Periventricular Arcuate Nucleus Research Articles

Effect of anti-Müllerian hormone in hypothalamic Kiss-1- and GnRH-producing cell models

Purpose: Anti-Müllerian hormone (AMH) is one of the local factors involved in follicle development. In addition, AMH and its receptor are broadly expressed throughout the body. In this study, we examined how AMH modifies gene expression of Kiss-1 and GnRH. Materials and methods: mHypoA-50 and mHypoA-55 cells were originated from the hypothalamic anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC), respectively, and these cells are known as Kiss-1 (which encodes kisspeptin) expressing cell models. These cells also express gonadotropin-releasing hormone (GnRH) genes. Our experiments were performed useing these cell models. Results: Both mHypoA-50 and mHypoA-55 hypothalamic cells expressed AMH and AMH receptor type 2 (AMHR2). Exogenous AMH failed to alter the expression levels of the Kiss-1 gene in both cell models but significantly increased GnRH gene expression by 1.73 ± 0.2-fold at 100 pM in mHypoA-50 AVPV cells and by 1.74 ± 0.17-fold at 1 nM in mHypoA-55 ARC cells. AMH also augmented GnRH protein expression in both cell models. Similar to the phenomenon observed in the hypothalamic cell lines, 100 pM AMH significantly increased GnRH, but not Kiss-1, mRNA expression in primary cultures of fetal rat brain cells. Kisspeptin-10 (KP10) increased Kiss-1 gene expression in mHypoA-55 ARC cells but this was blocked by AMH. AMH did not alter the expression of the kisspeptin receptor (Kiss1R) or that of neurokinin B or dynorphin A in mHypoA-55 ARC cells. Conclusions: It was demonstrated that AMH participates in hypothalamic-pituitary-gonadal axis control by stimulating GnRH expression. In addition, AMH might be a potent repressor of Kiss-1 gene expression induced by KP10.

Kisspeptin levels in idiopathic hypogonadotropic hypogonadism diagnosed male patients and its relation with glucose-insulin dynamic

Male hypogonadism is defined as the deficiency of testosterone or sperm production synthesized by testicles or the deficiency of both. The reasons for hypogonadism may be primary, meaning testicular or secondary, meaning hypothalamohypophyseal. In hypogonadotropic hypogonadism (HH), there is indeficiency in gonadotropic hormones due to hypothalamic or hypophyseal reasons. Gonadotropin-releasing hormone (GnRH) is an important stimulant in releasing follicular stimulant hormone (FSH), mainly luteinizing hormone (LH). GnRH omitted is under the effect of many hormonal or stimulating factors. Kisspeptin is present in many places of the body, mostly in hypothalamic anteroventral periventricular nucleus and arcuate nucleus. Kisspeptin has a suppressor effect on the metastasis of many tumors such as breast cancer and malign melanoma metastases, and is called “metastin” for this reason. Kisspeptin is a strong stimulant of GnRH. In idiopathic hypogonadotropic hypogonadism (IHH) etiology, there is gonadotropic hormone release indeficiency which cannot be clearly described.A total of 30 male hypogonatropic hypogonadism diagnosed patients over 30 years of age who have applied to Haydarpasa Education Hospital Endocrinology and Metabolic Diseases Service were included in the study. Compared to the control group, the effect of kisspeptin on male patients with hypogonatropic hypogonadism and on insulin resistance developing in hypogonadism patients was investigated in our study.A statistically significant difference was detected between average kisspeptin measurements of the groups (p < 0.01). Kisspeptin measurement of the cases in the patient group were detected significantly high. No statistically significant relation was detected among kisspeptin and LH/FSH levels. Although a positive low relation was detected between kisspeptin measurements of patient group cases and homeostasis model assessment of insulin resistance (HOMA-IR) measurements, this relation was statistically insignificant. When the patient and control groups were compared for HOMA-IR, no statistically significant difference was detected.The reason for high kisspeptin levels in the patient group compared to the control group makes us consider that there may be a GPR54 resistance or GnRH neuronal transfer pathway defect. When patients and control groups were compared for HOMA-IR, the difference was not statistically significant. It is considered that kisspeptin is one of the reasons for hypogonatropic hypogonadism and has less effect on insulin resistance.

Oestrogenic action of neonatal tamoxifen on the hypothalamus and reproductive system in female mice.

