Involvement of 5-HT1A receptors in passive avoidance learning in intact and ovariectomized female rats

The influence of chronic administration of 5-HT1A receptor agonist 8-OH-DPAT (0.05 mg/kg, s.c.) and 5-HT1A receptor antagonist NAN-190 (0.1 mg/kg, i.p.) injected for 14 days alone or in combination with 17beta-estradiol (0.5 microg i.m./rat/day) was studied on passive avoidance performance (PAR) and on behavior in the open field test in adult intact and ovariectomized (OVX) female rats. Administration of 5-HT1A receptor antagonist NAN-190 alone significantly improved PAR (p<0.05) in intact females with proestrus and estrus and in OVX females. Administration of 5-HT1A receptor agonist 8-OH-DPAT alone or in combination with 17beta-estradiol significantly (p<0.05) improved PAR in OVX rats and failed to normalize PAR in intact rats with proestrus and estrus. Results of the work specify the involvement of 5-HT1A receptors in the mechanisms of passive avoidance learning in OVX female rats.     

Effects of D2 receptor agonist and antagonist on behavior of intact and ovariectomized rats

The involvement of D2 dopaminergic receptors in behavioral responses during ovary cycle was assessed in adult intact female rats and ovariectomized (OVX) female rats. Quinperole (0.1 mg/kg), D2 receptor agonist and sulpiride (10.0 mg/kg), D2 receptor antagonist were injected chronically to adult intact and ovariectomized (OVX) female rats either separately or in combination with 17beta-estradiol (0.5 microg) within 14 days. Behavior of these animals was assessed in the "open field" test, whereas passive avoidance performance served as a model of learning. In intact rats, the passive avoidance performance was observed only in metestrous and diestrous. Chronic quinperole administration to intact females resulted in the appearance of the passive avoidance performance in proestrous and estrous, as distinct from the control animals. The passive avoidance performance was not reproduced in OVX rats. Quinperole per se or in combination with 17beta-estradiol completely restored the passive avoidance performance in OVX rats. Moreover, quinperole or sulpiride administration to OVX rats increased horizontal locomotor activity, exploratory behavior, and grooming behavior.     

Effects of ovariectomy and estrogen treatment on learning and hippocampal neurotransmitters in mice

This study examined the effects of long-term estrogen treatment (sc 17 beta-estradiol minipellets) on learning in C57BL/6J female and male mice using a position discrimination task in the T-maze and a win-stay task (1/8 arms baited) in the radial arm maze (RAM). In addition, hippocampal monoamines and ChAT activity were measured at the end of the study and correlated to task performance. Female sham-operated (gonadally intact) and ovariectomized (OVX) mice were treated with estrogen either for 7 or 40 days before the behavioral tests and intact male mice for 7 days before the behavioral tests. In sham-operated mice the 40-day estrogen treatment improved RAM performance and in OVX mice both the 7- and 40-day estrogen treatments improved the performance in both maze tasks. The estrogen treatment also improved RAM performance in males. The hippocampal ChAT, NA, 5-HIAA, and DOPAC levels were decreased in OVX mice. Furthermore, the effects of estrogen treatment on the levels of hippocampal 5-HT and its metabolite 5-HIAA were different in sham-operated than in OVX mice. We could find no correlation between cognitive measures and neurochemical variables. This study gives new information about the effects of estrogen on learning and hippocampal neurotransmitters in mice.     

Sex differences in neurochemical and behavioural effects of 8-hydroxy-2-(di-n-propylamino) tetralin.

A number of neurochemical investigations have shown that 5-hydroxytryptamine (5-HT) metabolism and turnover is greater in females than male rats. However increased 5-HT metabolism does not necessarily imply greater 5-HT release at the functional post-synaptic sites. Pharmacological research based on 5-HT receptor stimulation therefore gained attention. Studies of this type are complicated because of the multiplicity of 5-HT receptors in the central nervous system. Chemical ligands may not have sufficient selectivity, to specifically bind to a single receptor population. Moreover, both the density and distribution of 5-HT receptors may follow a different pattern in male and female rats. 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) is a centrally acting 5-HT agonist with a ligand binding profile showing selectivity towards 5-HT-1A receptor sites. The present article integrates research on neurochemical and behavioural effects of 8-OH-DPAT in male and female rats, in order to investigate sex-related differences in 5-HT-1A receptor dependent functions.     

