Development of the hypothalamic vasopressin system and nephrons in Meriones shawi during ontogenesis.

This study has evaluated the development of the hypothalamic vasopressin system and nephrons of the kidney in desert rodents, Meriones shawi, which effectively retain water by excretion of highly concentrated urine. The vasopressin system was studied immunocytochemically at the 18th fetal day, at the 2nd, 13th, 27th postnatal days and in adulthood. The kidneys were investigated at the 2nd, 13th postnatal days and in adulthood using microdissection technique. Occasional vasopressin-immunoreactive neurons were observed as early as the 18th fetal day, only in the paraventricular nucleus. From the 2nd postnatal day onwards, vasopressin neurons increased progressively in number, being mainly concentrated in the supraoptic and paraventricular nuclei, as well as in the ventral retrochiasmatic region. Transient neuronal populations were also observed at the 13th postnatal day in the lateral preoptic area and anterior hypothalamic nucleus. Apart from the neurons, the glandular cells of the tuberal lobe showed immunostaining from the 18th fetal day, the first age studied, until the 13th postnatal day. The fibers of differentiating vasopressin neurons grew towards the circumventricular/neurohemal organs, terminating in the organum vasculosum of the lamina terminalis and the lateral ventricles as early as the 18th fetal day, as well as the third ventricle, the posterior lobe and the external zone of the median eminence between the 2nd and 13th postnatal days. The kidney in 2-day-old Meriones comprised nephrons at different stages of development from an S-shaped body to well-differentiated nephrons. At the 13th postnatal day, as in adulthood, the nephrons were well differentiated and characterized by long, thin loops descending to different levels of papilla. Thus, according to our morphological data the hypothalamic vasopressin neurons and nephrons in the kidney of Meriones reach the definitive state by the end of the 2nd postnatal week.

Chronic RU486 treatment reduces age-related alterations of mouse hippocampal function.

The present study investigates the protective effect of a chronic blockade of the glucocorticoid receptor (type II) by a single weekly SC injection (20 mg/kg) of RU486 (a potent antiglucocorticoid) from mid-age (12 months old) until senescence (20 to 22 months old) on perturbations of some electrophysiological parameters classically observed in CA1 hippocampal slices of aged BALB/c mice. In this CA1 hippocampal area, no electrophysiological difference was observed at a stimulation frequency of 0.3 Hz. However, an important age-related effect was observed in not-treated animals concerning the three phases of the synaptic response during and after 4 Hz repetitive stimulation ith impairment of the frequency potentiation (FP). Interestingly, this electrophysiological disturbance disappeared completely in aged animals treated previously with RU486. Furthermore, a 10 microM CORT bath application had no effect in CA1 of aged animals, while it produced the classical type II-mediated population spike (PS) decrease in adult animals. This PS amplitude decrease was maintained in aged animals previously treated with RU486. These electrophysiological findings suggest an important type II-mediated glucocorticoid action on age-related alterations of hippocampal function.

Synergistic action of corticosterone on kainic acid-induced electrophysiological alterations in the hippocampus.

The present study investigates the effect of overexposure to high doses of the stress hormone corticosterone (CORT) on the electrophysiological changes produced in the hippocampus after local microinjection of KA. Extracellular recordings were performed in the CA1 area of mouse hippocampal slices prepared after a 7-day recovery period following KA microinfusion alone or combined with 3 days overexposure to CORT. The results showed that CORT shifts the KA response profile approximately 40-fold, since animals treated with a non-toxic dose of 0.01 microgram KA and CORT exhibited epileptic activity and a shift on the paired-pulse response similar to that observed in animals treated with high doses of KA (0.4 microgram). This synergistic action of CORT on the electrophysiological changes induced by KA was antagonized by the antiglucocorticoid RU486 whereas the antimineralocorticoid spironolactone was ineffective. These results suggest that CORT may play an important role in modulating the severity of KA-induced seizures in the hippocampal structure probably by GR-receptor mediated action.

Vasopressin in the brain of a desert hibernator, the jerboa (Jaculus orientalis): presence of sexual dimorphism and seasonal variation.

