Immuno-cytochemical demonstration, in the external region of the amphibian median eminence, of separate vasotocinergic and mesotocinergic nerve fibres

Brain-derived neurotrophic factor in the brain of Xenopus laevis may act as a pituitary neurohormone together with mesotocin

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, occurs abundantly in the brain, where it exerts a variety of neural functions. We previously demonstrated that BDNF also exists in the endocrine melanotroph cells in the intermediate lobe of the pituitary gland of the amphibian Xenopus laevis, suggesting that BDNF, in addition to its neural actions within the brain, can act as a hormone. In the present study, we tested whether BDNF, in addition to its neural and hormonal roles, can be released as a neurohormone from the neural pituitary lobe of X. laevis. By light immunocytochemistry, we show that BDNF is present in perikarya, in ventrolaterally projecting axons of the hypothalamic magnocellular nucleus and in the neural lobe of the pituitary gland, and that it coexists in these structures with the amphibian neurohormone, mesotocin. The neural lobe was studied in detail at the ultrastructural level. Two types of neurohaemal axon terminals were observed, occurring intermingled and in similar numbers. Type A is filled with round, moderately electron-dense secretory granules with a mean diameter of approximately 145 nm. Type B terminals contain electron-dense and smaller, ellipsoid granules (long and short diameter approximately 140 and 100 nm, respectively). BDNF is exclusively present in secretory granules of type A axon terminals. Double gold-immunolabelling revealed that BDNF coexists in these granules with mesotocin. Furthermore, we demonstrate in an superfusion study performed in vitro that mesotocin stimulates peptide release from the endocrine melanotroph cells. On the basis of these data, we propose that BDNF can act on these cells as a neurohormone.

Ontogeny of the hypothalamo-neurohypophysial system in the toad, Bufo melanostictus: an immunohistochemical study

Employing unlabeled antibody enzyme technique, the development of the hypothalamo-neurohypophysial system of the common Indian toad, Bufo melanostictus, has been studied by using antiserum raised in rabbit against bovine neurophysin. Immunoreactivity to the antiserum is first observed at stage 22 (Gosner, 1960) in the presumptive preoptic nucleus and at stage 23 in the presumptive median eminence and pars nervosa. As development proceeds, progressive increase in the immunoreactivity in all the components of the hypothalamo-neurohypophysial system is observed. The detection of neurohypophysial hormones (stages 22-23) much before the appearance of limb buds (stages 25-26) may be due to the greater sensitivity of the immunohistochemical technique.

Morphological changes of rat neurosecretory neurones after stereotaxic injection of kainic acid into the supraoptic nucleus or the supraoptico-hypophyseal tract

Kainic acid is a structural analogue of glutamic acid possessing neurotoxic property. In the present study, performed on rats, morphological changes of neurosecretory neurones after stereotaxic injection of kainic acid into the left supraoptic nucleus or into the left supraoptico-hypophyseal tract were investigated. It is shown that administration of kainic acid in a dose that leads to destruction of hippocampal pyramidal cells has no effects on supraoptic perikarya but does destroy neurosecretory axons. These results contradict the observations of many authors who reported that local injection of kainic acid into the brain causes degeneration of perikarya but leaves axons of passage unaffected.

The hypothalamo-hypophyseal system of Rana temporaria under osmotic stimulation with special reference to the hypothalamo-median eminence-distal lobe axis

The secretory activity of the hypothalamo-hypophyseal system in the frog Rana temporaria under conditions of dehydration has been studied histologically using two parameters, the amount of stained neurosecretory material and the amount of neurosecretory material labelled by a radioactive precursor. The results are indicative of an increased secretory activity of the hypothalamo-neural lobe system as a result of water deprivation. In addition the involvement of the preoptic nucleus-median eminence axis in osmoregulation is confirmed. The pattern of distribution of autoradiographic silver grains over the median eminence together with data from literature support the idea that mesotocine is involved in the regulation of the activity of the adenohypophysis.

Oxytocin/vasopressin-like immunoreactivity is present in the nervous system of hydra

Nerve cells have been found in hydra, which react with antisera to oxytocin, vasopressin and mesotocin. These nerve cells have a high density in the ectoderm of basal disk and tentacles and lower density in the ectoderm of peduncle, gastric region and hypostome. A very small number of nerve cells occur also in the endoderm of foot, gastric region and hypostome. By using a technique for simultaneous visualisation of nerve cells reacting with antisera to oxytocin and vasopressin, it can be shown that these nerve cells belong to a single population. In agreement with this, the staining of the nerve cells can be abolished by absorbing each antiserum with either oxytocin, vasopressin, [Lys8]vasopressin, vasotocin, mesotocin or isotocin, indicating that the antigenic determinant of hydra cross-reacts with those antibody subpopulations, which recognize common portions (sequence 1-2, 5-7, 9) of the oxytocin/vasopressin-like peptides. With radioimmunoassays that are specific for either oxytocin or vasopressin, only very low amounts of immunoreactivity were measured. In addition, the dilution curves in these assays were not parallel to the standards, indicating that the antigenic determinant of hydra is not oxytocin or vasopressin. The presence of oxytocin/vasopressin-like material in coelenterates, shows that this family of peptides is of great antiquity.

The topography of mesotocin and vasotocin systems in the brain of the domestic mallard and Japanese quail: immunocytochemical identification

The neurosecretory systems producing mesotocin (MT) and vasotocin (VT) (the avian homologues of oxytocin and vasopressin, respectively) were characterized in the brains of the domestic mallard and Japanese quail by means of indirect immunofluorescence techniques using specific antisera. In the anterior preoptic region, including the organum vasculosum of the lamina terminalis, and at different levels of the supraoptic and paraventricular nuclei, separate mesotocin- and vasotocin-producing neurons were identified. Mesotocinergic and vasotocinergic neurons were also located in the tuberomammillary area, among the ectomammillary tract fibers. The supraoptico-neurohypophysial tract, formed by vasotocin- and mesotocin-containing axons, enters the internal zone of the median eminence and ends in the posterior lobe of the pituitary. The external zone of the rostral median eminence appears to contain vasotocin and mesotocin fibers, which terminate in close contact with the capillaries of the hypophysial portal system.

Immunocytochemical localization of the vasopressinergic and the oxytocinergic neurons in the human hypothalamus

The human hypothalamic-neurohypophysial hormone-producing nuclei were investigated with the unlabeled antibody peroxidase-antiperoxidase complex (PAP) technique at the light microscopic level. The size, shape and location of the supraoptic, paraventricular, accessory supraoptic and suprachiasmatic nuclei were determined. It was demonstrated in the human hypothalamus, as well as in the hypothalamus of other mammals, that vasopressin and oxytocin are synthesized in separate neurons. In each of the nuclei of the magnocellular neurosecretory system, the distribution, ratios and structural features of the vasopressinergic and oxytocinergic neurons were determined. It was shown that the human suprachiasmatic nuclei contain numerous neurophysin-vasopressin-producing neurons.