Neuroendocrine asymmetry

Predominance of supraspinal innervation of the left ovary

In our previous studies using the viral transneuronal tracing technique we demonstrated the spinal and supraspinal components of the ovarian innervation. Since increasing number of data indicate the presence of morphological and functional laterality in the control of gonadal functions, we aimed to investigate whether cerebral structures trans-synaptically involved in the innervation of the ovary exhibit asymmetry or not. In one of the studies the left or the right ovary was injected with the red fluorescent protein expressing pseudorabies virus and the number of infected "red" autofluorescent neurons from the right and the left ovary was compared. In another study in order to have distinct labeling of cell groups connected with the right- and left-sided ovary in the same animal, a dual viral labeling was applied. The left- and right-sided ovary were inoculated with genetically engineered pseudorabies virus expressing a red fluorescent protein or a green fluorescent protein gene. Viral infection of brain nuclei including the dorsal vagal nucleus, caudal raphe nuclei, A5 noradrenergic cell group, hypothalamic paraventricular nucleus, from the left ovary in each case was enhanced when compared with labeling from the right gonad. Data suggest a predominance in the supraspinal innervation of the left ovary.

Ipsilateral vagotomy to unilaterally ovariectomized pre-pubertal rats modifies compensatory ovarian responses

The present study evaluates the participation of the vagus nerve in pre-pubertal rats with unilateral ovariectomy on puberty onset, and on progesterone, testosterone and estradiol serum levels, and the compensatory responses of the ovary. Unilateral vagotomy did not modify the onset of puberty in unilaterally ovariectomized rats. Ovulation rates of animals with the left vagus nerve sectioned and the left ovary in-situ was lower than in rats with only unilateral ovariectomy. Sectioning the left vagus to 32-day old rats with the left ovary in-situ resulted in lower compensatory ovarian hypertrophy than in rats with right unilateral ovariectomy. Twenty-eight or 32-day old animals with sectioning of the right vagus nerve and the right ovary in situ showed higher compensatory ovulation. Twenty-eight -day old rats with the right ovary in situ had higher progesterone and testosterone levels than animals of the same age with the left ovary in-situ. Compared to animals with the right ovary in situ, animals treated at 32-days of age, sectioning the ipsi-lateral vagus nerve resulted in higher progesterone levels. Higher progesterone levels were observed in 28- and 32 days old rats with the left ovary in situ and left vagus nerve sectioned. Thirty-two day old animals with the right ovary in situ and right vagus nerve sectioned had higher progesterone levels than rats of the same age with the left ovary in situ and left vagus nerve sectioned. Left vagotomy to 28-day old rats with the left ovary in situ resulted in higher testosterone levels, a reverse response to that observed in animals with sectioning of the right vagus and the right ovary in situ. Thirty-two day old rats with the left ovary in situ and left vagus nerve sectioned showed lower testosterone levels than animals without vagotomy and with the left ovary in situ.Twenty-eight -day old animals with the left vagus sectioned and left ovary in situ had lower estradiol serum levels than rats without unilateral vagotomy, a response similar to that observed in 32-day old rats with the right ovary in situ and right vagus nerve sectioned. Present results suggest an asymmetric regulation of steroid hormones secretion by the vagus nerve innervations in animals with unilateral ovariectomy, and those differences in testosterone serum levels observed are associated to the ovary remaining in-situ, vagal innervation and age when the animals were treated.

