Effects of 5HT1A Activation on Depression Profile Following 5-HT Depletion in Rats Lacking Social Attachment Since Weanling

OBJECTIVE: Post weanling isolation-reared (IR) rats are featured with depressive phenotype, yet its mechanism is not clearly defined particularly in terms of the involvement of central 5-HT1A receptors. The present study aims to examine the effects of 5HT1A activation on forced swim test (FST) in IR rats following 5-HT depletion. METHODS: Social control (SOC) and IR rats received an intracerebraoventricular (ICV) injection of 5-HT depletion agent, 5,7-DHT. 14 days after the surgery, rats were assessed their performance in FST with or without the challenge with a 5-HT1A agonist, 8-OH-DPAT. Rats were then sacrificed for analyzing their 5-HT tissue levels and the expressions of their 5-HA1A receptors in prefrontal cortex (PFC), hippocampus (HPX), and amygdala (AMY). RESULTS: 5,7-DHT decreased the tissue concentration of 5-HT in both IR and SOC rats. IR rats were more immobile and less sensitive to the lesion-induced immobility, however this effect was reversed by acute challenge of 8-OH-DPAT. 5,7-DHT lesion increased the expression of PFC 5-HT1A receptors. CONCLUSION: The integrity of central 5-HT system is developmentally crucial for the 5-HT1A-relevant depression profile in rats of social isolation.

Establishment of a rat model of premature ejaculation with 8-OH-DPAT / 中华男科学杂志

Objective@#To explore the feasibility and practicability of establishing a rat model of premature ejaculation (PE) by injection of 8-OH-DPAT into the subarachnoid space of the lumbosacral spinal cord segments.@*METHODS@#Twenty-four male Wistar rats were equally randomized into a PE model and a blank control group. The PE model was established by injection of 8-OH-DPAT in 10 ml normal saline at 0.8 mg per kg of the body weight per day into the subarachnoid space of the lumbosacral spinal cord segments and the control rats were injected with the same volume of normal saline only, both for 4 weeks. Another 24 female Wistar rats were injected subcutaneously with benzoic acid estradiol at 20 μg to induce estrus at 36 hours before mated with the male animals. At 2 and 4 weeks, the male rats were mated with the female ones for 30 minutes each time and meanwhile observed for their mating behavior indicators, such as mount latency, intromission latency, ejaculation latency, mount frequency, intromission frequency, and ejaculation frequency.@*RESULTS@#Compared with the controls, the PE model rats showed a significantly lower ejaculation latency (［712.35 ± 36.77］ vs ［502.35 ± 46.72］ s, P0.05).@*CONCLUSIONS@#A rat model of premature ejaculation was successfully established by injection of 8-OH-DPAT into the subarachnoid space of the lumbosacral spinal cord segments, which is of great significance for further study of the mechanism of premature ejaculation.

Effects of 5HT1A Activation on Gating Profile Following 5HT Depletion in Rats Lacking Social Attachment Since Weanling

OBJECTIVE: Central 5-HT1A receptor is involved in the modulation of sensorimotor gating function. However, its precise role is not clearly defined in developmentally social deprived (isolation rearing, IR) rats featured with impaired sensorimotor gating ability. We therefore aimed to examine the effects of 5HT1A activation on acoustic startle response (ASR) and prepulse inhibition (PPI) in IR rats in a condition of compromised presynaptic 5-HT functions. METHODS: Social control (SOC) and IR rats received an intracerebraoventricular (ICV) injection of 5-HT depletor, 5,7-DHT. Seven days later rats entered a protocol of 8-OH-DPAT, a 5-HT1A agonist, in which locomotor activity, ASR and PPI and their tissue levels of 5-HT were measured. RESULTS: Our results found that both IR and 5,7-DHT decreased the tissue concentration of 5-HT. IR-induced hyperactivity and gating impairment were unaffected by 5-HT depletion. 8-OH-DPAT strengthened the ASR in IR but not SOC rats and the drug-reduced PPI could be adjusted by 5,7-DHT pretreatment. 8-OH-DPAT at 100 μg/kg enhanced PPI in 5-HT-depleted SOC rats. However for IR rats, 8-OH-DPAT strengthened PPI in sham rats but downgraded it in depletion condition. CONCLUSION: The integrity of central 5-HT system is important to 5-HT1A-modulated sensorimotor gating in isolation-reared rats.

