Peripherally injected canabidiol reduces neuropathic pain in mice: Role of the 5-HT1A and TRPV1 receptors.

Cannabidiol (CBD) is the most abundant non-psychoactive component found in plants of the genus Cannabis. Its analgesic effect for the treatment of neuropathy has been widely studied. However, little is known about its effects in the acute treatment when Cannabidiol is administered peripherally. Because of that, this research was aimed to evaluate the antinociceptive effects of the CBD when administered peripherally for the treatment of acute neuropathic pain and check the involvement of the 5-HT1A and the TRPV1 receptors in this event. Neuropathic pain was induced with the constriction of the sciatic nerve while the nociceptive threshold was measured using the pressure test of the mouse paw. The technique used proved to be efficient to induce neuropathy, and the CBD (5, 10 and 30 µg/paw) induced the antinociception in a dosage-dependent manner. The dosage used that induced a more potent effect (30 µg/paw), did not induce a systemic response, as demonstrated by both the motor coordination assessment test (RotaRod) and the antinociceptive effect restricted to the paw treated with CBD. The administration of NAN-190 (10 µg/paw), a selective 5-HT1A receptor antagonist, and SB-366791 (16 µg/paw), a selective TRPV1 antagonist, partially reversed the CBD-induced antinociception. The results of the research suggest that the CBD produces the peripheral antinociception during the acute treatment of the neuropathic pain and it partially involved the participation of the 5-HT1A and TRPV1 receptors.

Role of 5-HT1A receptors in the ventral hippocampus in the regulation of anxiety- and panic-related defensive behaviors in rats.

Changes in 5-HT1A receptor (5-HT1AR)-mediated neurotransmission in the hippocampus have been associated with anxiety, depression and in the mode of action of antidepressant drugs. It has been commonly accepted that whereas the dorsal pole of the hippocampus (DH) is involved in cognitive processing, the ventral pole (VH) is associated with emotional regulation. However, to date, only a few studies have directly addressed the role played by VH 5-HT1ARs in anxiety and panic processing, and their results are conflicting. Here we report that intra-VH administration of the 5-HT1A receptor agonist 8-OH-DPAT, the endogenous agonist serotonin (5-HT), or the standard anxiolytic benzodiazepine midazolam impaired the acquisition of inhibitory avoidance in the elevated T-maze (ETM) of male Wistar rats, indicating an anxiolytic effect. Conversely, local injection of the 5-HT1AR antagonist WAY-100635 caused the opposite effect. These results were equally found in the Vogel conflict test. None of these drugs interfered with locomotor activity in the open-field test, nor did they alter the expression of the escape response in the ETM, a defensive behavior associated with panic. Pre-injection of a sub-effective dose of WAY-100635 in the VH blocked the anxiolytic effect of 5-HT or 8-OH-DPAT in the Vogel test, confirming the involvement of 5-HT1AR for this behavioral effect. The effect in this test was anxiety-selective as none of the drugs affected water consumption or nociception. In conclusion, our results suggest that 5-HT1ARs in the VH play a tonic inhibitory role in anxiety processing. These receptors, however, are not involved in the regulation of panic-related escape behavior.

Administration of low doses of the 5-HT1A receptor agonist 8-OH-DPAT attenuates the discriminative signal of amphetamine in the conditioned taste aversion procedure.

