The effect of castration upon the ultrastructure of the rat hypothalamus

Summary The neurosecretory hypothalamic nuclei and the inner zone of the median eminence of castrated rats were studied under the electron microscope. After one month of castration all the neurosecretory neurons of both nuclei show signs of hyperactivity characterized by dilated cisternae of the endoplasmic reticulum containing a macromolecular filamentous material and an increase in the number of ribosomes. After six months of castration, some neurosecretory neurons show an increased number of neurotubules and larger lysosomes than in the controls. Other neurons show a very significant hypertrophy of the endoplasmic reticulum, with large amounts of intracisternal filamentous material. These cells have few neurosecretory granules and in the adjacent synapses the number of granulated vesicles is increased. In the supraoptic nucleus there are two kinds of neurosecretory axons: the clear ones, which are similar to those that appear in control animals and the dark ones, which have smaller elementary granules. In the inner zone of the median eminence the axons show an increase in the number of neurosecretory granules with respect to the controls. After supplementary administration of sexual hormones, all the modifications produced by castration disappear. The ultrastructural changes observed in the neurosecretory nuclei after castration are discussed in relation to those previously described in the neurohypophysis under the same experimental conditions. A feedback regulatory action of sex hormones on hypothalamic neurosecretory neurons is postulated.Supported by grants from the Consejo Nacional de Investigaciones Científicas y Técnicas and by the Air Force Office of Scientific Research (AF-AFOSR 963-67).We are deeply indebted to Mrs. Defilippi-Novoa and Mr. Alberto Saenz for their skillful assistence.     

A paradoxical castration effect on LH-RH levels in male rat hypothalamus and serum

Serum and hypothalamic luteinizing hormone releasing hormone (LH-RH) was lowered in young mature male rats after castration. Testosterone injections raised the hypothalamic LH-RH content significantly. The mean value of serum LH level was elevated by testosterone, but not significantly. Hypothalamic LH-RH content was also lowered by hypophysectomy. In this circumstance, testosterone injections significantly increased LH-RH content. These results suggest that there may be a positive feedback of testosterone upon the hypothalamic LH-RH release and synthesis mechanisms.     

Neurotoxic effect of vincristine on ultrastructure of hypothalamus in rabbits.

The neurotoxic side-effects are a striking accompaniment of the therapy with vincristine (VCR). Data concerning the influence of VCR on the central nervous system are controversial. In the present study a schedule of VCR treatment was employed to develop the neurotoxic side effects in New Zealand rabbits. In all treated animals neurons were primarily and most severely affected cells. Most of them underwent degeneration. The consecutive stages of the increasing condensation of chromatin and cytoplasm of these cells were observed. Degeneration of the synaptic connections and secondary changes in myelin sheaths of degenerating axons were found. Debris of some death cells were localized intracellularly or as typical apoptotic bodies ingested by some glial cells. Astroglia underwent swelling and their processes separated dying neurons from the surroundings. All the results lead to conclusion that the VCR treatment concomitant with neurotoxic symptoms may affects regions of CNS lacking of blood-brain barrier. Neurons are most vulnerable cells of the brain parenchyma. The changes induced in neurons by the drug are characteristic in many aspects to those described in many cells undergoing apoptosis.     

Effects of galactoflavin-induced riboflavin deficiency upon rat hepatic cell ultrastructure.

The primary cytoplasmic effect of galactoflavin-induced riboflavin deficiency upon rat liver cells involved focal sites of degradation which were manifested by the formation of membranous whorls. The nuclear effect of riboflavin deficiency concerned fluctuations in the total number of perichromatin granules per nucleus. These granules increased in number during the deficiency reaching a peak at three weeks. Nucleoli appeared compact with no evidence for segregation of nucleolar components. The possible correlation between increased synthesis of perichromatin granules and altered protein synthesis is discussed.     