Morphological sex differences and laterality in the prepubertal medial amygdala

The medial amygdala (MeA) is crucial in the expression of sex-specific social behaviors. In adult rats the regional volume of the MeA posterodorsal subnucleus (MeApd) is approximately 50% larger in males than in females. The MeApd is also sexually dimorphic in prepubertal rats. We have recently shown that the left MeApd is significantly larger in prepubertal males than females. In contrast with volumetric sex differences elsewhere in the brain, however, we found no sex difference in the number of left MeApd neurons. In the present study we investigated the cellular bases of the sex difference in MeApd regional volume by quantifying the volume occupied by dendrites, axons, synapses, or glia, and by measuring MeApd dendritic morphology in 26-29-day-old male and female rats. We find that the volume occupied by dendritic shafts and glia completely accounts for the sex difference in left MeApd regional volume. Dendritic length measurements in the left hemisphere confirm that males have greater overall dendritic length, which is due to greater branching rather than to longer dendrite segments. In the right hemisphere the pattern of sex differences was different: Males have more MeApd neurons than females, whereas the dendritic morphology of individual neurons is not sexually dimorphic. These results highlight the importance of evaluating laterality in the MeA and suggest that the left and right MeA could play different roles in neuroendocrine regulation and sexually dimorphic social behaviors.

Innervation and serotoninergic receptors of the testis interact with local action of interleukin-1beta on steroidogenesis

Testosterone secretion by Leydig cells is affected by interleukin-1beta (IL-1beta). The aim of the present study was to investigate whether partial denervation of the testis or local administration of a serotonin (5-HT) receptor antagonist could alter the changes in testicular steoidogenesis induced by IL-1beta. Intratesticular administration of IL-1beta was combined with vasectomy or local injection of ketanserin (5-HT type 2 receptor antagonist) in immature hemicastrated rats and the effect of the interventions on testicular steroidogenesis was studied. One day after treatment with local injection of IL-1beta induced a significant rise in testosterone secretion that could be prevented by vasectomy (that also means transection of the inferior spermatic nerve). In a model in which neither IL-1beta nor ketanserin interfered with steroidogenesis, administration of the receptor antagonist just prior to IL-1beta treatment significantly reduced testosterone secretion. Data indicate interaction between testicular nerves and IL-1beta action and interaction between testicular 5-HT2 receptors and local effect of IL-1beta on testosterone secretion.

Thyroid hormones and retinoids: a possible link between genes and environment in schizophrenia

Phenotypic discordance for schizophrenia in monozygotic twins clearly indicates involvement of environmental factors as key determinants in disease development. Positive findings from genome scans, linkage and association studies apply in only a minority of those affected, while post-mortem brain investigations reveal altered expression of genes and proteins involved in numerous neurodevelopmental, metabolic and neurotransmitter pathways. Such altered expressions could result, on the one hand, from mutations in coding regions or polymorphisms in the promoter and regulatory regions in genes within those areas identified by gene searches or, on the other hand, from inadequate amounts of modulators, transporters and synthesizers of transcription factors necessary for regulation of the putative genes. Hormones and vitamins are such modulators. They could serve as bridges between genes and environment in schizophrenia. Multiple evidence supports the suggestion of retinoids and thyroid hormones as plausible actors in these roles. Both are not only essential for normal development of the central nervous system but also regulate the expression of many neurotransmitters, their synthesizing enzymes and receptors, and other genes in broader signaling transduction cascades affecting pathways that are altered in response to treatment. Functional and positional candidate genes include retinoic acid and thyroid hormone receptors, retinaldehyde dehydrogenases and deiodinases, which synthesize the powerful morphogens, retinoic acid and triiodothyronine, and the enzymes involved in their inactivation. This review highlights selective evidence supporting the retinoid and thyroid hormone hypotheses of schizophrenia.

Sexually dimorphic synaptic organization of the medial amygdala

The medial amygdala is important in social behaviors, many of which differ between males and females. The posterodorsal subnucleus of the medial amygdala (MeApd) is particularly sensitive to gonadal steroid hormones and is a likely site for gonadal hormone regulation of sexually dimorphic social behavior. Here we show that the synaptic organization of the MeApd in the rat is sexually dimorphic and lateralized before puberty. With the use of whole-cell voltage-clamp recording and quantitative electron microscopy, we found that, specifically in the left hemisphere, prepubertal males have approximately 80% more excitatory synapses per MeApd neuron than females. In the left but not the right MeApd, miniature EPSC (mEPSC) frequency was significantly greater in males than in females; mEPSC amplitude was not sexually dimorphic. Paired-pulse facilitation of EPSCs, an index of release probability, also was not sexually dimorphic, suggesting that greater mEPSC frequency is caused by a difference in excitatory synapse number. Electron microscopy confirmed that the asymmetric synapse-to-neuron ratio and the total asymmetric synapse number were significantly greater in the left MeApd of males than of females. In contrast to results for excitatory synapses, we found no evidence of sexual dimorphism or laterality in inhibitory synapses. Neither the frequency nor the amplitude of mIPSCs was sexually dimorphic or lateralized. Likewise, the number of symmetric synapses measured with electron microscopy was not sexually dimorphic. These findings show that the excitatory synaptic organization of the left MeApd is sexually differentiated before puberty, which could provide a sexually dimorphic neural substrate for the effects of hormones on adult social behavior.

