Memory Enhancement with Kynurenic Acid and Its Mechanisms in Neurotransmission.

Kynurenic acid (KYNA) is an endogenous tryptophan (Trp) metabolite known to possess neuroprotective property. KYNA plays critical roles in nociception, neurodegeneration, and neuroinflammation. A lower level of KYNA is observed in patients with neurodegenerative diseases such as Alzheimer's and Parkinson's diseases or psychiatric disorders such as depression and autism spectrum disorders, whereas a higher level of KYNA is associated with the pathogenesis of schizophrenia. Little is known about the optimal concentration for neuroprotection and the threshold for neurotoxicity. In this study the effects of KYNA on memory functions were investigated by passive avoidance test in mice. Six different doses of KYNA were administered intracerebroventricularly to previously trained CFLP mice and they were observed for 24 h. High doses of KYNA (i.e., 20-40 µg/2 µL) significantly decreased the avoidance latency, whereas a low dose of KYNA (0.5 µg/2 µL) significantly elevated it compared with controls, suggesting that the low dose of KYNA enhanced memory function. Furthermore, six different receptor blockers were applied to reveal the mechanisms underlying the memory enhancement induced by KYNA. The series of tests revealed the possible involvement of the serotonergic, dopaminergic, α and ß adrenergic, and opiate systems in the nootropic effect. This study confirmed that a low dose of KYNA improved a memory component of cognitive domain, which was mediated by, at least in part, four systems of neurotransmission in an animal model of learning and memory.

Antidepressant-like effects of kynurenic acid in a modified forced swim test.

BACKGROUND: Kynurenic acid (KYNA) is an L-tryptophan metabolite with neuromodulatory activities, regulating the release of neurotransmitters such as glutamate, dopamine (DA), and acetylcholine (Ach). Dysregulation of the kynurenine pathway has been associated with neurodegenerative, neurological, and psychological disorders such as Alzheimer's disease, Parkinson's disease, Huntington's disease, major depressive disorder, and schizophrenia. METHODS: The antidepressant-like effects of KYNA were studied with a modified mouse forced swimming test (FST), and the potential involvement of the serotonin (SER), norepinephrine, DA, Ach, N-methyl-D-aspartate, or gamma-aminobutyric acid subunit A (GABAA) receptors in its antidepressant-like effect was assayed by modified combination mouse FST. In combination studies, the mice were pretreated with the respective receptor antagonist, cyproheptadine (CPH), phenoxybenzamine, yohimbine, propranolol, haloperidol (HPD), atropine, MK-801, or bicuculline (BCL). RESULTS: The FST revealed that KYNA reversed immobility, climbing, and swimming times, suggesting the antidepressant-like effects of KYNA. Furthermore, the combination studies showed that CPH prevented the antidepressant-like effects of KYNA on immobility, climbing, and swimming times, whereas HPD reduced climbing time and BCL influenced immobility and climbing times and prevented the effects of KYNA on swimming time. CONCLUSIONS: The results demonstrated, for the first time, the presence of antidepressant-like effects of KYNA in a modified mouse FST. Furthermore, modified combination FST showed that the antidepressant-like actions of KYNA strongly interacted with 5-hydroxytryptamine type 2 SER-ergic receptors, weakly interacted with D2, D3, D4 DA-ergic receptors, and interacted moderately with GABAA receptors.

Changes in striatal dopamine release and locomotor activity following acute withdrawal from chronic nicotine are mediated by CRF1, but not CRF2, receptors.

