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.

Transneuronal labelling of nerve cells in the CNS of female rat from the mammary gland by viral tracing technique.

Using the viral transneuronal tracing technique, the cell groups in the CNS transneuronally connected with the female mammary gland were detected. Lactating and non-lactating female rats were infected with pseudorabies virus injected into the mammary gland. The other group of animals was subjected to virus injection into the skin of the back. Four days after virus injection, infected neurons detected by immunocytochemistry, were present in the dorsal root ganglia ipsilateral to inoculation and in the intermediolateral cell column of the spinal cord. In addition, a few labelled cells could be detected in the dorsal horn and in the central autonomic nucleus (lamina X) of the spinal cord. At this survival time several brain stem nuclei including the A5 noradrenergic cell group, the caudal raphe nuclei (raphe obscurus, raphe pallidus, raphe magnus), the A1/C1 noradrenergic and adrenergic cell group, the nucleus of the solitary tract, the area postrema, the gigantocellular reticular nucleus, and the locus coeruleus contained virus-infected neurons. In some animals, additional cell groups, among others the periaqueductal gray and the red nucleus displayed labelling. In the diencephalon, a significant number of virus-infected neurons could be detected in the hypothalamic paraventricular nucleus. In most cases, virus-labelled neurons were present also in the lateral hypothalamus, in the retrochiasmatic area, and in the anterior hypothalamus. In the telencephalon, in some animals a few virus-infected neurons could be found in the preoptic area, in the bed nucleus of the stria terminalis, in the central amygdala, and in the somatosensory cortex. At the longer (5 days) survival time each cell group mentioned displayed immunopositive neurons, and the number of infected cells increased. The pattern of labelling was similar in animals subjected to virus inoculation into the mammary gland and into the skin. The distribution and density of labelling was similar in lactating and non-lactating rats. The present findings provide the first morphological data on the localization of CNS structures connected with the preganglionic neurons of the sympathetic motor system innervating the mammary gland. It may be assumed that the structures found virus-infected belong to the neuronal circuitry involved in the control of the sympathetic motor innervation of the mammary gland.

Identification of CNS neurons involved in the innervation of the epididymis: a viral transneuronal tracing study.

Cell groups of the spinal cord and the brain transsynaptically connected with the epididymis (caput, cauda) were identified by means of the viral transneuronal tracing technique. Pseudorabies virus was injected into the caput or the cauda epididymidis, and after survival times 4 and 5 days, the spinal cord and brain were processed immunocytochemically. Virus-labeled neurons could be detected in the preganglionic sympathetic neurons (lower thoracic and upper lumbar segments) and following virus injection into the cauda epididymidis, also in the sacral parasympathetic nucleus (L6-S1). Virus-infected perikarya were present in several brain stem nuclei (lateral reticular nucleus, gigantocellular and paragigantocellular nucleus, A5 noradrenergic cell group, caudal raphe nuclei, locus coeruleus, Barrington's nucleus, nucleus of the solitary tract, periaqueductal gray) and in the diencephalon (hypothalamic paraventricular nucleus, lateral hypothalamus). At the longer survival time, some telencephalic structures also exhibited virus-labeled neurons. The distribution of infected neurons in the brain was similar after virus injection into the caput or cauda epididymidis; however, earlier onset of infection was observed after inoculation into the cauda. The present findings provide the first morphological data on a multisynaptic circuit of neurons innervating the epididymis and presumably involved in the control of epididymal functions. reserved.

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.

The central cannabinoid receptor inactivation suppresses endocrine reproductive functions.

The function of central cannabinoid (CB1) receptor was investigated in the regulation of the pituitary-gonad axis in CB1 receptor knockout male mouse. Serum luteinizing hormone (LH) and testosterone (T) levels and basal T secretion in vitro of testes were significantly decreased in mutant (CB1-/-) mice. The receptor agonist, anandamide (ANA), suppressed LH and T secretion in wild type (CB1+/+) mice but had no effect in receptor inactivated animals. The results are the first descriptions indicating the direct action of CB1 receptors on LH and T secretion and the immunohistological demonstration of CB1 receptors in the Leydig cells. The results also indicate that CB1 receptors are responsible for the effects of exogenous cannabinoids on reproductive 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.

Central nervous system structures labelled from the testis using the transsynaptic viral tracing technique.