Steroid-dependent plasticity in the medial amygdala

Behavioral sex differences have traditionally been thought to arise from gonadal steroids during a neonatal sensitive period. However, it is possible to sex-reverse certain behaviors by reversing the levels of circulating androgen in adult males and females. These results suggest that the sexually dimorphic substrates of sex behavior are subject to a high degree of plasticity, even in adulthood. I have found that circulating androgen exerts a trophic effect on the Nissl-stained morphology of an important nucleus in the control of sex behavior, namely, the posterodorsal subnucleus of the medial amygdala. First, sex-reversing the level of circulating androgen reversed the sex difference in soma size and regional volume of the posterodorsal subnucleus of the medial amygdala in adult rats. Interestingly, activation of both androgen and estrogen receptors was necessary for the post-castration maintenance of a masculine phenotype in terms of posterodorsal subnucleus of the medial amygdala cell size, whereas only estrogen receptor activity was necessary to maintain a masculine posterodorsal subnucleus of the medial amygdala volume. Then, we showed that seasonal variation in androgen was correlated with morphologic plasticity in the posterodorsal subnucleus of the medial amygdala of the Siberian hamster. However, if the experimental males were housed with females, their posterodorsal subnucleus of the medial amygdalas failed to regress in response to winter-like short daylengths. Furthermore, when male hamsters were castrated and treated with testosterone, the posterodorsal subnucleus of the medial amygdala responded to the hormone only if the animals were in summer-like photoperiods. Overall, these findings indicate that circulating androgens are critical for the maintenance of greater posterodorsal subnucleus of the medial amygdala regional volumes and soma sizes, and that environmental variables can regulate testosterone secretion and responsiveness.

Behavioural asymmetry is involved in regulation of autonomic processes: Left side presentation of food improves reproduction and lactation in cows

It is known that the right and left brain hemispheres differ in their ability to regulate autonomic processes in the organism. Direct unilateral stimulation of the brain provokes side-dependent endocrine, immune and other visceral reactions. Since brain hemispheres are mainly involved in the regulation of muscles and sensory organs on the contra lateral side of the body the activation of behavioural asymmetry stimulates the contra lateral half of the brain. The important theoretical and practical question of whether autonomic processes can be regulated via the behavioural asymmetry route remains unexplored. In this study, we report that the chronic presentation of an emotionally important stimulus-food-from the left side, improves reproductive performance in animals in a broad range of feeding conditions. The unilateral presentation of food can also influence lactation, but in this case the side-dependent effects are different under varying feeding conditions. This finding opens a simple practical approach to influence basic somatic functions in the organism.

Supraspinal connections of the reproductive organs: structural and functional aspects

Gonadal functions are governed by the hypothalamo-hypophyseal system. Other organs of the reproduction tract are under the regulatory action of gonadal steroids. In the past two decades several data have been accumulated on the involvement of fine-tuning control mechanisms which include autocrine and paracrine effects of biologically active substances produced locally and the regulatory action of nerves innervating the organs of the system. Recent studies using the viral transsynaptic technique have revealed cell groups in the central nervous system that are transneuronally connected with the male and female reproductive organs. This review summarizes neuromorphological data on the supraspinal innervation of reproductive organs and the functional significance of these brain areas in the control of reproduction.

