Differences in the Neurons That Project from the Dorsal Column Nuclei to the Diencephalon,Pretectum, and Tectum in the Cat

The dorsal column nuclei (DCN) project to a number of targets in the nervous system besides the ventroposterolateral nucleus (VPL) of the thalamus. Recent evidence obtained using double-labeling techniques indicates that DCN's diencephalic-projecting neurons differ in their location and morphology from those that project to some of its other targets, such as the cerebellum and tectum. The purpose of the present study was to characterize anatomically the DCN neurons that project another of DCN's targets, the pretectum, and to determine if any of these neurons have collateral projections to the tectum or diencephalon.

The projections were studied using two double-labeling methods. One method made use of either tritiated inactivated horseradish peroxidase ([³H]apoHRP) or tritiated N-acetyl wheatgerm agglutinin ([³H]WGA) as a marker and HRP or WGA conjugated to HRP. The other method made use of the dyes Fast Blue and Nuclear Yellow. In each cat, one marker was injected into the DCN-recipient portions of the pretectum, tectum, or diencephalon, and the other marker was injected into another of these three targets.

Neurons labeled by pretectal or tectal injections were of all sizes, fusiform and multipolar in shape, and similarly located. They were scattered through the rostral zone of DCN, but were distributed at the periphery of and at the junction between the gracile and cuneate nuclei in DCN's middle and caudal zones.

In contrast to the pretectal-and tectal-labeled neurons, neurons labeled by diencephalic injections were round and large. They were found throughout the DCN complex, but were concentrated in DCN's middle and caudal zones. When both the pretectum and diencephalon were injected in the same cat, the two groups of neurons occupied similar locations in the rostral zone, but were distinct in the middle and caudal zones, with the pretectal-projecting neurons surrounding the clusters of diencephalic-projecting neurons. Very few neurons were double-labeled.

These results demonstrate that the projections to the pretectum, tectum, and diencephalon originate from different populations of neurons within specific domains in DCN. When these results are compared with the results of electrophysiological and other anatomical studies, it appears that the pretectal- and tectal-projecting neurons may be part of a previously unrecognized system originating in DCN. In contrast with the well-known lemniscal system, recognized for its function in tactile discrimination, and composed of DCN's VPL-projecting neurons together with VPL's projections to the cerebral cortex, this other system may serve some role in the regulation of posture or the coordination of movement.     

Effect of Microstimulation of Movement-Evoking Cortical Foci on the Activity of Neurons on the Dorsal Column Nuclei

Cortical foci in which stimulation produced movement in either the forelimb or hindlimb were isolated in rats. In each experiment, two foci were selected: one for movement in the forelimb, and the other in the hindlimb. Stimulation was subsequently reduced in order to avoid eliciting a movement, and the effects of this stimulation on activity of gracile and cuneate neurons were examined. Both excitation and inhibition were observed and were found to be arranged in a somatotopic manner. Excitation was almost exclusively obtained when the receptive field (RF) of a given neuron corresponded to the body surfaces overlying the joints involved in the cortically evoked movement. A high percentage of neurons with RFs on body surfaces corresponding to, or adjacent to, the region of cortically induced movement were inhibited, while the activity of neurons with RFs distant to the site of movement was seldom modified. These results suggest that cortical influences exerted on the dorsal column nuclei (DCN) in rats are organized in a somatotopic manner.     

Tonic Descending Influences on Cat Spinal Cord Dorsal Horn Neurons

The extent and nature of tonic supraspinal influences was determined on cat spinal cord dorsal horn neurons that received both noxious (radiant heat) and nonnoxious (hair movement) inputs or only a nonnoxious input. The former cells receive a tonic inhibition that descends in the dorsolateral funiculi and which is selective for the noxious input. The latter neurons are under a tonic facilitation.     

