Karl M. Knigge

Ultrastructural changes in the median eminence of the rat following deafferentation of the basal hypothalamus

SummaryThis report concerns a light and electron microscopic investigation of the median eminence and dorsal infundibular stem of the rat following surgical isolation (deafferentation). Using a modification of the Halász technique, the basal hypothalamus, including the arcuate nucleus and median eminence were surgically isolated from surrounding structures. Special attention was directed to the contact (external) zone of the median eminence and rostral infundibulum where tuberohypophyseal axons as well as ependymal cell processes abut upon the abluminal basement membrane of the portal perivascular space. The results of this study to date suggest that 9, 20, and 40 days following surgical isolation, there is a distinct increase in the population of tuberohypophyseal dense core vesicles. It is suggested that deafferentation abolishes inhibitory and excitatory input that serves to modify the cellular dynamics of tuberohypophyseal neurosecretory elements. Comments are also made on the presence of cistern-like structures in the lateral median eminence; the presence of vesicle-like inclusions in terminal ependymal processes is discussed in relationship to the role that ependyma may play in linking the third ventricle with the adenohypophysis.

Corticotropin releasing factor: Immunocytochemical localization in rat brain

Using antiserum generated against the synthetic CRF1-41 we have immunocytochemically localized perikarya and processes in rat brain. Areas observed to have particularly dense accumulation of CRF-ir cells were in the extra-hypothalamic areas of nucleus accumbens septi, nucleus of the stria terminalis, the medial preoptic region, and the central amygdaloid nucleus. Within the hypothalamus cell bodies were scattered throughout the anterior hypothalamic region and densely packed in the paraventricular nucleus. Fibers appear most dense in the lateral septal region and throughout the external layer of the median eminence.

Nitrous oxide analgesia: partial antagonism by naloxone and total reversal after periaqueductal gray lesions in the rat

Analgesia induced by nitrous oxide was examined using radiant heat tail flick and electrical evoked foot flick tests in rats. Rats exposed to 80 and 60% nitrous oxide expressed statistically significant elevations of percent analgesia (% MPE) compared to air exposed rats. Rats exposed to 30% nitrous oxide showed no significant difference in percent analgesia. Pretreatment with naloxone (10 mg/kg s.c.) produced a significant decrease in %MPE and an increase in variance of response after exposures to 80% nitrous oxide in a double blind study. Kainic acid lesions of the ventral and caudal periaqueductal grey (PAG) reversed analgesia produced by 80% nitrous oxide in a crossover blink study compared to saline lesions. In conclusion, this evidence suggests that the caudal-PAG-raphe mangus-dorsal horn pain inhibition pathway is in part involved in the analgesia induced by nitrous oxide.

The ventricular system in neuroendocrine mechanisms

SummaryThis investigation has dealt with a light and electron microscopic autoradiographic analysis of the median eminence of the rat following intraventricular infusion of 3H-dopamine. This study has demonstrated that 3H-dopamine, once infused into the mammalian cerebral ventricular system, is rapidly and selectively absorbed by tanycytes and transported to the contact zone within 5 minutes after ventricular infusion. Certain axon terminals in the ependymal, hypendymal, and palisade-contact zones selectively sequester 3H-dopamine as do subpopulations of arcuate neurons. This picture of intense labelling of neurons and axon terminals is discussed with respect to monoaminergic re-uptake mechanisms. Uptake and transport of 3H-DA by tanycytes is discussed.

Topography of the ACTH-immunoreactive neurons in the basal hypothalamus of the rat brain

Cell bodies of the opiocortin neurons were stained immunocytochemically with ACTH antiserum and their location in the basal hypothalamus of the rat brain was mapped. They are present throughout the entire extent of the hypothalamus, from retrochiasmatic area to mammillary body. In the retrochiasmatic area they are a single, midline group horizontally oriented and lying close to the ventral surface. Throughout the extent of the median eminence, ACTH-ir perikarya are located in the arcuate nucleus, adjacent periventricular stratrum and internuclear space between arcuate and ventromedial nuclei; as a group, they are oriented in a dorso-lateral plane. In the mammillary region, the nucleus assumes a more horizontal orientation again, lying close to the ventral surface. No regional differences were noted in cell density except in the retrochiasmatic area and terminal portion of the mammillary region where they were approximately 30% fewer in number.