Unilateral paramedian-sagittal brain cut extending from the level of the anterior commissure to the midlevel of the third ventricle above the amygdala affects gonadal function in male rat: a lateralized effect

The aim of the present investigations was to study involvement of fiber systems to and from the insular cortex above the amygdala in the neural control of the hypophysio-testicular axis in male rats. Animals were subjected to a unilateral paramedian-sagittal brain cut above the amygdala, extending from the level of the anterior commissure to the midlevel of the third ventricle and causing among others partial deafferentation of the insular cortex. Right-sided cut induced a significant rise in basal testosterone secretion in vitro of both testes as compared to intact or sham-operated controls without affecting serum testosterone level. By contrast, left-sided cut slightly suppressed testicular steroidogenesis and significantly decreased serum testosterone concentration. In animals underwent sham or actual cut on either side, serum luteinizing hormone levels were similar, but significantly lower than those in intact controls. No change was observed in serum FSH concentration of any experimental group. The results indicate that afferent and efferent connections of the partially deafferented cortical regions including among others the insular cortex are involved in the control of testosterone secretion. The data further suggest functional laterality of the interrupted structures.

Interictal EEG discharges, reproductive hormones, and menstrual disorders in epilepsy

We evaluated reproductive endocrine function in women with unilateral temporolimbic epilepsy and normal control subjects to assess the effects of epilepsy, epilepsy laterality, and antiepileptic drug use on the cerebral regulation of hormonal secretion. The findings indicate that reproductive endocrine function differs between women with epilepsy and normal control subjects. Significant differences exist at all levels of the reproductive neuroendocrine axis, that is, hypothalamus, pituitary, and peripheral gland. Differences show significant relationships to the epilepsy itself as well as to medication use. Reproductive neuroendocrine changes occur in a stochastic manner such that the laterality of unilateral temporolimbic discharges is associated with predictable directional changes in hormonal secretion at all levels of the reproductive neuroendocrine axis. These directional changes are consistent with the finding that different reproductive disorders may develop in relation to left- and right-sided temporolimbic epilepsy. Hormonal changes can show close temporal relationship to the occurrence of interictal epileptiform discharges and may vary in relation to the laterality of the discharges. Antiepileptic drugs differ in their effects on reproductive hormone levels. There are notable differences between enzyme-inducing and noninducing drugs. Menstrual disorders are more common among women with interictal discharges as well as women with abnormal hormonal findings.

Local variation in helminth burdens of bank voles (Clethrionomys glareolus) from ecologically similar sites: temporal stability and relationships with hormone concentrations and social behaviour

Populations of bank voles (Clethrionomys glareolus) in a fragmented forest habitat in north-east Poland showed local differences in helminth infection intensity, morphometric measures and organ weights that were consistent with differences at the same locations two years previously. Although overall intensities of infection were lower than previously, and there were some differences in the relative intensities of individual helminth species, site differences remained significant and were consistent across replicated subsites. In keeping with site differences in helminth infection and adrenal gland weight and asymmetry, voles at site 1 (high intensity infection) had higher circulating concentrations of corticosterone than those at site 2 (low intensity infection). Since males were sampled outside the breeding season, and thus non-scrotal, testosterone levels were low and did not differ between sites. As previously, voles at site 1 also showed greater hind foot asymmetry. Dyadic interactions between males from the same and different sites in the laboratory showed that males from site 1 were significantly less aggressive, especially when confronted with intruder males from site 2. There was no relationship between aggressiveness and intensity of infection overall or at site 1, but a significant negative relationship emerged at site 2. Aggression thus appeared to be downregulated at the higher intensity site independently of individual levels of infection. Terminal corticosterone concentrations were greater at site 1 and lower among residents that initiated more aggression. While corticosterone concentrations rose over the period of testing, they did not correlate with the amount of aggression initiated or received.

