Effects of perinatal asphyxia on rat striatal cytoskeleton.

Perinatal asphyxia (PA) is a medical condition associated with a high short-term morbimortality and different long-term neurological diseases. In previous works, we have shown that neuronal and synaptic changes in rat striatum lead to ubi-protein accumulation in post-synaptic density (PSD) after six months of sub-severe PA. However, very little is known about the synaptic and related structural modifications induced by PA in young rats. In the present work, we studied neuronal cytoskeleton modifications in striatum induced by subsevere PA in 30-day-old rats. We observed a significant decrease in the number of neurons, in particular calbindin immunoreactive neurons after PA. In addition, it was also observed that actin cytoskeleton was highly modified in the PSD as well as an increment of F-actin staining by Phalloidin-alexa(488) in the striatum of PA rats. Using correlative fluorescence-electron microscopy photooxidation, we confirmed and extended confocal observations. F-actin staining augmentation was mostly related with an increment in the number of mushroom-shaped spines. Consistent with microscopic data, Western blot analysis revealed a ß-actin increment in PSD in PA rats. On the other hand, MAP-2 immunostaining was decreased after PA, being NF-200 expression unmodified. Although neuronal death was observed, signs of generalized neurodegeneration were absent. Taken together these results showed early post-synaptic F-actin cytoskeleton changes induced by PA with slightly modifications in the other components of the neuronal cytoskeleton, suggesting that F-actin accumulation in the dendritic spines could be involved in the neuronal loss induced by PA.

Behavioral effects of progesterone associated with rapid modulation of oxytocin receptors.

The ventromedial nuclei of the hypothalamus (VMN) are important for the control of feminine mating behavior, and hormone action within these nuclei has been causally related to behavior. Estradiol induces receptors for oxytocin in the VMN and in the area lateral to these nuclei over the course of 1 to 2 days, and progesterone causes, within 30 minutes of its application, a further increase in receptor binding and an expansion of the area covered by these receptors lateral to the VMN. The rapid progesterone effect appears to be a direct and specific effect of this steroid on the receptor or membrane, because it was produced in vitro as well as in vivo and was not mimicked by a variety of other steroids. The effect of progesterone occurred in the posterior part of the VMN, where oxytocin infusion facilitated feminine mating behavior; it did not take place in the anterior part of the VMN, where oxytocin infusion had no effect on mating behavior.

Nitric oxide increases in the rat retina after continuous illumination.

Continuous illumination (CI) of the retina induces an oxidative stress followed by the degeneration of photoreceptors. This phenomenon may be partially related to the excessive production of nitric oxide (NO). In order to confirm this hypothesis, the aims of this work are to determine NO levels during the illumination of the retina by electron paramagnetic resonance (EPR), and if an increase of NO is found, to characterize the NOS isoform responsible of the increment by using Western blot. Sprague-Dawley rats were continuously illuminated with white light (12,000 lux) for 2, 24, 48 h, 5 and 7 days while control rats were maintained at light/dark cycles of 12/12 h. Using EPR, an increase of NO signal was observed in the light exposed retinas peaking at 24 h of CI. Western blot analysis showed the expression of iNOS in the illuminated retinas with a peak after 24 h of CI, but did not show significant differences of nNOS among illuminated and control retinas. In summary, there is an increase of NO during CI. Further studies will reveal whether this mechanism is responsible for light induced photoreceptor degeneration.

Extensive enriched environments protect old rats from the aging dependent impairment of spatial cognition, synaptic plasticity and nitric oxide production.

In aged rodents, neuronal plasticity decreases while spatial learning and working memory (WM) deficits increase. As it is well known, rats reared in enriched environments (EE) show better cognitive performances and an increased neuronal plasticity than rats reared in standard environments (SE). We hypothesized that EE could preserve the aged animals from cognitive impairment through NO dependent mechanisms of neuronal plasticity. WM performance and plasticity were measured in 27-month-old rats from EE and SE. EE animals showed a better spatial WM performance (66% increase) than SE ones. Cytosolic NOS activity was 128 and 155% higher in EE male and female rats, respectively. Mitochondrial NOS activity and expression were also significantly higher in EE male and female rats. Mitochondrial NOS protein expression was higher in brain submitochondrial membranes from EE reared rats. Complex I activity was 70-80% increased in EE as compared to SE rats. A significant increase in the area of NADPH-d reactive neurons was observed in the parietotemporal cortex and CA1 hippocampal region of EE animals.

