptides, γ-aminobutyric acid A receptor subunit ß (GABAA ß subunits) and glutamic acid decarboxylase in the hypothalamic area. The results showed the difference in food intake between WT and KO mice was accompanied by differential expression of POMC, CART and GABAA ß2, and the difference in body weight between WT and KO mice was associated with significantly different expression levels of CART and GABAA ß2. As such, our data provide new insight into the role of 5-HT1A-R in both feeding behavior and the associated expression of neuropeptides and the GABAA receptor.

Altered expression of 5-HT1A receptors in adult rats induced by neonatal treatment with clomipramine.

Chronic administration of clomipramine (CMI) to neonatal rats produces behaviors that resemble a depressive state in adulthood. Dysfunctions in the activity of the central nervous system's serotonergic function are important in understanding the pathophysiology of depression. The serotonin system is implicated in major depression and suicide and is negatively regulated by somatodendritic 5-HT1A autoreceptors. Desensitization of 5-HT1A autoreceptors is implicated in the long latency of some antidepressant treatments. Alterations in 5-HT1A receptor levels are reported in depression and suicide. In this study, we analyzed the effect of neonatal administration of CMI on the activity of 5-HT1A receptors, both pre- and post-synaptically, by administering an agonist of 5-HT1A receptors, 8-OH-DPAT, and then subjecting the rats to the forced swimming test (FST) a common procedure used to detect signs of depression in rats. Also measured were levels of the mRNA expression of 5-HT1A receptors in the dorsal raphe (DR), the hypothalamus and the hippocampus. Wistar rats were injected twice daily with CMI at doses of 15mgkg(-1) or saline as vehicle (CON) via s.c. from postnatal day 8 for 14days. At 3-4months of age, one set of rats from each group (CON, CMI) was evaluated for the effect of a selective agonist to the 5-HT1A receptor subtype, 8-OH-DPAT, by testing in the FST. Also determined was the participation of the pre- or post-synaptic 5-HT1A receptor in the antidepressant-like action of 8-OH-DPAT. This involved administering an inhibitor of tryptophan hydroxylase, parachlorophenylalanine (PCPA), and pretreatment with 8-OH-DPAT before the FST test and to evaluate the rectal temperature and locomotor activity. The expression of the mRNA of the 5-HT1A receptors was examined in the dorsal raphe nucleus, the hypothalamus and the hippocampus using the semi-quantitative RT-PCR method. The results from this study corroborate that neonatal treatment with clomipramine induces a pronounced immobility in the FST when animals reach adulthood, manifested by a significant decrease in swimming behavior, though counts of climbing behavior were not modified. This effect was similar in magnitude when 8-OH-DPAT was administered to CON group. Furthermore, the administration of 8-OH-DPAT induces a significant and similar increase in rectal temperature and locomotor activity in both the CON as in the CMI group. Neonatal treatment with CMI resulted in a significant decrease in the expression of the mRNA of the 5-HT1A receptors in the DR (% more than vehicle) in adulthood. In the case of the postsynaptic receptors located in the hypothalamus and hippocampus, neonatal treatment with CMI induced a significant increase in the mRNA expression of the 5-HT1A receptors. These data suggest that neonatal treatment with CMI induces a downregulation of the mRNA of the 5-HT1A autoreceptors in the DR, and an increment in the expression of the postsynaptic 5-HT1A receptors. The results after the administration of PCPA and 8-OH-DPAT on FST, rectal temperature and locomotor activity for both groups suggest that the function of postsynaptic receptors remains unchanged. All together these data show that the depressive behavior observed in adulthood in this animal model may be associated with long-term alterations in the expression of the mRNA of the 5-HT1A receptors.

Anxiolytic-like effect of lavender essential oil inhalation in mice: participation of serotonergic but not GABAA/benzodiazepine neurotransmission.