Local variation in helminth burdens of Egyptian spiny mice (Acomys cahirinus dimidiatus) from ecologically similar sites: relationships with hormone concentrations and social behaviour

Populations of Egyptian spiny mice (Acomys cahirinus dimidiatus) in a fragmented montane wadi system in the Sinai showed significant differences in the abundance of gut helminths. Differences in parasite load between populations were positively associated with measures of androgen activity but showed no significant relationship with glucocorticoid activity. Social discrimination tests with adult males from different wadis showed that those from sites with greater helminth abundance were less likely to investigate odours from other males and were less aggressive when subsequently interacting with the odour donors. Subjects showed markedly more investigation towards the odours of males from distant wadis compared with those from their own or immediately neighbouring wadi, but were less aggressive when confronted with odour donors from distant wadis. Despite this, there was a positive relationship between the amount of investigation towards distant male odour and subsequent aggression towards the male. While aggressiveness was positively associated with measures of androgen and glucocorticoid activity, no significant relationship emerged with individual helminth infection. Thus aggressiveness appeared to relate to overall local population levels of infection rather than individual challenge.

Relationship of sexual dysfunction to epilepsy laterality and reproductive hormone levels in women

Sexual dysfunction has been reported to be common among women with epilepsy. Controlled studies, quantitative data, and investigations of potentially contributory factors, however, have been few. The purpose of this investigation was to determine if (1) sexual dysfunction is unusually common among women with partial seizures of temporal lobe origin (TLE), and (2) sexual dysfunction varies in relation to the laterality of EEG epileptiform discharges, antiepileptic drug use, and serum gonadal steroid levels. This controlled prospective investigation used a quantitative sexual rating scale and reproductive hormone measures to compare sexual dysfunction in women with left and right unilateral temporolimbic epilepsy and controls. Sexual dysfunction scores were significantly higher in women with TLE, and sexual dysfunction affected substantially more women with epilepsy than controls. Women with right-sided foci were affected more than women with left-sided foci. There was a significant inverse correlation between sexual dysfunction and bioactive testosterone levels in women with epilepsy as well as in controls. Serum estradiol was lower in women with TLE but did not correlate significantly with overall sexual dysfunction. The findings suggest that sexual dysfunction is significantly more common in women with right-sided epileptiform discharges than in controls and is inversely correlated with bioactive testosterone levels. The value of hormonal replacement or supplementation remains to be explored.

Lesion of the amygdala on the right and left side suppresses testosterone secretion but only left-sided intervention decreases serum luteinizing hormone level

The effect of right- and left-sided intra-amygdaloid injection of kainic acid on the hypothalamo-hypophyseal-testicular axis was studied in rats. Both right- and left-sided injection of the neurotoxin into the amygdala resulted in a significant decrease in basal testosterone secretion in vitro of both testes and in serum testosterone concentration. In addition, left-sided administration of kainic acid significantly suppressed serum luteinizing hormone level, while right-sided intervention did not alter this parameter. The results of the present study provide further evidence on the involvement of the amygdala in the control of testicular steroidogenesis. Furthermore, the observations suggest functional asymmetry of the amygdala concerning the mechanism of suppressed testosterone secretion.

Supraspinal connections of the ovary: structural and functional aspects

This review summarizes our recent studies using the viral transneuronal tracing technique to identify sites in the central nervous system (CNS) that are connected with the ovary. A neurotropic virus (pseudorabies virus) was injected into the ovary and various times after the inoculation the spinal cord and brain were examined for virus-infected neurons identified by immunocytochemistry. Such neurons could be detected in well-defined cell groups of the spinal cord (intermediolateral cell column), brain stem (vagal nuclei, area postrema, parapyramidal nucleus, caudal raphe nuclei, A1, A5, A7 noradrenergic cell groups, locus coeruleus, Barrington's nucleus, periaqueductal gray), hypothalamus (paraventricular nucleus, anterior hypothalamus, arcuate nucleus, zona incerta), and, at longer survival time, in some telencephalic structures (amygdala, bed nucleus of the stria terminalis). These findings provided the first neuromorphological evidence for the existence of a multisynaptic neuronal pathway between the brain and the ovary presumably involved in the neuronal control of the organ. The observations indicate that there is a significant overlap of CNS structures connected with the ovary, the testis, other organs and organ systems, suggesting similar neuronal circuitries of the autonomic nervous system innervating the different organs. The known descending neuronal connections between the CNS structures labeled from the ovary by the viral transneuronal tracing technique and the findings suggesting a pituitary independent interplay between certain cerebral structures such as the hypothalamus, the amygdala, and the ovary are also summarized in this review.

