Neonatal 5HT activity antagonizes the masculinizing effect of testosterone on the luteinizing hormone release response to gonadal steroids and on brain structures in rats

Hypothalamic 5HT concentrations are transiently lower in male compared to female Wistar rats in the second week post partum (pp) and our previous findings have shown that pharmacologically potentiating 5HT activity over this period feminizes certain aspects of sexually differentiated behaviours in adult males and androgenized females. In order to investigate whether neonatal testosterone and 5HT interact to influence physiological and morphological brain sexual differences, females, androgenized females and males were treated with the 5HT2 agonist (-) [2,5 dimethoxy-4-iodophenyl]-2-amino propane HCl [(-) DOI], over days 8-16 pp. In androgenized females (250 microg testosterone proprionate, day 2 pp) (-) DOI prevented the delay in vaginal opening, but did not prevent the androgen-induced constant oestrus in females treated with 100 microg TP, day 2 pp. (-) DOI overcame the neonatal androgen effect in suppressing the positive feedback of ovarian steroids in a few males and androgenized females. (-) DOI had a feminizing effect on the volume of the anteroventral periventricular nucleus (normally smaller in males), by significantly increasing its volume in male and androgenized females. It also had a significant antagonistic effect on the testosterone-induced increase in the volume of the sexually dimorphic nucleus of the preoptic area in males and androgenized females. These findings support the view that raised 5HT activity in the second week of life antagonizes the masculinizing effect of neonatal testosterone.     

Interactions of 5-HT2 receptor agonists with acetylcholine in spinal analgesic mechanisms in rats with neuropathic pain

Serotonin type 2 (5-HT(2)) receptors reportedly inhibit neuropathic pain in the spinal cord, but little is known about how spinal 5-HT(2) receptors might act against such abnormal sensitivity. We examined whether the cholinergic and tachykinin systems were involved in the antiallodynic effect of intrathecally administered 5-HT(2) receptor agonists in rats with nerve injury. Allodynia was produced by tight ligation of the left L5 and L6 spinal nerves, and determined by applying von Frey hairs to the left hindpaw. Effects of intrathecal pretreatment with 5-HT(2) receptor antagonists (ketanserin and RS-102221), muscarinic receptor antagonists (atropine and scopolamine), a choline uptake blocker (hemicholium-3), and an NK(1) receptor antagonist (L-706336) were assessed in rats subsequently given a 100- micro g intrathecal dose of a 5-HT(2) receptor agonist either alpha-methyl-5-HT or iododimethoxy aminopropane (DOI). Antiallodynic effects of 5-HT(2) receptor agonists were attenuated by the 5-HT(2A) receptor antagonist ketanserin (30 micro g), but not by the 5-HT(2C) receptor antagonist RS-102221 (40 micro g). Muscarinic receptor antagonists (30 micro g each), the choline uptake blocker (10 micro g), and the NK(1) receptor antagonist (30 micro g) also inhibited the antiallodynic effects of 5-HT(2) receptor agonists. Antiallodynic effects of intrathecally administered 5-HT(2) receptor agonists may be mediated by spinal release of acetylcholine induced via 5-HT(2A) and NK(1) receptors.     

Benzodiazepine receptor and serotonin 2A receptor modulate the aversive-like effects of nitric oxide in the dorsolateral periaqueductal gray of rats

Rationale Escape reactions induced by electrical stimulation of the dorsolateral periaqueductal gray (dlPAG) are inhibited by local administration of benzodiazepine (BZ) or serotonin (5-HT) receptor agonists. Nitric oxide (NO) is a gas messenger that may mediate aversive behaviors. NO donors injected into the dlPAG induce escape reactions.Objectives To test the hypothesis that the escape reactions induced by a NO donor in the dlPAG would be attenuated by pre-treatment with BZ-receptor or 5-HT-receptor agonists.Methods Male Wistar rats with cannulae aimed at the dlPAG received microinjections of vehicle (0.2 l), the BZ midazolam maleate (80 nmol), the 5-HT_1A-receptor agonist 8-OH-DPAT (8 nmol or 16 nmol) or the 5-HT_2A/2C-receptor agonist DOI (16 nmol) 10 min before the administration of the NO donor SIN-1 (150 nmol). Behavioral observation took place immediately after the last injection in an open arena over a 10-min period.Results SIN-1 induced escape reactions characterized by running and jumps. Pre-treatment with DOI, but not 8-OH-DPAT, partially inhibited the effects of SIN-1. Pre-treatment with midazolam maleate, however, completely prevented the effects of the NO donor.Conclusion The results suggest that the aversive-like effects of NO donor in the dlPAG may be modulated by the BZ and 5-HT_2A/2C receptors.     