Neuroendocrine Regulation of Metabolism.

Given the current environment in most developed countries, it is a challenge to maintain a good balance between calories consumed and calories burned, although maintenance of metabolic balance is key to good health. Therefore, understanding how metabolic regulation is achieved and how the dysregulation of metabolism affects health is an area of intense research. Most studies focus on the hypothalamus, which is a brain area that acts as a key regulator of metabolism. Among the nuclei that comprise the hypothalamus, the arcuate nucleus is one of the major mediators in the regulation of food intake. The regulation of energy balance is also a key factor ensuring the maintenance of any species as a result of the dependence of reproduction on energy stores. Adequate levels of energy reserves are necessary for the proper functioning of the hypothalamic-pituitary-gonadal axis. This review discusses valuable data presented in the 2015 edition of the International Workshop of Neuroendocrinology concerning the fundamental nature of the hormonal regulation of the hypothalamus and the impact on energy balance and reproduction.

Effect of synthetic steroids on GABAA receptor binding in rat brain.

Neuroactive steroids, like allopregnanolone (A) and pregnanolone (P), bind to specifics sites on the GABAA receptor complex and modulate receptor function. They are capable to inhibit or stimulate the binding of GABAA receptor-specific ligands, like t-butyl-bicyclophosphorothionate, flunitrazepam and muscimol. We have previously characterized a set of oxygen-bridged synthetic steroids (SS) analogs to A or P using synaptosomes. Considering that the subunit composition of the GABAA receptor throughout the central nervous system affects the magnitude of the modulation of the GABAA receptor by NAS, we evaluated the action of two selected SS, in brain sections containing the cerebral cortex (CC) and hippocampus (HC) using quantitative receptor autoradiography. Both SS affected the binding of the three ligands in a similar way to A and P, with some differences on certain CC layers according to the ligand used. One of the SS, the 3α-hydroxy-6,19-epoxypregn-4-ene-20-one (compound 5), behaved similarly to the natural neuroactive steroids. However, significant differences with compound 5 were observed on the HC CA2 region, making it steroid suitable for a specific action. Those differences may be related to structural conformation of the SS and the subunits' composition present on the receptor complex.

Anatomical localization of the effects of 17 beta-estradiol on oxytocin receptor binding in the ventromedial hypothalamic nucleus.

Oxytocin (OT) neurotransmission plays a role in the facilitation of steroid-dependent sexual receptivity in the rat. One way in which the ovarian steroid 17 beta-estradiol (E2) has been shown to modulate OT transmission is by increasing OT receptor binding in certain brain areas involved in the regulation of female sexual behavior such as the ventromedial hypothalamic nucleus (VMN). This study was undertaken to describe the distribution of OT receptors within the VMN that are regulated by physiological levels of E2. With quantitative autoradiographic methods, we measured [3H]OT binding in ovariectomized female rats implanted with Silastic capsules containing cholesterol, 5% E2, or 100% E2. In addition, plasma E2 levels, pituitary progestin receptor binding, and uterine weights were measured in animals from each treatment group. Results of this study showed that physiological levels of E2 increased [3H]OT binding in caudal regions of the ventrolateral VMN and stimulated maximal uterine growth and pituitary progestin receptor binding. However, in more rostral VMN sections, E2 induced a dose-dependent increase in [3H]OT binding. These data suggest that ovarian steroids sensitize the brain to OT by increasing OT receptor binding in certain brain areas involved in the regulation of sexual receptivity.

The regulation of oxytocin receptor binding in the ventromedial hypothalamic nucleus by testosterone and its metabolites.

Oxytocin (OT) receptor binding in the ventromedial hypothalamic nucleus is regulated by testosterone (T) in male rats. However, T is metabolized in the brain, and many of the central effects of T are mediated by its metabolites. The experiments reported here were designed to determine whether T affects OT receptor binding directly or through the action of its metabolites 17 beta-estradiol and 5 alpha-dihydrotestosterone. Adult male rats were either sham operated or castrated and treated 1 week later with T propionate (TP), 17 beta-estradiol benzoate (EB), dihydrotestosterone benzoate (DHTB), DHTB plus EB, or oil. OT receptor binding was assessed autoradiographically using [125I]d(CH2)5[Tyr(Me)2,Thr4,Tyr-NH2(9)]OVT. In addition, seminal vesicle weights were measured as an index of androgenic activity. These experiments showed that TP and DHTB plus EB increased OT receptor binding in the ventromedial hypothalamic nucleus to the levels in intact males. Treatment with EB alone partially reinstated binding to the levels in intact males, while DHTB treatment was without effect. Castrated males treated with either TP or DHTB had seminal vesicle weights comparable to those of gonadally intact males and greater than those of animals in all other steroid conditions, indicating that sufficient levels of circulating steroids were attained in these groups. These data suggest that the induction of hypothalamic OT receptor binding by T is the result of the combined actions of estradiol and dihydrotestosterone. However, the mechanism underlying this interaction is unknown.