Effects of sympathetic denervation on follicular distribution, oestradiol and progesterone serum levels in prepubertal hemi-ovariectomized female guinea pig

Hemi-gonadectomy performed in prepubertal female guinea pigs is followed by a compensatory ovarian hypertrophy (COH) and compensatory ovulation (CO). Sympathetic denervation diminished the COH (left ovary: 28 +/- 1.6% versus 46 +/- 4% (control), P < 0.05; and right ovary: 21.3 +/- 3.2% versus 34.2 +/- 3.7% (control), P < 0.01) and does not modify the CO. The mean follicular diameter increased only in the right ovary of hemi-gonadectomized animals. This increase is greater in the hemi-gonadectomized-denervated groups. The mean follicular diameter measured in the right and left ovaries showed an opposite response in hemi-ovariectomized and hemi-ovariectomized-denervated animals: the diameter increased in the right ovary without modifications in the left. Present results add further support to the participation of ovarian innervation on the mechanisms, which regulate follicular development.

Effects of functional peripheral sympathetic denervation induced by guanethidine on follicular development and ovulation of the adult female guinea pig

The present study investigates the effects of functional sympathetic peripheral denervation induced by guanethidine sulphate (GTD) to adult female guinea pigs in the follicular (FPh) or luteal phases (LPh) on their oestrous cyclicity and ovulation. No differences were observed in oestrous cyclicity or the average number of corpora lutea present in the ovaries between the control and denervated animals. Guanethidine sulphate administration resulted in a significant decrease in ovarian norepinephrine content, higher for the left ovary than for the right one. Serum oestrogen and progesterone concentrations, the mean of follicles, and its diameter were different, depending on the oestral cycle in which the treatment was performed. These results suggest that in adult normal female guinea pigs, ovarian innervation participates in the regulation of follicular development in an inhibitory way.

Effects of guanethidine administration on compensatory ovarian hypertrophy, compensatory ovulation and follicular development in the prepubertal female guinea pig

We analyzed the participation of sympathetic ovarian innervation in the prepubertal female guinea pig on regulation of compensatory ovarian hypertrophy (COH) and compensatory ovulation at puberty. The COH of the left ovary was significantly higher that of the right one (left ovary: 41.5+/-5.2 vs. 27.5+/-5.6%, p<0.05, Kruskal-Wallis test). The sympathetic denervation induced by guanethidine administration beginnings at birth or on day 10 resulted in a significant increase of the COH by each ovary (p<0.05, Kruskal-Wallis test). Only one of the six untreated control guinea pigs sacrificed at the follicular phase ovulate. All the hemiovariectomized animals with the left ovary in situ ovulated, while only two out of five with the right ovary in situ did (100 vs. 40%: p<0.001, Kruskal-Wallis test), unlike the denervated animals, which did not ovulate. The number of corpora lutea present in the ovaries was similar among all groups of animals. These results demonstrate differences in the follicular diameter in untreated female guinea pigs and add further support to the concept of asymmetrical response of the ovaries to denervation.

Local variation in endoparasite intensities of bank voles (Clethrionomys glareolus) from ecologically similar sites: morphometric and endocrine correlates

Much interest has centred recently on the role of adaptive trade-offs between the immune system and other components of life history in determining resistance and parasite intensities among hosts. Steroid hormones, particularly glucocorticoids and sex steroids, provide a plausible mechanism for mediating such trade-offs. A basic assumption behind the hypothesis, however, is that steroid activity will generally correlate with reduced resistance and thus greater parasite intensities. Here, we present some findings from a field study of bank voles (Clethrionomys glareolus) in which we have looked at associations between parasite intensities, anatomical and morphometric measures relating to endocrine function and life history variation in three local populations inhabiting similar but mutually isolated woodland habitats. In general, sites with greater parasite intensities were those in which male C. glareolus had significantly larger adrenal glands, testes and seminal vesicles for their age and body size. Females also showed a site difference in adrenal gland weight. Some aspects of site-related parasite intensity were associated with asymmetry in adrenal gland weight and hind foot length, which may have reflected developmental effects on glucocorticoid activity.