Rostral ventral medulla 5-HT1A receptors selectively inhibit the somatosympathetic reflex

The role of the 5-hydroxytryptamine (5-HT1A) receptors in the rostral ventrolateral medulla (RVLM) on somatosympathetic, baroreceptor, and chemoreceptor reflexes was examined in anesthetized rats. Microinjection of the selective 5-HT1A agonist 8-hydroxy-di-n-propylamino tetralin (8-OH-DPAT) decreased arterial blood pressure and splanchnic sympathetic nerve activity (SNA). Electrical stimulation of the hindlimb evoked early and late excitatory sympathetic responses. Bilateral microinjection in the RVLM of 8-OH-DPAT markedly attenuated both the early and late responses. This potent inhibition of the somatosympathetic reflex persisted even after SNA and arterial blood pressure returned to preinjection levels. Preinjection of the selective 5-HT1A antagonist NAN-190 in the RVLM blocked the sympathoinhibitory effect of 8-OH-DPAT and attenuated the inhibitory effect on the somatosympathetic reflex. 8-OH-DPAT injected in the RVLM did not affect baroreceptor or chemoreceptor reflexes. Our findings suggest that activation of 5-HT1A receptors in the RVLM exerts a potent, selective inhibition on the somatosympathetic reflex.     

Involvement of D1 receptors in depression-like behavior of ovariectomized rats

The aim of the present study was to explore the mood effects of D1 receptor agonist, SKF-38393 and D1 receptor antagonist, SCH-23390 alone or in combination with a low dose of 17β-estradiol (17β-E2) in the adult ovariectomized female rats (OVX). OVX rats of Wistar strain were used in all experiments. Two weeks after surgery rats were chronically treated with vehicle, a low dose of 17β-E2 (5.0 μg/rat), SKF-38393 (0.1 mg/kg), SCH-23390 (0.1 mg/kg), SKF-38393 plus 17β-E2 or SCH-23390 plus 17β-E2 for 14 days before the forced swimming test. We found that SCH-23390 significantly decreased immobility time in the OVX females. A combination of SCH-23390 with a low dose of 17β-E2 induced more profound decrease of immobility time in the OVX rats compared to the rats treated with SCH-23390 alone. On the contrary, SKF-38393 failed to modify depression-like behavior in the OVX rats. In addition, SKF-38393 significantly blocked the antidepressant-like effect of 17β-E2 in OVX rats. Thus, the D1 receptor antagonist SCH-23390 alone or in combination with a low dose of 17β-E2 exerted antidepressant-like effect in OVX female rats, while the D1 receptor agonist SKF-38393 produced depressant-like profile on OVX rats.     

5-HT(7)-like receptors mediate serotonergic modulation of photo-responsiveness of the medulla bilateral neurons in the cricket,Gryllus bimaculatus

Serotonin (5-HT) suppresses the photo-responsiveness of medulla bilateral neurons (MBNs) that are involved in the coupling mechanism of the bilaterally paired optic lobe circadian pacemakers in the cricket, Gryllus bimaculatus. We found that forskolin, a highly specific activator of adenylate cyclase, mimicked the effects of serotonin on the MBNs. This fact suggests the involvement of cyclic 3', 5'-adenosine monophosphate (cAMP) in mediating the action of serotonin. We therefore tested the effects of various 5-HT receptor agonists and antagonists that are coupled to adenylate cyclase to specify the receptor involved. Application of 8-OH-DPAT that has affinity for both 5-HT(1A) and 5-HT(7) receptors suppressed the photo-responsiveness, like forskolin. The inhibitory effect of 8-OH-DPAT was effectively blocked by clozapine, a high affinity 5-HT(7) receptor antagonists with a very low affinity for 5-HT(2). Ketanserin, a selective 5-HT(2) antagonist, and NAN-190, a 5-HT(1A) antagonist, did not block it. These results suggest that serotonergic suppression of the photo-responsiveness of the MBNs is mediated by 5-HT(7)-like receptor subtypes.     