Time course of the estradiol-dependent induction of oxytocin receptor binding in the ventromedial hypothalamic nucleus of the rat.

Oxytocin (OT) transmission is involved in the steroid-dependent display of sexual receptivity in rats. One of the biochemical processes stimulated by the ovarian steroid 17 beta-estradiol (E2) that is relevant to reproduction is the induction of OT receptor binding in the ventromedial hypothalamic nucleus (VMN). The purpose of these experiments was to determine if E2-induced changes in OT receptor binding in the VMN occur within a time frame relevant to cyclic changes in ovarian steroid secretion. OT receptor binding was measured in the VMN of ovariectomized rats implanted for 0-96 h with E2-containing Silastic capsules. The rate of decay of OT receptor binding was measured in another group of animals 6-48 h after capsule removal. Receptors were labeled with the specific OT receptor antagonist [125I]d(CH2)5[Tyr(Me)2,Thr4,Tyr-NH2(9)]OVT, and binding was measured with quantitative autoradiographic methods. In addition, plasma E2 levels and uterine weights were assessed in animals from each treatment condition. Significant increases in E2-dependent OT receptor binding and uterine weight occurred within 24 h of steroid treatment. After E2 withdrawal, OT receptor binding and uterine weight decreased significantly within 24 h. These results are consistent with the hypothesis that steroid modulation of OT receptor binding is necessary for the induction of sexual receptivity.

3 Beta-hydroxysteroid dehydrogenase expression in rat spinal cord.

In adult male rats, 3beta-hydroxysteroid dehydrogenase/delta5-delta4-isomerase (3beta-HSD) expressing cells were identified in the spinal cord from the cervical to the sacral segments. An in situ hybridization study, using an oligonucleotide common to the four known isoforms of rat 3beta-HSD, revealed its mRNA in gray matter. Measurements of optical densities in autoradiograms showed the following regional distribution: dorsal horn (layers I-III) > central canal (layer X) > or = ventral horn (layers VIII-IX) > ventral funiculus = lateral funiculus. At the cellular level, the number of grains was higher on the large motoneurons than on small neurons of the dorsal horn, but the grain density per cell was similar. Further evidence for the expression of 3beta-HSD in the spinal cord was obtained by western blot analysis, which revealed an immunoreactive protein of approximately 45 kDa in the dorsal and ventral parts of the spinal cord. Castration and adrenalectomy did not influence the expression of 3beta-HSD mRNA and protein. Gas chromatography/mass spectrometry measurements showed higher levels of pregnenolone and progesterone in the spinal cord than in the plasma. After castration and adrenalectomy, their levels remained elevated in the spinal cord, suggesting that these neurosteroids may be synthesized locally. The wide distribution of 3beta-HSD, and the high levels of pregnenolone and progesterone in the spinal cord even after castration and adrenalectomy, strongly suggest a potential endogenous production of progesterone and an important signalling function of this steroid in the spinal cord.

Modulation of basal ganglia neurotransmission by the classical antipsychotic fluphenazine is due in part to the blockade of dopamine D1-receptors.

Classical antipsychotics, such as fluphenazine, influence neurotransmission by blocking both dopamine D1- and D2-receptors which in turn results in widespread adaptive changes in the neurochemistry of the basal ganglia. The purpose of the present study was to determine the role of D1-receptors in mediating some of these neurochemical events, including changes in D1- and D2-receptor binding, and the expression of preproenkephalin and glutamic acid decarboxylase mRNAs. For these experiments, rats were given a depot injection of fluphenazine decanoate or injected twice daily for 21 days with the D1-receptor antagonist SCH-23390. An additional group received both fluphenazine and SCH-23390 and controls were given saline. Fluphenazine administration decreased D2-receptor binding throughout the basal ganglia while SCH-23390 was without effect. In contrast to the uniform reduction in D2-receptor binding, fluphenazine altered D1-receptor binding in a region-dependent manner. Region-dependent changes were also observed in animals given SCH-23390 which increased binding in the entopeduncular nucleus and posterior caudate-putamen without affecting other brain regions. Both fluphenazine and SCH-23390 significantly enhanced preproenkephalin and glutamic acid decarboxylase (GAD) mRNA expression in the anterior striatum. Fluphenazine also increased GAD mRNA levels in the entopeduncular nucleus. Together, these results indicate that the attenuation of D1-receptor-mediated neurotransmission modulates a number of clinically relevant neurochemical processes in the basal ganglia.