In the present study, the transneuronal transport of neurotrophic virus technique was used to identify cell groups of the spinal cord and the brain that are transsynaptically connected with the testis. Pseudorabies virus was injected into the testis and after survival times of 3-6 days, the spinal cord and brain were processed immunocytochemically using a polyclonal antibody against the virus. Virus-infected perikarya were detected in the preganglionic neurones of the spinal cord (T10-L1, L5-S1) and in certain cell groups and areas of the brain stem, the hypothalamus and the telencephalon. In the brain stem, the cell groups and areas in which labelled neurones were present included, among others, the nucleus of the solitary tract, the caudal raphe nuclei, the locus coeruleus and the periaqueductal grey of the mesencephalon. In the hypothalamus, virus infected perikarya were observed in the paraventricular nucleus and in certain other cell groups. Telencephalic structures containing labelled neurones included the preoptic area, the bed nucleus of the stria terminalis, the central amygdala and the insular cortex. These data identify a multisynaptic circuit of neurones in the spinal cord and in the brain which may be involved in the control of testicular functions.

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.

Central nervous system structures connected with the endocrine glands. findings obtained with the viral transneuronal tracing technique.

This review is a summary of recent neuromorphological observations on the existence of multisynaptic neural pathways between the endocrine glands and the central nervous system (CNS) and its structures involved in this pathway. Introduction of the viral transneuronal tracing technique has made possible investigations of multisynaptic connections. The utility of this approach is based on the ability of the neurotropic virus to invade and replicate in neurons, and then gradually infect synaptically linked second-order, third-order. etc. neurons. Injecting the virus into the endocrine glands, this technique was used to identify cell groups in the spinal cord and in the brain which are connected with the adrenal gland, the gonads and the pancreas. Injection of the virus into these organs resulted in viral labeling of neurons in practically identical structures of the CNS including the intermediolateral cell column of the spinal cord, the vagal nuclei and certain other cell groups in the brain stem. In the hypothalamus the most intensive labeling was in the parvocellular part of the paraventricular nucleus and in the telencephalon labeled nerve cells were detected in the amygdala, the bed nucleus of the stria terminalis and in the preoptic area. It is known that the labeled CNS structures are members of descending pathways arising from the hypothalamic paraventricular nucleus or from other cell groups and terminating on neurons of the vagal nuclei and the intermediolateral cell column of the spinal cord. Experimental data support the view that the CNS structures and pathways connected with the endocrine glands are involved in the neural control of these organs.

Effect of intratesticular administration of TRH or anti-TRH antiserum on function of rat testis.

The effect of intratesticular administration of thyrotropin-releasing hormone (TRH) and anti-TRH antiserum on steroidogenesis was studied in immature and adult rats. In 9-day-old animals local administration of the neuropeptide resulted in an increase in basal testosterone secretion in vitro. Similar treatment of 15-day-old rats suppressed hCG-stimulated testosterone secretion with no change in basal testosterone production. In both immature groups the treatment did not affect serum testosterone concentration. By contrast, in adults TRH decreased serum testosterone level, but did not influence basal and hCG-stimulated testosterone secretion. Both in immature and adult rats, the changes in steroidogenesis were evident 1 hour posttreatment. Five days after the administration of anti-TRH antiserum into the remaining testis of immature rats subjected to hemicastration just prior to the antiserum treatment, the alterations in steroidogenesis were opposite to those detected after treatment with TRH. In 9-day-old rats the antiserum suppressed steroidogenesis, while in 15-day-old animals it stimulated testosterone secretion. The results suggest that testicular TRH might exert a local action on testicular steroidogenesis, and the effect is age-dependent.

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.

Neuronal labeling in the rat brain and spinal cord from the ovary using viral transneuronal tracing technique.

In the present investigations the viral transneuronal labeling method, which is able to reveal hierarchial chains of central nervous system (CNS) neurons, was applied to identify sites in the CNS connected with the ovary and presumably involved in the control of ovarian functions. Pseudorabies virus was injected into the ovaries of rats and a few days later (at various times after the injection) the spinal cord and brain were examined for virus-infected neurons from the ovary. The virus-labeled nerve cells were identified by immunocytochemistry using polyclonal antiviral antibody. Virus-labeled neurons were detected both in the spinal cord and the brain. In the spinal cord such elements were observed in the intermediolateral cell column, in the dorsal horn close to the marginal zone and in the central autonomic nucleus. In the medulla oblongata and pons, neurons of several nuclei and cell groups (area postrema, nucleus of the solitary tract, dorsal vagal complex, nucleus ambiguus, paragigantocellular nucleus, parapyramidal nucleus, A1, A5 and A7 cell groups, caudal raphe nuclei, locus ceruleus, subceruleus nucleus, Barrington's nucleus, Kölliker-Fuse nucleus) were found to be transneuronally labeled. In the mesencephalon, the ventrolateral part of the periaqueductal gray matter contained virus-labeled neurons. In the diencephalon, a very intensive cell body labeling was observed in the hypothalamic paraventricular nucleus and a few virus-infected neurons could be detected in the lateral and dorsal hypothalamus, in the arcuate nucleus, zona incerta, perifornical area and in the anterior hypothalamus. Concerning the telencephalic structures, virus-labeled cells were found in the bed nucleus of the stria terminalis and in the central amygdala nucleus. These findings provide the first neuromorphological evidence for the existence of a multisynaptic neuronal pathway between the ovary and the CNS, and give a detailed account of the structures involved in this pathway.