Mixed agonist/antagonist properties of NAN-190 at 5-HT1A receptors: behavioural and in vivo brain microdialysis studies

1-(2-Methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine, NAN-190, is a novel compound with putative 5-HT1A antagonist properties. In the present study, the effects of NAN-190 were examined with regard to functional pre- and post-synaptic 5-HT1A receptor-mediated events, using in vivo brain microdialysis and behavioural techniques. Our findings provide evidence that NAN-190 acts as a mixed agonist/antagonist at central 5-HT1A receptors. Thus, NAN-190 blocked (+)8-OH-DPAT-induced behaviour in reserpinized rats, indicating antagonist properties at postsynaptic 5-HT1A receptors. However, the compound was also able to decrease the release of 5-HT in vivo, tentatively due to an agonist action at somatodendritic 5-HT1A autoreceptors. These data extend previous information on the pharmacological profile of NAN-190 and further emphasizes the difference between pre- and postsynaptic 5-HT1A receptors in brain.     

Hippocampal Serotonin 5-HT1A Receptor Enhances Acetylcholine Release in Conscious Rats

Abstract: We investigated changes in the extracellular levels of acetylcholine (ACh) following local application of serotonergic agents to the dorsal hippocampus of freely moving rats by means of perfusion using a microdialysis technique. Perfusion of serotonin (5-HT; 10 μM, for 30 min at a rate of 3 μl/min), dissolved in Ringer's solution containing 10 μM eserine, showed no marked effect on the extracellular levels of ACh. 8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 20 μM), a 5-HT_1A agonist, increased ACh levels, whereas 7-trifluoromethyl-4-(4-methyl-1 -piperazinyl)-pymoto[1,2-a]quinoxaline (CGS-12066B; 100 μM), a 5-HT_1B agonist, decreased it. Clomipramine (2 μM), an uptake inhibitor of 5-HT, had no effect on ACh levels. Following perfusion of 1-(2-methoxyphenyl)-4-[4- (2-phthalimido)butyl]piperazine (NAN-190; 10 μM), which is a selective 5-HT_1A antagonist, the effect of 8-OH-DPAT was totally abolished, whereas CGS-12066B decreased extracellular ACh levels. 5-HT, as well as Clomipramine, had a decreasing effect on ACh levels after pretreatment with NAN-190. These results indicate that the 5-HT_1A receptor, which exists in the dorsal hippocampus, enhances the spontaneous ACh release, and that the mechanism of serotonergic modulation of ACh release partly depends on both the stimulatory control via the 5-HT_1A receptor and the suppressive one via the 5-HT_1B receptor in the dorsal hippocampus of rats.     

Do imipramine and dihydroergosine possess two components--one stimulating 5-HT1 and the other inhibiting 5-HT2 receptors?

The mechanisms by which imipramine and dihydroergosine stimulate the 5-HT syndrome in rats and inhibit the head-twitch response in rats and mice were studied. Imipramine- and dihydroergosine-induced stimulation of the 5-HT syndrome was inhibited stereoselectively by propranolol, a high affinity ligand for 5-HT1 receptor sites, but not by ritanserin, a specific 5-HT2 receptor antagonist. (-)-Propranolol potentiated the inhibitory effect of imipramine, but not of dihydroergosine on the head-twitch response, while ritanserin was without effect. Neither imipramine nor dihydroergosine were able to stimulate the 5-HT syndrome in the animals pretreated with p-chlorophenylalanine. As expected, 8-OH-DPAT, a selective 5-HT1A receptor agonist, stimulated, and 5-HT1B agonists CGS 12066B and 1-(trifluoromethylphenyl)piperazine (TFMPP) failed to stimulate the 5-HT syndrome induced in rats by pargyline and 5-HTP administration. A higher dose of ritanserin inhibited the syndrome. While 8-OH-DPAT alone produced all behavioral components of the 5-HT syndrome, dihydroergosine or imipramine alone even at very high doses never produced tremor or a more intensive forepaw padding as seen when these drugs were given in combination with pargyline and 5-HTP. A single administration of (-)-propranolol also inhibited the head-twitch response. This effect lasted in mice longer than after ritanserin administration. In in vitro experiments dihydroergosine expressed approximately twenty-fold higher affinity for 3H-ketanserin binding sites than imipramine. The results suggest that imipramine and dihydroergosine possess two components--one stimulating the 5-HT syndrome in rats by a presynaptic, presumably 5-HT1A-mediated mechanism, and the other inhibiting 5-HT2 binding sites.     

