Neurochemical effects of 5-HT1 receptor ligands in pigeons

Cananga odorata essential oil reverses the anxiety induced by 1-(3-chlorophenyl) piperazine through regulating the MAPK pathway and serotonin system in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Cananga odorata essential oil, known as ylang-ylang essential oil (YYO), was commonly used in the aromatherapy for relaxation and mood adjusting use. In our previous study, YYO played anxiolytic effects on the mice in several behavioral tests that based on the instinctive responses to novel environments.

AIM OF THE STUDY

To investigate the effects and mechanisms of YYO reversing the anxiety induced by 5-HT2C receptor agonist 1-(3-chlorophenyl) piperazine (m-CPP).

MATERIALS AND METHODS

m-CPP was administrated to the male ICR mice to develop an anxiety model. The anxiolytic effect of YYO (0.1%, 1% and 10%, v/v) was evaluated in the elevated plus maze (EPM) test after odor exposure. Western blot was used to detect the phosphorylation levels of extracellular signal-regulated kinase 1/2 (ERK1/2) and cAMP response element-binding protein (CREB) and the expression of c-Fos in the prefrontal cortex (PFC) and hippocampus after the EPM test. Serotonin and its metabolite change in the brain were detected by liquid chromatogram with an electrochemical detector. The effect of YYO on the plasma corticosterone level was evaluated using enzyme-linked immunosorbent assay (ELISA) after the odor exposure.

RESULTS

The behavior analysis showed that m-CPP (2 mg/kg and 4 mg/kg) could induce anxiety behaviors in the mice while diazepam (2 mg/kg) reversed the anxiety behavior induced by m-CPP. YYO dose-dependently increased the time and number of entries in the open arms (p < 0.05) compared to the Tween 80 group. YYO reduced the phosphorylation levels of ERK1/2 (p < 0.05) in both PFC and hippocampus. Down-regulations of phosphor-CREB (p < 0.05) and c-Fos (p < 0.05) were only observed in the hippocampus. YYO also affected the brain serotonin metabolism and reduced the blood plasma corticosterone level of the m-CPP treated mice.

CONCLUSION

YYO odor exposure could reverse the anxiety behaviors generated by m-CPP. The anxiolytic effect of YYO was associated with the ERK1/2/CREB pathway in the hippocampus and relevant to the serotonin system.

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.

Differential serotonergic modulation of two types of aggression in weakly electric fish

Agonistic aggression has provided an excellent framework to study how conserved circuits and neurochemical mediators control species-specific and context-dependent behavior. The principal inhibitory control upon aggression is serotonin (5-HT) dependent, and the activation of 5-HT(1A) receptors is involved in its action. To address whether the serotonergic system differentially regulates different types of aggression, we used two species of weakly electric fish: the solitary Gymnotus omarorum and the gregarious Brachyhypopomus gauderio, which display distinctive types of aggression as part of each species' natural behavioral repertoire. We found that in the reproduction-related aggression displayed by B. gauderio after conflict resolution, the serotonergic activity follows the classic pattern in which subordinates exhibit higher 5-HT levels than controls. After the territorial aggression displayed by G. omarorum, however, both dominants and subordinates show lower 5-HT levels than controls, indicating a different response of the serotonergic system. Further, we found interspecific differences in basal serotonin turnover and in the dynamic profile of the changes in 5-HT levels from pre-contest to post-contest. Finally, we found the expected reduction of aggression and outcome shift in the territorial aggression of G. omarorum after 8-OH-DPAT (5-HT(1A) receptor agonist) administration, but no effect in the reproduction-related aggression of B. gauderio. Our results demonstrate the differential participation of the serotonergic system in the modulation of two types of aggression that we speculate may be a general strategy of the neuroendocrine control of aggression across vertebrates.

Influence of serotonergic transmission and postsynaptic 5-HT2C action on the feeding behavior of Coturnix japonica (Galliformes: Aves)

We investigated the role of 5-HT2C receptors and serotonergic transmission in the feeding behavior control of quails. Administration of serotonin releaser, fenfluramine (FEN) and 5-HT2C agonists, mCPP and MK212, 1.0 and 3.3 mg/Kg induced significant inhibition of food intake in previously fasted fowls (0.71 ± 0.18 g and 0.47 ± 0.2 g; 0.49 ± 0.22 g and 0.48 ± 0.29 g; 0.82 ± 0.13 g and 0.71 ± 0.16 g, respectively). Control groups ranged from 2.89 ± 0.21 g to 2.97 ± 0.22 g, 60 min after reintroduction of food, P < 0.0001). Similar results were obtained with normally fed quails. Both serotonin releaser and 5-HT2C agonists, in a 3.3 mg/Kg dose, induced hypophagy (FEN, 0.78 ± 0.08 g; mCPP, 0.89 ± 0.07 g; MK212, 1.25 ± 0.17 g vs. controls, 2.05 ± 0.12 g, 120 min after food was presented, P < 0.0001 to P < 0.01). Previous administration of 5-HT2C antagonist, LY53857 (5.0 mg/Kg) blocked the hypophagic response induced by 5-HT2C agonists 60 min after food was reintroduced. Current data show a modulatory role of serotonin release and postsynaptic 5-HT2C receptors in the feeding behavior of quails.