Lesion of the insular cortex affects luteinizing hormone and testosterone secretion of rat. Lateralized effect

The possible involvement of the insular cortex in the neural control of the hypophyseal-testicular axis was studied in male rats. Right- but not left-sided lesion of the insular cortex resulted in a significant decrease in basal testosterone secretion in vitro and serum testosterone concentration. Both right- and left-sided lesions of the insular cortex induced significant increase in serum luteinizing hormone (LH) concentration. Unilateral lesion of the insular cortex on either sides had no effect on serum follicle stimulating hormone (FSH) level. The results indicate that the insular cortex is involved in the control of testosterone and LH secretion. The data further suggest that the right insular cortex plays a predominant role in the control of male endocrine reproductive processes.

Environmental light-darkness conditions induce changes in brain and peripheral pyroglutamyl-peptidase I activity

To evaluate the influence of light and darkness on brain pyroglutamyl-peptidase I (pGluPI) activity, four experimental groups of rats were compared at the same time-point (10.00 h). Two groups were designed with a standard 12-12 h light-dark cycle: In group A, the lights were on from 7.00 h to 19.00 h, and the experiment was done under light conditions; in group B, the lights were on from 19.00 h to 7.00 h, and the experiment was done under darkness conditions. Two additional groups were designed with nonstandard light-dark conditions: In group C, the animals were subjected to constant light, and the experiment was done under light conditions. In group D, animals were subjected to constant darkness, and the experiment was done under darkness conditions. Light (vs darkness) and standard (vs nonstandard) conditions produced significant changes on pGluPI activity in specific structures; the data suggested that endogenous substrates of pGluPI such as thyrotropin-releasing hormone and gonadotropin-releasing hormone, might be modified in parallel. There was left predominance in the retina under light conditions on a standard schedule (group A). The regional pattern of distribution of activity was similar in groups on a standard schedule (A vs B) and in groups tested under constant light-dark conditions (C vs D). However, this pattern differed between groups subjected to standard vs constant light-dark conditions (A and B vs C and D). These results support an influence of environmental light and darkness on pGluPI activity, which may reflect concomitant changes in its susceptible substrates and consequently in their functions.

Asymmetry of the neuroendocrine system

There is information on the lateralization of hypothalamic, limbic, and other brain structures involved in the control of the endocrine glands. Sided differences between paired glands, including their peripheral innervation, and relevant clinical observations on asymmetry are also known. Data suggest predominance of the right half of brain structures in controlling gonadal function.

The effect of callosotomy on testicular steroidogenesis in hemiorchidectomized rats: a pituitary-independent regulatory mechanism

In recent years, increasing number of data indicate that cerebral structures exert a direct, pituitary-independent, neural regulatory action on the endocrine glands. In addition, both experimental and clinical observations indicate functional asymmetry of the control system. Therefore, the objective of the present study was to study the effect of callosotomy on testicular steroidogenesis and serum gonadotrop concentrations in rats subjected to left- or right-sided orchidectomy. In animals underwent callosotomy plus left-sided orchidectomy the basal testosterone secretion in vitro of the remaining (right) testis was significantly higher than that of intact controls, and of rats subjected to sham surgery plus left orchidectomy. In contrast, either sham operation or callosotomy plus right-sided orchidectomy did not interfere with testicular steroidogenesis. Sham surgery or callosotomy plus left orchidectomy induced a significant rise in serum follicle-stimulating hormone concentration while right orchidectomy combined either with sham surgery or callosotomy did not alter this parameter. There was no statistically significant difference between experimental groups in serum testosterone and luteinizing hormone concentrations. The results indicate the involvement of the corpus callosum in a pituitary-independent neural control of testicular steroidogenesis. The data further suggest a different response in steroidogenesis of the left and the right testis following hemicastration and callosotomy.