Gender-related distinctions in protein kinase C activity in rat vascular smooth muscle

Gender differences in vascular reactivity have been suggested; however, the cellular mechanisms involved are unclear. We tested the hypothesis that the gender differences in vascular reactivity reflect gender-related, possibly estrogen-mediated, distinctions in the expression and activity of specific protein kinase C (PKC) isoforms in vascular smooth muscle. Aortic strips were isolated from intact and gonadectomized male and female Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). Isometric contraction was measured in endothelium-denuded aortic strips. PKC activity was measured in the cytosolic and particulate fractions, and the amount of PKC was measured using Western blots and isoform-specific anti-PKC antibodies. In intact male WKY rats, phenylephrine (Phe, 10(-5) M) and phorbol 12,13-dibutyrate (PDBu, 10(-6) M) stimulated contraction to 0.37 +/- 0.02 and 0.42 +/- 0.02 g/mg tissue wt, respectively. The basal particulate/cytosolic PKC activity ratio was 0.86 +/- 0.06, and Western blots revealed alpha-, delta-, and zeta-PKC isoforms. Phe and PDBu increased PKC activity and caused significant translocation of alpha- and delta-PKC from the cytosolic to particulate fraction. In intact female WKY rats, basal PKC activity, the amount of alpha-, delta-, and zeta-PKC, the Phe- and PDBu-induced contraction, and PKC activity and translocation of alpha- and delta-PKC were significantly reduced compared with intact male WKY rats. The basal PKC activity, the amount of alpha-, delta-, and zeta-PKC, the Phe and PDBu contraction, and PKC activity and alpha- and delta-PKC translocation were greater in SHR than WKY rats. The reduction in Phe and PDBu contraction and PKC activity in intact females compared with intact males was greater in SHR ( approximately 30%) than WKY rats ( approximately 20%). Phe and PDBu contraction and PKC activity were not significantly different between castrated males and intact males but were greater in ovariectomized (OVX) females than intact females. Treatment of OVX females or castrated males with 17 beta-estradiol, but not 17 alpha-estradiol, subcutaneous implants caused significant reduction in Phe and PDBu contraction and PKC activity that was greater in SHR than WKY rats. Phe and PDBu contraction and PKC activity in OVX females or castrated males treated with 17 beta-estradiol plus the estrogen receptor antagonist ICI-182,780 were not significantly different from untreated OVX females or castrated males. Thus a gender-related reduction in vascular smooth muscle contraction in female WKY rats with intact gonads compared with males is associated with reduction in the expression and activity of vascular alpha-, delta-, and zeta-PKC. The gender differences in vascular smooth muscle contraction and PKC activity are augmented in the SHR and are possibly mediated by estrogen.     

Effects of highly or relatively selective 5-HT1A receptor agonists on lordosis in female rats

To investigate the role of serotonin (5-HT) receptor 1A or 7 in regulating lordosis behavior in female rats, ovariectomized rats were treated with 3 kinds of receptor agonists and lordosis behavior was observed. The injected agents were the selective 5-HT1A receptor agonist, buspirone (BUS), the highly selective 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino)tetralin ((+/-)8-OH-DPAT), and the 5-HT1A and 5-HT7 receptor agonist, (R)-8-hydroxy-2-(di-n-propylamino)tetralin ((+)8-OH-DPAT). A behavioral test was performed after ovariectomy and subcutaneous implantation of a silicon tube containing estradiol. Female rats in which the lordosis quotient (LQ) was over 70 were intraperitoneally injected with several doses of these agents. As a result, in the BUS group, the dose of 3 mg/kg bw, but not 1 mg/kg was effective for suppressing lordosis. On the other hand, an inhibitory effect was observed from 0.25 mg/kg and 0.5 mg/kg in the (+)8-OH-DPAT and (+/-)8-OH-DPAT groups, respectively. In the time-course experiment, in all drug-treated groups, LQ decreased to lower than 20 after 15 min and low LQ continued for 1 hr at least. Measurement of locomotor activity using an infrared sensor system showed no relation between the decrease in lordosis by these agents and spontaneous locomotion. These results indicate that 5-HT1A is strongly involved in the lordosis-inhibiting circuit of the serotonin neurons.     