ETHNOPHARMACOLOGICAL RELEVANCE: Lavandula angustifolia (lavender) inhalation has been used in folk medicine for the treatment of anxiety, and clinical and animal studies have corroborated its anxiolytic effect, although its mechanism of action is still not fully understood. AIMS OF THE STUDY: The objective of the present study was to determine whether the GABAA/benzodiazepine complex or serotonin neurotransmission mediates the anxiolytic-like effect of lavender essential oil. MATERIALS AND METHODS: Male Swiss mice were subjected to the marble-burying test after being exposed to the aroma of lavender essential oil (1-5%), amyl acetate (5%; used as a behaviorally neutral odor), or distilled water for 15 min via inhalation. Additionally, the effect of 5% lavender essential oil was also evaluated in mice subjected to the elevated plus maze. GABAA/benzodiazepine mediation was evaluated by pretreating the mice with the GABAA receptor antagonist picrotoxin before the marble burying test and [(3)H]flunitrazepam binding to the benzodiazepine site on the GABAA receptor. Serotonergic mediation was studied by pretreating the mice with O-methyl-[3H]-N-(2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl)-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride (WAY100635), a serotonin 5-HT1A receptor antagonist before the marble burying test. We also evaluated changes in the pharmacologically induced serotonin syndrome and the effects of combined administration of subeffective doses of lavender essential oil and the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). RESULTS: Lavender essential oil (1-5%) decreased the number of marbles buried compared with the control and amyl acetate groups. In the elevated plus maze, 5% lavender essential oil inhalation increased the percentage of time spent on and number of entries into the open arms compared with controls. No effect was seen in the number of closed arm entries or number of beam interruptions in the automated activity chamber. Pretreatment with the GABAA receptor antagonist picrotoxin (0.5mg/kg) did not modify the behavioral effect of 5% lavender essential oil in the marble-burying test. Lavender essential oil also did not alter [(3)H]flunitrazepam binding to the benzodiazepine site on the GABAA receptor. Pretreatment with the serotonin 5-HT1A receptor antagonist WAY100635 (3mg/kg) blocked the anxiolytic-like effect of lavender essential oil and the 5-HT1A receptor agonist 8-OH-DPAT (3mg/kg). A combination of ineffective doses of 8-OH-DPAT (0.5mg/kg) and lavender essential oil (0.1%) reduced the number of marbles buried. Finally, 5% lavender essential oil attenuated the serotonin syndrome induced by 40 mg/kg fluoxetine plus 80 mg/kg 5-hydroxytryptophan. CONCLUSIONS: These results indicate an important role for the serotonergic system in the anxiolytic-like effect of lavender essential oil.

Augmentative effect of spinosin on pentobarbital-induced loss of righting reflex in mice associated with presynaptic 5-HT1A receptor.

OBJECTIVES: This study investigated whether spinosin potentiates pentobarbital-induced loss of righting reflex (LORR) in mice via 5-HT(1A) receptors. METHODS: Our primary endpoint for sedation was LORR. In addition, the basal rectal temperature was measured. KEY FINDINGS: The results demonstrated that the 5-HT(1A) agonist 8-OH-DPAT (s.c.) induced reductions in duration of LORR at 0.1, 0.5 and 1.0 mg/kg (P < 0.01), and prolongation of LORR latency at 0.5 and 1.0 mg/kg (s.c., P < 0.01) in pentobarbital (45 mg/kg, i.p.)-treated mice. This effect of 8-OH-DPAT was antagonized either by 5-HT(1A) antagonist p-MPPI (5 mg/kg, i.p.) or by spinosin (15 mg/kg, i.g.) with significance, respectively. Co-administration of spinosin and p-MPPI both at ineffective doses (spinosin at 5.0 mg/kg, i.g. and p-MPPI at 1.0 mg/kg, i.p.) showed significant augmentative effects in reducing latency to LORR, and increasing LORR duration (P < 0.01) in pentobarbital-treated mice. On the other hand, spinosin inhibited 8-OH-DPAT-induced hypothermia, which has been generally attributed to the activation of somatodendritic 5-HT(1A) autoreceptors in mice. CONCLUSIONS: Based on our previous results and the present data, it should be presumed that presynaptic 5-HT(1A) autoreceptor mechanisms may be involved in the inhibitory effect of spinosin on 8-OH-DPAT-induced hypothermia and also in the potentiating effect of spinosin on pentobarbital-induced LORR in mice.

Interactions between corticotropin-releasing factor and the serotonin 1A receptor system on acoustic startle amplitude and prepulse inhibition of the startle response in two rat strains.

Both the neuropeptide, corticotropin-releasing factor (CRF) and the serotonin 1A (5-HT(1A)) receptor systems have been implicated in anxiety disorders and there is evidence that the two systems interact with each other to affect behavior. Both systems have individually been shown to affect prepulse inhibition (PPI) of the acoustic startle response. PPI is a form of sensorimotor gating that is reduced in patients with anxiety disorders including post-traumatic stress and panic disorder. Here, we examined whether the two systems interact or counteract each other to affect acoustic startle amplitude, PPI and habituation of the startle response. In experiment 1, Brown Norway (BN) and Wistar-Kyoto (WKY) rats were administered ether an intraperitoneal (IP) injection of saline or the 5-HT(1A) receptor agonist, 8-OH-DPAT 10 min prior to receiving an intracerebroventricular (ICV) infusion of either saline or CRF (0.3 µg). In a second experiment, rats were administered either an IP injection of saline or the 5-HT(1A) receptor antagonist, WAY 100,635 10 min prior to receiving an ICV infusion of saline or CRF. Thirty min after the ICV infusion, the startle response and PPI were assessed. As we have previously shown, the dose of CRF used in these experiments reduced PPI in BN rats and had no effect on PPI in WKY rats. Administration of 8-OH-DPAT alone had no effect on PPI in either rat strain when the data from the two strains were examined separately. Administration of 8-OH-DPAT added to the effect of CRF in BN rats, and the combination of 8-OH-DPAT and CRF significantly reduced PPI in WKY rats. CRF alone had no effect on baseline startle amplitude in either rat strain, but CRF enhanced the 8-OH-DPAT-induced increase in startle in both strains. Administration of WAY 100,635 did not affect the CRF-induced change in PPI and there were no interactions between CRF and WAY 100,635 on baseline startle. The results suggest that activation of the 5-HT(1A) receptor can potentiate the effect of CRF on endophenotypes of anxiety disorders in animal models. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Cannabidiol, a non-psychotropic component of cannabis, attenuates vomiting and nausea-like behaviour via indirect agonism of 5-HT(1A) somatodendritic autoreceptors in the dorsal raphe nucleus.