Regulation by dopaminergic neurotransmission of dopamine D2 mRNA and receptor levels in the striatum and nucleus accumbens of the rat.

The effect of dopamine depletion or pharmacological blockade of dopamine receptors on striatal and accumbens dopamine D2 mRNA and receptor levels was assessed by in situ hybridization histochemistry and receptor autoradiography. The time course of pharmacological blockade with haloperidol demonstrates a complex mode of regulation of dopamine D2 mRNA and receptor levels. By day 8 of haloperidol treatment, D2 mRNA and receptor levels were decreased (up to 20%) in the medial and anterior aspects of the caudate-putamen (mCPU and aCPU) and the nucleus accumbens (NAc). However, by day 21 of haloperidol treatment, D2 mRNA and receptor were increased relative to vehicle-injected controls. Likewise, unilateral dopamine depletion due to 6-hydroxydopamine (6-OHDA) lesions of mesencephalic dopaminergic neurons resulted in decreased levels of D2 receptor mRNA by day 8 post-lesion in the ipsilateral mCPU, aCPU and the NAc. However, at days 14 or 21 post-lesion, there was a reversal of the effect with increases of up to 22% in all brain regions ipsilateral to the lesion. Although no decreases in receptor level were observed at day 8, significant increases in receptor level in all three brain regions were detected at days 14 and 21 post-lesion. The results demonstrate that midbrain dopaminergic innervation exerts tonic effects on the levels of dopamine D2 receptor and mRNA in the caudate-putamen and the nucleus accumbens of the rat. Changes in receptor level are frequently accompanied by comparable changes in mRNA level, indicating a mass action relationship between receptor level and receptor biosynthesis in these forebrain regions in the rat.

Progestin receptor induction and sexual behavior by estradiol treatment in male and female rats.

Abstract Sex differences in the induction of cytosolic progestin receptors (CPR) by estrogen priming were correlated with the sex differences in behavioral responses. We evaluated the temporal relationship between CPR in several brain regions and pituitary and the time-course of 17beta-estradiol (E(2)) activation of female sexual behavior in gonadectomized male and female rats implanted with subcutaneous E(2) Silastic capsules for 6 h, 24 h and 48 h. Both CPR levels and mating behavior increase monotonically with the time of E(2) exposure. Induction of CPR was observed in the periventricular region of the preoptic area (PVPOA), arcuate nucleus (ARC), ventromedial nuclei (VMN) and pituitary in both sexes. A small induction of CPR was found in parietal cortex. The VMN in female rats showed a significant E(2)-induced CPR increase at all times of exposure, while in male rats this induction was only significant after 24 h. Significant sex differences in absolute CPR levels and E(2)-induced receptors were found in the following structures: VMN, 18 h after 6 h of E(2) treatment and after 24 h and 48 h of continuous E(2) exposure; PVPOA, only after 48 h of continuous E(2) exposure; ARC at 24 h and 48 h; and pituitary after all E(2) treatment. Mating behavior was tested under two conditions: E(2) alone (2 h after removal of E(2) capsules) and E(2)+progesterone (2 h after a progesterone injection given 10 min after concluding the first test). Receptivity was first observed after 24 h E(2) exposure in female rats, whereas in male rats a small response appeared only after 48 h of E(2) exposure. After progesterone priming, the time of E(2) exposure necessary for expression of female sexual behavior was reduced to 6 h in females and 24 h in males. The appearance of mating behavior appears to follow that of inducible CPR in the VMN in both sexes. In addition, the CPR levels associated with the first receptivity either by male rats (16.6 fmol/mg protein) or female rats (15.3 fmol/mg protein) are very similar suggesting the presence of a threshold level controlling the expression of feminine sexual behavior. It is likely that inhibitory neural input plays a role in determining the threshold level of E(2)-induced CPR, which is sufficient to trigger lordosis behavior.