In vivo Microdialysis of 5-Hydroxyindoleacetic Acid and Glutamic Acid in the Hamster Suprachiasmatic Nuclei

SYNOPSIS. The technique of in vivo brain microdialysis rapidlyis becoming a popular tool for research on the neurochemicalbasis of physiological and behavioral functions. The presentstudy describes the application of microdialysis to investigatethe endogenous release of 5-hydroxyindoleacetic acid (5-HIAA)and glutamic acid in the suprachiasmatic nuclei (SCN) of hamsters.There were apparent circadian patterns of release of both ofthese neurosecretions, with peak levels occurring during thedark phase. Pharmacological manipulations of serotonin releaseand reuptake, using tetrodotoxin and citalopram, respectively,provided evidence that the nocturnal increase in 5-HIAA reflectsan increase in serotonergic synaptic activity, rather than intraneuronalmetabolism of unreleased serotonin. These results illustratethe usefulness of the microdialysis technique for studies onthe neurochemistry of central pacemaker function.     

Role of the Proteasome in Excitotoxicity-Induced Cleavage of Glutamic Acid Decarboxylase in Cultured Hippocampal Neurons

Glutamic acid decarboxylase is responsible for synthesizing GABA, the major inhibitory neurotransmitter, and exists in two isoforms—GAD65 and GAD67. The enzyme is cleaved under excitotoxic conditions, but the mechanisms involved and the functional consequences are not fully elucidated. We found that excitotoxic stimulation of cultured hippocampal neurons with glutamate leads to a time-dependent cleavage of GAD65 and GAD67 in the N-terminal region of the proteins, and decrease the corresponding mRNAs. The cleavage of GAD67 was sensitive to the proteasome inhibitors MG132, YU102 and lactacystin, and was also abrogated by the E1 ubiquitin ligase inhibitor UBEI-41. In contrast, MG132 and UBEI-41 were the only inhibitors tested that showed an effect on GAD65 cleavage. Excitotoxic stimulation with glutamate also increased the amount of GAD captured in experiments where ubiquitinated proteins and their binding partners were isolated. However, no evidences were found for direct GADs ubiquitination in cultured hippocampal neurons, and recombinant GAD65 was not cleaved by purified 20S or 26S proteasome preparations. Since calpains, a group of calcium activated proteases, play a key role in GAD65/67 cleavage under excitotoxic conditions the results suggest that GADs are cleaved after ubiquitination and degradation of an unknown binding partner by the proteasome. The characteristic punctate distribution of GAD65 along neurites of differentiated cultured hippocampal neurons was significantly reduced after excitotoxic injury, and the total GAD activity measured in extracts from the cerebellum or cerebral cortex at 24h postmortem (when there is a partial cleavage of GADs) was also decreased. The results show a role of the UPS in the cleavage of GAD65/67 and point out the deregulation of GADs under excitotoxic conditions, which is likely to affect GABAergic neurotransmission. This is the first time that the UPS has been implicated in the events triggered during excitotoxicity and the first molecular target of the UPS affected in this cell death process.     

Mass Fragmentographic Determination of γ-Aminobutyric Acid and Glutamic Acid in Discrete Amygdaloid Nuclei of Rat Brain

A mass fragmentographic method for the simultaneous quantification of gamma-aminobutyric acid (GABA) and glutamic acid is described. In a convenient one-step reaction, the two amino acids were derivatized with pentafluoropropionic anhydride and pentafluoropropanol. The derivatization products were stable for several days. The technique has been applied to the assay of GABA and Glu in five amygdaloid nuclei of the rat brain. The GABA level was high in the central and medial nuclei, whereas the Glu level was high in the lateral and basal nuclei. The regional distribution of GABA was different from that of Glu within the amygdaloid nuclei.     