Effect of 5-HT1A receptors in the hippocampal DG on active avoidance learning in rats / 中国应用生理学杂志

<p><b>OBJECTIVE</b>To investigate the effects of serotonin (5-HTIA) receptors in the hippocampal dentate gyrus (DG) on active avoidance learning in rats.</p><p><b>METHODS</b>Totally 36 SD rats were randomly divided into control group, antagonist group and agonist group(n = 12). Active avoidance learning ability of rats was assessed by the shuttle box. The extracellular concentrations of 5-HT in the DG during active avoidance conditioned reflex were measured by microdialysis and high performance liquid chromatography (HPLC) techniques. Then the antagonist (WAY-100635) or agonist (8-OH-DPAT) of the 5-HT1A receptors were microinjected into the DG region, and the active avoidance learning was measured.</p><p><b>RESULTS</b>(1) During the active avoidance learning, the concentration of 5-HT in the hippocampal DG was significantly increased in the extinction but not establishment in the conditioned reflex, which reached 164.90% ± 26.07% (P <0.05) of basal level. (2) The microinjection of WAY-100635 (an antagonist of 5-HT1A receptor) into the DG did not significantly affect the active avoidance learning. (3) The microinjection of 8-OH-DPAT(an agonist of 5-HT1A receptor) into the DG significantly facilitated the establishment process and inhibited the extinction process during active avoidance conditioned reflex.</p><p><b>CONCLUSION</b>The data suggest that activation of 5-HT1A receptors in hipocampal DG may facilitate active avoidance learning and memory in rats.</p>

5-HT(1A) receptors are involved in the modulation of respiratory rhythmical discharge activity in the medulla oblongata slice preparation of neonatal rats / 生理学报

The present study was carried out to determine the role of 5-HT(1A) receptors in the generation and modulation of basic respiratory rhythm. Neonatal (aged 0-3 d) Sprague-Dawley rats of either sex were used. The medulla oblongata slice was prepared and the surgical procedure was performed in the modified Kreb's solution (MKS) with continuous carbogen (95% O2 and 5% CO2), and ended in 3 min. In cold MKS, a 600-700 microm single transverse slice was cut, which was rostral to the edge of area postrema and retained the hypoglossal nerve roots and some parts of the ventral respiratory group. The preparation was quickly transferred to a recording chamber and continuously perfused with carbogen-saturated MKS at a rate of 4-6 mL/min at 27-29 degrees C. Glass adsorb-electrodes containing Ag-AgCl needle were attached to the ventral roots of the hypoglossal nerve. Respiratory rhythmical discharge activity (RRDA) of the rootlets of hypoglossal nerve was recorded. Ten medulla oblongata slice preparations were divided into two groups. In group I, 5-HT(1A) receptor specific agonist (+/-)-8-hydroxy-2-(di-N-propylamino)tetralin hydrobromide (8-OHDPAT, 20 micromol/L) was added into the perfusion solution for 10 min first, after washing out, the 5-HT(1A) antagonist [4-iodo-N-[2-[4-methoxyphenyl]-1-piperazinyl]ethyl]-N-2-pyridynyl-benzamide hydrochloride] (PMPPI, 10 micromol/L) was applied to the perfusion solution for 10 min. In group II, after application of 8-OHDPAT for 10 min, additional PMPPI was added into the perfusion solution for 10 min. The discharges of the rootlets of hypoglossal nerve were recorded. Signals were amplified and band-pass filtered (100-3.3 kHz). Data were sampled (1-10 kHz) and stored in the computer via BL-420 biological signal processing system. Our results showed that 8-OHDPAT increased the respiratory cycle (RC) and expiratory time (TE) as well as reduced the integral amplitude (IA), but the changes of the inspiratory time (TI) were not statistically significant. PMPPI induced a significant decrease in RC, TE and TI, but the changes of IA were not statistically significant. The effect of 8-OHDPAT on the respiratory rhythm was partially reversed by additional application of PMPPI. Taken together with previous results, 5-HT(1A) receptors may play an important role in the modulation of RRDA in the medulla oblongata slice preparation of neonatal rats.