Several studies have reported that low doses of the 5-HT1A receptor agonist 8-OH-DPAT reduce cocaine-induced locomotor activity. However, it has also been reported that high doses of 8-OH-DPAT do not substitute for or alter the discriminative signal of cocaine (COC) or amphetamine (AMPH). This study aimed to evaluate the effects of low and high doses of the 5-HT1A agonist 8-OH-DPAT on the discriminative signal of AMPH using conditioned taste aversion as a drug discrimination procedure. Additionally, to establish a correlation between the behavioral effects in drug discrimination and changes in dopamine (DA) and gamma-aminobutyric acid (GABA) concentrations, we evaluated the effect of systemic administration of low or high doses of the 5-HT1A receptor agonist 8-OH-DPAT and of the 5-HT1A receptor antagonist WAY100135 on DA and GABA extracellular concentrations in the nucleus accumbens (nAcc) and ventral tegmental area (VTA), respectively, using cerebral microdialysis. The behavioral results showed that low but not high doses of 8-OH-DPAT produced a reduction in the AMPH-induced discriminative signal, while WAY100135 administration prevented such effects. The microdialysis results showed that a low dose of 8-OH-DPAT decreased extracellular DA concentrations in the nAcc and increased GABA concentrations in the VTA. Pretreatment with WAY100135 prevented these effects. These data support the hypothesis that 5-HT1A receptors modulate the behavioral effects of psychostimulant drugs, such as AMPH, through somatodendritic 5-HT1A autoreceptors in the raphe nucleus indicating that 5-HT1A receptors may be an important target for the development of pharmacological treatments for psychostimulant addiction.

Modulation of the storage of social recognition memory by neurotransmitter systems in the insular cortex.

The insular cortex (IC) receives projections from prefrontal, entorhinal and cingulate cortex, olfactory bulb and basal nuclei and has reciprocal connections with the amygdala and entorhinal cortex. These connections suggest a possible involvement in memory processes; this has been borne out by data on several behaviors. Social recognition memory (SRM) is essential to form social groups and to establish hierarchies and social and affective ties. Despite its importance, knowledge about the brain structures and the neurotransmitter mechanisms involved in its processing is still scarce. Here we study the participation of NMDA-glutamatergic, D1/D5-dopaminergic, H2-histaminergic, ß-adrenergic and 5-HT1A-serotoninergic receptors of the IC in the consolidation of SRM. Male Wistar rats received intra-IC infusions of substances acting on these receptors immediately after the sample phase of a social discrimination task and 24h later were exposed to a 5-min retention test. The intra-IC infusion of antagonists of D1/D5, ß-adrenergic or 5-HT1A receptors immediately after the sample phase impaired the consolidation of SRM. These effects were blocked by the concomitant intra-IC infusion of agonists of these receptors. Antagonists and agonists of NMDA and H2 receptors had no effect on SRM. The results suggest that the dopaminergic D1/D5, ß-adrenergic and serotonergic 5-HT1A receptors in the IC, but not glutamatergic NMDA and the histaminergic H2 receptors, participate in the consolidation of SRM in the IC.

Interaction between estradiol and 5-HT1A receptors in the median raphe nucleus on acquisition of aversive information and association to the context in ovariectomized rats.

The median raphe nucleus (MRN) is related to stress resistance and defensive responses, a crucial source of serotonergic neurons that project to prosencephalic structures related to stress and anxiety. Estrogen receptors were identified in this mesencephalic structure. It is possible that the estrogen action is related to serotonin effect on somatodendritic 5-HT1A receptors, inhibiting the function of serotonergic neurons and thus preventing of the stress effect and inducing anxiolysis. So, in order to evaluate these aspects, female Wistar rats were ovariectomized and 21 days later were given a direct microinjection of estradiol benzoate (EB) (1200 ng) into the MRN, preceded by microinjections of saline or WAY100.635 (100 ng), a 5-HT1A receptor antagonist. Immediately after the two microinjections, the ovariectomized rats were conditioned with an aversive event (foot shock) session in a Skinner box. Twenty-four hours later, they were exposed to the same context in a test session for 5 min for behavioral assessment: freezing, rearing, locomotion, grooming, and autonomic responses (fecal boluses and micturition). EB microinjection in the MRN prior to the exposure of animals to the foot shocks in the conditioning session did not alter their behavior in this session, but neutralized the association of the aversive experience to the context: there was a decrease in the expression of freezing and an increased rearing activity in the test session. This effect was reversed by prior microinjection of WAY100.635. In conclusion, EB acted on serotonergic neurons in the MRN of the ovariectomized rats, impairing the association of the aversive experience to the context, by co-modulating the functionality of somatodendritic 5-HT1A.