The aim of the present study was to investigate the participation of corticotropin-releasing factor (CRF) receptors (CRF1 and CRF2) in the alterations of the dorsal and ventral striatal dopamine release and the vertical and horizontal locomotor activity observed in rats following chronic nicotine treatment and consequent acute withdrawal. In this purpose, male Wistar rats were exposed to repeated intraperitoneal (ip) injection with nicotine or saline solution for 7 days. On the 8th day or the 9th day the rats were injected intracerebroventricularly (icv) with selective CRF1 antagonist antalarmin or selective CRF2 antagonist astressin2B or saline solution. Thirty minutes after the icv injection the changes of the horizontal and vertical locomotor activity were recorded in an in vivo conducta system. Immediately after the behavioral recordings the changes of the dorsal and ventral striatal dopamine release were determined in an in vitro superfusion system. On the 8th day, the horizontal and vertical locomotor activities and the dorsal and ventral striatal dopamine releases increased significantly in nicotine-treated rats, compared to the saline-treated ones. On the 9th day, the horizontal locomotor activity and the dorsal striatal dopamine release increased significantly, whereas the vertical locomotor activity and the ventral striatal dopamine release decreased significantly in nicotine-treated rats, compared to the saline-treated ones. All the changes observed were attenuated significantly by antalarmin, but not astressin2B. The present study demonstrates that the changes of striatal dopamine release and locomotor activity observed following chronic nicotine treatment and consequent acute withdrawal are mediated by CRF1, but not CRF2, receptor.

The effects of the urocortins on the hypothalamic-pituitary-adrenal axis - similarities and discordancies between rats and mice.

The urocortins (Ucn I, Ucn II and Ucn III) are structural analogues of corticotropin-releasing factor (CRF). The aim of our present experiments was to compare the effects of the urocortins on the hypothalamic-pituitary-adrenal (HPA) axis in rats and mice, including the hypothalamic adrenocorticotropic hormone (ACTH) secretagogues, such as CRF and arginine vasopressin (AVP). Therefore, male CFLP mice and male Wistar rats were injected intracerebroventricularly (icv) with 0.5, 1, 2 and 5 µg/2 µl of Ucn I, Ucn II or Ucn III. After 30 min the animals were decapitated, and then, hypothalamic CRF and AVP concentrations and plasma ACTH and corticosterone (CORT) levels were measured. All measurements were performed by enzyme-linked immunosorbent assays (ELISA), except that of the plasma CORT level, which was determined by chemofluorescent assay. Ucn I increased significantly the hypothalamic CRF and AVP concentrations in both rats and mice. Ucn II and Ucn III influenced significantly only the hypothalamic CRF concentration in rats, without affecting the hypothalamic AVP concentration. In contrast, Ucn II and Ucn III increased significantly only the hypothalamic AVP concentration in mice, without affecting the hypothalamic CRF concentration. The hypothalamic changes were reflected more or less accurately by changes of the plasma ACTH and CORT levels. The present experiments demonstrate that the urocortins regulate the HPA axis centrally via modulation of the hypothalamic ACTH secretagogues and that there are some similarities and discordancies between rats and mice regarding this regulation.

Kisspeptin modulates pain sensitivity of CFLP mice.

Kisspeptin, a hypothalamic neuropeptide, is a member of the RF-amide family, which have been known to modify pain sensitivity in rodents. The aim of the present study was to investigate the effect of kisspeptin-13 (KP-13), an endogenous derivative of kisspeptin, on nociception in adult male and female CFLP mice and the possible interaction of KP-13 with morphine on nociception. Mice were injected with different doses of KP-13, 30, 60 and 120 min after of which the nociceptive sensitivity were assessed via the tail-flick test. To investigate the receptor involved in the mediation a kisspeptin receptor antagonist (KP-234) pretreatment was applied before KP-13 administration. Furthermore, we investigated the effect of KP-13 on the acute antinociceptive effect of morphine, on acute morphine tolerance and on naloxone-precipitated withdrawal. Last, the Von Frey test was used in order to assess KP-13's effect on mechanical nociception. Our results showed that KP-13 decreased the nociceptive threshold of both males and females independent of sex, which was prevented by KP-234. Furthermore, KP-13 treatment depressed the acute antinociceptive effect of morphine and attenuated the development of morphine tolerance. KP-13 also induced a mechanical hypersensitivity. These data underlie kisspeptin's hyperalgesic action and argues for the role of kisspeptin receptor 1 in the mediation of its action. Furthermore, our results suggest that central KP-13 administration can modify the acute effects of morphine.