CNS structures presumably involved in vagal control of ovarian function

The contribution of the vagus nerve to viral transneuronal labeling of brain structures from the ovaries demonstrated recently by us was investigated. Unilateral vagotomy was performed prior to ipsilateral intraovarian virus injection. Virus-infected neurons were visualized by immunostaining. In vagotomized rats such neurons were detected only in certain cell groups of the brain (parapyramidal nucleus, A(1), A(5) cell group, caudal raphe nuclei, hypothalamic paraventricular nucleus, lateral hypothalamus). Vagotomy interfered with labeling of several structures that were labeled in controls, including area postrema, nucleus of the solitary tract, dorsal vagal complex, nucleus ambiguus, A(7) cell group, Barrington's nucleus, locus coeruleus, periaqueductal gray, dorsal hypothalamus. Findings provide a morphological basis to study the functional significance of brain structures presumably involved in the control of ovarian function and acting via the vagus or the sympathetic nerves.

Lateralized effects of medial prefrontal cortex lesions on neuroendocrine and autonomic stress responses in rats

The medial prefrontal cortex (mPFC) is highly activated by stress and modulates neuroendocrine and autonomic function. Dopaminergic inputs to mPFC facilitate coping ability and demonstrate considerable hemispheric functional lateralization. The present study investigated the potentially lateralized regulation of stress responses at the level of mPFC output neurons, using ibotenic acid lesions. Neuroendocrine function was assessed by plasma corticosterone increases in response to acute or repeated 20 min restraint stress. The primary index of autonomic activation was gastric ulcer development during a separate cold restraint stress. Restraint-induced defecation was also monitored. Plasma corticosterone levels were markedly lower in response to repeated versus acute restraint stress. In acutely restrained animals, right or bilateral, but not left mPFC lesions, decreased prestress corticosterone levels, whereas in repeatedly restrained rats, the same lesions significantly reduced the peak stress-induced corticosterone response. Stress ulcer development (after a single cold restraint stress) was greatly reduced by either right or bilateral mPFC lesions but was unaffected by left lesions. Restraint-induced defecation was elevated in animals with left mPFC lesions. Finally, a left-biased asymmetry in adrenal gland weights was observed across animals, which was unaffected by mPFC lesions. The results suggest that mPFC output neurons demonstrate an intrinsic right brain specialization in both neuroendocrine and autonomic activation. Such findings may be particularly relevant to clinical depression which is associated with both disturbances in stress regulatory systems and hemispheric imbalances in prefrontal function.

Intratesticular serotonin affects steroidogenesis in the rat testis

The effect of intratesticular administration of serotonin (5-HT), ketanserin (5-HT2 receptor antagonist), and 5,7-dihydroxytryptamine (5,7-DHT) (the neurotoxin that destroys serotoninergic neural elements) on steroidogenesis was studied in immature and adult rats. In adults, bilateral intratesticular injection of 5-HT resulted in a significant decrease in basal but not in hCG-stimulated testosterone secretion and in serum testosterone concentration, whereas ketanserin induced a significant rise in steroidogenesis 1 h post-treatment. There was no effect 1 day after administration of 5-HT or ketanserin, and 7 days after the injection of 5,7-DHT. In immature rats 1 day after bilateral testicular administration of ketanserin, basal testosterone secretion in vitro was significantly suppressed. In immature hemicastrates, local injection of 5-HT resulted (1 day post-treatment) in a significant rise in steroidogenesis while administration of 5,7-DHT decreased testosterone secretion 7 days after the injection of the neurotoxin. The results indicate that in adult rats 5-HT exerts a suppressive, whereas in immature rats, a stimulatory action on steroidogenesis occurs. Data also suggest that, in both age groups, the effect of 5-HT is mediated through 5-HT2 receptors. The observation that in immatures administration of the neurotoxin resulted in an effect similar to that found following the treatment with the receptor antagonist suggests that, in this age group, 5-HT derived from local neural elements might also be involved in the control of 5-HT on Leydig cell steroidogenesis.