An antagonistic 5-HT receptor system in the auricles of the systemic heart complex of Sepia officinalis L. (Cephalopoda) shows 5-HT1 and 5-HT4 subtype properties

In pharmacological bioassays on isolated ring-shaped auricle preparations of Sepia officinalis, the action of the specific 5-hydroxytryptamine (5-HT) agonists 8-OH-DPAT (5-HT1a), CP-93129 (5-HT1b), TFMPP (5-HT1b) and RS-67333 (5-HT4) on these autonomously contractile compartments was studied. 8-OH-DPAT and CP-93129 induced mainly positive effects on frequency and tone on the isotonically suspended auricles. The positive effect of 8-OH-DPAT on frequency was blocked by the specific 5-HT1a antagonist NAN-190. The 5-HT1b agonist TFMPP caused similar effects on tone and a positive impact on the auricular amplitude. The highly specific 5-HT4 agonist RS-67333 induced an effect opposite to the action of 5-HT1 agonists inducing mainly negative effects on frequency, amplitude and tone, causing a diastolic standstill at a concentration of 10(-6) M. These negative effects were blocked by the adenylyl cyclase inhibitor SQ-22,536 in the absence of a diastolic standstill. The opposing action of 5-HT1 and 5-HT4 agonists on auricular contractile activity suggests that an antagonistic 5-HT-receptor system exists within the auricular myocardial cells of S. officinalis, probably consisting of 5-HT1- and 5-HT4-like subtypes. The results also suggest that adenylyl cyclase acts as the intracellular target enzyme of both signal transduction mechanisms.     

Activation of the external urethral sphincter central pattern generator by a 5-HT(1A) receptor agonist in rats with chronic spinal cord injury

We recently demonstrated that treatment with the 5-HT(1A/7) receptor agonist [(R)-(+)-8-hydroxy-2-di-n-propylamino]tetralin (8-OH-DPAT) increases bladder capacity in chloralose-anesthetized female cats with chronic spinal cord injury. In the current study, we investigated the effects of 8-OH-DPAT on bladder capacity and external urethral sphincter (EUS) activity in urethane-anesthetized female rats (initial body mass 175-200 g) with chronic spinal cord injury (transsection at T10). Cystometric study took place 8-12 wk posttranssection. Intravesical pressure was monitored in urethane-anesthetized rats with a transvesical catheter, and EUS activity was assessed electromyographically. Spinal cord injury disrupts phasic activity of the EUS, resulting in decreased voiding efficiency and increased residual volume. 8-OH-DPAT induced a dose-dependent decrease in bladder capacity (the opposite of its effect in chronic spinal cord-injured cats) with an increase in micturition volume and decrease in residual volume resulting from improvement in voiding efficiency. The unexpected improvement in voiding efficiency can be explained by the 8-OH-DPAT-induced emergence of phasic EUS relaxation. Phasic EUS relaxation was also altered by 8-OH-DPAT in spinally intact rats, whereas the 5-HT(1A) receptor antagonist N-tert-butyl-3-[4-(2-methoxyphenyl)-piperazin-1-yl]-2-phenylpropanamide (WAY-100635), on its own, was without effect. It remains to be determined when phasic relaxation is restored after spinal cord injury, and indeed whether it is ever truly lost or is only temporarily separated from excitatory input.     

Serotonergic mechanisms mediating spawning and oocyte maturation in the zebra mussel,Dreissena polymorpha

