Inverted pyramidal neurons and their axons in the neocortex of reeler mutant mice

Summary Inverted pyramidal neurons are very abundant in the cerebral cortex of the adult reeler mutant mouse. Two types of inverted pyramid are found in rapid Golgi impregnations. In the first type the axon starts from the base of the cell body and bends towards the white matter. In the second type, which is more common, the axon emerges from the apical dendritic tree and descends directly towards the white matter.Despite its abnormal topography, the site of origin of the axon in pyramids of the second type displays a normal differentiation, when analysed with the electron microscopic Golgi technique, suggesting that the ectopic initial axon segment is able to fulfil its normal functions.     

Immunocytochemical investigation of the hypothalamo-neurohypophysial system in birds

Summary The results of an immunohistochemical investigation of the hypothalamo-neurohypophysial system in several species of birds have shown that: (1) mesotocin and vasotocin are synthesized in separate neurons; (2) in all species investigated the distribution of mesotocinergic and vasotocinergic perikarya follows a common pattern; (3) the external zone of the avian anterior median eminence contains exclusively vasotocinergic nerve fibers, originating in supraoptic and ventral paraventricular regions; (4) the distribution of immunoreactive elements in the neural lobe shows a definite species-dependent pattern.     

Cell Damage Associated with Changing the Medium of Mesencephalic Cultures in Serum-Free Medium Is Mediated via N-Methyl-D-Aspartate Receptors

Dopaminergic neurons from embryonic rat mesencephalon were grown in simple serum-free media. The cells develop over a period of several weeks in vitro, particularly between day 14 and day 23. Removing the culture medium and replacing it with fresh medium during this interval caused severe damage to the cultures; this damage is mediated by excitatory amino acids acting through glutamate receptors. Damage could be completely prevented by antagonists of the N-methyl-D-aspartate subtype of glutamate receptor. As expected, medium that contains glutamate (i.e., Ham's F-12 medium) caused damage; however, medium that contains no glutamate or aspartate (i.e., Dulbecco's modified Eagle medium) also caused severe damage, and most of the damage was dependent on the presence of glutamine in the medium. The presence of the antibiotics penicillin and streptomycin greatly enhanced damage caused by medium change.     

Metabolism of Guanine and Guanine Nucleotides in Primary Rat Neuronal Cultures

The metabolic fate of guanine and of guanine ribonucleotides (GuRNs) in cultured rat neurons was studied using labeled guanine. 8-Aminoguanosine (8-AGuo), an inhibitor of purine nucleoside phosphorylase, was used to clarify the pathways of GMP degradation, and mycophenolic acid, an inhibitor of IMP dehydrogenase, was used to assess the flux from IMP to GMP and, indirectly, the activity of the guanine nucleotide cycle (GMP----IMP----XMP----GMP). The main metabolic fate of guanine in the neurons was deamination to xanthine, but significant incorporation of guanine into GuRNs, at a rate of approximately 8.5-13.1% of that of the deamination, was also demonstrated. The turnover rate of GuRNs was fast (loss of 80% of the radioactivity of the prelabeled pool in 22 h), reflecting synthesis of nucleic acids (32.8% of the loss in radioactivity) and degradation to xanthine, guanine, hypoxanthine, guanosine, and inosine (49.3, 4.3, 4.1, 1.1, and 0.5% of the loss, respectively). Of the radioactivity in GuRNs, 7.9% was shifted to adenine nucleotides. The accumulation of label in xanthine indicates (in the absence of xanthine oxidase) that the main degradative pathway from GMP is that to xanthine through guanosine and guanine. The use of 8-AGuo confirmed this pathway but indicated the operation of an additional, relatively slower degradative pathway, that from GMP through IMP to inosine and hypoxanthine. Hypoxanthine was incorporated mainly into adenine nucleotide (91.5%), but a significant proportion (6%) was found in GuRNs.(ABSTRACT TRUNCATED AT 250 WORDS)     

Efferent neurons of the lateral-line system and the VIII cranial nerve in the brainstem of anurans