Tamoxifen, a selective oestrogen receptor modulator, is widely used for both the treatment and prevention of breast cancer in women; however, it is known to have adverse effects in the female reproductive system. Growing evidence suggests that oestrogen-sensitive neuron populations of the anteroventral periventricular (AVPV) nucleus and arcuate (ARC) nucleus, especially kisspeptin neurons, play a pivotal role in the timing of puberty onset and reproductive function. The aim of the present study was to evaluate whether neonatal exposure to tamoxifen affects oestrogenic actions in the brain and reproductive function in mice. On 1 to 5 postnatal days, female pups were injected subcutaneously with sesame oil (sham), oestradiol benzoate (EB; 20 µg kg-1), tamoxifen (0.4 mg kg-1) or EB+tamoxifen. Control mice received no treatment. Mice in the EB, tamoxifen and tamoxifen+EB groups exhibited advanced vaginal opening, disrupted oestrous cycles and a decreased follicular pool. Conversely, in these groups, there was a reduction in kisspeptin (Kiss1) mRNA expression, the neuronal density of AVPV and ARC nuclei and LH and oestradiol concentrations in the serum. The results of the present study confirm oestrogenic actions of tamoxifen in the brain and reproductive system. In addition, we show, for the first time, that tamoxifen has oestrogenic effects on the oestrogen-sensitive hypothalamic AVPV and ARC nuclei controlling the reproductive axis in female mice.

Influence of lesions in the limbic-hypothalamic system on metabolic response of acetate to daily repeated heat exposure in rabbit.

The effects of lesions in the basal medial hypothalamus and limbic structure on the acetate metabolic responses to daily repeated heat exposure in the liver of rabbits have been investigated. The results obtained were summarized as follows: (1) THe acetate metabolic responses to the 1st heat exposure (heat exposure on the 1st day) were altered by the lesions in the periventricular arcuate nucleus (ARC), ventromedial hypothalamus (VMH), stria terminalis (ST) and dorsal fornix (FX). (2) The acetate metabolic responses to heat exposure were completely abolished by the ten times repetition of heat exposure in the rabbits with lesions in ARC or VMH. They were similar to sham-operated animals. (3) The acetate metabolic responses to heat exposure remained even after the ten times repetition of heat exposure in the rabbits with lesions in ST and FX indicating the differences from sham-operated animals. (4) From these results, it might be suggested that the basal medial hypothalamus and limbic structure participated in the mechanism of acetate metabolic response to the 1st heat exposure, but only these limbic structure played some roles in the complete disappearance process of acetate metabolic responses to heat exposure by the ten times repetition of heat exposure.

Influence of lesions in the limbic-hypothalamic system on metabolic response of acetate to daily repeated immobilization stress.

The effects of lesions in the basal medial hypothalamus and limbic structure on the acetate metabolic responses to daily repeated exposure to immobilization stress in the liver of rabbits have been investigated. The experimental results were as follows: (1) The acetate metabolic response to the 1st exposure to immobilization stress (exposure on the 1st day) were considerably altered by lesions in the periventricular arcuate nucleus (ARC) ventromedial hypothalamus (VMH), stria terminalis (ST) and dorsal fornix (FX). (2) The acetate metabolic responses to immobilization stress were completely abolished by seven times repetition of immobilization stress in the rabbits with lesions in ARC, VMH and FX; they were similar to sham-operated groups. (3) In rabbits with ST lesions, the acetate metabolic responses to the 7th exposure (exposure on the 7th day) to immobilization stress were exactly the same as those after the 1st exposure of immobilization stress, but these metabolic responses were completely abolished by the seven times repetition of exposure in the sham-operated animals. (4) These results suggest that firstly, the ARC, VMH, amygdala(AMYG)-ST system and dorsal hippocampus(HPC)-FX system are involved in the acetate metabolic responses to the 1st exposure of immobilization stress, and secondly, that only the AMYG-ST is involved in the disappearance process of acetate metabolic responses to immobilization stress by the daily repetition of immobilization stress.

Influence of lesions in the limbic-hypothalamic system on adrenocortical responses to daily repeated exposures to immobilization stress in rabbits.