Anxiolytic- and antidepressant-like actions of Urocortin 2 and its fragments in mice.

The aim of the present study was to investigate the potential anxiolytic- and antidepressant-like actions of Urocortin 2 (Ucn2) and its two fragments, Ucn2 (1-21) and Ucn2 (22-38), in mice, in an attempt to identify the biologically active sequence of this 38 amino acid neuropeptide. In this purpose, male C57BL/6 mice were treated intracerebroventricularly (icv) with 0.125, 0.25, 0.5 and 1 µg/2 µl of Ucn2, Ucn2 (1-21) or Ucn2 (22-38). After 30 min, the mice were evaluated in an elevated plus-maze test and a forced swim test for anxiety- and depression-like behavior, respectively. Each test lasted 5 min. Ucn2 at dose of 0.25 µg/2 µl and Ucn2 (1-21) at dose of 0.125 µg/2 µl, but not Ucn2 (22-38), increased significantly the number of entries into and the time spent in the open-arms, without influencing the total number of entries. In parallel, the same doses of Ucn2 and Ucn2 (1-21), but not Ucn2 (22-38), increased significantly the climbing and the swimming activity, while decreasing significantly the time of immobility. In addition, Ucn2 at doses of 0.125 µg/2 µl and 0.5 µg/2 µl decreased significantly the time of immobility, but they did not change the other parameters. The present study demonstrates that Ucn2 exerts anxiolytic- and antidepressant-like effects in C57BL/6 mice, which are mediated by the N-terminal, but not the C-terminal fragment of the peptide. The establishment of the smallest active sequence by further fragmentation of Ucn2 (1-21) may allow the synthesis of new anxiolytic and antidepressant drugs.

The effects of CRF and urocortins on the sociability of mice.

The aim of our study was to determine the role of corticotropin-releasing factor (CRF), the urocortins (Ucn1, Ucn2 and Ucn3) and their receptors (CRF1 and CRF2) in the sociability of mice. Male CFLP mice were administered intracerebroventricularly (icv) with CRF and urocortins alone or in combination with antalarmin (specific CRF1 antagonist) and astressin2B (specific CRF2 antagonist) and then investigated in a Crawley social interaction test arena, that consists of three chambers. An unknown male in a cage was put in the first chamber and an empty cage was put in the opposite chamber. The tested male was habituated with the middle chamber for 5min and then allowed to explore the remaining chambers for 5min, during which the number of entries and the time of interaction were measured. Intracerebroventricular administration of CRF decreased significantly the number of entries and the time of interaction with the unknown male and these effects were blocked by antalarmin, but not astressin2B. In contrast, central administration of Ucn1 increased significantly the number of entries into the chamber of the unknown male, without changing the time of interaction and this effect was blocked by astressin2B, but not antalarmin. Central administration of Ucn2 and Ucn3 didn't influence remarkably the number of entries, but it reduced the time of interaction between the male mice. Our study suggests that CRF and Ucn1 may play important, but different roles in sociability, and that Ucn2 and Ucn3, playing similar roles, must be also involved in social interactions.

The effects of CRF and urocortins on the preference for social novelty of mice.