The distribution of vasopressin innervation in the brain of the jerboa (Jaculus orientalis) was investigated, with special attention to sex differences and seasonal variations. Vasopressin perikarya were observed in the paraventricular and supraoptic nuclei, the suprachiasmatic nucleus, the periventricular nucleus, the medial preoptic area, the bed nucleus of the stria terminalis, and the medial amygdaloid nucleus. In addition, vasopressin cell bodies were observed in the ventral retrochiasmatic area. After treatment with colchicine, vasopressin perikarya were also observed around the organum vasculosum laminae terminalis, in the medial diagonal band of Broca, and in the dorsal medial preoptic nucleus. Vasopressin fibers were also found to be more widespread in the jerboa brain than in other rodents. Fibers were observed in the medial diagonal band of Broca, the stria medullaris, the tuber cinerum, the area postrema, the medial vestibular nucleus, and the dorsal motor nucleus of the vagus. Sexual dimorphism and seasonal variation in vasopressin immunoreactivity were observed in areas that not only showed a testosterone-dependent vasopressin innervation in other rodents but also in the paratenial and mediodorsal thalamic nuclei, the tuber cinerum, the supramammillary complex, the zona incerta, the interpeduncular complex, and the dorsal and medial raphe nuclei. A denser vasopressin innervation was observed in spring/summer (sexual active period) than in autumn. Numerous brain structures contained vasopressin receptors (cerebral cortex, hypothalamus, substantia nigra, dentate gyrus, thalamic nuclei, superior colliculus, dorsal cochlear nucleus, and cerebellum); no sex- or season-related differences were observed. These data indicate a high level of vasopressin in the jerboa brain, which may reflect an adaptation to its harsh bioclimatic environment.

Alpha-adrenoceptors and monoamine contents in the cerebral cortex of the rodent Jaculus orientalis: effects of acute cold exposure.

The tritiated adrenergic antagonists prazosin ([3H]PRZ) and idazoxan ([3H]IDA, or RX-781094) bind specifically and with high affinity to alpha 1- and alpha 2-adrenoceptors respectively, and were used to measure adrenoceptors in membrane preparations obtained from the cerebral cortex of Jaculus orientalis. Membrane preparations were also obtained from a group of cold exposed animals, to determine whether these adrenoceptors could be modified by a thermic stress. The density of receptors (Bmax; maximum binding capacity) and the dissociation constant (Kd 25 degrees C) were estimated by iterative modelling, and by using the procedure of Hill. After acute cold exposure (16 hr, 5 degrees C) there was a decrease in the affinity of the alpha 1-adrenoceptors, as judged by the Kd 25 degrees C for [3H]PRZ, with no changes in the Bmax. The alpha 2-sites did not show any significant changes, as revealed by [3H]IDA binding. Pretreatment of the membrane preparations from control animals with the disulfide and sulfhydryl reactives DL-dithiothreitol, 5,5'-dithiobis-(2-nitrobenzoic acid) and N-ethylmaleimide decreased specific [3H]PRZ and [3H]IDA binding, with minor changes in non-specific counts, indicating that the fixation of these ligands was to the receptor proteins. The endogenous cortical monoamine contents were also determined in the frontal cerebral cortex of these same animals, using high performance liquid chromatography with electrochemical detection. The catecholamine levels and their major metabolites were found to be stable in the cortex after the acute thermic stress, but there was a marked reduction in serotonin with a normal content in 5-hydroxyindole-3-acetic acid.

Behavioral consequences of dietary vitamin deficiency in young and middle-aged rats.

The behavioral correlates of vitamin A and B 6 dietary deficiency in young adult rats (Experiment 1) and middle-aged, retired breeder rats (Experiment 2) were examined. Male and female rats received either vitamin A deficient, vitamin B6 deficient, or normal control diets for two and a half months. Body weight, eating, and drinking of water and adulterated fluids were monitored. Pyridoxine deficiency generally had greater effects on consummatory behavior and weight gain than vitamin A deficiency, but this effect was influenced by the rats' age and sex. Wheel running, (Experiment 1), increased above control levels in both the vitamin delete groups. Vitamin A and B 6 deplete diets may affect behavior before an animal displays classical physical signs. Furthermore, such behavioral changes are not restricted to young, rapidly growing male rats; instead, their character is influenced by both the sex and age of the animal.