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.

Neuroendocrine asymmetry.

The information available at present clearly indicates that asymmetry exists from the level of elementary particles to the human cerebral cortex, the latest stage of evolution. Cerebral lateralization is one of the well-known asymmetries. This paper summarizes the data published in the past decades on the asymmetry of the neuroendocrine system. The information on the sided-differences between the gonads, adrenals, and thyroid lobes and that on the lateralization of hypothalamic, limbic, and other brain structures participating in the control of the endocrine glands as well as relevant clinical observations are reviewed here. The innervation of the peripheral endocrine glands is also briefly summarized because the afferent and efferent fibers of these glands may represent one part of the pathway involved in neuroendocrine asymmetry. The data reviewed clearly indicate that some kind of asymmetry (morphological, biochemical, physiological, pathological) is evident at different levels of the neuroendocrine system (at limbic, hypothalamic, peripheral endocrine glands and their innervation) and there are species, sex, and age differences. Most of the information accumulated deals with the CNS-gonadal system. A majority of the observations suggest that in both male and female rats there is a predominance of the right half of brain structures controlling gonadal function. The asymmetry, however, is not restricted to CNS structures: it also exists at the level of the gonads, including their innervation. It appears that the characteristic pattern of the CNS-gonadal system becomes fixed only after sexual maturation. Very few reports are available suggesting some kind of asymmetry of the CNS-adrenal cortex and the CNS-thyroid system. There are convincing findings consistent with the view that in addition to the hypothalamo-adenohypophyseal system acting via the general circulation on the peripheral endocrine glands, there is also a pure neural link between the CNS and the gonads, the CNS and the adrenal gland, and also between the CNS and the thyroid. This link contains afferent and efferent pathways and is able to modulate the functional activity or the responsiveness of the gland. It may also serve as a neural reflex arc. It is assumed that the neuroendocrine asymmetry expresses itself through (i) hypophysiotrophic neurohormones and hormones of the peripheral endocrine glands, (ii) neural pathways, or (iii) a combination of (i) and (ii). The authors hope that this publication, in addition to providing an overview, will also stimulate research, both basic and clinical, in this exciting area of neuroendocrinology.

Fine-tuning control of testicular functions.

The effect of testicular administration of peptides synthesized in the testis (somatostatin, oxytocin) or peptide antagonists (opioid receptor antagonists naloxone, nalmefene, anti-corticotrop hormone-releasing hormone antiserum, beta-endorphin antiserum), partial denervation of the testis, and combination of local treatment with peptides/peptide antagonists and denervation was studied on testicular steroidogenesis in immature hemicastrated rats. The observations indicate that beta-endorphin, corticotrop hormone-releasing hormone, oxytocin, and somatostatin exert a stimulatory, whereas enkephalin has an inhibitory action on steroidogenesis. Surgical (vasectomy) or pharmacological (local injection of 6-hydroxydoparnine) denervation suppresses testosterone secretion. Following partial denervation of the testis the effect of naloxone or oxytocin on steroidogenesis observed in fully innervated gonad is not present or the effect is paradoxical. These results indicate that steroidogenesis is fine-tuned by local peptide actions, and neural inputs. Data further suggest an interaction between local peptide action and neural control.

Local effect of PACAP and VIP on testicular function in immature and adult rats.

PACAP, VIP, anti-PACAP and anti-VIP antisera were injected intratesticularly. In 9-day-old hemicastrated rats PACAP or VIP decreased basal testosterone secretion. In 22-day-old hemicastrates VIP but not PACAP reduced compensatory testicular hypertrophy, however, neither PACAP nor VIP altered steroidogenesis. Anti-VIP antiserum to this age group increased testosterone production and enhanced compensatory testicular hypertrophy. In adult hemicastrates neither the peptides nor the antisera influenced steroidogenesis. Neither in immatures nor in adults treatment of both testes with PACAP or VIP had any effect. Data indicate that both PACAP and VIP might exert a local action on testicular steroidogenesis, on compensatory testicular hypertrophy, and these effects are age-dependent.