In order to elucidate the role of the limbic-hypothalamic system in the adrenocortical responses to repeated immobilization stress, the influences of daily repeated exposures of immobilization stress on the adrenocorticoid formation in adrenal slices of rabbits with lesions of various sites of the hypothalamus and limbic structures had been investigated. The experimental results obtained were as follows: (1) Lesions in periventricular arcuate nucleus (ARC) and ventromedial hypothalamus (VMH) decreased the rates of adrenocortical responses to the 1st immobilization exposure (exposure on the 1st day), but did not alter the rates of adrenocortical responses to the 4th immobilization exposure (exposure on the 4th day). (2) Lesions in stria-terminalis (ST) and dorsal fornix (FX) did not alter the rates of adrenocortical responses to the 1st immobilization exposure, but increased the rates of adrenocortical responses to the 4th immobilization exposure. (3) The adrenocortical responses to immobilization stress were completely abolished by the seven times repetition of exposures in each sham-operated group and in the animals with lesions of ARC and VMH, but in the rabbits with lesions of ST and FX the adrenocortical responses to immobilization stress were not abolished by the seven times repetition of exposures. (4) These results suggested that such basal medial hypothalamus participated in the mechanisms of adrenocortical responses to the 1st exposure of immobilization stress, but did not participate in the disappearance process of adrenocortical responses to immobilization stress by the seven times repetition of exposures. On the other hand, it might be supposed that the amygdala(AMYG)-ST system and dorsal hippocampus(HPC)-FX system do not participate in the mechanism of adrenocortical responses to the 1st immobilization exposure, but these limbic areas played some roles in the disappearance process of the adrenocortical responses to immobilization stress by the seven times repetition of exposures.

Influence of lesions of the limbic-hypothalamic system on adrenocortical responses to daily repeated heat exposures in rabbits.

The effects of lesions in the basal medial hypothalamus and limbic structure upon the responses of adrenocorticoids formation in adrenal slices of rabbits to daily repeated heat exposures has been investigated. (1) The adrenocortical responses to heat exposure on the 1st day were decreased by lesions in the periventricular arcuate nucleus (ARC), ventromedial hypothalamus (VMH), stria terminalis (ST) and dorsal fornix (FX). (2) There were no effects of heat exposure on the 10th day upon the adrenocorticoid formation in either the sham-lesioned rabbits or the rabbits with the lesions of ARC, VMH and ST. (3) In rabbits with the FX lesions, the adrenocorticoids formation was significantly increased by heat exposure on the 10th day. (4) These results suggested that the basal medial hypothalamus, amygdala (AMYG)-ST system and dorsal hippocampus (HPC)-FX system participated in the mechanisms of adrenocortical responses to heat exposure on the 1st day, but only the HPC-FX system played some roles in complete disappearance process of adrenocortical responses to heat exposure by repetition of exposures.

Influence of lesions in the limbic-hypothalamic system on insulin responses to daily repeated cold exposures in rabbits.

The effects of lesions in the basal medial hypothalamus and limbic structures on the responses in plasma levels of insulin and glucose to daily repeated cold exposure in rabbits have been investigated. The results obtained were summarized as follows: (1) The 1st cold exposure (cold exposure on the 1st day) decreased insulin levels and increased glucose levels, and these responses of insulin and glucose to cold exposure gradually decreased and then completely abolished by daily repetition of exposures in intact rabbits and each sham-operated group. (2) The lesions of periventricular arcuate nucleus (ARC), stria terminalis (ST) and dorsal fornix (FX) had no effects on the insulin responses to the 1st cold exposure, but the rates of insulin responses to the 1st cold exposure were decreased by the lesions of ventromedial hypothalamus (VMH). (3) The ARC lesions had no effects on the glucose responses to the 1st cold exposure, but the glucose responses to the 1st cold exposure were abolished by VMH lesions and were altered by lesions of ST and FX. (4) The insulin responses to cold exposure were abolished by daily repetition of exposures in rabbits with ARC lesions as same in the cases of sham-operated animals, but the insulin responses to cold exposure persisted even after daily repetition of exposures in rabbits with lesions of VMH, ST and FX different from sham-operated animals. (5) The glucose responses to cold exposure were abolished by daily repetition of exposures in rabbits with lesions of ARC and ST as same as in the cases of sham-operated animals, but the glucose responses to cold exposure persisted even after daily repetition of exposures in rabbits with FX lesions different from sham-operated animals.

Influence of lesion of the limbic-hypothalamic system on metabolic responses of acetate to daily repeated cold exposures in rabbits.