La administración del antagonista GABA A bicuculina previene los efectos de la administración del agonista 5-HT 1A 8-OH-DPAT en las propiedades discriminativas de la anfetamina / Administration of GABA A receptor antagonist bicuculline prevents the effects of administration of 5-HT 1A receptor agonist on the discriminative properties of amphetamine

Resumen En esta investigación se evaluaron los efectos de la administración sistémica del antagonista GABAA bicuculina sobre los efectos del agonista 5-HT1A 8-OH-DPAT en las propiedades discriminativas de la anfetamina (ANF) utilizando el condicionamiento de aversión a los sabores. Los resultados mostraron que ni el 8-OH-DPAT, ni la bicuculina, sustituyeron la señal discriminativa de la ANF. Sin embargo, la administración del 8-OH-DPAT disminuyó la señal discriminativa de la ANF, y la administración de la bicuculina, previa a la administración del 8-OH-DPAT más una dosis de ANF, previno el efecto del 8-OH-DPAT sobre la señal discriminativa de la ANF. Estos datos apoyan la hipótesis de que las conductas relacionadas con la adicción a las drogas, como la ANF, involucran diferentes sistemas de neurotransmisión como la DA, la 5-HT y el GABA.

Abstract In this research, the effects of systemic administration of the GABAA receptor antagonist bicuculline on the effects of 5-HT1A receptor agonist 8-OH-DPAT on the discriminative properties of the AMPH using the conditioned taste aversion procedure were evaluated. The results showed that neither 8-OH-DPAT nor bicuculline administration did not substitute for AMPH. However, the 8-OH-DPAT administration decreased the discriminative signal of AMPH and the bicuculline administration, prior to the 8-OH-DPAT administration plus a dose of AMPH prevented the effect of the 8-OH-DPAT on discriminative signal of AMPH. These data support the hypothesis that addiction-related behaviors of drugs such as AMPH involve several neurotransmitter systems such as DA, 5-HT and GABA.

Effects of intra-prelimbic prefrontal cortex injection of cannabidiol on anxiety-like behavior: involvement of 5HT1A receptors and previous stressful experience.

The prelimbic medial prefrontal cortex (PL) is an important encephalic structure involved in the expression of emotional states. In a previous study, intra-PL injection of cannabidiol (CBD), a major non-psychotomimetic cannabinoid present in the Cannabis sativa plant, reduced the expression of fear conditioning response. Although its mechanism remains unclear, CBD can facilitate 5HT1A receptor-mediated neurotransmission when injected into several brain structures. This study was aimed at verifying if intra-PL CBD could also induce anxiolytic-like effect in a conceptually distinct animal model, the elevated plus maze (EPM). We also verified if CBD effects in the EPM and contextual fear conditioning test (CFC) depend on 5HT1A receptors and previous stressful experience. CBD induced opposite effects in the CFC and EPM, being anxiolytic and anxiogenic, respectively. Both responses were prevented by WAY100,635, a 5HT1A receptor antagonist. In animals that had been previously (24h) submitted to a stressful event (2h-restraint) CBD caused an anxiolytic, rather than anxiogenic, effect in the EPM. This anxiolytic response was abolished by previous injection of metyrapone, a glucocorticoid synthesis blocker. Moreover, restraint stress increased 5HT1A receptors expression in the dorsal raphe nucleus, an effect that was attenuated by injection of metyrapone before the restraint procedure. Taken together, these results suggest that CBD modulation of anxiety in the PL depend on 5HT1A-mediated neurotransmission and previous stressful experience.

The role of 5-HT1A receptors in the anti-aversive effects of cannabidiol on panic attack-like behaviors evoked in the presence of the wild snake Epicrates cenchria crassus (Reptilia, Boidae).