Summary

The zebra mussel, Dreissena polymorpha, is a freshwater biofouling bivalve unintentionally introduced in the 1980s into North America from Europe. Oocyte maturation (germinal vesicle breakdown, GVBD) and spawning of the zebra mussel can be triggered with serotonin (5-hydroxytryptamine, 5-HT). In pharmacological experiments to characterize the receptor mediating spawning, the serotonin receptor agonists 8-OH-DPAT, TFMPP, and 1-(1-naphthyl)piperazine were effective at stimulating spawning; whereas, 2-methylserotonin and alpha-methylserotonin had no effect. In experiments with antagonists of serotonin receptors ketanserin and propranolol had no effect; mianserin, NAN-190, and cyproheptadine had partial inhibitory effects; and methiothepin was a very effective antagonist. Metergoline had mixed agonist/antagonist properties. Ergotamine was the most effective activator of spawning in females. Compared to serotonergic receptors in other organisms, the receptors that activate spawning in zebra mussels resemble 5HTlym, 5HTdro2 and human 5HT1Dβ, which are receptors that may act both by inhibiting adenylyl cyclase and by activating phospholipase C. In zebra mussels, 5-HT and 8-OH-DPAT activate GVBD in gonad fragments, a process also initiated by manual dissection of gonad fragments. GVBD can be inhibited by pre-treatment of ovaries with forskolin and theophylline, suggesting an inhibitory role for cyclic AMP. The Ca²⁺ ionophore A23187 can trigger GVBD and polar body formation. Thus, oocyte maturation in zebra mussels may be initiated via serotonergic receptors simultaneously inhibiting adenylyl cyclase and activating Ca²⁺ mechanisms.     

Peripheral 5-carboxamidotryptamine induces hindlimb scratching by stimulating 5-HT1A receptors in rats.

Treatment of rats with 5-carboxamidotryptamine (5-CT) or 5-methoxy-tryptamine (5-MeOT) induces a hindlimb scratch response. These compounds have high affinity for 5-HT1A and 5-HT1D receptors. The selective 5-HT1A receptor agonist N,N-dipropyl-5-CT (DP-5-CT) also induced hindlimb scratching while the selective 5-HT1D receptor agonist, sumatriptan, did not. 5-CT-induced hindlimb scratching was inhibited dose-dependently by several 5-HT1A antagonists (BMY 7378, NAN-190, MDL 73005EF and pindobind-5-HT1A) as well as the non-selective 5-HT antagonist, methiothepin. Pretreatment of rats with the serotonin (5-HT) synthesis inhibitor, p-chlorophenylalanine (PCPA) or the 5-HT depleting agent, reserpine, markedly attenuated 5-CT-induced hindlimb scratching. These data suggest that hindlimb scratching induced by 5-HT agonists may not be centrally mediated but rather may be mediated by a neuronal 5-HT1A receptor localized outside the blood-brain barrier.     

Role of Somatodendritic and Postsynaptic 5-HT1A Receptors on Learning and Memory Functions in Rats

Memory impairment is a major problem afflicting mankind. The association between memory functions and neurotransmitter functions is of great interest for understanding brain function. Serotonergic pathways play an important role in the modulation of memory functions but the importance of its receptor types and subtypes on memory functions is still unclear. Activation and blockade of various serotonin (5-HT) receptors has been reported to alter cognitive processes and 5-HT receptor antagonism could be beneficial in the treatment of cognitive diseases. The role of 5-HT on memory functions is complicated. Among the 5-HT receptors subtypes, 5-HT(1A) receptors are of special interest because these receptors are present in the brain areas involved in learning and memory functions such as hippocampus and cortex. The present study was therefore designed to investigate the effect of activation and blockade of somatodendritic and/or postsynaptic 5-HT(1A) receptor on learning and memory functions in rats using modified version of water maze. In this study, 8-OH-DPAT (8-hydroxy-2-(di-N-propylamino) tetralin) at 0.3?mg/kg significantly enhanced learning acquisition (LA), short-term memory (STM) and long term memory (LTM) of rats pre-injected with saline suggesting that the activation of pre-synaptic 5-HT(1A) receptors by its agonist enhanced the memory functions of rats. Conversely, rats injected with 8-OH-DPAT at 1.0?mg/kg exhibited impaired LA and STM and had no effect on LTM. It was also shown in this study that blockade of 5-HT(1A) receptors by spiperone enhanced LA, had no effect on STM but impaired the LTM, which showed that the blockade of 5-HT(1A) receptors by its antagonist exerts different effect on different types of memory. This study suggests that 5-HT(1A) receptor could be used as a significant pharmacological target for the treatment of CNS diseases. Unraveling the role of serotonin in cognition and memory disorders could provide better therapy and it may lead to new insights in our understandings of learning and memory.     