The effects of the lesions of basal medial hypothalamus and limbic structure on the acetate metabolic responses to daily repeated cold exposures in rabbit's liver has been investigated. The results obtained were summarized as follows: (1) The lesions of periventricular arcuate nucleus (ARC) had no effects on the acetate metabolism and on the acetate metabolic responses to the 1st cold exposure (cold exposure on the 1st day). (2) The metabolic pattern of acetate and the acetate metabolic responses to the 1st cold exposure were altered by the lesions of ventromedial hypothalamus (VMH), stria terminalis (ST) and dorsal fornix (FX). (3) The effects of cold exposure on the acetate metabolism were completely abolished by the seven times repetition of cold exposures in the rabbits with the lesions of ARC, VMH or ST, as the same as in each sham-operated group. (4) The acetate metabolic responses to cold exposure remained after the seven times repetition of cold exposure in the rabbits with the lesions of FX, but those disappeared completely in sham-operated animals. (5) From these results, it might be suggested that the VMH, amygdala(AMYG)-ST system, dorsal hippocampus(HPC)-FX system played some roles in the metabolic regulation of acetate and in the mechanisms of acetate metabolic responses to the 1st cold exposure, but the ARC did not participate in those mechanisms. And it was suggested that the HPC-FX system participated in the acetate metabolic adaptation to daily cold exposures, but the basal medial hypothalamus and AMYG-ST system did not participate in this process.

Influence of Electrical Stimulation of the Hypothalamus on Ovarian Steroidogenesis in Hypophysectomized and Adrenalectomized Rats

The effects of electrical stimulation of the lateral hypothalamic area (LHA), periventricular arcuate nucleus (ARC) and ventromedial hypothalamic nucleus (VMH) on the rates of 14C transfer from 14C-1 acetate into ovarian steroids in ovarian slices of hypophysectomized and adrenalectomized (H-A) rats were investigated. The 14C transfer rates into estrogen and 20 alpha-hydroxypregn-4-en-3-one (20 alpha-OH-P) were decreased by LHA stimulation. The stimulation of the ARC and VMH increased the rates of 14C transfer into estrogen, progesterone and 20 alpha-OH-P. From these results, it might be suggested that these hypothalamic structures were involved in the regulation of ovarian steroidogenesis without participation of the pituitary and adrenal.

Influence of lesions of the limbic-hypothalamic system on metabolic response of pyruvate to daily repeated immobilization stress in rabbits.

The pyruvate metabolic response to the 1st exposure (exposure on the 1st day) to immobilization stress (IMO) were considerably altered by lesions of the periventricular arcuate nucleus (ARC), ventromedial hypothalamus (VMH), stria terminalis (ST) and dorsal fornix (FX). The pyruvate metabolic responses to IMO were completely abolished by seven times repetition of exposure to IMO in the rabbits with lesions of ARC and VMH; they were similar to sham-operated groups. In rabbits with lesions of ST and FX, the pyruvate metabolic responses to the 7th exposure (exposure on the 7th day) to IMO were almost the same as those after the 1st exposure to IMO, but these metabolic responses were completely abolished by the seven times repetition of exposure to IMO in the sham-operated animals. These results suggest that firstly the ARC, VMH, amygdala (AMYG)-ST system and dorsal hippocampus (HPC)-FX system are involved in the pyruvate metabolic responses to the 1st exposure to IMO, and secondly, that the AMYG-ST system and the HPC-FX system are involved in the disappearance process of pyruvate metabolic responses to IMO by the daily repetition of exposure to IMO.

Influence of lesions in the limbic-hypothalamic system on metabolic responses of pyruvate to daily repeated heat exposures in rabbits.

The effects of lesions of the limbic-hypothalamic structures on the pyruvate metabolic responses to daily repeated heat exposures in the liver of rabbits have been investigated. The experimental results were as follows: 1. The pyruvate metabolic responses to the 1st heat exposure (heat exposure on the 1st day) were altered by lesions of periventricular arcuate nucleus (ARC), ventromedial hypothalamus (VMH), stria terminalis (ST) and dorsal fornix (FX). 2. The pyruvate metabolic responses to heat exposure were completely abolished by the ten times repetition of daily heat exposures in rabbits with lesions of ARC, VMH and ST, as same as in each sham-operated group. 3. In rabbits with FX lesions, the pyruvate metabolic responses to heat exposure remained even after the ten times repetition of daily heat exposures. 4. From these results, it might be suggested that ARC, VMH, amygdala (AMYG)-ST system and dorsal hippocampus (HPC)-FX system played a certain role in the mechanisms of pyruvate metabolic responses to the 1st heat exposure, but only the HPC-FX system participated in the process of pyruvate metabolic adaptation to daily repeated heat exposures.

