Neuroscience
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The rate of overflow and disappearance of dopamine from the extracellular fluid of the rat striatum has been measured during neuronal stimulation. Overflow of dopamine was induced by electrical stimulation of the medial forebrain bundle with biphasic pulse trains. The instantaneous concentration of dopamine was measured with a Nafion-coated, carbon fiber microelectrode implanted in the brain. ⋯ The increase in stimulated overflow observed after L-DOPA (250 mg/kg) could be modelled by a 1.6-fold increase in the amount of dopamine release with no alteration of the uptake parameters. The increase in modelled by an increase in Km. In addition, the fit of the modelled data to the experimental data was improved when diffusion from the release and uptake sites was considered.
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The localization of glycine receptors was immunocytochemically examined in the rat brain using a monoclonal antibody against the affinity-purified glycine receptor. Glycine receptors were concentrated in the lower brainstem, whereas no immunoreactivity was observed in the diencephalon and forebrain except in a few diencephalic nuclei. The highest density of receptors was found in the cranial motor nuclei, reticular formation, parabrachial area, dorsal and ventral cochlear nuclei, and dorsal and ventral tegmental nuclei. ⋯ In the cerebellar cortex, the immunoreactivity was exclusively seen along the dendrites of the Purkinje cells. On the other hand, glycine receptors were detected on the cellular membrane of the soma of the cochlear nuclei, trigeminal motor nucleus, parabrachial area, lateral reticular nucleus, dorsal nucleus of the lateral lemniscus, cerebellar nuclei, trigeminal spinal nucleus, anterior horn and reticular formation. In other regions, the receptors were evenly distributed throughout the neuropil.
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Purine-induced depression of dorsal horn neurons in the cat spinal cord: enhancement by tachykinins.
The neurokinins, physalaemin, substance P, neurokinin A and bradykinin, were tested on the responses of single spinal neurons to the purines, adenosine 5'-triphosphate (ATP) and adenosine 5'-monophosphate and to GABA. Experiments were done on anaesthetized cats, recording extracellularly from functionally identified sensory neurons in the lumbar dorsal horn. All compounds were administered by iontophoresis. ⋯ The depressant response to adenosine 5'-monophosphate was also enhanced by physalaemin: ejections of adenosine 5'-monophosphate subthreshold to affect the on-going firing rate caused depression after physalaemin application in 3 of 8 units (average depression: 35.0 +/- 3.3%). On the other hand, depression induced by GABA was unaffected by physalaemin in every case (n = 8); in 4 of these cases GABA was tested on units for which purine-induced depression was enhanced by physalaemin. Thus, physalaemin preferentially affected depressant responses to ATP and to adenosine 5'-monophosphate.(ABSTRACT TRUNCATED AT 400 WORDS)
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Cerebral blood flow was sequentially determined (every 2-3 min) with helium clearance in two "vulnerable" structures: the hippocampus and the frontoparietal cortex during bicuculline (n = 11) and kainic acid (n = 9)-induced seizures in unanaesthetized, spontaneously breathing rats. Tissue partial pressures of oxygen and carbon dioxide were continuously and simultaneously evaluated in the same brain areas. All these variables were measured by mass spectrometry with a single gas sampling cannula previously implanted in each structure. ⋯ In both structures, tissue partial pressure of oxygen was first lowered while tissue partial pressure of carbon dioxide was elevated; with the occurrence of the wet dog shakes, tissue partial pressure of O2 increased and tissue partial pressure of CO2 decreased. The changes in tissue gases were maximal during status epilepticus and tended to return to their basal levels thereafter, but no decrease in tissue partial pressure of O2 was observed, even 4 h after kainic acid administration. Histological analysis demonstrated ischaemic cell changes, particularly in the limbic system.(ABSTRACT TRUNCATED AT 400 WORDS)
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The projections of the subiculum, as the main output structure of the hippocampal formation, to the striatum were studied in the rat using the anterograde tracer Phaseolus vulgaris leucoagglutinin. It appears that not only the entire nucleus accumbens, part of the so-called ventral striatum, receives fibres from the subiculum, but that the hippocampal projection area in the striatum includes also the most medial, ventral, rostral and caudal parts of the caudate-putamen complex. Moreover, a relatively small number of fibres and terminals are present in the striatal elements of the medial part of the olfactory tubercle. ⋯ Very sparse projections are found to the contralateral nucleus accumbens, arranged in a topographical manner similar to the ipsilateral projections. An important observation with respect to the structure of the nucleus accumbens is that the subicular terminations are inhomogeneously distributed, although a relation with earlier described mosaic patterns in the connectivity and neurochemical composition of the nucleus is not yet clear. Subicular fibres have their densest terminations in relatively cell-poor regions of the nucleus accumbens, and in particular tend to avoid small cell clusters.