Steroid regulation and sex differences in [(3) h]muscimol binding in hippocampus, hypothalamus and midbrain in rats.

The gonadal steroids estradiol and progesterone have previously been shown to modulate the specific binding of the GABA(A) agonist, [(3) H]muscimol, in the CA1 region of the hippocampus, the ventromedial nucleus of the hypothalamus and the midbrain central gray of ovariectomized female rats. In this report we show a sex difference in the level of binding in the very caudal ventromedial nucleus of the hypothalamus. In contrast to females, there is no steroid modulation of [(3) H]muscimol binding in the ventromedial nucleus of the hypothalamus and midbrain central gray of males. These effects may be functionally related to GABAergic control of female sexual behavior. In contrast, steroid modulation of [(3) H]muscimol binding in the CA1 region of the hippocampus occurred to the same degree in males and females, and there was no difference in the level of binding in any region of the hippocampus between gonadectomized males and females. Incubation of brain slices with progesterone or its metabolite 5α-3α-pregnanolone dissolved in ethanol, produced a significant increase in [(3) H]muscimol binding in most brain regions as compared to control brain slices treated with ethanol alone. Moreover, there was also a marked increase in [(3) H]muscimol binding in all brain areas in the control condition which contained 100 mM ethanol, as compared to brain slices not preincubated with ethanol. The increase in binding after in vitro treatment with either progesterone or 5α-3α-pregnanolone is notably different from that seen after progesterone given in vivo 4 h prior to assay in that it is not site-specific, does not depend on prior treatment with estradiol and shows no sex difference. These results suggest different mechanisms for progesterone effects on the GABA(A) receptor when administered in vivo as compared to in vitro.

Light-dark differences in behavioral sensitivity to oxytocin.

Ovariectomized female rats treated with estradiol benzoate (EB) and progesterone (P) were infused intracerebroventricularly with a low (200 ng) or high (1 microgram) dose of oxytocin (OT). The low dose of OT facilitated lordosis behavior only during the dark phase of the light-dark cycle in females that were pretreated with low doses of EB (2 micrograms) and P (250 micrograms). In contrast, the high dose of OT facilitated lordosis behavior during both the light and the dark phases but only in long-term ovariectomized females that were primed with large amounts of EB (2 x 10 micrograms) and P (500 micrograms). In females that were primed with lower amounts of ovarian steroids, the high dose of OT failed to increase levels of lordosis responding in either the dark or light phase. Thus, when female rats are treated with physiological amounts of ovarian hormones and OT, they are more sensitive to the facilitative effects of the OT on lordosis behavior during the dark phase.

3 beta-hydroxysteroid dehydrogenase isomerase (3beta-HSD) activity in the rat sciatic nerve: kinetic analysis and regulation by steroids.

We have shown that progesterone (PROG) has a stimulatory effect on myelin formation after sciatic nerve injury. PROG is synthesized from pregnenolone (PREG) by the enzyme 3 beta-hydroxysteroid dehydrogenase isomerase (3beta-HSD). At the occasion of the 15th International Symposium of the Journal of the Steroid Biochemistry and Molecular Biology, we presented some of our recent results demonstrating, expression and activity of the enzyme 3beta-HSD in the rat sciatic nerve. We determined the kinetic properties of 3beta-HSD and its regulation by PROG and estradiol. The expression of 3beta-HSD protein was assessed by Western-blot analysis, and the 3beta-HSD activity was evaluated by incubating homogenates with [3H]-PREG as substrate and NAD(+) as cofactor. Levels of steroids formed were calculated either by extrapolation of the relationship between the tritiated peaks obtained by thin layer chromatography (TLC) and the initial amount of PREG, or by gas chromatography-mass spectrometry (GC-MS) determination. A rapid increase in PROG formation was found between 0 and 50min of incubation and no significant change was observed between 1 and 4h. The calculated K(m) value was close to the values obtained for the 3beta-HSD types I and IV isoforms. Trilostane caused a potent inhibition of the rate of conversion of PREG to PROG. When we tested the effects of progesterone and estradiol on 3beta-HSD activity, a significant inhibition was obtained.

Steroid hormones as mediators of neural plasticity.