Influence of 5-HT1A agonist on the feeding behavior of Coturnix japonica (Galliformes: Aves)

In this study, we investigate the effect of serotonin receptor 5-HT1A stimulation on the feeding behavior of quails (Coturnix japonica). The administration of 5-HT1A agonist, 8-OH-DPAT (0.05 to 5.0 mg/Kg) dose-dependently inhibited the food intake in normally fed quails. Greater inhibition was attained with 5.0 mg/kg (0.93 ± 0.21 g vs. 5.83 ± 0.25 g, P < 0.05, 2 h after food offer). A comparable response was obtained from previously fasted quails. At end of 2 h, a higher dose of 8-OH-DPAT induced more intense hypophagy (1.59 ± 0.41 g vs. 6.85 ± 1.04 g, P < 0.0001). Previous treatment with the antagonist 5-HT1A/beta-adrenergic, propranolol, failed to block the inhibitory action of 8-OH-DPAT, but instead, intensified it (controls, 5.22 ± 1.09 g; 8-OH-DPAT, 1.41 ± 0.19 g; propranolol + 8-OH-DPAT, 0.44 ± 0.25 g, P < 0.01, for all comparisons). The administration of an isolated higher dose of propranolol induced a hypophagic action (controls, 4.5 ± 0.8 g vs. propranolol, 2.0 ± 0.2 g, P < 0.01). Current outcomes suggest a possible role of 5-HT1A receptor on the feeding behavior of quails, as opposed to mammals. On the other hand, the intensified hypophagy induced by previous administration of propranolol raises the hypothesis of a beta-adrenergic excitatory mechanism that controls the feeding behavior of quails.

Behavioral effects of 8-OH-DPAT injections into pontine and mesencephalic areas containing 5-HT-immunoreactive perikarya in the pigeon

This study examined the distribution of 5-HT-immunoreactive perikarya (5-HT-IRp) and the effects of local injections of 8-OH-DPAT into 5-HT-IRp-containing pontine and mesencephalic regions on feeding and drinking behaviors in free-feeding pigeons. When infused into the midline 5-HT-IRp-containing areas, 8-OH-DPAT (6.1 nmol) reliably elicited drinking and, to a lesser extent, feeding responses during the first hour after injection. These responses were significantly higher than the ingestive indexes observed (1) after vehicle (ascorbic acid 0.1%, 200 nl) injections at the same sites and (2) after 8-OH-DPAT injections into adjacent sites devoid of 5-HT-IRp. Increases in drinking were proportionally higher than those observed in feeding and a significant negative correlation was observed between water and food after midline 8-OH-DPAT injections. Similar dipsogenic responses were observed after injections of different 8-OH-DPAT doses (0.6, 2.0, and 6.1 nmol). Pretreatment with local injections of p-MPPI (an antagonist of 5-HT1A receptors) attenuated the ingestive responses evoked by 8-OH-DPAT injections. Injections of 8-OH-DPAT into lateral 5-HT-IRp-containing sites evoked only inconsistent and weak ingestive responses. These results indicate that 5-HT1A receptor-mediated circuits located in the midline superior raphe system of the pigeon may play an important role in mechanisms controlling water intake, similar to that observed in mammals.

Ingestive behaviors and metabolic fuels after central injections of 5-HT1A and 5-HT1D/1B receptors agonists in the pigeon

The effects of intracerebroventricular injections of 8-OH-DPAT (a 5-HT1A agonist; 3, 15 or 30 nmol) or GR46611 (a 5-HT1B/1D agonist; 3, 15 or 30 nmol) on feeding, drinking, preening and sleep-like behaviors were investigated in free-feeding (FF) pigeons. The effects of these 5-HT agonists on blood glucose and free fatty acids levels were also examined. Injections of 8-OH-DPAT evoked intense lipolytic and dipsogenic effects, but failed to affect feeding, non-ingestive behaviors and glycemic levels. On the other hand, GR46611 evoked significant increases in food intake (at the higher dose), as well as lipolytic and hyperglycemic effects, but left drinking and other non-ingestive behaviors unchanged. These effects are opposed to those found in rodents, and may be associated with the diverse, species-specific nature and distribution of these receptors, underscoring the need to examine the functional aspects of the 5-HT1 receptor family in a more extensive range of non-rodent species.