Effects of 8-OH-DPAT on respiratory rhythmical discharge activity in isolated neonatal rat brainstem slice / 南方医科大学学报

<p><b>OBJECTIVE</b>To investigate the role of 5-HT1A receptors in the generation and modulation of basic respiration rhythm.</p><p><b>METHODS</b>Brainstem slices of 20 newborn SD rats (0-3 days) were prepared and respiratory rhythmical discharge activity (RRDA) of the hypoglossal nerve was recorded by suction electrode on these preparations including the medial region of the nucleus retrofacialis (mNRF) with the hypoglossal nerve rootlets retained, and the effects of 5-HT1A receptors on RRDA were investigated by application of specific agonist of 5-HT1A receptors 8-OH-DPAT in the perfusion solution. The 20 neonatal rats were divided into 4 groups and the brainstem slices were perfused continuously for 10 min with different concentrations of 8-OH-DPAT (1, 5, 10, 20 micromol/L, respectively). RRDA was recorded before and 1, 3, 5 min after 8-OH-DPAT perfusion.</p><p><b>RESULTS</b>The respiratory cycles (RC) varied significantly between the different time points of 8-OH-DPAT administration (F=181.219, P<0.001), which was the shortest before 8-OH-DPAT administration and increased progressively after administration till reaching the maximum 5 min after the administration. The RC also varied significantly between different 8-OH-DPAT concentrations (F=61.675, P<0.001). At each time point after 8-OH-DPAT administration, RC was the shortest with 1 micromol/L and maximum with 20 micromol/L 8-OH-DPAT. A crossover effect was observed between the time and administered 8-OH-DPAT concentration (F=22.940, P<0.001). The integrated amplitude (IA) was significantly different between different time points of 8-OH-DPAT administration (F=20.949, P<0.001), and the application of 10 and 20 micromol/L 8-OH-DPAT resulted in significant IA decrement (F=5.050, P=0.017; F=51.389, P=0.001, respectively). Different concentrations of 8-OH-DPAT also significantly affected IA (F=41.027, P<0.001), and at each time point after administration, IA was the maximum with 1 micromol/L and minimum with 20 micromol/L 8-OH-DPAT, also showing a crossover effect between time and 8-OH-DPAT concentration (F=3.483, P=0.002).</p><p><b>CONCLUSIONS</b>8-OH-DPAT induces a dose-dependent increase in RC and a dose-dependent inhibition of the IA and burst frequency, with long-lasting inhibitory effect on the inspiration. 5-HT1A receptors play an important role in the modulation of the RRDA in isolated neonatal rat brainstem slice.</p>

Inhibition of 8-OH-DPAT on spontaneous unit discharges of 5-hydroxytryptamine inhibitory unit in rat primary somatosensory cortex / 中国应用生理学杂志

<p><b>AIM</b>To investigate the effect of 5-hydroxytryptamine (5-HT) on spontaneous unit discharges of primary somatosensory cortex (SI-SUD) and the role of 5-HT1A receptor in 5-HT inhibitory effect on SI-SUD in rat.</p><p><b>METHODS</b>The SI-SUD was recorded before and during microiontophoresis of 5-HT and 8-OH-DPAT (the selective agonist for 5-HT1A receptor. The changes of mean of interspike interval (MISI) of SI-SUD were analysed and handled with the statistics.</p><p><b>RESULTS</b>(1) Effects of 5-HT on SI-SUD may be inhibitory (48/96), excitatory (26/96) or non-responsive (22/96), and the major effect is inhibitory. (2) In 20 of 5-HT inhibited units, 17 are also inhibited with microiontophoresis of 8-OH-DPAT, but 3 have no obvious response to 8-OH-DPAT.</p><p><b>CONCLUSION</b>The major effect of 5-HT on SI-SUD is inhibitory. In majority of 5-HT inhibited units, 5-HT1A receptor may be existence, which may involve in the inhibition of 5-HT on SI-SUD.</p>

Involvement of central serotonergic systems in dextromethorphan-induced behavioural syndrome in rats.

