Neuroscience
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The release of dopamine in the nucleus accumbens of anaesthetized rats was evoked either by electrical stimulation of the mesolimbic dopaminergic pathway or by local ejection of N-methyl-D-aspartate in the ventral tegmental area. Untreated carbon-fibre electrodes implanted in the nucleus accumbens were held at +400 mV versus a reference electrode, and the oxidation current was continuously monitored. Despite a poor selectivity to dopamine versus other oxidizable compounds such as ascorbic acid, the evoked responses were solely due to dopamine overflow in the extracellular fluid since they were closely correlated with the stimulations and exhibited all the expected characteristics related to a dopamine release. ⋯ Fourth, inhibition of dopamine reuptake by nomifensine induced a five-fold decrease in the rate of decline of the evoked oxidation current. Fifth, contribution of noradrenaline and serotonin to the observed effects seems unlikely since specific reuptake blockers (desipramine and sertraline, respectively) did not alter them. Dopaminergic neurons discharge either in a single spike mode with a mean firing rate below 5 Hz or in a bursting pattern (intraburst frequency: 10 to 20 Hz).(ABSTRACT TRUNCATED AT 250 WORDS)
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The characteristic electroencephalographic patterns within the hippocampus are theta and sharp waves. Septal neurons are believed to play an essential role in the rhythm generation of the theta pattern. The present study examined the physiological consequences of complete and selective damage of septohippocampal cholinergic neurons on hippocampal theta activity in rats. ⋯ No changes were observed in the gamma (50-100 Hz) band. These findings indicate that the integrity of the septohippocampal GABAergic projection is sufficient to maintain some hippocampal theta activity. We hypothesize that cholinergic neurons serve to increase the population phase-locking of septal cells and thereby regulate the magnitude of hippocampal theta.
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Animal models of event-related potentials have recently been developed in rats in order to gain further understanding of the psychobiological variables which underlie these waveforms. In the present study, unanesthetized male Wistar rats, chronically implanted with electrodes, were utilized in order to: (i) compare event-related potentials recorded following the presentation of passively presented auditory stimuli from different neocortical, hippocampal and perihippocampal sites; (ii) test the effects of changes in stimulus probability and loudness on event-related potentials recorded from those sites; and (iii) record event-related potentials from rats who were actively performing in a tone discrimination task. The results of these studies showed that in all electrode sites (frontal cortex, parietal cortex, entorhinal cortex, hippocampus) a series of large amplitude potentials in the 10-200 ms latency range could be recorded in response to passively presented stimuli. ⋯ These potentials can be recorded in limbic (hippocampus and amygdala) and cortical (parietal cortex) brain sites. The event-related potentials recorded in rats respond to changes in stimulus parameters in a similar fashion to those previously described in monkeys and human subjects. The identification of a rat model of event-related potentials provides an opportunity to further explore the neural origins of event-related potentials, to estimate the role of genetics in determining individual variation in waveforms, as well as to provide electrophysiological assays of the effects of various drugs on neurosensory and cognitive processing.
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By means of a monoclonal mouse immunoglobulin G2a antibody against the rat liver glucocorticoid receptor and the indirect immunoperoxidase technique, the distribution of glucocorticoid receptors in neuronal and glial cell populations was mapped in the central nervous system of the male rat. The mapping was complemented by computer-assisted morphometric and microdensitometric evaluation of glucocorticoid receptor immunoreactivity in many brain regions. The quantitative analysis allowed us to achieve for the first time an objective characterization of glucocorticoid receptor distribution in the CNS, thus avoiding the ambiguities of previous mapping studies based on subjective evaluations. ⋯ Eight brain regions involving sensory, motor and limbic areas were shown to have a similarity with regard to glucocorticoid receptor-immunoreactive parameters at the level of 95%. The density of glucocorticoid receptor-immunoreactive nerve cells appeared to be the main factor in determining such a very high level of similarity. Overall, our results emphasize that glucocorticoids may appropriately tune networks of different areas to obtain optimal integration and in this way improve survival of the animal under challenging conditions.
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Supraspinal afferents to the pontine micturition center, Barrington's nucleus, were investigated in the rat by visualization of the retrograde tracer, cholera-toxin subunit B, in neurons following iontophoretic injection into Barrington's nucleus. Tissue sections from five rats with injections primarily localized in Barrington's nucleus revealed numerous retrogradely labeled neurons throughout all rostrocaudal levels of the periaqueductal gray (particularly its ventrolateral division), in the lateral hypothalamic area (particularly medial to the fornix), and in the medial preoptic nucleus. Retrogradely labeled neurons were also consistently found in the nucleus of the solitary tract, in the vicinity of the lateral reticular nucleus, nucleus paragigantocellularis, parabrachial nucleus, Kölliker-Fuse nucleus, cuneiform nucleus, raphe nucleus and zona incerta. ⋯ The present results suggest that Barrington's nucleus in the rat receives neuronal inputs from brainstem nuclei as well as from forebrain limbic structures including hypothalamic nuclei, the medial preoptic nucleus, and cortical areas involved in fluid balance or blood pressure regulation. In light of the role of Barrington's nucleus in micturition, the integration of these various inputs may be important for co-ordinating urinary function with fluid and cardiovascular homeostasis. Additionally, as neurons in Barrington's nucleus are immunoreactive for the stress-related neurohormone, corticotropin-releasing hormone, these diverse inputs may regulate stress-related functions of this nucleus.