Bradykinin Stimulates Phosphoinositide Hydrolysis and Mobilization of Arachidonic Acid in Dorsal Root Ganglion Neurons

Cultures of fetal rat dorsal root ganglion neurons (7 days in culture) were prelabeled with myo-[3H]inositol or [3H]arachidonic acid for 24 h and stimulated with 10 microM bradykinin for time intervals of 5-300 s. The incubation was terminated by addition of 5% perchloric acid to extract inositol phosphates or organic solvent to extract lipids. Inositol phosphates were resolved by anion-exchange HPLC; lipids were resolved by TLC. Bradykinin stimulation resulted in a 10-fold increased accumulation of inositol 1,4,5-trisphosphate (IP3) and inositol bisphosphate (IP2) (fivefold) by 5 s. The increase in IP3 was transient (half maximal by 1 min), whereas stimulated IP2 levels were sustained for several minutes. Even longer term increases were observed in inositol monophosphate. Stimulation also resulted in a threefold increase in arachidonic acid which was preceded by transient increases in diacylglycerol (twofold) and arachidonoyl-monoacylglycerol (threefold). The temporal lag in the accumulation of arachidonic acid with respect to diglyceride and monoglyceride suggested the involvement of di- and monoglyceride lipases in arachidonic acid mobilization. A role for phospholipase A2 is also possible, because pretreatment of cultures with quinacrine partially blocked arachidonic acid release. Bradykinin-stimulated arachidonic acid release was decreased in the presence of calcium channel blockers nifedipine or verapamil (50 microM), or EDTA (2.5 mM). The role of calcium was verified further in that accumulation of phosphatidic acid, diacylglycerol, and arachidonic acid was maximally stimulated by treatment with the calcium ionophore A23187 (20 microM).     

Glutamic Acid Decarboxylation in Chlorella

The decarboxylation of endogenous free glutamic acid by Chlorella pyrenoidosa, Marburg strain, was induced by a variety of metabolic poisons, by anaerobic conditions, and by freezing and thawing the cells. The rate of decarboxylation was proportional to the concentration of inhibitor present. Possible mechanisms which relate the effects of the various conditions on glutamate decarboxylation and oxygen consumption by Chlorella are discussed.     

Co-localization of Glutamic Acid Decarboxylase and Phosphate-activated Glutaminase in Neurons of Lateral Reticular Nucleus in Feline Thalamus

Immunohistochemical methods were used to label singly and/or in combination glutamic acid decarboxylase (GAD, the sole synthesizing enzyme for the inhibitory neurotransmitter γ-aminobutyric acid) and phosphate-activated glutaminase (GLN, a synthesizing enzyme for glutamate) in neurons of lateral reticular nucleus (LRN) of thalamus of adult cats. (1) GAD- and GLN-immunoreactivity (IR) exhibited matching regional patterns of organization within LRN. (2) GAD- and GLN-IR co-localized within most if not all LRN neuronal cell bodies as shown by light microscopy. (3) GAD- and GLN-IR had distinct subcellular localizations in LRN neurons as shown by correlative light/electron microscopy. LRN neurons are important conceptual models where strongly inhibitory cells receive predominant excitatory glutamatergic afferents (from neocortex). Consistent with known actions of intermediary astrocytes, LRN neurons demonstrate GLN enrichment synergistically coupled with glutamatergic innervation to supplement the glutamate pool for GABA synthesis (via GAD) and for metabolic utilization (via the GABA shunt/tricarboxylic acid cycle) but not, apparently, for excitatory neurotransmission. Special issue dedicated to John P. Blass.     