Presynaptic 5-HT1A receptors in immunomodulation

It is shown that a selective agonist of 5-HT1A receptors 8-OH-DPAT in a low dose (0.1 mg/kg), which is known to affect mainly the presynaptic 5-HT1A receptors increased the immune response at the peak of reactions (the forth or fifth day after immunization with sheep red blood cells - SRBC) in CBA mice and Wistar rats. Treatment of the animals with the drug 15 min prior to antigen injection raised the number of plaque-forming cells (lgM-PFC) and rosette-forming cells (RFC) in the spleen. The preliminary blockade of 5-HT1A receptor with a selective antagonist of 5-HT1A receptors WAY-100635 (0.1 mg/kg) prevented the immunostimulating effect of 5-HT 1A receptors agonist 8-OH-DPAT, whereas WAY-100635 administration alone in the same dose didn't change the immune response. Activation of 5-HT1A receptors under conditions of electrical lesion of 5-HTergic neurons of the nucleus raphe was unable to enhance the immune reactions, as it did in sham-operated rats. The data obtained indicate that the somatodendric 5-HT1A autoreceptors are involved in immunomodulation.     

Reduced Efficacy of 8-OH-DPAT's Inhibition of Lordosis Behavior by Prior Estrogen Treatment

The effects of bilateral VMN infusion with the 5-HT1A receptor agonist, (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 200, 1000, or 2000 ng), on lordosis behavior were examined in hormonally primed ovariectomized rats. When rats were given a single injection with 25 microg estradiol benzoate followed 48 h later with 500 microg progesterone, inhibition of lordosis behavior was evident at all doses of 8-OH-DPAT. However, when rats were treated with 25 microg estradiol benzoate followed 7 days later with a second injection of 25 microg estradiol benzoate and then progesterone, none of the doses of 8-OH-DPAT effectively inhibited lordosis behavior. In some rats, cannulae were located near the most rostral portion of the VMN. In these rats, there was no effect of the second estrogen treatment on the response to 8-OH-DPAT. Therefore, a second experiment was performed to specifically evaluate the effects of two estradiol benzoate treatments on the response to bilateral 8-OH-DPAT infusion in the rostral VMN. In contrast to the reduced effectiveness of the 8-OH-DPAT infusion in the mid to caudal VMN in rats given two injections with estradiol benzoate, 2000 ng 8-OH-DPAT continued to effectively inhibit lordosis behavior following the 5-HT1A receptor agonist's infusion into the more rostral areas. These findings are discussed in relation to earlier studies in which the potency, but not the efficacy, of 8-OH-DPAT was reduced following systemic treatment with the 5-HT1A receptor agonist.     

Nad-299 antagonises 5-HT-stimulated and spiperone-inhibited [35S]GTPgammaS binding in cloned 5-HT1A receptors

In Chinese Hamster Ovary (CHO) cells expressing cloned human 5-hydroxytryptamine1A A (5-HT1A) receptors, (R)-3-N,N-dicyclobutylamino-8-fluoro-[6-3H]-3,4-dihydro-2H-1-benzopyan-5-carboxamide ([3H]NAD-299) exhibited high affinity (Kd = 0.16 nM) and labeled 34% more receptors than 8-hydroxy-2-([2,3-3H]di-n-propylamino)tetralin ([3H]8-OH-DPAT). NAD-299 behaved as a silent antagonist in [35S]GTPgammaS binding similar to N-tert-butyl-3-(4-(2-methoxyphenyl)-piperazin-1-yl)-2-phenylpropanamide (WAY-100635) and (S)-5-fluoro-8-hydroxy-2-(di-n-propylamino)tetralin ((S)UH-301). 5-HT and 5-carboxamidotryptamine (5-CT) stimulated [35S]GTPgammaS binding 2.5-fold while spiperone and methiothepin inhibited [35S]GTPgammaS binding 1.4-fold. Furthermore, NAD-299 antagonised both the 5-HT stimulated and the spiperone inhibited [35S]GTPgammaS binding to basal levels. The KiL/KiH ratios for spiperone (0.66), methiothepin (0.39), WAY-100635 (0.32), (S)UH-301 (0.94), NAD-299 (1.29), NAN-190 (1.23), (S)pindolol (5.85), ipsapirone (13.1), buspirone (24.6), (+/-)8-OH-DPAT (47.3), flesinoxan (55.8), 5-HT (200) and 5-CT (389) correlated highly significantly with the intrinsic activity obtained with [35S] GTPgammaS (r = 0.97).