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Ejaculation requires an interplay of peripheral actors comprising, among others, smooth and skeletal fibers, glandular and endothelial cells. These actors are driven by vegetative and somatic innervations, deriving essentially from the spinal cord, in turn controlled by cerebral structures and endocrine factors, mostly steroids; These controls require sensitive afferences and command two steps, emission under autonomic control, and ejaculation per se which further involves somatic motoneurons. This review first describes the peripheral innervation of the part of the genital tract concerned in ejaculation, in which the sympathetic component is predominant and releases noradrenalin and neuropeptides; however parasympathetic and somatic components also play a role. At the spinal level, control circuits are organized into networks influenced by spinal structures, which have been discovered through selective lesions or stimulations, as well as by retrograde trans-synaptic tracing with neurotropic viruses. Among these structures, the median preoptic area and the hypothalamic paraventricular nucleus are major regulation sites. On the other hand, serotoninergic and also dopaminergic and adrenergic systems are implicated as well in the command of ejaculation; the latter constitute priviledged targets for a pharmacological treatment of dysfunctions.

Penile erection is caused by a change of the activity of efferent autonomic pathways to the erectile tissues and of somatic pathways to the perineal striated muscles. The sympathic outflow is mainly antierectile, the sacral parasympathic outflow is proerectile and the pudendal outflow, through contraction of the perineal striated muscles, enhances an erection already present. Spinal neurones controlling erection are activated by afferents from the genitals. It is likely that these primary afferents do not directly stimulate the spinal sympathetic, parasympathetic and somatic nuclei, but do through spinal interneurones. This spinal network is able of integrating information from periphery to elicit reflexive erections. It also receives supraspinal descending pathways from pons and hypothalamic nuclei, among the latter, the paraventricular nucleus and the medial preoptic area. These structures are likely involved to regulate penile erection in more integrated and coordinated responses occurring during sexual behavior. By receiving ascending projections from the spinal level which convoy informations from genitals, they could reinforce penile erection. Role of putative neuromediators or regulatory peptides is evoked.

Relaxation of arterial and cavernous smooth muscle fibers, leading to the filling of the sinusoidal spaces with blood, are the local mechanisms of erection. Smooth muscle relaxation results from activation of parasympathetic neural pathway and probably simultaneous inhibition of the sympathetic outflow. Reflexive erection elicited by recruitment of penile afferents conveyed by the dorsal penile nerve involves both autonomic and somatic efferents. This reflex is mediated at the spinal cord level and modulated by supraspinal influences. Serotonergic pathways originating in the raphe nuclei mediate inhibitory control on reflexive erection. Several hypothalamic areas such as the medial preoptic area and the paraventricular nucleus are the source of descending pathways and/or represent important integrating centers. Dopamine acting at the medial preoptic area level may regulate penile erection. Neuroendocrine regulation may vary depending on the context in which erection occurs, for example, coitus, in response to extrinsic or psychogenic stimuli, and rapid eye movement sleep.

The relationship between stress and hypertension has long been a topic of debate. Until recently, no animal (nor physical) model existed which incorporated these two parameters together, hence accurate assessments of their interactions were postulations, at best. The borderline hypertensive rat (BHR) is an animal model in which arterial hypertension will ensue only when the rat is subjected to a chronic stressor. Therefore, this animal model offers an opportunity to study the physiological consequences of a given stressor on the entire organism during the course of the development of hypertension. The cardiovascular and humoral effects of chronic exposure to a physiological stressor on the BHR, at rest and during exposure to an acute and novel stress, have been examined and are presented in this paper. The involvement of the central nervous system in the regulation of this stress induced hypertensive state has been hypothesized to play a major role in the regulation of the stress and hypertensive relationship. Of particular importance are the endogenous opioids and their influence on the maintenance of homeostasis during periods of physiological stress. The localization of the endogenous opioid enkephalin in the paraventricular nucleus of the hypothalamus (PVN), an important brain region in the regulation of the stress response further substantiates the involvement of the opioid system during stress induced hypertension. Immunohistochemical data on the localization of ENKergic fibers in the PVN and other brain regions are similarly discussed in this paper.

The immunohistochemical technique for the vasopressin localisation shows the presence of this hormone in neurons of the rat supra-chiasmatic nucleus. Different experimental conditions induce modifications of the supra-chiasmatic vasopressin, and, in the same time, the storage of immunoreactive peptide in the fibres terminating in the external zone of the median eminence. However, the supra-chiasmatic, supraoptic and paraventricular changes are not obligatory similar.

Using the rapid Golgi technique four types of neurons have been observed in the paraventricular nucleus : magnocellular neurosecretory neurons, parvocellular neurons with "extrahypophyseal" axon, parvocellular neurons with recurrent axon (possibly inhibitory interneurons) and neurons of reticular type.