The aim of the present study was to determine the role of corticotropin-releasing factor (CRF), the urocortins (UCN 1, UCN 2 and UCN 3) and their receptors (CRF1 and CRF2) in the preference for social novelty of mice. Male CFLP mice were administered intracerebroventricularly (ICV) with CRF, UCN 1, UCN 2 or UCN 3 and/or antalarmin or astressin 2B, selective antagonists of CRF1 receptor and CRF2 receptor, respectively. The mice were investigated in a Crawley social interaction test arena consisting of three chambers: an unknown female was set in the first chamber and a known female, with which the male was familiarized previously for 24h, was set in the third chamber. First the tested male was habituated with the middle chamber for 5min and then allowed to explore the remaining chambers for 5min, during which the number of entries and the time of interaction were measured. CRF decreased significantly the number of entries and the time of interaction with the unknown female, but not the known female. UCN 1 decreased significantly the number of entries into the chamber of the unknown female, but not the known female, without changing the time of interaction. All decreasing effects were reversed by antalarmin, but not astressin 2B. UCN 2 and UCN 3 didn't influence significantly any of the parameters. The present study suggests that CRF and UCN 1 decrease the preference for social novelty by activating CRF1 receptor, while UCN 2 and UCN 3, activating selectively CRF2 receptor, do not participate to male-female interaction.

Antiamnesic properties of analogs and mimetics of the tripeptide human urocortin 3.

Amnesia is a deficit in memory caused by brain damage, disease, or trauma. Until now, there are no successful medications on the drug market available to treat amnesia. Short analogs and mimetics of human urocortin 3 (Ucn 3) tripeptide were synthetized and tested for their action against amnesia induced by eletroconvulsion in mice. Among the 16 investigated derivatives of Ucn 3 tripeptide, eight compounds displayed antiamnesic effect. Our results proved that the configuration of chiral center of glutamine does not affect the antiamnesic properties. Alkyl amide or isoleucyl amide at the C-terminus may lead to antiamnesic compounds. As concerned the N-terminus, acetyl, Boc, and alkyl ureido moieties were found among the active analogs, but the free amino function at the N-terminus usually led to an inactive derivatives. These observations may lead to the design and synthesis of small peptidomimetics and amino acid derivatives as antiamnesic drug candidates, although the elucidation of the mechanism of the action requires further investigations.

Anxiolytic effect of the GPR103 receptor agonist peptide P550 (homolog of neuropeptide 26RFa) in mice. Involvement of neurotransmitters.

The GPR103 receptor is a G protein-coupled receptor, which plays a role in several physiological functions. However, the role of the GPR103 receptor in anxiety has not been clarified. The first aim of our study was to elucidate the involvement of the GPR103 receptor in anxious behavior. Mice were treated with peptide P550, which is the mouse homolog of neuropeptide 26RFa and has similar activity for the GPR103 receptor as neuropeptide 26RFa. The anxious behavior was investigated using an elevated plus-maze paradigm. The second aim of our study was to investigate the underlying neurotransmissions. Accordingly, mice were pretreated with a nonselective muscarinic acetylcholine receptor antagonist, atropine, a γ-aminobutyric acid subunit A (GABAA) receptor antagonist, bicuculline, a non-selective 5-HT2 serotonergic receptor antagonist, cyproheptadine, a mixed 5-HT1/5-HT2 serotonergic receptor antagonist, methysergide, a D2, D3, D4 dopamine receptor antagonist, haloperidol, a nonselective α-adrenergic receptor antagonist, phenoxybenzamine and a nonselective ß-adrenergic receptor antagonist, propranolol. Our results demonstrated that peptide P550 reduces anxious behavior in elevated plus maze test in mice. Our study shows also that GABAA-ergic, α- and ß-adrenergic transmissions are all involved in this action, whereas 5-HT1 and 5-HT2 serotonergic, muscarinic cholinergic and D2, D3, D4 dopaminergic mechanisms may not be implicated.

The action of neuropeptide AF on passive avoidance learning. Involvement of neurotransmitters.