Testicular injection of 5,6-dihydroxytryptamine or vasectomy interferes with the local stimulatory effect of oxytocin on testicular steroidogenesis in immature rats.

Previous studies indicated that in immature rats testicular administration of oxytocin stimulates testicular steroidogenesis. In the present study, testicular treatment with oxytocin (50 ng) was combined with pharmacological or surgical denervation of the testis in hemigonadectomized immature rats. For denervation 5,6-dihydroxytryptamine (160 micrograms/testis), a substance that destroys serotoninergic neuronal elements, was injected intratesticularly or vasectomy was performed, which also includes transection of the inferior testicular nerve. In 9-day-old animals both vasectomy and pretreatment of the testis with 5,6-dihydroxytryptamine prevented the oxytocin-induced rise in serum testosterone concentration. In addition, intratesticular injection of oxytocin combined with vasectomy resulted in a significant increase in in vitro basal testosterone secretion of the testis. A similar effect was not observed in the 5,6-dihydroxytryptamine-pretreated group receiving oxytocin. The results indicate that testicular innervation is involved in the control of local peptide effects, and data further suggest a differential role of these neural elements in intratesticular regulatory processes.

Effect of intratesticular administration of somatostatin on testicular function in immature and adult rats.

Somatostatin has been demonstrated in the testis. In the present investigations the effect of intratesticular injection of somatostatin on serum testosterone level and in vitro basal testosterone secretion of the testis was studied in immature and adult rats. Intratesticular injection of somatostatin in adult rats with two testes in situ decreased serum testosterone concentration and basal testosterone secretion in vitro. Similar treatment in immature animals had no effect on the parameters studied. In immature hemicastrates, however, local administration of the peptide induced a significant rise both in basal testosterone secretion in vitro and serum testosterone level, and resulted in an increase in testicular weight. In adult hemicastrates the peptide did not influence testicular functions. These results indicate that somatostatin might play a modulatory role in testicular steroidogenesis. The data also suggest that the effect of somatostatin is age-dependent, and that hemicastration might modify local action of the peptide.

Effect of intratesticular administration of oxytocin on testicular steroidogenesis in immature rats.

The possible physiological role of testicular oxytocin in testicular steroidogenesis was studied in immature rats. In 5-, 9-, and 25-day-old animals one of the testes was injected with 20, 50, and 200 ng of oxytocin, respectively, then the contralateral gonad was removed. Rats were killed 1 h, 1 day, or 7 days post-surgery. In each age group studied intratesticular injection of oxytocin resulted in a significant increase in basal testosterone secretion in vitro and/or serum testosterone concentration. Data indicate that in immature rats oxytocin of testicular origin might act as a local stimulator of steroidogenesis.

Involvement of a direct neural mechanism in the control of gonadal functions.

Much time has been devoted to study of the hypothalamo-hypophyseal-gonadal axis. However, there is now evidence of a complementary control mechanism for the gonads, namely a pituitary-independent, direct neural link that exists between the central nervous system and the gonads. We investigated whether mediobasal temporal lobe structures could control gonadal functions by a purely neural mechanism or whether they acted through the classical hypothalamo-hypophyseal system. Right- or left-sided deafferentiation of the temporal lobe was combined with right- or left-sided hemicastration in adult and prepubertal male and female rats. In adult females right-sided deafferentiation, regardless of the side of hemiovariectomy significantly reduced the extent of compensatory ovarian hypertrophy. Similar lesions on the left side did not interfere with the usual compensatory ovarian growth. This difference in compensatory hypertrophy between right- and left-sided lesioned rats was observed even in the face of a significant drop in serum LH concentrations in both groups. In pre- and postpubertal females temporal lobe lesion in either side was unable to alter compensatory hypertrophy or serum LH or progesterone concentrations. In adult male rats only left-sided deafferentiation combined with left orchidectomy resulted in decreased T production, while in prepubertal male rats, only right-sided brain surgery plus left orchidectomy resulted in a significant decrease in basal testosterone secretion of the remaining testis. These findings indicate that mediobasal temporolimbic structures are involved in the neural control of gonadal functions. It appears that this lateralized mechanism is age- and sex-dependent.