Kinetic characterization of GABA-transaminase from cultured neurons and astrocytes

The enzymatic mechanism and the kinetic parameters of GABA-transaminase extracted from cultured mouse cerebral cortex neurons and astrocytes were studied. Neuronal as well as astrocytic GABA-transaminase obeyed a bi bi ping-pong reaction mechanism. The estimated K_m-values for -ketoglutarate and GABA were significantly lower for astroglial GABA-transaminase compared to the neuronal enzyme suggesting a possible existence of cell specific isozymes of GABA-transaminase. The observed enzymatic mechanism and the magnitude of the estimated kinetic parameters imply that GABA-transaminase synthesized in the two types of cultured neural cells is mechanistically and kinetically equivalent to the enzyme synthesized in the brainin vivo.     

Distribution of 5-HT (serotonin) immunoreactivity in the central nervous system of the inshore hagfish,Eptatretus burgeri

Summary Immunohistochemical techniques were used to study the distribution of serotonin in the central nervous system of the hagfish,Eptatretus burgeri, in order to produce a detailed map of serotonin-containing structures. In the hypothalamus, many serotonin-containing neurons contacted the cerebrospinal fluid. Most of the serotonin-containing cell bodies were located in the raphe region, where they were compactly distributed at the level of the nucleus motorius tegmenti pars anterior but more diffusely distributed at the level of the nucleus motorius tegmenti pars posterior. Serotonin-containing cell bodies and varicose fibers were widely distributed throughout the brain and upper spinal cord segments, but the distribution density was not even. On the basis of its abundance, serotonin can be judged to have an important function in the control of the hagfish central nervous system. From a phylogenetic point of view, serotonin-containing neurons in the raphe region appear to be a common property of all classes of vertebrates studied except the lampreys, whereas serotonin-containing cerebrospinal fluid-contacting neurons may be considered to be a primitive condition in all nonmammalian vertebrates.     

An immunocytochemical study of the optic ganglia of the crayfish Astacus leptodactylus (Nordmann 1842) with antisera against biologically active peptides of vertebrates and invertebrates

Summary The peptidergic system in the optic ganglia of Astacus leptodactylus is characterized by the immunocytochemical application of 15 antisera raised against biologically active peptides of vertebrates and invertebrates. Positive reactions were found with anti-FMRFamide, antiMSH, anti-vasotocin, anti-gastrin, anti-CCK, anti-oxytocin, anti-secretin, anti-glucagon and anti-GIP. Based on immunochemical reaction and localization it is possible to distinguish 30 cell groups. Only part of these cell groups is found in the known classical neurosecretory cell regions. This observation demonstrates a more extensive peptidergic system than formerly recognized. The morphology of this peptidergic system suggests that one part is neurohormonal and the other part neurotransmitter-like or neuromodulatory.     

Actions of Excitatory Amino Acids on Somatostatin Release from Cortical Neurons in Primary Cultures

L-Glutamate, N-methyl-D-aspartic acid (NMDA), quisqualate, and kainate were found to increase endogenous somatostatin release from primary cultures of rat cortical neurons in a dose-dependent manner. The rank order of potency calculated from the dose-response curves was quisqualate greater than glutamate = NMDA greater than kainate, with EC50 values of 0.4, 20, and 40 microM, respectively. Alanine, glutamine, and glycine did not modify the release of somatostatin. The stimulation of somatostatin release elicited by L-glutamate was Ca2+ dependent, was decreased by Mg2+, and was blocked by DL-amino-5-phosphonovaleric acid (APV) and thienylphencyclidine (TCP), two specific antagonists of NMDA receptors. The NMDA stimulatory effect was strongly inhibited by APV in a competitive manner (IC50 = 50 microM) and by TCP in a noncompetitive manner (IC50 = 90 nM). The release of somatostatin induced by the excitatory amino acid agonists was not blocked by tetrodotoxin (1 microM), a result suggesting that tetrodotoxin-sensitive, sodium-dependent action potentials are not involved in the effect. Somatostatin release in response to NMDA was potentiated by glycine, but the inhibitory strychnine-sensitive glycine receptor did not appear to be involved. Our data suggest that glutamate exerts its stimulatory action on somatostatin release essentially through an NMDA receptor subtype.     

Sensory receptors of the ovipositor ofTrichogramma maidis [Hym.:Trichogrammatidae]

Sensory receptors of the ovipositor ofTrichogramma maidis are described. Sense organs are found on the 2^nd valvifers (1 type), on the tip of the 3^rd valvulae (2 types) and on the 1^st valvulae (4 types). The nature and possible functions of these sensilla are discussed.      