Dextromethorphan, a noncompetitive blocker of the N-methyl-D-aspartate (NMDA) type of glutamate receptor, at 45, 60 and 75 mg/kg, ip doses induced a behavioural syndrome characterised by reciprocal forepaw treading, lateral head-weaving, hind-limb abduction and flat body posture. Such type of behavioural syndrome is induced by 8-hydroxy-2- (di-n-propylamino) tetralin (8-OH-DPAT) by directly stimulating the central postsynaptic 5-hydroxytryptamine (5-HT, serotonin) receptors of the 5-HT1A type. Pretreatment with buspirone (5, 10 mg/kg, ip) and l-propranolol (10, 20 mg/kg, ip) antagonised the behavioural syndrome induced by 8-OH-DPAT and dextromethorphan. Pretreatment with p-chlorophenylalanine (100 mg/kg/day x 4 days) antagonised the behavioural syndrome induced by dextromethorphan and dexfenfluramine but had no significant effect on 8-OH-DPAT induced behavioural syndrome. This indicates that dextromethorphan induces the behavioural syndrome by releasing 5-HT from serotonergic neurons with resultant activation of the postsynaptic 5-HT1A receptors by the released 5-HT. Pretreatment with fluoxetine (10 mg/kg, ip) significantly potentiated the behavioural syndrome induced by dextromethorphan and 5-hydroxytryptophan but significantly antagonised dexfenfluramine induced behavioural syndrome. This indicates that dextromethorphan releases 5-HT by a mechanism which differs from that of dexfenfluramine. Dextromethorphan may be releasing 5-HT by blocking the NMDA receptors and thereby counteracting the inhibitory influence of l-glutamate on 5-HT release.

Preventive Effect of Serotonergic Drugs on LPS-Induced Acute Anorexia in Rats

The aim of the present study was to determine whether serotonergic drugs could reverse lipopolysaccharide (LPS) -induced anorexia in rats. LPS (500microgram/kg body weight) and all serotonergic drugs, except for 8-OH-DPAT (subcutaneous), were injected intraperitoneally into Sprague-Dawley rats. Without the LPS injection, 8-OH-DPAT (1A agonist), metergoline (1/2 antagonist), and mianserin (2A/2C antagonist) exerted no effects on food intake at any of the doses tested, but ketanserin (2A antagonist) caused an increase of food intake at 4 mg/kg. RS-102221 (2C antagonist) reduced food intake at 2 and 4 mg/kg. LPS reduced food intake 1 hour after injection, and food intake remained low until the end of measurement period (24 hours) (p< 0.05). Pretreatment of rats with 8-OH-DPAT partially recovered of cumulative food intake at all measured times (2, 4, 6, 8, and 24 hours after LPS injection). Pretreatment with metergoline resulted in a partial recovery of cumulative food intake at 2, 4, 6, and 8 hours, but not at 24 hours. Ketanserin caused partial recovery at 2 and 4 hours only. Mianserin and RS-102221 had no effects on LPS-reduced food intake. A variety of serotonergic drugs ameliorated anorexic symptoms, which suggesting that the serotonin system plays a role in LPS-induced anorexia.

A brain microdialysis study on 5-HT release in freely moving rat lines selectively bred for differential 5-HT1A receptor function

Breeding for high and low hypothermic responses to systemic administration of a serotonin1A (5-HT1A) receptor agonist (8-hydroxy-2-(di-n-propylamino)tetralin, 8-OH-DPAT) has resulted in high DPAT-sensitive (HDS) and low DPAT-sensitive (LDS) lines of rats, respectively. These lines also differ in several behavioral measures associated with stress. In the present microdialysis study we observed that basal 5-HT concentrations in the prefrontal cortex and dorsal hippocampus did not differ significantly between HDS and LDS rats. Thus, behavioral differences between the HDS and LDS lines might not be attributed to differences in basal 5-HT release. However, both lines had lower basal levels of 5-HT release than their randomly bred control group (random DPAT-sensitive, RDS) in the prefrontal cortex (mean ± SEM, pg/20 æl, was 3.0 ± 0.4 for LDS, 3.8 ± 0.3 for HDS and 6.4 ± 0.6 for RDS; F(2,59) = 5.8, P<0.005). The administration of (±)-fenfluramine (10 mg/kg) induced a greater increase in hippocampal 5-HT levels in HDS rats (500 percent) as compared with LDS (248 percent) or RDS (243 percent) rats (P<0.0001). There were no significant differences in the prefrontal cortex among lines, with a fenfluramine-induced 5-HT increase of about 900 percent in the three groups. This differential response to fenfluramine may be due to functional alterations of hippocampal 5-HT reuptake sites in the HDS line