Effects of selective serotonin2 ligands on behaviors evoked by stress in the rat

Serotonin (5-HT) has been implicated in the regulation of the stress response. Two experiments were conducted to investigate the possibility that the 5-HT_{2A, 2C} agonist DOI would reduce behavioral responsiveness to stress, and that selective blockade of one or both of these receptor subtypes would reverse this effect. Stressors employed were mild tail pinch and an illuminated open field. In Experiment 1 DOI (0.1, 0.5, 1.0 mg/kg, s.c.) was found to decrease stress-evoked oral behavior directed at food and to increase rearing behavior in a dose-dependent fashion. Neither of these effects was reversed by spiperone (5-HT_2A antagonist) or SDZ SER-082 (5-HT_2C antagonist). DOI also increased the frequency of head shaking. This effect was reversed by SDZ SER-082. In Experiment 2 DOI was injected singly or in combination with ketanserin (5-HT_{2A, 2C} antagonist). DOI decreased tail pinch-evoked oral behavior directed at food, the amount of food eaten, and increased vocalization. In the open field DOI decreased rearing, increased the number of head shakes, and increased the incidence of flat body posture. While ketanserin alone (0.5, 2.5, 5.0 mg/kg) had no effect on any behavioral measure, coadministration of ketanserin (5.0 mg/kg) with DOI (0.5 and 1.0 mg/kg) significantly blocked the effects of DOI on oral behavior directed at food, eating, rearing, head shaking, and flat body posture. It is concluded that the observed effects of DOI on behaviors evoked by stress were mediated by activation of both 5-HT_2A and 5-HT_2C receptors.     

Investigation of the role of 5-HT2 receptor subtypes in the control of the bladder and the urethra in the anaesthetized female rat

Background and purpose:

Micturition is controlled by central 5-HT-containing pathways. 5-HT₂ receptors have been implicated in this system especially in control of the urethra, which is a drug target for treating urinary incontinence. This study investigates the role of each of the three subtypes of this receptor with emphasis on sphincter regulation.

Experimental approach:

Recordings of urethral and bladder pressure, external urethral sphincter (EUS) EMG, as well as the micturition reflex induced by bladder distension along with blood pressure and heart rate were made in anaesthetized rats. The effects of agonists and antagonists for 5-HT₂ receptor subtypes were studied on these variables.

Key results:

The 5-HT_2C agonists Ro 60-0175, WAY 161503 and mCPP, i.v., activated the EUS, increased urethral pressure and inhibited the micturition reflex. The effects of Ro 60-0175 on the EUS were blocked by the 5-HT_2C antagonist SB 242084 and the 5-HT_2A antagonists, ketanserin and MDL 100907. SB 242084 also blocked the inhibitory action on the reflex, while the 5-HT_2B antagonist RS 127445 only blocked the increase in urethral pressure. The 5-HT_2A receptor agonist DOI given i.v. or i.t. but not i.c.v. activated the EUS.

Conclusions and implications:

5-HT_2A/2C receptors located in the sacral spinal cord activate the EUS, while central 5-HT_2C receptors inhibit the micturition reflex and 5-HT_2B receptors, probably at the level of the urethra, increase urethral smooth muscle tone. Furthermore, 5-HT_2B and 5-HT_2C receptors do not seem to play an important role in the physiological regulation of micturition.     

Development of a tweezers-type coincidence imaging detector

OBJECTIVE: When employing F-18-fluorodeoxyglucose (FDG)-guided surgery to detect positron accumulation in isolated small organs, sampling these organs from opposite directions is a useful way of determining a tumor's position, similar to sampling a small organ with tweezers. The coincidence method is suitable for this purpose because only the positrons between two detectors can be detected. For this purpose, we developed a tweezers-type coincidence imaging detector. METHODS: The detector employs two depth-of-interaction (DOI) detectors positioned at the tip of the tweezers and images the positron distribution between them using the coincidence method. The DOI detector consists of a 4 x 3 Gd(2)SiO(5):Ce (GSO) array optically coupled to a one-dimensionally arranged quad-photomultiplier tube. These GSOs were arranged to form a DOI detector using the Anger principle. The useful field of view is 20 mm x 15 mm. With these configurations, we could resolve 4 x 3 GSO arrays on a position histogram. RESULTS: Because the imaging detectors were positioned at the tip of the tweezers, one could easily sample the target part manually from opposed sides. A real-time image in coincidence between these two DOI detectors could be obtained. The point spread functions were approximately 3-mm full width at half-maximum (FWHM) parallel to the tweezers and 4-mm FWHM perpendicular to them. The sensitivity was approximately 1% when the two imaging detectors were 10 mm apart. CONCLUSIONS: With these results, we conclude that the developed tweezers-type imaging detector has a potential to be a new instrument in nuclear medicine.     