Intra-abdominal castration in the rat

Normal rat posture results in proximity of the scrotum to bedding and feces, which predisposes rats to postoperative complications if castration is done using standard scrotal and prescrotal approaches. This column describes a ventral abdominal approach for castration in the rat.     

Changes in rat brain opiate receptor content upon castration and testosterone replacement.

The saturable binding of naltrexone-³H in the brains of castrated male rats exceeds that found in intact animals by a factor of two. This increase is androgen dependent since testosterone replacement reduced the binding to control levels. Scatchard analysis of the saturation curves revealed that the change in binding reflects increased available binding sites and is not due to increased binding affinity. This relationship between testosterone and brain opiate receptors provides for the participation of endorphins in the regulation of pituitary gonadotropins by gonadal hormones. The increased content of opiate receptors in the brains of castrated rats correlates with the greater brain N-demethylation of morphine establishing a further link between this biotransformation and agonist action.     

The kallikrein-kinin system in the rat hypothalamus

Summary High molecular weight kininogen (HKg) and T kininogen (TKg) were detected and localized by immunocytochemistry in adult rat hypothalamus. In addition, kininogens were measured by their direct radioimmunoassay (RIA) or by indirect estimation of kinins released after trypsin hydrolysis and high pressure liquid chromatography (HPLC) separation of bradykinin (BK) and T kinin. A specific HKg immunoreactivity demonstrated with antibodies directed against the light chain (LC) of HKg was colocated with SRIF in neurons of hypothalamic periventricular area (PVA) projecting to external zone (ZE) of median eminence (ME). Heavy chain (HC) immunoreactivity which could be related to HKg or to low molecular weight kininogen (LKg) was detected in some other systems: i) parvocellular neurons of suprachiasmatic (SCN) and arcuate nuclei containing SRIF, ii) magnocellular neurons (mostly oxytocinergic) of paraventricular (PVN) and supraoptic (SON) nuclei, iii) neurons of dorsomedian and lateral hypothalamic areas. TKg immunostaining was restricted to magnocellular neurons of PVN, SON, accessory nuclei (mostly vasopressinergic) and to parvocellular neurons of SCN (vasopressinergic). TKg projections are directed towards the internal zone (ZI) of ME, but very few immunoreactive terminals are detectable in neurohypophysis. TKg staining parallels with vasopressin during water deprivation, and is undetectable in homozygous Brattleboro rats. In some magnocellular neurons, TKg and HC (related to HKg or LKg) are coexpressed. TKg, was also detected in hypothalamus and cerebellum extracts by direct RIA, and BK and T kinin were identified after trypsin hydrolysis. HKg and LKg can act as precursor of BK which can play a physiological role as releasing factor, neuromodulator — neurotransmitter, — or modulator of local microcirculation in hypothalamus. The three kininogens are also potent thiolprotease inhibitors which could modulate both the maturation processes of peptidic hormones and their inactivation and catabolism.     

The 5 alpha-reductase activity of the subcortical white matter, the cerebral cortex, and the hypothalamus of the rat and of the mouse: possible sex differences and effect of castration

Previous studies have shown that the central nervous system is able to convert testosterone into 17-beta-hydroxy-5-alpha-androstan-3-one (DHT), by the action of the enzyme 5-alpha-reductase. The data here presented show that, in the brain of the rat and the mouse of both sexes, the 5-alpha-reductase activity is more concentrated in the subcortical white matter than in the hypothalamus and in the cerebral cortex. The enzymatic activity is apparently higher in the rat than in the mouse brain. The formation of DHT in the subcortical white matter, in the hypothalamus and in the cerebral cortex of both rats and mice does not show any sexual difference. Moreover, in the rat no effect of short- or long-term castration or neonatal castration or testosterone replacement could be observed on the formation of DHT in the three brain structures considered (even in the subcortical white matter, the cerebral tissue more active in converting testosterone into DHT). The present data support the view that the 5-alpha-reductase present in the brain is not under androgenic control.