Neuropeptide AF (NPAF) is an amidated octadecapeptide, which is member of the RFamide peptide family. NPAF is encoded by the farp-1 gene and acts through the G protein coupled NPFF-1 and NPFF-2 receptors. NPAF is involved in several physiological functions of the central nervous system, however we have little evidence about the involvement of NPAF in learning and memory. Therefore, the aim of the present study was to investigate the action of NPAF on consolidation of memory in a passive avoidance learning paradigm in mice. We have also investigated the underlying neurotransmissions and the action of NPAF on ß-amyloid-induced memory impairment. Accordingly, mice were pretreated with a nonselective muscarinic acetylcholine receptor antagonist, atropine, a non-selective 5-HT2 serotonergic receptor antagonist, cyproheptadine, a mixed 5-HT1/5-HT2 serotonergic receptor antagonist, methysergide, a D2, D3, D4 dopamine receptor antagonist, haloperidol, a non-selective opioid receptor antagonist, naloxone, a nitric oxide synthase inhibitor, nitro-l-arginine, a α1/α2ß-adrenergic receptor antagonist, prazosin, a nonselective ß-adrenergic receptor antagonist, propranolol or ß-amyloid 25-35 in combination with NPAF administration. Our results demonstrate for the first time that NPAF improves the consolidation of passive avoidance learning. This effect is mediated through muscarinic cholinergic, 5HT1- and 5HT2-serotoninergic, dopaminergic, nitrergic and α- and ß-adrenergic neurotransmissions, but not by opioid transmission, since atropine, cyproheptadine, methysergide, haloperidol, nitro-l-arginine, prazosin and propranolol reversed the action of NPAF, whereas naloxone was ineffective. The present study also shows that NPAF reverses the ß-amyloid 25-35-induced memory impairment.

The effect of kisspeptin on the regulation of vascular tone.

Kisspeptin has been implicated in cardiovascular control. Eicosanoids play a crucial role in the activation of platelets and the regulation of vascular tone. In the present study, we investigated the effect of kisspeptins on eicosanoid synthesis in platelets and aorta in vitro. Platelets and aorta were isolated from Wistar-Kyoto rats. After preincubation with different doses of kisspeptin, samples were incubated with [1-(14)C]arachidonic acid (0.172 pmol/mL) in tissue culture Medium 199. The amount of labeled eicosanoids was measured with liquid scintillation, after separation with overpressure thin-layer chromatography. Kisspeptin-13 stimulated the thromboxane synthesis. The dose-response curve was bell-shaped and the most effective concentration was 2.5 × 10(-8) mol/L, inducing a 27% increase. Lipoxygenase products of platelets displayed a dose-dependent elevation up to the dose of 5 × 10(-8) mol/L. In the aorta, kisspeptin-13 induced a marked elevation in the production of 6-keto-prostaglandin F1α, the stable metabolite of prostacyclin, and lipoxygenase products. Different effects of kisspeptin on cyclooxygenase and lipoxygenase products indicate that beyond intracellular Ca(2+) mobilization, other signaling pathways might also contribute to its actions. Our data suggest that kisspeptin, through the alteration of eicosanoid synthesis in platelets and aorta, may play a physiologic and (or) pathologic role in the regulation of vascular tone.

The effects of CRF and urocortins on the hippocampal glutamate release.

Corticotropin-releasing factor (CRF) is a hypothalamic neurohormone and an extrahypothalamic neurotransmitter that regulates the hypothalamic-pituitary-adrenal (HPA) axis. The urocortins (UCN I, UCN II and UCN III) are CRF-related peptides, which may also regulate the HPA axis directly or indirectly, by modulation of extrahypothalamic neurotransmitters, such as amygdalar GABA and hippocampal glutamate. Our previous in vitro superfusion studies have already demonstrated that CRF and UCN I stimulate the amygdalar GABA release in rats. The aim of the present study was to investigate the effects of CRF, UCN I, UCN II and UCN III on the glutamate release elicited electrically from rat hippocampal slices in similar in vitro conditions. In order to investigate the participation of CRF receptors (CRFR1 and CRFR2) in this process, hippocampal slices were pretreated with antalarmin, a selective antagonist of CRFR1 or astressin 2B, a selective antagonist of CRFR2. CRF and UCN I at 100 nM decreased significantly the hippocampal glutamate release evoked by electrical stimulation. In contrast, 100 nM of UCN II and UCN III did not affect significantly the hippocampal glutamate release enhanced by electrical stimulation. The decreasing effects of CRF and UCN I were reversed by antalarmin, but not by astressin 2B, both being administered in equimolar doses. Our results demonstrate that CRF and UCN I inhibit the glutamate release in the hippocampus via CRFR1 and that CRFR2 does not participate to this process. Based on the previous and the present results we conclude that CRFR1 agonists can activate the HPA axis not only directly, but also indirectly by increasing the amygdalar GABA release and decreasing the hippocampal glutamate release.