The effect of serotonin on penicillin-induced epileptiform activity

Objective: This study was aimed at examining the epileptiform activity of the 5-HT₂ serotonin receptor agonist and antagonist, and 5-hydroxytryptophan (5-HTP) in penicillin-induced epilepsy in albino Wistar rats.

Methods: For this purpose, 90 albino male Wistar rats were used in this study. Epileptiform activity was induced by an injection of penicillin, an agonist of GABAA receptor, (500?IU, i.c.) into the somatomotor cortex. Thirty minutes after the injection of penicillin, 2,5-dimethoxy-4-iodoamphetamine (DOI, an agonist of 5-HT₂ receptor) (0.5, 1, 2 and 4?mg/kg, i.p.), methysergide, an antagonist of 5-HT₂ receptor, (1, 10, 20, 50 and 100?µM, i.c.v.) and 5-HTP, precursor of 5-HT, (25, 50, 75 and 100?mg/kg, i.p.) were administered, respectively.

Results: DOI, at the doses of 1 and 2?mg/kg, significantly decreased penicillin-induced epileptiform activity (p?<?0.05). Methysergide, at the doses of 20, 50 and 100?µM, significantly increased the mean spike frequency of penicillin-induced epileptiform activity (p?<?0.05). The doses of 50, 75 and 100?mg/kg of 5-HTP decreased the mean spike frequency of penicillin-induced epileptiform activity (p?<?0.05). The mean of amplitude of penicillin-induced epileptiform activity did not significantly change in any of the groups (p?>?0.05).

Conclusion: The electrophysiological data from the present study suggest that serotonin 5-HT₂ receptors have an important role in controlling penicillin-induced epileptiform activity in the rat.     

The receptor mechanisms underlying the disruptive effects of haloperidol and clozapine on rat maternal behavior: A double dissociation between dopamine D2 and 5-HT2A/2C receptors

Many antipsychotic drugs disrupt active components of maternal behavior such as pup approach, pup retrieval and nest building at clinically relevant doses in postpartum female rats. However, the neurochemical mechanisms underlying such a disruptive effect remain to be determined. This study examined the neurochemical mechanisms that mediate the disruptive effects of haloperidol (a typical antipsychotic) and clozapine (an atypical antipsychotic) on rat maternal behavior. Postpartum rats were administered with haloperidol (0.2 mg/kg, sc) or clozapine (10.0 mg/kg, sc) together with either vehicle (saline or water), quinpirole (a selective dopamine D₂/D₃ agonist, 0.5 or 1.0 mg/kg, sc), or 2,5-dimethoxy-4-iodo-amphetamine (DOI, a selective 5-HT_2A/2C agonist, 1.0 or 2.5 mg/kg, sc), and their maternal behaviors were tested at different time points before and after drug administration. Haloperidol and clozapine treatment disrupted pup approach, pup retrieval, pup licking and nest building. Pretreatment of quinpirole, but not DOI, dose-dependently reversed the haloperidol-induced disruptions. In contrast, pretreatment of DOI, but not quinpirole, dose-dependently reversed the clozapine-induced disruptions. Quinpirole pretreatment even exacerbated the clozapine-induced disruption of pup retrieval and nest building. These findings suggest a double dissociation mechanism underlying the disruption of haloperidol and clozapine on rat maternal behavior. Specifically, haloperidol disrupts maternal behavior primarily by blocking dopamine D₂ receptors, whereas clozapine exerts its disruptive effect primarily by blocking the 5-HT_2A/2C receptors. Our findings also suggest that 5-HT receptors are involved in the mediation of rat maternal behavior.     

Profiles of DARPP-32 in the insular cortex with schizophrenia: a postmortem brain study

In patients with schizophrenia, various physical disorders are sometimes discovered only when they have reached a later and more severe stage. This phenomenon is believed to be caused, at least in part, by an increase in pain threshold. The gamma-aminobutyric acid (GABA)-ergic and glutamatergic systems in the rostral agranular insular cortex (RAIC) are thought to be involved in the regulation of pain threshold. However, no postmortem studies of the cerebral cortex have previously been published. Dopamine and cAMP-regulated phosphoprotein 32 kD (DARPP-32), which is involved in the GABAergic and glutamatergic systems, is considered to be crucial for elucidating the pathogenesis of schizophrenia.Using specific antibodies, we conducted immunohistochemical examinations of the RAIC in 10 subjects from a healthy control group, and 11 subjects from a schizophrenia group. The sex, age, and postmortem interval (PMI) of the schizophrenia group were matched to those of the healthy control group. We revealed that the density of DARPP-32-immunoreactive (IR) neurons in the II and III layers of the RAIC was significantly decreased (p < 0.05) in the schizophrenia group compared with the healthy control group. Our findings could partially explain the molecular basis of the pain threshold abnormalities found in patients with schizophrenia.