Neuroprotective Effect of 8-OH-DPAT on Long-term Sequelae from Prenatal Ischemia in Rats

The role of 5-hydroxytryptamine (5-HT)1A receptor activity in prenatal ischemia was studied, by injecting 8-hydroxy-dipropylaminotetraline (8-OH-DPAT; 50 microgram/kg, s.c.), a 5-HT1A agonist on gestation day 17, and 30 min later inducing transient ischemia by ligating the uterine vessels for 30 min. On postnatal day 95, rats that had experienced prenatal ischemia showed impaired motor coordination and reduced concentration of 5-HT in the cerebellum compared with Sham-operated controls. In addition, they showed increased 5-HT1A receptor densities in the cerebral cortex. Pretreatment with 8-OH-DPAT ameliorated the behavioral and neurochemical sequelae measured in the present study. The results suggest that 5-HT1A receptors protect the brain from ischemic insult and/or facilitate recovery after prenatally experienced ischemia.

Neurobehavioral teratology due to hypoxic exposure in newborn rats

BACKGROUND AND PURPOSE: Neurobehavioral teratology is a term used for the postnatal effects on behavior of prenatal exposure to drug or to specific environment. Perinatal hypoxia is a major risk factor for development of behavioral abnormalities, such as cerebral palsy, mental retardation and learning disability. The objective of this study is to investigate the effects of neonatal hypoxia on long-term changes of behavior and neurochemical system and to learn the role of 5-hyroxytryptamine(5-HT) in hypoxic stress. METHODS: Sprague-Dawley rats were grouped by hypoxia and/or 5-HT receptor antagonist treatment. Exposure to 100% N2 gas was done in postnatal day(PND) 2 for 12 minutes. NAN-190 HBr or ketanserin tartrate or both were injected intraperitoneally 30 minutes before exposure to hypoxic environment. Rats were weighed periodically and examined the eye opening. Wire maneuver test was done on PND 22. Between PND 40-55 and PND 63-84, explorative behavior test and Rota-Rod test were done serially. They were sacrificed in PND 100, and aminergic neurotransimitters and their metabolites were measured by High Performance Liquid Chromatography - Electrochemical Detection(HPLC ECD) system. Receptor binding assay was done using 8-OH-DPAT and ketanserin HCl in brain cortex. RESULTS: The group treated with 5-HT receptor antagonist and hypoxia showed higher death rate than 5-HT receptor antagonist or hypoxia alone. There were no differences in weight gain, eye opening, and the result of wire maneuver test among each groups. In explorative behavior test, NAN+N2 group in male and NAN group in female showed markedly increased activities. In Rota-Rod test, NAN and NAN+N2 groups in both male and female showed decreased motor coordination. There were no differences in the concentration of aminergic neurotransmitters and their metabolites, when measured in PND 100 according to the brain sites. There were no differences in pKd of 5-HT receptors measured on PND 100. But Bmax of 5-HT1A receptor were low in N2, NAN and NAN+N2 groups. NAN and NAN+N2 groups showed elevated Bmax of 5-HT2A/2C receptor. CONCLUSION: Exposure to hypoxia in neonatal period causes long-lasting neurobehavioral changes with neurochemical abnormalities, and 5-HT receptor activity has a role in that mechanism.

Agents that affect cAMP levels or protein kinase A activity modulate memory consolidation when injected into rat hippocampus but not amygdala

