Efferent projection of the nucleus praeopticus medialis to the median eminence in rats

Neuronal regeneration and estrous cycle restoration after locus coeruleus-periventricular gray substance section

The locus coeruleus (LC) was anatomically separated from the periventricular gray substance (PVG) by means of knife cuts in the adult female rat presenting regular estrous cycling. This resulted in a transient suppression of the estrous cycling that lasted 10-13 days after surgery. After this period, irregular or regular cycling activity was observed. The regular cycling was restored 30-45 days after the knife cuts. Golgi impregnation of some of the brains of these rats revealed regenerative elements in the knife-cut-insulted area. Thus, blood vessels, macrophagic-like elements, and glial-like elements were observed in close relation with the knife-cut pathway. Additionally, well-defined stained neurons typical of the LC and PVG were observed in close proximity to the knife-cut pathway. Dendritic and axon projections towards the insulted area were observed. Well defined axons were seen across the knife-cut pathway. These data support, first, that the LC-PVG communication is part of a circuitry for the modulation of gonadotropic activity, and second, that in the restoration of the estrous cyclicity after the knife cut, regenerative processes leading to a LC-PVG functional reconnection occurred after the knife cut.

Tachykinergic synaptic inputs to neurons of the medial preoptic region which project to the rat arcuate nucleus

Anatomical relationships between tachykinin-containing terminals and neurons of the medial preoptic area that innervate the arcuate nucleus were studied using silver staining of the retrograde tracer wheat germ agglutinin-apoperoxidase-gold (WGA-ApoHRP-gold) complex injected in the arcuate nucleus and pre-embedding immunocytochemistry for neurokinin A (NKA). At the histological level, retrogradely labeled cells not stained for NKA were seen to be surrounded by numerous NKA-immunopositive punctate profiles, in particular in the dorsal part of the medial preoptic area. At the ultrastructural level, retrogradely labeled cell bodies and dendritic profiles displayed highly electron-dense silver particle accumulations over the cytoplasm. The were seen in synaptic contact with one or several NKA-immunoreactive axon terminals containing small clear vesicles and dense-cored vesicles. Such synapses were either symmetrical or asymmetrical. The occurrence of synaptic contacts between tachykinin terminals and cells innervating the arcuate nucleus in the medial preoptic region provides a morphological support for a tachykinergic regulation of preoptic afferences to the arcuate nucleus. These results suggest that tachykinins are implicated in the indirect control of neuronal activity in the arcuate nucleus notably via the preoptic area. Consequently, tachykinins are potentially able to regulate indirectly numerous neuroendocrine events involving the tuberoinfundibular system.

Projections of the medial preoptic nucleus: a Phaseolus vulgaris leucoagglutinin anterograde tract-tracing study in the rat

The projections of the medial preoptic nucleus (MPN) were examined by making injections of the anterogradely transported lectin Phaseolus vulgaris leucoagglutinin (PHA-L) into the MPN and charting the distribution of labeled fibers. The evidence indicates that the MPN projects extensively to widely distributed regions in both the forebrain and brainstem, most of which also supply inputs to the nucleus. An important neuroendocrine role for the MPN is underscored by its extensive projections to almost all parts of the periventricular zone of the hypothalamus, including the anteroventral periventricular, anterior part of the periventricular, paraventricular (PVH), and arcuate nuclei, and a role in autonomic mechanisms is indicated by projections to such regions as the dorsal and lateral parvicellular parts of the PVH, the lateral parabrachial nucleus, and the nucleus of the solitary tract. Other projections of the MPN suggest participation in the initiation of specific motivated behaviors. For example, inputs to two nuclei of the medial zone of the hypothalamus, the ventromedial and dorsomedial nuclei, may be related to the control of reproductive and ingestive behaviors, respectively, although the possible functional significance of a strong projection to the ventral premammillary nucleus is presently unclear. The execution of these behaviors may involve activation of somatomotor regions via projections to the substantia innominata, zona incerta, ventral tegmental area, and pedunculopontine nucleus. Similarly, inputs to other regions that project directly to the spinal cord, such as the periaqueductal gray, the laterodorsal tegmental nucleus, certain medullary raphe nuclei, and the magnocellular reticular nucleus may also be involved in modulating somatic and/or autonomic reflexes. Finally, the MPN may influence a wide variety of physiological mechanisms and behaviors through its massive projections to areas like the ventral part of the lateral septal nucleus, the bed nucleus of the stria terminalis, the lateral hypothalamic area, the supramammillary nucleus, and the ventral tegmental area, all of which have extensive connections with regions along the medial forebrain bundle. Although the PHA-L method does not allow a clear demonstration of possible differential projections from each subdivision of the MPN, our results suggest that each of them does give rise to a unique pattern of outputs.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of locus coeruleus and periventricular gray substance lesions on suprachiasmatic damage-induced persistent estrous