The role of limbic-hypothalamic systems in metabolic responses of phenylalanine to repeated cold exposures in rabbits.

In this study we examine the effects of lesions to limbic or hypothalamic structures on the metabolic responses of phenylalanine in liver slices prepared from rabbits exposed to cold stress (-20 degrees C) for 12 hours at a fixed time once a day. The results were as follows: 1. The 1st cold exposure (cold exposure on the 1st day) had marked and various effects on phenylalanine metabolism, and the metabolic responses of phenylalanine to cold exposure gradually decreased and then completely disappeared with repetitions of exposure in intact rabbits. 2. The metabolic patterns and responses of phenylalanine to the 1st cold exposure were altered by lesioning the periventricular arcuate nucleus (ARC), ventromedial hypothalamus (VMH), stria terminalis (ST) or dorsal fornix (FX). 3. The complete abolishment of the metabolic responses to cold exposure by its repetition was observed in rabbits with lesions in the ARC or VMH as well. 4. In contrast, metabolic responses of phenylalanine to cold exposure in rabbits with lesions in the ST or FX remained even after six exposures. These results suggest that the ARC, VMH, amygdala (AMYG)-ST system and dorsal hippocampus (HPC)-FX system played a role in the metabolic regulation of phenylalanine and in the metabolic responses of phenylalanine to the 1st cold exposure and that the AMYG-ST and HPC-FX systems, but not the ARC or VMH, participated in the process of the metabolic adaptation of phenylalanine to cold exposure.

Influence of lesions in the limbic-hypothalamic system on metabolic response of pyruvate to daily repeated cold exposure in rabbits.

The effects of lesions of the limbic-hypothalamic structures on the pyruvate metabolic responses to daily repeated cold exposures in the liver of rabbits have been investigated. The experimental results were as follows: The metabolic pattern of pyruvate and the pyruvate metabolic responses to the 1st cold exposure (cold exposure on the 1st day) were altered by lesions of periventricular arcuate nucleus (ARC), ventromedial hypothalamus (VMH), stria terminalis (ST) and dorsal fornix (FX). The pyruvate metabolic responses to cold exposure were completely abolished by seven times repetition of daily cold exposures in rabbits with lesions of ARC, VMH and FX, as well as in each sham-operated group. In rabbits with ST lesions, the pyruvate metabolic responses to cold exposure remained even after the seven times repetition of daily cold exposures. From these results, it might be suggested that the ARC, VMH, amygdala (AMYG)-ST system and dorsal hippocampus (HPC)-FX system played a certain role in the metabolic regulation of pyruvate and in the mechanisms of pyruvate metabolic responses to the 1st cold exposure, but that only the AMYG-ST system participated in the process of pyruvate metabolic adaptation to daily repeated cold exposures.

Influence of the electrical stimulation of the hypothalamus on adrenocortical steroidogenesis in hypophysectomized rats.

The electrical stimulation of the ventromedial hypothalamus (VMH), lateral hypothalamic area (LHA), periventricular arcuate nucleus (ARC), and posterior hypothalamus (PHY), on 14C transfer rates from 14C-1-acetate into adrenocortical steroids in adrenal slices of hypophysectomized rats were investigated. The 14C transfer rates into corticosterone and cortisol were increased by the stimulation of the VMH, ARC, and PHY, but decreased by the stimulation of the LHA. From these results, it might be suggested that these hypothalamic structures were involved in the regulation of adrenocortical steroidogenesis without participation of the pituitary.

