Neuroscience
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The net transport of glucose from blood to the cerebrospinal fluid compartment of cats was measured by ventriculocisternal perfusion to determine over a large range of serum glucose concentrations the influence of serum glucose levels and their changes on the net transport rate. Changes in serum glucose levels were followed within minutes by corresponding changes in cerebroventricular effluent fluid glucose concentration. At mean values of serum glucose concentration of 6.2 mM and cerebrospinal fluid formation rate of 24.3 microliter/min, the net glucose influx rate was 1.6 mmol/min. ⋯ It is concluded that during perfusion over a wide range of serum glucose concentrations, a saturable mediated glucose transport mechanism can be demonstrated. Changes in serum glucose are rapidly reflected in corresponding effluent fluid glucose levels. From effluent fluid-to-serum glucose concentration ratios and calculations of the glucose in newly formed cerebrospinal fluid, the technique, however, overestimates the glucose influx rates at normal serum glucose levels.
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To clarify the circuitry through which opioid compounds modulate spinal and trigeminal nociceptive transmission, we have examined the synaptic associations formed by leucine-enkephalin-containing (enkephalin) neurons in the superficial dorsal horn of the cat. As described previously, punctate enkephalin immunoreactivity is concentrated in the marginal layer (lamina I) and in both the outer and inner layers of the substantia gelatinosa (lamina IIo and IIi). In colchicine treated cats, enkephalin perikarya are most numerous in lamina I and at the border between laminae I and II. ⋯ These include inputs which may derive from primary afferent axons. Enkephalin neurons, in turn, influence nociceptive transmission predominantly through postsynaptic mechanisms. Finally, while we did not observe enkephalin terminals presynaptic in an axoaxonic relationship, the possibility that enkephalin neurons modulate the excitability of fine fiber nociceptive and nonnociceptive afferents via "nonsynaptic interactions" is discussed.
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Comparative Study
Intracellular and extracellular electrophysiology of nigral dopaminergic neurons--1. Identification and characterization.
Intracellular recordings were obtained from directly identified rat nigral dopamine cells in vivo. This identification was based on an increase in glyoxylic acid-induced catecholamine fluorescence in the impaled dopamine neurons. One of three compounds was injected intracellularly into each cell to produce the heightened fluorescence: (1) L-DOPA, to increase the intracellular dopamine content by precursor loading; (2) tetrahydrobiopterin, a cofactor for tyrosine hydroxylase, to increase intracellular dopamine concentration through activation of the rate-limiting enzyme for dopamine synthesis and (3) colchicine, to arrest intraneuronal transport and thus allow the build-up of dopamine synthesizing enzymes and dopamine in the soma. ⋯ Intravenously administered apomorphine demonstrated the same inhibitory effect on cell firing that was previously reported to occur when recording extracellularly from identified dopaminergic neurons. The determination of the electrophysiological characteristics of a population of cells directly identified as containing a specific neurotransmitter (in this case, dopamine) may allow one to construct better models of a system's functioning. Thus, the high input resistance and long time constant of dopamine-containing cells, combined with their burst/pause firing mode, may be important functionally with respect to a possible modulatory effect of dopamine in postsynaptic target areas.
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The speed of execution of complex movements depends on both the local, differential properties of the trajectory and on some of its more global metric parameters. The effects of these global factors were studied in free, writing-like movements with either piece-wise constant, or regularly changing curvature. ⋯ Furthermore, it is shown that the average tangential velocity over identifiable segments of the trajectory also depends on the corresponding average curvature. The implications of these results vis-à-vis the central representation and planning of movements are discussed.
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Projections to the basal ganglia from four auditory cortical fields in the cat were studied by combining microelectrode-mapping of the neurons' best frequencies with autoradiographic and histochemical tract-tracing techniques. Each auditory field is a source of projections to the homolateral basal ganglia. The distribution of labeling within the basal ganglia is related to the cortical field in which the injection site is located. ⋯ By comparison, two adjacent sheets of tissue were labeled when two injections were made into the low best-frequency and high best-frequency representations of the same auditory field. Double-injection, double-tracer experiments revealed that adjacent sheets of tissue received projections from different best-frequency loci. These observations suggested a degree of tonotopic organization to this projection system which was equipoise to the evidence obtained for a topographic organization.