To assess the relation between the suprachiasmatic nucleus and the locus coeruleus, persistent estrous was induced in female rats by damage of the suprachiasmatic nucleus followed with electrolytic damage of the locus coeruleus. Locus coeruleus lesions resulted in a transient loss of persistent estrous indicated by sustained diestrous aspect of the vaginal smears. There was a direct correlation between duration of estrous loss and the amount of locus coeruleus damage. Simultaneous damage to the periventricular gray substance, adjacent to the locus coeruleus, prevented the suppression effects of locus coeruleus damage upon persistent estrous. These results suggest a physiological role of the locus coeruleus and periventricular gray substance in the modulation of the neuroendocrine control of ovarian function due to suprachiasmatic nucleus activity.

Neural projections of the preoptic-suprachiasmatic region to the median eminence in the rat: a quantitative autoradiographic study

The possibility of a preferential distribution of projections from the preoptic-suprachiasmatic region (POA-Sch) to the median eminence in the male rat was studied using autoradiographic and computer procedures. A cocktail of [3H]leucine-[3H]proline was injected into the POA-Sch. Animals were killed after either 1, 4, or 24 h of incorporation time (IT). The number of silver grains per 25-micron square was counted throughout the median eminence. Squares with silver grain densities at or above the 75 percentile of the population for any given IT group were labeled as "concentrating areas." The distribution of these concentrating areas in median eminence tissue was analyzed utilizing univariate procedures. Visual inspection of the distribution of silver grain densities in a rostrocaudal fashion indicated the likelihood of uneven distribution; however, these differences were not statistically significant. In the dorsoventral plane, results indicated that the highest silver grain density was at 50 to 75 micron from the floor of the 3rd ventricle. Such distribution was apparent both ipsi- and contralateral to the injection site, but was greater on the ipsilateral side.

Stimulatory role for medial preoptic/anterior hypothalamic area neurones in growth hormone and prolactin secretion. A kainic acid study

The role of preoptic/anterior hypothalamic area (PO/AHA) neurones in the regulation of basal patterns of growth hormone (GH) and prolactin (Prl) secretion was investigated in unanesthetized male rats prepared with chronic indwelling venous cannulae. PO/AHA injections of the neurotoxin kainic acid (KA) substantially reduced both GH and Prl secretion. Histological examination of tissue sections indicated that KA treatment had produced extensive neuronal loss and gliosis in the medial (m) but not the periventricular (p) PO/AHA. These findings suggest that m-PO/AHA neurones are facilitatory to the basal secretion of both GH and Prl. It is proposed that GH-facilitatory m-PO/AHA neurones provide an inhibitory input to the GH release-inhibiting factor neurones which are known to reside in the p-PO/AHA. Prl-facilitatory m-PO/AHA neurones may secrete, or stimulate the secretion of a Prl releasing factor.

Cells of origin of the afferent fibers to the median eminence in the rat

The cell bodies of origin of axons terminating in the median eminence have been identified by retrograde axonal transport of horseradish peroxidase (HRP) or 125I-wheat germ agglutinin (WGA). The tracers were injected into the median eminence by pressure and under direct visual control, using a ventral surgical approach. The retrogradely labeled cells are exclusively located within the hypothalamus. The most heavily labeled cells are parvocellular neurons in the arcuate nucleus, the periventricular area, the medial part of the paraventricular nucleus, and the rostral paraventricular nucleus; a few cells are also located in the rostral part of the preoptic area immediately lateral and dorsal to the organum vasculosum of the lamina terminalis (OVLT). Less heavily located cells are found in the magnocellular neurosecretory nuclei, including the lateral parts of the paraventricular and rostral paraventricular nuclei, the supraoptic nucleus, and the accessory magnocellular nuclei. Retrogradely labeled cells are not found in the ventromedial hypothalamic nucleus, except for a few lightly labeled cells in the posterior division of the nucleus. However, if the injected tracer spreads into the arcuate nucleus, labeled cells are present throughout the ventromedial nucleus. Labeled cells are not found in other parts of the hypothalamus, including lateral and posterior portions of the preoptic area, the anterior hypothalamic area, and the suprachiasmatic nucleus, or in catecholaminergic cell groups of the midbrain, pons, and medulla. Control injections of HRP into the posterior pituitary and the ventromedial nucleus produce patterns of cell labeling which are very distinct from that seen with injections into the median eminence. Following injections into the posterior pituitary, the cells of the magnocellular neurosecretory nuclei are all heavily labeled, but small cells in the parvocellular neuronal groups are not labeled. Direct injections into the ventromedial nucleus resulted in labeled cells in widespread parts of the hypothalamus, as well as in the bed nucleus of the stria terminalis and the lateral septum, in parts of the amygdaloid complex and the subiculum, and in several cell groups in the midbrain, pons, and medulla.