Glutamate Decarboxylase Distribution in Discrete Motor Nuclei in the Cat Brain

Abstract: The distribution of activity of glutamate decarboxylase (GAD), the enzyme synthesising γ-aminobutyric acid (GABA), was measured in the cat brain by means of microdissection of the structures from frozen slices and a radioisotopic assay for the enzyme. About 20 cerebral regions were chosen for study because of their role in sensorimotor integration. GAD presented an uneven distribution among these areas. Highest activities were found in the basal ganglia, particularly in the substantia nigra and in the globus pallidus, and to a lesser extent in the cerebellum. Relatively low levels of the enzyme were found in the thalamus and in the cerebral motor cortex. Special detailed studies were made in the caudate nucleus, the substantia nigra, and in the red nucleus for the purpose of defining the intranuclear distribution of their GABAergic innervation. There were only small differences in the rostro-caudal distribution of the enzyme in the head of the caudate nucleus but GAD activity was higher in the ventral than in the dorsal part of the structure. In the substantia nigra, GAD activity was high in both the medial and intermediate thirds of the structure. The GAD activity decreased from the caudal to the rostral part of the nucleus. GAD levels were lower in the caudal part of the red nucleus than in the rostral part. These results indicate that GABA would be present as a putative neurotransmitter in many motor nuclei of the cat brain. In view of the general inhibitory action of this amino acid, this could be related to the presence of inhibitory responses widely distributed in these nuclei as identified by mean of electrophysiological studies. The origin of these GABAergic innervations in many cases remains to be determined.     

Distribution of Calretinin-Immunopositive Neurons in the Cat Lumbar Spinal Cord

Journal of Evolutionary Biochemistry and Physiology - A variety of neural networks in the central nervous system is determined by the heterogeneity of its constituent neuronal populations....     

Postsynaptic Currents in Dorsal Root Ganglion Neurons Co-cultured with Spinal Cord Neurons

In co-cultured dorsal root ganglion (DRG) neurons and spinal cord neurons from newborn rats, using a voltage-clamp technique in the whole-cell configuration enabled us to observe in DRG neurons the effects evoked by extracellular local electrical stimulation of cells corresponding to spinal cord neurons in their morphological characteristics. Such stimulation caused the appearance of postsynaptic currents (PSC) in DRG neurons in 9% of the cases. The mean delay of these currents (measured from the stimulus leading edge) was 4.7 ± 0.29 msec, the mean time to peak was 2.6 ± 0.77 msec, and the decay time constant = 14.5 ± 1.04 msec. The reversal potential of evoked PSC (ePSC) was close to the equilibrium potential for chloride ions estimated by the Nernst equation. Application of 20 M bicuculline induced practically complete and reversible ePSC block. The conclusion was drawn that these currents arise due to activation of the chloride channels operated by GABA receptors and, hence, represent an inhibitory PSC. Thus, one may deem it proved that spinal cord neurons can establish functional inhibitory synapses with DRG neurons.     

Self-Initiated Behavioral Act-Related Neuronal Activity in the Region of the Raphe Nuclei of the Cat

In experiments on awake cats, we recorded the activity of 79 putative serotonergic (STE) neurons localized within the region of the brainstem dorsal and anterior central raphe nuclei. The animals were trained to perform a self-initiated (voluntary) movement, to press a pedal by the forelimb; an additional limitation was to perform the movement not earlier than after a definite time interval. Changes in the activity of STE neurons related to the preparation for and performance of the movement and reactions to presentation of a feedback conditioning signal preceding the reward and receipt of the food reward were most clearly manifested. More than 50% of the units changed their activity before the movement initiation. Most neurons responded to presentation of a positive conditioning signal by phasic activation, while a negative signal informing them of the absence of the reward evoked considerably weaker reactions. We hypothesize that reactions of STE neurons forestalling the movement initiation can provide activation of the neocortex necessary for the movement performance within a preset time interval. Activating and inhibitory reactions observed within the period of expectation of a feedback conditioning signal and developing after presentation of this signal can be related to a noticeable role of the STE system in the formation of memory engrams and development of emotional states.     