Male Wistar rats were trained in one-trial step-down inhibitory avoidance using a 0.4-mA footshock. At various times after training (0, 1.5, 3,6 and 9 h for the animals implanted into the CA1 region of the hippocampus; 0 and 3 h for those implanted into the amygdala), these animals received microinfusions of SKF38393 (7.5 mug/side), SCH23390 (0.5 mug/side), norepinephrine (0.3 mug/side), timolol (0.3 mug/side), 8-OH-DPAT (2.5 mug/side), NAN-190 (2.5 mug/side), forskolin (0.5 mug/side), KT5720 (0.5 mug/side) or 8-Br-cAMP (1.25 mug/side). Rats were tested for retention 24 h after training. When given into the hippocampus 0 h post-training, norepinephrine enhanced memory whereas KT5720 was amnestic. When given 1.5 h after training, all treatments were ineffective. When given 3 or 6 h post-training, 8-Br-cAMP, forskolin, SKF38393, norepinephrine and NAN-190 caused memory facilitation, while KT5720, SCH23390, timolol and 8-OH-DPAT caused retrograde amnesia. Again, at 9 h after training, all treatments were inffective. When given into the amygdala, norepinephrine caused retrograde facilitation at 0 h after training. The other drugs infused into the amygdala did not cause any significant effect. These data suggest that in the hippocampus, but not in the amygdala, a cAMP/protein kinase A pathway is involved in memory cosolidation at 3 and 6 h after training, which is regulated by D1, Beta, and 5HT1A receptors. This correlates with data on increased post-training cAMP levels and a dual peak of protein kinase A activity and CREB-P levels (at 0 and 3-6 h) in rat hippocampus after training in this task. These results suggest that the hippocampus, but not the amygdala, is involved in long-term storage of step-down inhibitory avoidance in the rat.

Role of lipids in receptor mediated signal transduction.

A new strategy has been successfully applied to reconstitute the brain specific serotonin 5-HT1A receptor-G protein-adenylate cyclase complex. A mild method of tissue preparation gave a stable, membrane-bound form of the receptor (SBP) which retained its natural lipid content. Treatment of SBP with serotonin (1 microM) and 3-[(3-cholamidopropyl) dimethyl ammonio]-1-propanesulphonate (CHAPS) (2%) solubilized the ligand-receptor-G protein-ligand complex along with the associated phospholipids and cholesterol. Dialysis of this extract (SBDS) against buffer containing 25% ethylene glycol produced a stable, reconstituted and active preparation (SBDSE) of vesicles which upon centrifugal separation followed by gentle resuspension retained 95-100% [3H] 8-OH-DPAT binding activity as well as 60% [3H] GppNHp binding and adenylate cyclase activities of SBDSE. The reconstituted receptor preparation compared well with the membrane-bound form in displaying a similar value for KD (2.1 nM) and a single affinity state for [3H] 8-OH-DPAT binding (Bmax = 118 fmol/mg). However, in sharp contrast to the membrane-bound receptor which was negatively coupled to adenylate cyclase, agonist treatment of the solubilized and reconstituted receptor resulted in an increase in adenylate cyclase. This change in receptor-adenylate cyclase coupling following reshuffling of membrane lipids during solubilization and reconstitution suggested that membrane lipids could have a profound effect on receptor-effector coupling. To study the effect of membrane lipid composition on receptor-mediated signal transduction in a stabler and more natural system, neural cells derived from different parts of the brain (hippocampus, HN2; CNS, NCB-20; dorsal root ganglion, F-11) and a non-neural cell line (CHO), all with differing membrane lipid compositions, were selected. Since no known cell line contains the serotonin 5-HT1A receptor (5-HT1A-R), stable transfection of the selected cell lines with a DNA construct encoding the human 5-HT1A-R was carried out and this resulted in a late increase of [3H] 8-OH-DPAT binding in the stationary phase only in the cell lines of neural origin. In the non-neural cell line (CHO), which also displayed marked difference in membrane lipids, the receptor was positively coupled to the phospholipase C-IP3-[Ca2+]i cascade. Even though GPLC was present in the NCB-20 and F-11 cells as evidenced by a bradykinin receptor-mediated increase in inositol phosphates in these cells 8-OH-DPAT treatment resulted in no change in phospholipase C in any of the cell lines of neural origin.(ABSTRACT TRUNCATED AT 400 WORDS)

Serotonin mechanisms in animal models of anxiety

1. Responses to serotonergic drugs in animal models of anxiety are reviewed. Pre- and postsynaptic mechanisms and multiple sites of postsynaptic action contribute to conflicting findings. 2. Paradoxical responses to both serotonergic and non-serotonergic agents support the concept of multiple anxiety mechanisms. Non-anxiety factors, such as effects on cognition and behavioral inhibition, must also be taken into account. 3. Immediate 'anxiogenic' and delayed 'anxiolytic' effects most closely mimic the clinical effects of recently introduced anxiolytic drugs such as the selective serotonin reuptake inhibitors and buspirone. Thus the relevance to anxiety of immediate 'anxiolytic' effects of such agents in animal models is in question