Summary The octavo-lateral efferent system of several anuran species was studied by means of retrograde transport of horseradish peroxidase. This system is organized similarly in all larval anurans and in all adult aglossids. All have two groups of efferent neurons in the nucleus reticularis medialis between the VIIIth and the IXth motor nucleus. The caudal group consists of efferent neurons that supply the posterior lateral-line nerve (NLLp) and a considerably smaller group of neurons supplying both the NLLp and the anterior lateral-line nerve (NLLa). The rostral group is composed of efferent neurons supplying the NLLa, neurons projecting to the inner ear and neurons supplying both the inner ear and the NLLa. Efferent neurons of the VIIIth cranial nerve exhibit a rostrocaudal cytoarchitectonic differentiation. Caudal perikarya, which are rounder in shape than those of the rostral part, have a dendritic projection to the superior olive. It is suggested that this differentiation reflects a functional differentiation of acoustic and vestibular efferent neurons.Labeled neurons were ipsilateral to the site of application of HRP. None were found in the vestibular nuclei or in the cerebellum.Efferent axons projecting to neuromasts of the NLLa leave the medulla with the VIIth nerve, axons projecting to neuromasts of the NLLp exit via the IXth nerve. Cell counts and the observation of axonal branching revealed that efferent units of both the lateral-line and the VIIIth-nerve system supply more than one receptor organ. In contrast to the lateral-line system, dendrites of efferent neurons of the VIIIth nerve project dorsally onto its nuclei, and afferents of the VIIIth nerve project onto efferent neurons. These structures most probably represent a feedback loop between the afferent and efferent systems of the VIIIth cranial nerve.     

Long-term effects of dexamethasone and nerve growth factor on adrenal medullary cells cultured from young adult rats

Summary Normal postnatal rat chromaffin cells and rat pheochromocytoma cells are known to show extensive Nerve Growth Factor (NGF)-induced process outgrowth in culture, and this outgrowth from the postnatal chromaffin cells is abolished by the corticosteroid dexamethasone. To determine whether adult rat chromaffin cells respond to NGF and dexamethasone, dissociated adrenal medullary cells from 3-month-old rats were cultured for 30 days in the presence or absence of these agents. Such cultures contained typical chromaffin cells, chromaffin cells with processes, and neurons. Fewer than 2 % of normal adult chromaffin cells formed processes under any of the conditions studied, and statistically significant changes in this proportion were not detectable in the presence of NGF or dexamethasone. Adrenal medullary neurons, however, were observed only in the presence of NGF, in cultures with or without dexamethasone, and thus appear to be previously unreported NGF targets which require NGF for survival or process outgrowth. Dexamethasone markedly increased total catecholamine content, total content of epinephrine, and tyrosine hydroxylase activity in cultures with or without NGF. In contrast, postnatal rat chromaffin and rat pheochromocytoma cells which have been studied in culture do not produce epinephrine under any of these conditions. It is concluded that rat adrenal chromaffin cells undergo age-related changes in both structural and functional plasticity. The in vitro characteristics of rat pheochromocytoma cells more closely resemble those of postnatal than of adult rat chromaffin cells, but may not entirely reflect the properties of the majority of chromaffin cells in either age group.     

Afferent connections of physiologically identified neuronal complexes in the paraventricular nucleus of conscious Pekin ducks involved in regulation of salt- and water-balance

Summary The afferent connections of the paraventricular nucleus (PVN) of the domestic mallard (Pekin duck), Anas platyrhynchos, were demonstrated by means of microiontophoretic injection of horseradish peroxidase (HRP). To place the HRP injection exactly into the PVN, its location was identified prior to the injection by observing antidiuretic reactions to electrostimulations within the rostral hypothalamus of conscious, hydrated animals. Antidiuresis was induced only when electrostimulation was applied to a distinct hypothalamic area. Two different patterns of antidiuresis were observed: (i) an immediate reduction in rate of production of urine, and (ii) antidiuresis preceded by a period of increase in production of urine. Repeated stimulation of the same site with the same parameters resulted in decreasing antidiuretic effects. At the site where stimulation had elicited the most pronounced antidiuresis of either response type, HRP was injected microiontophoretically.Histological examination after 3–8 days of survival revealed delicate injection sites located exclusively in the periventricular portion of the PVN. Adjacent to the dorsal portion of the PVN retrogradely labeled tanycytes and intraependymal neurons were scattered in the ventricular wall. As demonstrated in neurohistological and electron-microscopic investigations, this ependymal region exhibits a particular arrangement of tanycytes and small neurons (10–15 m in diameter), some of which belong to the neurosecretory type.Additional HRP-labeled neuronal perikarya afferent to the PVN were demonstrated in the contralateral PVN, and on the ipsilateral side in the lateral septum, lateral hypothalamic area and locus coeruleus. Within the nuclei of the solitary tract, stained nerve cells were found ipsilateral as well as contralateral to the injection site.Several of the neurons demonstrated may be considered as candidates for the transmission of signals originating from various receptive structures relevant for the control of avian salt- and water-balance. The physiological results conform to the concept that neurons of the PVN influence urine formation by controlling the release of arginine-vasotocin (AVT). Evidence that suggests additional modes of control exerted by these neurons in salt- and water-balance is presented.Supported by grants from the Deutsche Forschungsgemeinschaft (Ko 758/1; Si 230/4-4)Portions of these results were presented on the occasion of the 54th Meeting of the Deutsche Physiologische Gesellschaft (Korf et al. 1981 a) and the 76th Meeting of the Anatomische Gesellschaft (Korf et al. 1981 b)     