Increased Number of Dorsal Root Ganglion Neurons in Vitamin-E-Deficient Rats

Quantitative and morphometric observations were carried out on neurons of L₃-L₆ dorsal root ganglia (DRGs) in control and vitamin-E-deficient rats at different ages. Controls were fed a standard diet and sacrificed at 1 or at 5 months of age; deficient rats were fed a diet without vitamin E from 1 to 5 months of age and then sacrificed. No significant difference in total number of neurons was found, but an increase in neuron sizes, a decrease in nucleus-cytoplasm ratio, and a more circular neuron shape were found in controls with increasing age (from 1 to 5 months). In L₃-L₆ DRGs of vitamin-E-deficient rats (5 months of age), a higher number of neurons was found than in those of either young or adult controls. Moreover, some morphometric characteristics of neurons in the deficient rats were similar to those of neurons in 1-month-old controls. The findings suggest that vitamin E deficiency can trigger events resulting in appearance of new neurons, possibly anticipating phenomena that normally occur in aging.     

谷氨酸在心肺脑复苏中的影响

心跳呼吸骤停及心肺脑复苏(CPCR)的过程均导致机体发生缺血/再灌注损伤(I瓜)等复杂的病理生理变化.脑的缺血再灌注损伤是一个快速的级联反应,包括能量代谢障碍、氧自由基的生成增多、兴奋性氨基酸释放增加、炎性细胞因子释放增加等.这些环节紧密连接,互为因果,形成恶性循环,最终导致神经元的凋亡或坏死.谷氨酸是大脑中一种关键的兴奋性神经递质,它的过多释放在神经元损伤发展过程中起着重要作用.随着细胞外高浓度谷氨酸的结合,N-甲基-D-天冬氨酸受体(NMDAR)开放,大量Ca2+内流,导致细胞内钙超载,是引起脑损伤的共同通路.本文就神经兴奋毒性的研究进行综述.     

Product Inhibition of the Fermentative Formation of Glutamic Acid

The addition of penicillin to cells of Corynebacterium glutamicum growing in 5-liter fermentors initiated the excretion of glutamic acid. The rate of glutamate production in fermentors declined continuously with time and reached 75% of the initial rate in 24 hr after penicillin had been added. The addition of glutamate to resting cell suspensions had only a slight effect on sugar utilization but caused a marked decrease in glutamate excretion. It is suggested that the high level of glutamate accumulating in the fermentation broth is responsible for inhibiting its own production.     

Characteristics of Gamma-Oscillations in Responses of Neurons of the Cat Lateral Geniculate Body

There were studied characteristics of gamma-oscillations in responses of neurons of the lateral geniculate body (LGB) in cat to exposure in their receptive fields (RF) of half-tone and binary test images. The gamma-oscillations were observed in 38.8% of cases (69 cells). The spectral characteristics (SC) (the band 20–100 Hz) of the neuronal responses to adequate stimuli (on- and off-responses correspondingly of on- and off-neurons) were analyzed. The total of 5930 poststimulus histograms (PSTH) of responses constructed from 177 900 neuronal impulse responses were considered. The mean value of the SC dominant frequencies of the whole sample of the neuronal responses amounted to 44.74 ± 21.46 Hz. In this cell sample, the neurons were revealed, which generated oscillations with markedly different frequencies in response to the same stimuli. Based on this property, three types of neurons were determined, with the mean oscillation frequencies of 26.95 ± 4.35, 52.02 ± 9.05, and 85.79 ± 7.19 Hz. The histograms of distribution of peak frequency values in SC of the neuronal responses and of index values of these oscillation peaks also revealed three maxima that corresponded to the frequencies of the three described types of neurons. The mean values of dominant frequencies of gamma-oscillations in responses of all three types of neurons remained constant (within the limits of dispersion) at changes of spatial-brightness parameters of test stimuli as well as at changes of the neuronal excitation level (the number of impulses in responses). The oscillation index values of dominant frequencies depended on parameters of the test images and correlated with the neuronal excitation level (the coefficient of correlation was 0.78 from data of 5930 CX). The suggestion is made about the existence in the neuronal network of the synchronization mechanisms functioning on the principle of multiple synchronization.