RFamide Peptides Inhibit the Expression of Melanotropin and Growth Hormone Genes in the Pituitary of an Agnathan, the Sea Lamprey, Petromyzon marinus

Neuropeptides with the Arg-Phe-amide motif at their C termini (RFamide peptides) were identified in the brains of several vertebrates, and shown to have important physiological roles in neuroendocrine, behavioral, sensory, and autonomic functions. The present study identified RFamide peptides, which are teleost prolactin-releasing peptide (PrRP) homologs, in the sea lamprey, Petromyzon marinus and characterized their effect on the release of pituitary hormones in vitro. Two RFamide peptides (RFa-A and RFa-B) were isolated from an acid extract of sea lamprey brain, including hypothalamus by Sep-Pak C18 cartridge, affinity chromatography using anti-salmon PrRP serum, and reverse-phase HPLC on an ODS-120T column. Amino acid (aa) sequences and mass spectrometric analyses revealed that RFa-A and RFa-B consist of 25 and 20 aa, respectively, and have 75% sequence identity within the C-terminal 20 aa. The RFa-B cDNA encoding a preprohormone of 142 aa was cloned from the lamprey brain, and the deduced aa sequence from positions 48-67 was identical to the sequence of RFa-B. However, the preprohormone does not include an aa sequence similar to the RFa-A sequence. Cell bodies, which were immunoreactive to anti-salmon PrRP serum, were located in the periventricular arcuate nucleus, ventral part of the hypothalamus, and immunoreactive fibers were abundant from the hypothalamus to the brain. A small number of immunoreactive fibers were detected in the dorsal half of the rostral pars distalis of the pituitary, close to the GH-producing cells. In addition, anti-salmon PrRP immunoreactivities were observed in the pars intermedia, corresponding to melanotropin cells. Likewise, signal of RFa-B mRNA was detected not only in the brain but also in the pars intermedia. The synthetic RFa-A and -B inhibited GH mRNA expression in a dose-dependent fashion in vitro, which is comparable to the inhibitory effect of teleost PrRP on GH release. Both RFa-A and -B also inhibited the expression of proopiomelanotropin mRNA, but no effects were observed in the expression of proopiocortin and gonadotropin beta mRNAs. The results indicate that RFamide peptides, which are teleost PrRP homologs, are present in the hypothalamus and pituitary of sea lamprey, and may be physiologically involved in the inhibition of GH and melanotropin release in the sea lamprey pituitary.

Lack of evidence for an impairment of tuberoinfundibolar dopaminergic neurons in aged male rats of the Sprague-Dawley strain.

Circulating prolactin (PRL) levels, dopamine (DA) content, in vitro basal and stimulus-evoked endogenous DA release from arcuate-periventricular nuclei median-eminence fragments were studied in young (4 months) and old (24-25 months) male rats of Sprague-Dawley strain. Serum PRL levels did not differ in young and aged animals. In addition DA tissue content, basal and K+- or d-amphetamine evoked endogenous DA release did not show age-related differences. These results suggest that in male rats of the Sprague-Dawley strain the activity of tuberoinfundibular dopaminergic (TIDA) neurons does not change during senescence, unlike what happens in other strains of rats.

Effect of different organic and inorganic blockers of calcium entry on the release of endogenous dopamine from tuberoinfundibular neurones

In the present study the effect of different blockers of calcium entry belonging to different chemical classes on basal and K +-elicited release of endogenous dopamine (DA) from tuberoinfundibular dopaminergic neurones was studied in vitro. For this purpose fragments of hypothalamus containing arcuate-periventricular nuclei and median eminence were incubated in vitro and endogenous DA released into the medium was assayed by radioenzymatic assay. The organic blockers of calcium entry, nitrendipine, nimodipine, nifedipine, diltiazem and flunarizine did not modify basal or K +-evoked release of endogenous DA, unless very large concentrations (100μM) of nifedipine or diltiazem were used. The phenylalkylamine methoxyverapamil (D-600) consistently inhibited K +-stimulated release of endogenous DA in concentrations of 50 and 100 μM. Cobalt and lanthanum, two ions with an ionic radius similar to that of calcium and which are known to inhibit calcium fluxes through nerve membranes, significantly blocked release of endogenous DA elicited by 35 mM K +. In summary, the results of the present study showed that calcium channels in the tuberoinfundibular dopaminergic system displayed a different sensitivity to various classes of blockers of calcium entry. Inorganic blockers of calcium entry, like lanthanum and cobalt, appeared to be the most effective in blocking Ca 2+-dependent release of endogenous DA, whereas, among the organic calcium antagonists, phenylalkylamines seemed to possess a certain degree of effectiveness.

Effects of estrogen on neuronal excitability in the hippocampal-septal-hypothalamic system.