动态神经网络中的同步振荡

目前有一种假设认为同一视觉对象是由一群神经元的同步振荡活动来表征的。这一神经元发放活动的时间特性,是解决视觉信息处理中“结合问题（Ｂｉｎｄｉｎｇｐｒｏｂｌｅｍ）”的可能机制。本文用我们所提出的一种简化现实性神经网络模型［１］所构造的时滞非线性振子网络［２］,模拟生物神经网络的同步振荡活动。并考虑了振子各参数的设置与振荡活动的关系,以及网络振子间耦联对同步活动的影响．     

Presynaptic Nicotinic Receptors Stimulate Increases in Intraterminal Calcium of Chick Sympathetic Neurons in Culture

Abstract: Stimulation of chick sympathetic neurons in culture by the cholinergic agonists acetylcholine, nicotine, and 1,1-dimethyl-4-phenylpiperazinium (all at 10–1,000 µmol/L) induced concentration-dependent increases of free calcium levels measured by fura 2 fluorescence in neuronal processes. The response evoked by acetylcholine had both nicotinic and muscarinic components, whereas that induced by 1,1-dimethyl-4-phenylpiperazinium was purely nicotinic. Tetrodotoxin (0.3 µmol/L) blocked completely the increase of intraterminal free calcium level evoked by electrical stimulation. On the other hand, stimulation with 1,1-dimethyl-4-phenylpiperazinium still evoked 20–25% of the control response in the presence of tetrodotoxin. The concentration-response relationship of 1,1-dimethyl-4-phenylpiperazinium stimulation did not differ in the absence and in the presence of tetrodotoxin. The nicotinic antagonists d -tubocurarine (10 µmol/L) and mecamylamine (10 µmol/L), but not α-bungarotoxin (125 nmol/L), prevented the increase of intraterminal free calcium level evoked by 1,1-dimethyl-4-phenylpiperazinium (100 µmol/L) in the presence of tetrodotoxin. These observations indicate the presence of nicotinic receptors on neuronal processes that increase the intraterminal concentration of free calcium and probably modulate transmitter release. Their pharmacological properties are similar to those of nicotinic receptors located on neuronal cell bodies.     

Amino acid concentrations and selected enzyme activities in rat auditory,olfactory, and visual systems

Homogenates of specific brain regions of three sensory systems (auditory, olfactory, and visual) were prepared from pigmented Long-Evans Hooded rats and assayed for amino acid concentrations and activities of glutaminase, aspartate aminotransferase (total, cytosolic, and, by difference, mitochondrial), malate dehydrogenase, lactate dehydrogenase, and choline acetyltransferase. Comparing the quantitative distributions among regions revealed significant correlations between AAT and aspartate, between glutaminase and glutamate, between glutamate and glutamine, and between AAT plus glutaminase, or glutaminase alone, and the sum of aspartate, glutamate, and GABA, suggesting a metabolic pathway involving the synthesis of a glutamate pool as precursor to aspartate and GABA. Of the inhibitory transmitter amino acids, GABA concentrations routinely exceeded those of glycine, but glycine concentrations were relatively high in brainstem auditory structures.     

Neurosecretion XVII. Experimentally induced release of neurosecretory material by exocytosis in the insect Leucophaea maderae

Summary In the corpora cardiaca of the insect Leucophaea the administration of serotonin elicits ultrastructural features indicative of the extrusion of neurosecretory material by exocytosis. The response to the stimulus and the process of extrusion seem to occur at considerable speed. Nearly all of the 30 test animals, fixed at various intervals starting as early as 3 min after the injection of the drug, show granules captured at the moment of leaving the axon as well as fully exteriorized secretory material. The fact that many of these granules are much smaller than the typical neurosecretory type speaks for intracellular fragmentation of the latter prior to the discharge of this cellular product. After 25 min or more the extruded electron dense structures show signs of breakdown. The apparent speed of these phenomena accounts for the dearth of omega-type configurations observed in unstimulated specimens of this species. The possible relationship between the membrane phenomena involved in exocytosis and the transient protrusions of bounding membranes of neurosecretory granules described in earlier papers remains to be clarified.Supported by N.S.F. research grant BMS 74-12456     

Localization of glyoxylic acid-induced histofluorescence in surgically isolated medial basal hypothalamus of the rat

Summary Examination of glyoxylic acid-induced catecholamine histofluorescence in the hypothalamic median eminence of adult male rats revealed a linear pattern of fine varicosities coursing through the ependymal and fibrous zones, suggestive of juxtaposition to tanycytes. In order to determine the origin of these terminals, adult rats were subjected to complete isolation of the medial basal hypothalamus, using a small Halasz-Pupp knife. As rapidly as 24h after this deafferentation degenerative axon profiles were observed dorsal, as well as anterior and lateral, to the knife track. Occasionally at three days postoperatively, and routinely by seven days after surgery, fine-sized new fibres were seen passing through the knife wound. The linear profiles of varicosities observed in the normal median eminence remained traceable in the experimental preparations; the site of origin for these terminals therefore appears to be neurons of the arcuate (A12) and rostral periventricular (A14) regions. The results also indicate that fibres innervating the isolated area are capable of morphologically demonstrable new growth. The observations bear functional implications in assessing endocrine regulation following MBH isolation of the type used in this study.This study was supported by USPHS Postdoctoral Fellowship 5-F₂2-HD00630 (CT) and USPHS Grant NS-11642 (JRS). The authors wish to express their appreciation to Yvonne Cheung and Patricia Walker for technical assistance