Discriminative stimulus effects of m-chlorophenylpiperazine as a model of the role of serotonin receptors in anxiety

Serotonin is known to play a role in anxiety. The roles of serotonin reuptake and 5-HT1A receptors have been well characterized, but the contribution of other serotonin receptor subtypes is not as clear. 1-(3-Chlorophenyl)-piperazine (mCPP), which binds non-selectively to a wide range of serotonin receptors, has often been used to produce anxiety in humans and in animal models. Because functional assays indicate that mCPP is significantly more potent at 5-HT2C receptors, it may serve as a tool to investigate the contribution of 5-HT2C receptors to anxiety. This paper reviews the results of behavioral tests using mCPP, including the drug discrimination assay, to model anxiety. Although the discriminative stimulus effects of mCPP do not seem to be a useful screen for general anxiolytics, they do seem to be useful for characterization of the contribution of 5-HT1B and 5-HT2C receptors to the mediation of anxiety-like behaviors.

Effects of acute treatment with 8-OH-DPAT and fluoxetine on aggressive behaviour in male song sparrows (Melospiza melodia morphna)

The role of serotonin in modulating male aggressive behaviour was investigated in male song sparrows, Melospiza melodia morphna, using two different serotonergic drugs, fluoxetine and 8-OH-DPAT. Fluoxetine is a selective serotonin reuptake inhibitor of the neuronal reuptake pump increasing synaptic concentrations of serotonin, and 8-OH-DPAT is a specific serotonin (5-HT1A) receptor agonist. The serotonergic control of aggression in passerines has not been previously investigated. We examined these behaviours within a controlled setting using a laboratory simulated territorial intrusion, with a hierarchical scale to quantify male-male aggressive behaviour. Utilizing this scale, we quantified the extent of male aggressive behaviour in two experiments. In experiment 1, song sparrows were given 100 micro l, s.c. injections of either fluoxetine (10 mg/kg) or 8-OH-DPAT (1 mg/kg). Experiment 2 was a dose-response study using three doses of 8-OH-DPAT (0.1, 1 and 10 mg/kg). In both studies, aggressive behaviour was measured 1 h after injection for 10 min in response to the presence of a novel male decoy combined with playback of conspecific song. Both drugs significantly reduced male aggressive behaviour, and 8-OH-DPAT did so in a dose-dependent manner. The effect of the two drugs upon general activity was also measured using infra-red perch hop detectors. Activity levels were not effected by either fluoxetine or 8-OH-DPAT at all of the respective doses, indicating that the reduction in aggressive behaviour was specific. These results demonstrate that, in a passerine species, the serotonergic system negatively regulates male-male aggressive behaviour. These results further demonstrate that aggression can be effectively studied in a laboratory setting and natural aggressive responses can be elicited using this method.

Atypical angiotensin receptors may mediate water intake induced by central injections of angiotensin II and of serotonin in pigeons

Intracerebroventricular (i.c.v.) injection of serotonin (5-HT) in pigeons dose-dependently evokes a prompt and intense drinking behavior, which resembles that evoked by i.c.v. injections of angiotensin II (ANGII) in the same species. In the present study, we have examined the possible participation of central ANGII receptors in both ANGII- and 5-HT-evoked drinking behavior. The effects of i.c.v. injections of 5-HT (155 nmol), avian ANGII ([Asp(1),Val(5)]-ANGII, 0.1 nmol) or vehicle were studied in pigeons pretreated 20 min before with i.c.v. injections of the nonspecific ANGII receptor antagonist [Sar(1),Ile(8)]-ANGII (SAR; 1, 0.1 or 0.01 nmol), the AT(1) receptor antagonist losartan (2 or 4 nmol), the AT(2) receptor antagonist PD 123,319 (2 or 4 nmol) or vehicle (NaCl 0.15 M, 1 microl, n = 8/group). Immediately after treatment, they were given free access to water and drinking behavior was recorded during the next 60 min. At the doses presently used both 5-HT and ANGII treatments evoked comparable water intake amounts with similar behavioral profiles. While pretreatment with SAR dose-dependently reduced the water intake evoked by both 5-HT and ANGII, neither losartan nor PD 123,319 pretreatment affected the drinking induced by these treatments. The present results indicate that ANGII- and 5-HT-induced drinking in pigeons may be mediated by AT receptors possibly different from mammalian AT(1) and AT(2) receptors and suggest that activation of ANGII central circuits is a necessary step for the intense drinking induced by i.c.v. injections of 5-HT in this species.