The effects of electrical stimulation of the medial preoptic area (MPO) upon unit firing in the periventricular arcuate nucleus, and that of the dorsal hippocampus (DHPC) on medial septo-preoptic and arcuate (ARC) neurons, were investigated in Wistar and Sprague-Dawley female rats throughout the 4-day estrous cycle. Unit activity was recorded using stereotaxically-oriented tungsten microelectrodes under light urethane anesthesia. Repetitive stimulation of monophasic square waves varying only in current intensity was used. The following results were obtained: (a) An increase in activity of all ARC neurons recorded was induced by MPO stimulation on each day of the estrous cycle. (b) The minimum current (threshold) effective in increasing activity in the ARC neurons varied throughout the estrous cycle; the lowest threshold was observed in proestrus and the highest on the first day of diestrus. Also, the threshold current of MPO stimulation required in increase ARC activity was found to be elevated after ovariectomy and markedly reduced to the levels of the proestrous animal by estrogen treatment. (c) Stimulation of the DHPC (field CA3) increased activity in the medial septum but decreased activity in the MPO. Two pools of neurons, one increased and one decreased by DHPC stimulation, were observed in the ARC. (d) Variation in the threshold hippocampal stimulation during the estrous cycle was observed in the response of MPO and ARC neurons (the stimulation was effective only in proestrus and estrus); but not in that of medial septal neurons. (e) In addition, the spontaneous activity of septal; MPO; and ARC neurons was increased at proestrus or after estrogen injection. The present results suggest that plasma levels of estrogen play an essential role in the cyclic process of the regulation of ovulation by way of the selective facilitation of neuronal excitability in specific functional neural pathways. Furthermore, the results support the existence of a hippocampal inhibitory projection originating in field CA3 and terminating in the final common pathway, MPO to ARC.

Neuro-correlate of limbic-hypothalamo-pituitary-gonadal axis in the rat: change in limbic-hypothalamic unit activity induced by vaginal and electrical stimulation.

The present study deals with the effect of vaginal stimulation (VS) with a glass rod on unit activity in the brain and the correlation of the activity of each area under certain hormonal conditions. The frequency characteristics of the neuronal discharges in the brain stem, limbic structures, and hypothalamus were recorded, using stereotaxically oriented steel micro-electrodes, in adult female rats under light urethane anesthesia. The following results were obtained: (1) The level of ‘spontaneous’ activity in the anterior hypothalamic, preoptic, and septal areas of estrogen-primed spayed rats was higher than that observed in ovariectomized, non-estrogen-primed rats. (2) Significant and discriminated responses induced by VS were observed only in the estrous state, that is, after estrogen priming in the case of the ovariectomized animals. (3) These responses were almost independent of the EEG activity level, and could be discriminated from the response to other peripheral stimuli such as pinching. (4) The firing rate of hypothalamic neurones, depending on their locations, increased or decreased during and only immediately after VS (‘phasic response’), by means of which the EEG after-reaction was induced. Reciprocal changes were observed between the periventricular arcuate nucleus (ARC) (facilitated) and ventromedial hypothalamus (VMH) (inhibited), and between the basal and medial parts of the anterior hypothalamic area (AHA) (inhibited) and the medial preoptic area (MPO) (facilitated). (5) Neurone activity in the ventromedial part of the midbrain reticular formation (MRF), in the dorsal hippocampus (DHPC), in the medial complex of the amygdala (AMYG) and lateral septum, was enhanced during and for some minutes after VS (‘tonic response’), with the appearance of the EEG after-reaction. (6) The MRF may play a significant role in discriminating vaginal impulses from other peripheral sensory afferents. Interrelations of the unit activity in the above portions of the brain in estrogen-primed rats were examined by electrical stimulation and the results were as follows: (1) The VMH and ARC nuclei were reciprocally interrelated, and there exists an inhibitory pathway between them that may subserve changes in functional activity. (2) Electrical stimulation of the MPO and the AHA decreased unit activity of the VMH and increased that in the ARC. (3) The cornu ammonis of DHPC and the medial complex of the AMYG had a reciprocal relationship with the hypothalamus. In other words, the DHPC increased AHA activity and decreased MPO activity, while the AMYG influenced these nuclei conversely. Similarly, the DHPC increased and the AMYG decreased unit discharge in the ARC, while they exerted a reverse influence on the VMH activity. It is therefore suggested that the DHPC mainly activates the AHA-ARC circuit and the medial AMYG activates the MPO-ARC circuit, while both the hippocampus and amygdala may participate in different functional reorganizations activated by responses to VS.