Light and electron microscope methods which can be used to examine the possibilities of co-occurrence of peptides are reviewed. The results obtained using some of them are exposed and discussed, concerning i/the light microscope demonstration of the CRF/vasopressin coexistence in rat and guinea-pig. ii/the electron microscope demonstration of the granular colocalization of LH-RH/C-terminal ACTH and somatostatin/enkephalin in the guinea-pig median eminence.

Immunocytochemical visualization, and comparative morphological analysis of the paraventriculo-infundibular CRF-positive system was performed in new-born dogs and young cats. Our studies underline the identity of this system and its structural similarity among Mammals. They confirm the interspecificity of the antigenic sites recognized by our ovine CRF-antibodies.

Techniques of in situ hybridization for the detection of mRNA on histological sections are described and commented upon. The main applications of the procedure are discussed and the potential uses of this new method for the analysis of gene expression in endocrine and nervous systems are presented.

Confrontations of immuno-stainings as well as sequential stainings with corticoliberin and vasopressin antisera were performed on contiguous sections of human median eminence (ME) or hypothalamic paraventricular nucleus (PVN). Results show that a double immunoreactivity to both IS is expressed in some parvicellular PVN perikarya, and suggest that such a double immunoreactivity can be possible in some ME fibers. Similar results had been previously obtained in animals only under experimental conditions.

The hypothalamus contains two distinct zones which affect the activity of myocardial and vascular muscle. The median ventricular nucleus stimulates the liberation of peripheral catecholamines and, by so stimulating the adrenoreceptors, opens up the slow calcium canals. The resulting stimulation of the myocardial and vascular muscle cells causes tachycardia, and an increase in myocardial contraction and in peripheral resistance. The paraventricular nucleus antagonises these effects by inhibiting peripheral catecholamine secretion so blocking or slowing the passage of Ca++ through the slow calcium canals. The study of effective, active concentration of D 600, a powerful calcium antagonist, shows that the paraventricular nucleus is not a direct calcium antagonist like D 600 whose effects are not potentiated, and confirms that it acts indirectly by inhibiting peripheral noradrenaline secretion.

Electrical stimulation of the hypothalamic paraventricular nucleus results in bradycardia and hypotension. A direct transtemporal approach was used to implant an insulated electrode in the site of the third ventricle. The bradycardia and hypotension have been studied previously and have been shown to be due to inhibition of the alpha and beta vascular and myocardiac adrenergic receptors. The effects of this inhibition on the electrical appearances and the mechanical and phonocardiographic parameters of myocardial contractility were observed in this present study. The force and velocity of LV isometric contraction were reduced as shown by reduction in dP/dT, the delay in its peak and the reduction of the angle between the upstroke of ventricular contraction with the base line. The onset of left ventricular ejection was delayed. The high frequency (60 and 140 Hz) components of the first heart sound disappeared, confirming their contribution to the intensity of this sound. The ECG rapid QRS phase and AV conduction time were unchanged, but the slow phase of the T wave became more negative as the depressant effect on the myocardium increased.

The results obtained with various methods applied to the cytochemical detection of carbohydrates at an ultrastructural level, confirm the existence of glycoproteins in neurosecretory material in the neurohypophysis as well as in the hypothalamic magnocellular nuclei. This glycoproteic component, however, is not present in all the secretory granules and, according to their cytochemical behaviour, it is possible to distinguish two types of neurosecretory fibres: one where all the granules respond negatively; the other where most of the granules are reactive. The existence of two types of neurons corresponding to these two fibres cannot yet be asserted, but seems very likely, perhaps connected with the hormonal duality of the magnocellular nuclei. The reactions are also positive on the Golgi apparatus, in accordance with its function in glycoprotein synthesis. But the difference of reactivity between the Golgi cisternae and the neurosecretory product suggests that glycoprotein synthesis is still going on in the neurosecretory granules outside the Golgi area.

Two peptides have a strong corticotropin releasing factor (CRF) activity: arginine vasopressine (AVP) and a 41-residue peptide (41-CRF). Both peptides are present in high concentration in the PVN of the Rat, a zone of the hypothalamus at which electrical stimulation elicits ACTH release. Since homozygous Brattleboro Rats (Di/Di) congenitally lack endogenous AVP, it was of interest to compare the ACTH and corticosterone release after electrical stimulation of the PVN in Long-Evans (L.E.) and Di/Di Rats. In both L.E. and Di/Di Rats, there is a significant increase in plasma ACTH and corticosterone after electrical stimulation of the PVN. However, corticosterone levels are significantly lower in Di/Di than in L.E. Rats whether the Rats have been stimulated or not. It is concluded that a physiological CRF activity is present in the PVN of Di/Di Rats independently of the CRF like activity of AVP.

Immunocytological investigations on the hypothalamus of the red fox with rabbit anti-SRIF showed large or small perikarya in the supra-optical and paraventricular nuclei. In the median eminence SRIF-positive nerve fibres and their endings have a characteristic distribution in areas different from those of LH-RH containing nerve fibres.