Short analogs and mimetics of human urocortin 3 display antidepressant effects in vivo.

Peptide analogs of urocortin 3[36­38] (Ucn 3[36­38]), obtained with deletion or replacement of amino acids of the original human urocortin 3 sequence, were designed, synthesized, and tested in vivo for treatment of depression. Based on the results of the biological tests of the peptide analogs, several new peptidomimetics of the above short analogs of urocortin 3, including urea- and azapeptides, were also designed and synthesized and found to preserve the antidepressant-like effect of the 38 amino acid long original neuropeptide. The molecular modifications of urocortin 3[36­38] led to an improved understanding of the relationship between molecular structure and biological activity of this peptide, and the novel peptidomimetics could be further tested for possible clinical treatment of depression.

Neuropeptide AF induces anxiety-like and antidepressant-like behavior in mice.

Little is known about the action of neuropeptide AF (NPAF) on anxiety and depression. Only our previous study provides evidence that NPAF induces anxiety-like behavior in rats. Therefore, the aim of the present study was to investigate the action of NPAF on depression-like behavior and the underlying neurotransmissions in mice. In order to determine whether there are species differences between rats and mice, we have investigated the action of NPAF on anxiety-like behavior in mice as well. A modified forced swimming test (mFST) and an elevated plus maze test (EPMT) were used to investigate the depression and anxiety-related behaviors, respectively. Mice were treated with NPAF 30min prior to the tests. In the mFST, the animals were pretreated with a non-selective muscarinic acetylcholine receptor antagonist, atropine, a non-selective 5-HT2 serotonergic receptor antagonist, cyproheptadine, a mixed 5-HT1/5-HT2 serotonergic receptor antagonist, methysergide, a D2/D3/D4 dopamine receptor antagonist, haloperidol, a α1/α2ß-adrenergic receptor antagonist, prazosin or a non-selective ß-adrenergic receptor antagonist, propranolol 30min before the NPAF administration. In the mFST, NPAF decreased the immobility time and increased the climbing and swimming times. This action was reversed completely by methysergide and partially by atropine, whereas cyproheptadine, haloperidol, prazosin and propranolol were ineffective. In the EPMT, NPAF decreased the time spent in the arms (open/open+closed). Our results demonstrate that NPAF induces anti-depressant-like behavior in mice, which is mediated, at least in part, through 5HT2-serotonergic and muscarinic cholinergic neurotransmissions. In addition, the NPAF-induced anxiety is species-independent, since it develops also in mice.

The action of orexin B on passive avoidance learning. Involvement of neurotransmitters.