Melanotropic peptides in the mammalian brain: The melanin-concentrating hormone

Melanin-concentrating hormone (MCH) has been identified in neurons of the mammalian brain. This review summarizes some current information regarding the cell biology of this neuropeptide and the topography of MCH-immunoreactive (-IR) neurons in several species including mouse, rat, hamster, guinea pig, rabbit, dog and monkey; and atlas of MCH-IR neurons in the hypothalamus and subthalamus of the brain of guinea pig is presented. Based upon the location of this MCH cell group, it is hypothesized that they may be functionally involved in circuits of extrapyramidal motor systems from striatal centers to the thalamus and cerebral cortex and to the midbrain and spinal cord.

Intrasellar Neural-adenohypophyseal Choristoma: A Morphological and Immunocytochemical Study

A patient with mild acromegaly had recurrence of symptoms and signs of a chiasmal-area lesion seventeen years after radiation therapy for a presumed pituitary adenoma. A mass was found anterior to the pituitary gland. Abnormal tissue removed from the sphenoid sinus and sella turcica consisted of a predominantly ganglion-cell lesion. A few ganglion cells were immunoreactive for somatostatin. There were some small cysts lined by cells with immunostaining for glial fibrillary acidic protein, growth hormone or prolactin. Some cells with vacuoles and eosinophilic granules showed immunostaining for growth hormone, prolactin, ACTH, and β-endorphin and, thus, appeared to be of adenohypophyseal origin. Cases of intrasellar ganglioncell lesions have been reported, most of them associated with pituitary adenomas and acromegaly. The findings in this case are discussed in relation to the hypothesis that displaced, hypothalamic-type ganglion cells may produce a growth hormone-releasing factor that stimulates the development of a growth hormone-secreting pituitary adenoma. An alternative hypothesis is suggested that includes this concept, but also allows for the influence of non-neuronal cells on neuronal differentiation and for the possible influence of adenohypophyseal hormones on the replication of hypothalamic-type neurons in the lesion.

Identification of catecholamine and luteinizing hormone-releasing hormone (LHRH)-containing neurons in primary cultures of dispersed cells of the basal hypothalamus.

Primary cultures of dispersed cells were prepared from 3-5 mg pieces of basal hypothalami of 10-12-day-old rats. The tissue included median eminence, arcuate nucleus and variable amounts of adjacent hypothalamus and preoptic area. The dispersion procedure consisted basically of tissue trypsinization and mechanical dissociation of cells. They were cultured in a modified L-15 medium in an air atmosphere. Neurons survived approximately 3 months. On the basis of morphological characteristics, two basic cell types could be distinguished. One was a larger (50 mum diameter) multipolar cell; microspectrofluorometric analysis revealed that a small percentage of these neurons contained a catecholamine. A second type was smaller, fusiform or ovoid and generally bipolar; a significant number of these were immunoreactive for the releasing hormone LHRH.

Immunocytochemical localization of luteinizing hormone-releasing hormone (LHRH) in Vibratome-sectioned brain.

Immunocytochemical localization of neuropeptides such as luteinizing hormone-releasing hormone (LHRH) is generally performed on Bouins fixed tissue sections, following tissue dehydration in alcohols and embedment in paraffin. When the final reaction product accurately reflects content and distribution of the neuropeptide has not been examined carefully. Our data indicate a decrease in radioimmunoassayable LHRH content of brain fixed in Bouins solution and a further significant reduction following dehydration with alcohol. In order to circumvent this loss of hormone, sections of fixed brain were cut on a Vibratome at 30 micron and collected in phosphate-saline buffer. These Vibratome sections revealed a significantly greater amount of overall immunoreactivity and fiber distribution as compared to paraffin-embedded sectioned tissue. These results suggest that certain neuropeptides, soluble in alcohol, can be extracted during dehydration processes necessary for paraffin embedment.

Transport Capacity of Median Eminence

The capacity for and mechanism of transport of thyroxine (T4) by the median eminence has been examined in vivo. Following an intravenous injection of 125I-thyroxine, the median eminence acc