BACKGROUND AND PURPOSE: To evaluate the hypothesis that activation of somatodendritic 5-HT(1A) autoreceptors in the dorsal raphe nucleus (DRN) produces the anti-emetic/anti-nausea effects of cannabidiol (CBD), a primary non-psychoactive cannabinoid found in cannabis. EXPERIMENTAL APPROACH: The potential of systemic and intra-DRN administration of 5-HT(1A) receptor antagonists, WAY100135 or WAY100635, to prevent the anti-emetic effect of CBD in shrews (Suncus murinus) and the anti-nausea-like effects of CBD (conditioned gaping) in rats were evaluated. Also, the ability of intra-DRN administration of CBD to produce anti-nausea-like effects (and reversal by systemic WAY100635) was assessed. In vitro studies evaluated the potential of CBD to directly target 5-HT(1A) receptors and to modify the ability of the 5-HT(1A) agonist, 8-OH-DPAT, to stimulate [(35) S]GTPγS binding in rat brainstem membranes. KEY RESULTS: CBD suppressed nicotine-, lithium chloride (LiCl)- and cisplatin (20 mg·kg(-1) , but not 40 mg·kg(-1) )-induced vomiting in the S. murinus and LiCl-induced conditioned gaping in rats. Anti-emetic and anti-nausea-like effects of CBD were suppressed by WAY100135 and the latter by WAY100635. When administered to the DRN: (i) WAY100635 reversed anti-nausea-like effects of systemic CBD, and (ii) CBD suppressed nausea-like effects, an effect that was reversed by systemic WAY100635. CBD also displayed significant potency (in a bell-shaped dose-response curve) at enhancing the ability of 8-OH-DPAT to stimulate [(35) S]GTPγS binding to rat brainstem membranes in vitro. Systemically administered CBD and 8-OH-DPAT synergistically suppressed LiCl-induced conditioned gaping. CONCLUSIONS AND IMPLICATIONS: These results suggest that CBD produced its anti-emetic/anti-nausea effects by indirect activation of the somatodendritic 5-HT(1A) autoreceptors in the DRN. LINKED ARTICLES: This article is part of a themed section on Cannabinoids in Biology and Medicine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7.

Sexually dimorphic serotonergic dysfunction in a mouse model of Huntington's disease and depression.

Depression is the most common psychiatric disorder in Huntington's disease (HD) patients. In the general population, women are more prone to develop depression and such susceptibility might be related to serotonergic dysregulation. There is yet to be a study of sexual dimorphism in the development and presentation of depression in HD patients. We investigated whether 8-week-old male and female R6/1 transgenic HD mice display depressive-like endophenotypes associated with serotonergic impairments. We also studied the behavioral effects of acute treatment with sertraline. We found that only female HD mice exhibited a decreased preference for saccharin as well as impaired emotionality-related behaviors when assessed on the novelty-suppressed feeding test (NSFT) and the forced-swimming test (FST). The exaggerated immobility time displayed by female HD in the FST was reduced by acute administration of sertraline. We also report an increased response to the 5-HT(1A) receptor agonist 8-OH-DPAT in inducing hypothermia and a decreased 5-HT(2A) receptor function in HD animals. While tissue levels of serotonin were reduced in both male and female HD mice, we found that serotonin concentration and hydroxylase-2 (TPH2) mRNA levels were higher in the hippocampus of males compared to female animals. Finally, the antidepressant-like effects of sertraline in the FST were blunted in male HD animals. This study reveals sex-specific depressive-related behaviors during an early stage of HD prior to any cognitive and motor deficits. Our data suggest a crucial role for disrupted serotonin signaling in mediating the sexually dimorphic depression-like phenotype in HD mice.