The extensive projection of orexigenic neurons and the diffuse expression of orexin receptors suggest that endogenous orexins are involved in several physiological functions of the central nervous system, including learning and memory. Our previous study demonstrated that orexin A improves learning, consolidation and retrieval processes, which involves α- and ß-adrenergic, cholinergic, dopaminergic, GABA-A-ergic, opiate and nitrergic neurotransmissions. However, we have little evidence about the action of orexin B on memory processes and the underlying neuromodulation. Therefore, the aim of the present study was to investigate the action of orexin B on passive avoidance learning and the involvement of neurotransmitters in this action in rats. Accordingly, rats were pretreated with the selective orexin 2 receptor (OX2R) antagonist, EMPA; the γ-aminobutyric acid subunit A (GABA-A) receptor antagonist, the bicuculline; a D2, D3, D4 dopamine receptor antagonist, haloperidol; the nonselective opioid receptor antagonist, naloxone; the non-specific nitric oxide synthase (NOS) inhibitor, nitro-l-arginine; the nonselective α-adrenergic receptor antagonist, phenoxybenzamine and the ß-adrenergic receptor antagonist, propranolol. Our results demonstrate that orexin B can improve learning, consolidation of memory and retrieval. EMPA reversed completely the action of orexin B on memory consolidation. Bicuculline blocked fully; naloxone, nitro-l-arginine, phenoxybenzamine and propranolol attenuated the orexin B-induced memory consolidation, whereas haloperidol was ineffective. These data suggest that orexin B improves memory functions through OX2R and GABA-ergic, opiate, nitrergic, α- and ß-adrenergic neurotransmissions are also involved in this action.

Involvement of neurotransmitters in the action of the nociceptin/orphanin FQ peptide-receptor system on passive avoidance learning in rats.

The nociceptin/orphanin FQ peptide (NOP) receptor and its endogenous ligand plays role in several physiologic functions of the central nervous system, including pain, locomotion, anxiety and depression, reward and drug addiction, learning and memory. Previous studies demonstrated that the NOP-receptor system induces impairment in memory and learning. However, we have little evidence about the underlying neuromodulation. The aim of the present study was to investigate the involvement of distinct neurotransmitters in the action of the selective NOP receptor agonist orphan G protein-coupled receptor (GPCR) SP9155 P550 on memory consolidation in a passive avoidance learning test in rats. Accordingly, rats were pretreated with a nonselective muscarinic acetylcholine receptor antagonist, atropine, a γ-aminobutyric acid subunit A (GABA-A) receptor antagonist, bicuculline, a D2, D3, D4 dopamine receptor antagonist, haloperidol, a nonselective opioid receptor antagonist, naloxone, a non-specific nitric oxide synthase inhibitor, nitro-L-arginine, a nonselective α-adrenergic receptor antagonist, phenoxybenzamine and a ß-adrenergic receptor antagonist, propranolol. Atropine, bicuculline, naloxone and phenoxybenzamine reversed the orphan GPCR SP9155 P550-induced memory impairment, whereas propranolol, haloperidol and nitro-L-arginine were ineffective. Our results suggest that the NOP system-induced impairment of memory consolidation is mediated through muscarinic cholinergic, GABA-A-ergic, opioid and α-adrenergic receptors, whereas ß-adrenergic, D2, D3, D4-dopaminergic and nitrergic mechanisms are not be implicated.

Orexin A-induced anxiety-like behavior is mediated through GABA-ergic, α- and ß-adrenergic neurotransmissions in mice.

Orexins are hypothalamic neuropeptides, which are involved in several physiological functions of the central nervous system, including anxiety and stress. Several studies provide biochemical and behavioral evidence about the anxiogenic action of orexin A. However, we have little evidence about the underlying neuromodulation. Therefore, the aim of the present study was to investigate the involvement of neurotransmitters in the orexin A-induced anxiety-like behavior in elevated plus maze (EPM) test in mice. Accordingly, mice were pretreated with a non-selective muscarinic cholinergic antagonist, atropine; a γ-aminobutyric acid subunit A (GABA-A) receptor antagonist, bicuculline; a D2, D3, D4 dopamine receptor antagonist, haloperidol; a non-specific nitric oxide synthase (NOS) inhibitor, nitro-l-arginine; a nonselective α-adrenergic receptor antagonist, phenoxybenzamine and a ß-adrenergic receptor antagonist, propranolol 30min prior to the intracerebroventricular administration of orexin A. The EPM test started 30min after the i.c.v. injection of the neuropeptide. Our results show that orexin A decreases significantly the time spent in the arms (open/open+closed) and this action is reversed by bicuculline, phenoxybenzamine and propranolol, but not by atropine, haloperidol or nitro-l-arginine. Our results provide evidence for the first time that the orexin A-induced anxiety-like behavior is mediated through GABA-A-ergic, α- and ß-adrenergic neurotransmissions, whereas muscarinic cholinergic, dopaminergic and nitrergic neurotransmissions may not be implicated.