The potential anxiolytic and antipanic properties of cannabidiol have been shown; however, its mechanism of action seems to recruit other receptors than those involved in the endocannabinoid-mediated system. It was recently shown that the model of panic-like behaviors elicited by the encounters between mice and snakes is a good tool to investigate innate fear-related responses, and cannabidiol causes a panicolytic-like effect in this model. The aim of the present study was to investigate the 5-hydroxytryptamine (5-HT) co-participation in the panicolytic-like effects of cannabidiol on the innate fear-related behaviors evoked by a prey versus predator interaction-based paradigm. Male Swiss mice were treated with intraperitoneal (i.p.) administrations of cannabidiol (3 mg/kg, i.p.) and its vehicle and the effects of the peripheral pre-treatment with increasing doses of the 5-HT1A receptor antagonist WAY-100635 (0.1, 0.3 and 0.9 mg/kg, i.p.) on instinctive fear-induced responses evoked by the presence of a wild snake were evaluated. The present results showed that the panicolytic-like effects of cannabidiol were blocked by the pre-treatment with WAY-100635 at different doses. These findings demonstrate that cannabidiol modulates the defensive behaviors evoked by the presence of threatening stimuli, and the effects of cannabidiol are at least partially dependent on the recruitment of 5-HT1A receptors.

Efecto de la restricción física: sobre el papel de los receptores 5-HT1A en la proliferación linfocitaria / Effect of phisical restraints: the role of the 5-HT1A in lymphocyte proliferation

El estrés afecta el sistema inmunológico, sin embargo, no hay reportes sobre receptores de serotonina en linfocitos. Se estudiaron los receptores 5-HT1A y la proliferación linfocitaria de ratas macho adultas luego de restricción física. Fueron colocadas en cajas de Plexiglass durante 5 horas diarias por 1, 3 ó 5 días. Se extrajo sangre cardíaca, se aislaron los linfocitos por gradiente de densidades y adhesión al plástico; se cultivaron con el agonista 8-hidroxi-di-n-propil-aminotetralina(8-OH-DPAT) ó el antagonista N-(2-(4-(2-metoxifenil)-1-piperazinetil)-N-(2-piridinil) ciclohexanocarboxamida (WAY-100635) de los receptores 5-HT1A y del mitógeno concanavalina A. La proliferación se midió con sales de tetrazolio. La 8-OH-DPAT no afectó la proliferación. El WAY-100635 disminuyó la proliferación. La restricción física aumentó la sensibilidad al efecto del WAY-100635, lo cual podría deberse a cambios en la expresión o a una modulación funcional de los receptores por efecto del estrés, como se ha reportado previamente en cerebro de rata.

Stress affects the immune system, however, little is known about the effects on specific modifications of lymphocytes serotonin receptors. The effects of restraint stress on the role of 5-HT1A receptors in lymphocyte proliferation were evaluated in male adult rats. They were placed in Plexiglass boxes, during 5 daily hours for 1, 3 or 5 consecutive days. Next day a blood sample was obtained by cardiac punction. Lymphocytes were isolated by density gradient and adhesionto plastic. They were cultured with agonist 8-hydroxy-di-n-propyl-aminotetralin (8-OH-DPAT) or antagonist N-(2-(4-(2-methoxyphenyl)-1-piperazinyl) ethyl)-N-(2-pyridiyl) cyclohexanecarboxamide (WAY-100635) of 5-HT1A receptors and the mitogen concanavalin A. Proliferation was measured by tetrazolium salts. 8-OH-DPAT did not modify cell proliferation; WAY-100635 diminished it. Restraint stress increased the susceptibility to effect of WAY-100635. These results suggest changes in the expression or functional modulation of 5-HT1A receptors in lymphocytes by stress, similar to previous reports on serotonergic system in rat brain.