Tyrosine Hydroxylase Regulation: Apparent Kinetic Alterations Following Incubation of Brain Slices in a Sodium-free Medium

In an attempt to determine if alterations in intraneuronal Ca2+ may regulate tyrosine hydroxylase activity, brain slices were subjected to experimental manipulations known to increase the intraneuronal concentration of free Ca2+ ions. Incubation of either striatal or olfactory tubercle slices in a Na+-free medium for 15 min at 37 degrees resulted in a marked increase in the activity of tyrosine hydroxylase present in the 20,000 g supernatant fraction of homogenates prepared from the slices. Tyrosine hydroxylase isolated from slices previously incubated in a Na+-free, choline-enriched medium or in a Na+-free, sucrose-enriched medium exhibited maximal activities when assayed at pH 6.0 and 7.0, respectively. However, the percentage stimulation of enzyme activity induced by incubation of the slices in a Na+-free medium was maximal when the enzyme assays were performed at pH 7.0. The observed increase in enzyme activity seems to be mediated by a decrease in the apparent Km of the enzyme for pteridine cofactor, regardless of whether the kinetic enzyme analyses were conducted at pH 6.0 or 7.0, and by an increase in the Ki of the enzyme for end-product inhibitor dopamine. The apparent kinetic changes in the enzyme do not seem to result from alterations in the endogenous dopamine content of the slices, and they are independent of any increase in dopamine release that might have occurred as a response to the augmented intraneuronal Ca2+ concentration. Furthermore, the activation of tyrosine hydroxylase produced by incubating slices in a Na+-free medium is observed even in slices depleted of dopamine by pretreatment of rats with reserpine 90 min before preparation of brain slices. The activation of tyrosine hydroxylase observed under these experimental conditions does not seem to be mediated by cAMP or by a cAMP-dependent phosphorylation process. It is suggested that the changes in tyrosine hydroxylase reported are mediated primarily by a rise in the free Ca2+ concentration within the nerve tissue. These observations are consistent with the hypothesis that the kinetic activation of tyrosine hydroxylase produced after depolarization of central dopaminergic neurons may occur through a Ca2+-dependent even other than transmitter release.     

Neurochemical Studies of the Mesolimbic Dopaminergic Pathway: Somatodendritic Mechanisms and GABAergic Neurones in the Rat Ventral Tegmentum

Abstract: The rat ventral tegmentum (containing dendrites and somata of mesolimbic neurones) contained 1.3 μg/g of dopamine, which was reduced to 40% of the control level by reserpine. Slices of ventral tegmentum were able to accumulate and release (elevated potassium or protoveratrine A) exogenous [³H]dopamine. In parallel studies the uptake mechanism in ventral tegmentum was shown to be virtually identical to the nerve terminal uptake of [³H]dopamine by slices of nucleus accumbens. The release of [³H]dopamine was indistinguishable from that observed in substantia nigra, where there is substantial evidence for dendritic mechanisms. Basal adenylate cyclase activity was present, but dopamine-stimulated activity was not detected. A high GABA concentration (7.7 μmol/g) was present in ventral tegmentum, in conjunction with an uptake and a release mechanism for [³H]GABA. GABA and muscimol elicited a small, reproducible efflux of [³H]dopamine, but an interaction between dopamine and [³H]GABA efflux was not observed. The results are in accord with transmitter roles for dopamine and GABA in the somatoden-dritic area of mesolimbic dopaminergic neurons.     

Ultrastructural changes in neurons and neuroglia of the avian telencephalon (Hyperstriatum Accessorium) following tri-ortho-cresyl-phosphate intoxication

Summary Ultrastructural reactions of neurons of the avian forebrain following tri-ortho-cresyl-phosphate (TOCP) poisoning are described. These neurons show a marked increase in the rough endoplasmic reticulum (RER), with RER specializations such as lamellar bodies and subsurface cisternae, as well as a proliferation of the Golgi complex and neurofilaments. In addition, an increase in the number of dense bodies and mitochondrial osmiophilia is noted. Similar changes can also be observed in the neuroglia. These alterations appear 10–13 days after TOCP ingestion.