Transmitter mediation of the anxiolytic action of apelin-13 in male mice.

The widespread distribution of apelin-13 and apelin receptors in the brain and periphery suggests an important function of this neuropeptide in regulatory processes in the organism. In previous work we found that apelin-13 facilitates the consolidation of passive avoidance learning in rats. In the present work we demonstrate that apelin-13 exerts anxiolytic action in an elevated plus maze in mice. In order to assess the possible involvement of transmitters in this action, the animals were pretreated with the following receptor blockers in doses which themselves did not influence the behavioral paradigm: atropine (a nonselective muscarinic acetylcholine receptor antagonist), haloperidol (a D2, D3, D4 dopamine receptor antagonist), phenoxybenzamine (a nonselective α1-adrenergic receptor antagonist), methysergide (a nonselective 5-HT2 serotonergic receptor antagonist), propranolol (a ß-adrenergic receptor antagonist), naloxone (a nonselective opioid receptor antagonist) and bicuculline (a γ-aminobutyric acid subunit A receptor antagonist. Phenoxybenzamine, haloperidol, propranolol and methysergide prevented the action of apelin-13, whereas atropine, naloxone and bicuculline were ineffective. The data suggest that apelin-13 elicits its anxiolytic action via α-adrenergic, dopaminergic, ß-adrenergic and 5-HT2 serotonergic mediation.

Neurotransmissions of antidepressant-like effects of neuromedin U-23 in mice.

Neuromedin U (NmU) is a widely distributed and multifunctional peptide in the central nervous system and the peripheral tissues. Little is know about the mechanisms of NmU on brain functions. The rodent isoform of the NmU, NmU-23, has been shown to have anxiolytic effects involved in the ß-adrenergic and cholinergic nervous systems in elevated plus maze test. NmU-23 was tested for antidepressant-like effects in modified forced swimming test (FST) in mice and furthermore, the involvement of the adrenergic, serotonergic, cholinergic, dopaminergic or gaba-ergic receptors in the antidepressant-like effect of NmU-23 was studied in modified mice FST. Mice were pretreated with a non-selective α-adrenergic receptor antagonist phenoxybenzamine, an α1/α2ß-adrenergic receptor antagonist, prazosin, an α2-adrenergic receptor antagonist, yohimbine, a ß-adrenergic receptor antagonist, propranolol, a mixed 5-HT1/5-HT2 serotonergic receptor antagonist, methysergide, a non-selective 5-HT2 serotonergic receptor antagonist, cyproheptadine, nonselective muscarinic acetylcholine receptor antagonist, atropine, D2,D3,D4 dopamine receptor antagonist, haloperidol or γ-aminobutyric acid subunit A (GABAA) receptor antagonist, bicuculline. NmU-23 showed the antidepressant-like effects by decreasing the immobility time and increasing the climbing and swimming time. Prazosin, haloperidol, and bicuculline prevented the effects of NmU-23 on the climbing and swimming time. Methysergide and cyproheptadine prevented the effects of NmU-23 on the immobility, swimming and climbing time. Atropine prevented the effects of NmU-23 on the climbing time. Phenoxybenzamine, yohimbine and propranolol did not change the effects of NmU-23. The results demonstrated that the antidepressant-like effect of NmU-23 is mediated, at least in part, by an interaction of the α2-adrenergic, 5-HT1-2 serotonergic, D2,D3,D4 dopamine receptor, muscarinic acetylcholine receptors and γ-aminobutyric acid subunit A (GABAA) receptor in a modified mouse FST.