Steroid and thyroid hormone receptors are expressed in the developing brain and persist throughout adult life. They mediate a variety of effects on the brain, ranging from developmental effects of thyroid hormone and the process of sexual differentiation to the cyclic changes during reproductive cycles in adult female animals. This review summarizes data from the author's laboratory on three topics: (1) actions of extradiol and progesterone on the ventromedial nucleus of the hypothalamus in adult female and male rats, showing both the cyclicity and the consequences of brain sexual differentiation; (2) actions of estradiol on the cholinergic neurons of the basal forebrain of the female and male rat, reflecting the plasticity of the adult cholinergic system as well as sex differences which are developmentally programmed; and (3) diverse actions of estrogens, thyroid hormone and glucocorticoids on the morphology of hippocampal neurons. The review concludes by discussing the interactions between "organizational" (i.e. developmental) effects and the "activational" effects of steroids on the mature nervous system in relation to the environmental control of brain gene expression.

Binding of the anti-inflammatory steroid deflazacort to glucocorticoid receptors in brain and peripheral tissues. In vivo and in vitro studies.

Deflazacort (DFC) is a heterocyclic glucocorticoid with anti-inflammatory activity but with decreased side effects. In this study, we have evaluated the capacity of DFC and other glucocorticoids to reach the central nervous system (CNS) in vivo by measuring changes of [3H]dexamethasone (DEX) binding to glucocorticoid receptors (GR) in vitro. GR occupation was effected by DEX in the cerebral cortex, hippocampus, pituitary, liver and thymus, with DFC showing a similar profile except for the cerebral cortex. In contrast, corticosterone weakly occupied GR in the thymus, pituitary and hippocampus and methyl-prednisolone was active only in peripheral tissues. Furthermore, IC50 for DEX in vitro amounted to 15-17 nM in the hippocampus and liver, whereas IC50 for the active metabolite 21-deacetyl-DFC (21-OH-DFC) was 4 times higher. 21-OH-DFC bound to type II and was absent from type I GR. When tested in equipotent doses based on IC50 analysis, DFC and DEX similarly induced in vivo ornithine decarboxylase activity in hippocampus and liver, although body weight loss after chronic treatment was significantly less for DFC. The results show that DFC distributes on the CNS similarly to DEX, induces ornithine decarboxylase activity but presents less intensive catabolic effects, making it suitable for use as an anti-inflammatory steroid during chronic therapeutic regimes.

Time-dependent effects of dexamethasone on glutamate binding, ornithine decarboxylase activity and polyamine levels in the transected spinal cord.

Evidence exists that the spinal cord is a glucocorticoid-responsive tissue, and glucocorticoids have beneficial effects in cases of spinal cord injury. Using sham-operated rats, spinal cord transected (TRX) rats, and TRX animals receiving dexamethasone (DEX) 5 min or 24 h post-lesion, we have examined the following GC-sensitive parameters 6 h after DEX treatment: (1) binding of glutamate to NMDA-sensitive receptors; (2) the activity of ornithine decarboxylase (ODC); and (3) levels of polyamines. We found that glutamate binding in the dorsal horn (Laminae 1-2) and central canal were upregulated in TRX rats, whereas DEX had an additional stimulatory effect. 24 h post-lesion, glutamate binding was unmodified in TRX or TRX+DEX rats. ODC activity was increased 10-fold in rats killed on the day of transection but only 2-fold 24 h post-lesion. DEX reduced ODC activity on transection day but highly increased it when given 24 h after surgery. The content of the polyamines spermidine and spermine were unchanged after TRX or DEX treatment, in contrast to putrescine which increased in TRX rats and further increased in TRX+DEX rats when measured the day post-lesion. Thus, parallel increases in ODC and putrescine 1 day after the lesion, suggest that glucocorticoid effects on growth responses due to polyamines may develop at a late period. The changes of glutamate binding in the dorsal horn and central canal due to early glucocorticoid treatment, further suggest hormonal modulation of neurotransmission in sensitive areas of the deafferented spinal cord.

Characterization of dopamine receptor binding sites in the subthalamic nucleus.

Experiments were undertaken to determine the distribution and binding profile of dopamine (DA) receptors within a key extra-striatal region of the rat basal ganglia, the subthalamic nucleus (STh). Analysis of [125I]NCQ-298 autoradiograms showed that binding sites of the D2-receptor family are abundant in the STh. Competition studies indicated that these sites were specifically of the D2 subtype. However, contrary to previously published data, [125I]SCH-23982 autoradiograms failed to reveal D1 receptor binding in the STh. These data suggest that DA acting at D2 receptors may directly modulate STh neural activity and furthermore that the antagonism of STh D2 receptor binding by neuroleptics may be involved in the expression of extrapyramidal motor disturbances.