Hypophagic and dipsogenic effects of central 5-HT injections in pigeons

The present work describes a series of experiments designed to examine the possible role of central 5-HT circuits in the control of feeding and drinking in pigeons. Acute effects (within 1 h) of intracerebroventricular (ICV) injections of 5-HT (0, 9.7, 19.4, 38.7, 77.5, 155, and 310 nmol) in 24-h food-deprived (24FD) pigeons included strong hypophagic and dipsogenic responses at the three higher doses. Total food intake and the duration of feeding behavior were reduced, and latency for the start of eating increased. Total 1-h water intake in 5-HT-treated pigeons usually increases to reach a volume equivalent to 10% of their body weight. Similarly, potent dipsogenic effects of ICV 5-HT, but no food intake decreases, were observed in food-satiated animals. Feeding behavior induced by ICV injection of adrenaline (30 nmol) in satiated pigeons was abolished by previous (20 min before) ICV 5-HT (155 nmol) injections. Catecholamine treatment did not affected the dipsogenic effect of 5-HT injections. Decreases in food intake were similarly observed after ICV or subcutaneous injections of equimolar 5-HT doses (155 nmol) in 24FD pigeons, but systemic 5-HT injections evoked no drinking behavior. Central injections of the 5-HT(2a/2c) agonist DOI (56 nmol) induced similar decreases in duration and amount of food intake in 24FD animals. No dipsogenic effect was observed with either DOI doses. In 24FD pigeons, the 5-HT1a agonist 8-OH-DPAT (30.5 nmol) induced strong dipsogenic effects, as well as increase in food intake duration. These data may indicate an involvement of 5-HT circuits in food intake as well as in water intake control systems in the pigeon, and that serotoninergic effects in these functional domains are mediated by independent mechanisms.

Behavioural and neurochemical responses of male and female chicks to cat odour

In the first experiment male chicks were exposed to neutral and cat odours at days 4, 7, or 10 after hatching. Of the chicks tested at day 4, few made contact with either odour cloth, but those tested at day 7 made fewer contacts with the cat odour cloth, compared with the neutral odour, spent less time in contact with it, and spent more time in the zone furthest from the cloth. These clear differences were not seen in the group tested at day 10. In a second experiment, the behaviour of day 7 male chicks was compared in the presence of neutral, disinfectant, chick blood or cat odours, and the most extreme differences were between neutral and cat odours. In a third experiment, both male and female chicks were exposed to cat odour at day 7 and both showed similar avoidance. After exposure to cat odour both sexes showed significantly reduced GABA enhancement of benzodiazepine binding; which is a change associated with increased fear. However, after exposure to cat odour, they also showed significant decreases in 5-HT availability evidenced by lower basal and K(+)-evoked [3H]-5-HT release and, in the male chicks only, by an increased [3H]-5-HT uptake from archistriatal slices. These changes in 5-HT function are in the direction associated with reduced fear and would, therefore, seem to be adaptive and compensatory in function. Neither male nor female chicks showed any differences in [14C]-GABA release or uptake as a result of exposure to cat odour. Although the pattern of response to cat odour was the same in both male and female chicks at day 7, there were significant sex differences in 5-HT and GABA tone and benzodiazepine binding; these sex differences were also found in day 10 chicks. The importance of these for sex differences in trait anxiety is discussed.

Antiemetic effects of 5-HT1A agonists in the pigeon

Ditolyguanidine (DTG) induced a dose-dependent emetic response in pigeons, with 100% of the birds vomiting after 5.6 mg/kg. Retching and vomiting originally induced by DTG could be conditioned to the test situation. Both the unconditioned and conditioned emetic responses were dose-dependently blocked by 8-hydroxy-(di-n-propylamino)tetralin (8-OH-DPAT) and LY228729, agonists at the 5-HT1A subtype of serotonin receptor, but not by the 5-HT3, antagonist tropisetron. Higher doses (0.25-0.5 mg/kg) of tropisetron exhibited intrinsic emetic activity which could also be prevented by 8-OH-DPAT. NAN-190, a putative 5-HT1A partial agonist, produced both an antiemetic response when administered before DTG and also attenuated the antiemetic effects of 8-OH-DPAT. Pentobarbital blocked the conditioned, but not the unconditioned DTG-induced emesis. These results support the possibility that 5-HT1A agonists exhibit antiemetic activity against a broad range of emetic stimuli, including conditioned vomiting which is usually resistant to pharmacological attenuation.