Neuroscience
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Intracellular recordings were made from neurones in the thalamic reticular nucleus (TRN) and ventro-basal (VB) thalamus in slices of rat midbrain in vitro. Electrical stimulation of the medial lemniscus or TRN resulted in the generation of complex synaptic potentials containing disynaptic inhibitory post-synaptic potentials (IPSPs) in VB thalamocortical neurones. Analysis of the excitatory synaptic responses in TRN neurones indicates they can produce burst output response irrespective of the level of sub-threshold membrane potential. ⋯ This is consistent with the location of these receptor types on the presynaptic terminals of TRN axons in the VB thalamus. This raises the possibility that, during periods of intense excitatory activity, glutamate release could influence the release of GABA from TRN axon terminals in the thalamus. In addition, as NAAG is located in the axons and terminals arising from the TRN, there is the possibility that this dipeptide is also released by these terminals to control the release of GABA during periods of high activity in the TRN.
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Comparative Study
Detection and discrimination of carvone enantiomers in rats with olfactory bulb lesions.
Rats with lesions of dorsal and dorsolateral bulbar sites known to be differentially responsive to carvone enantiomers were tested for their ability to detect (+)-carvone, to discriminate between (+)-carvone from (-)-carvone, and to discriminate (+)-carvone from mixtures of both enantiomers after they had been pre-trained or not pre-trained on these tasks prior to surgery. In postoperative tests, rats pre-trained on the enantiomer discrimination problems made somewhat fewer errors than those not pre-trained, but experimental rats performed as well as controls (those that had one intact olfactory bulb) within both conditions and on each task. These results indicate that removal of most bulbar sites known to be differentially responsive to carvone enantiomers and the consequent disruption of normal patterns of bulbar input produced in response to carvones are largely without effect on the ability of rats to discriminate between these odors.
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Na(+) currents were recorded using patch-clamp techniques from small-diameter (<25 micrometers) dorsal root ganglion neurons, cultured from adult rats (>150 g). Late Na(+) currents maintained throughout long-duration voltage-clamp steps (>/=200 ms) were of two types: a low-threshold, tetrodotoxin-sensitive (TTX-s) current that was largely blocked by 200 nM TTX, and a high-threshold, TTX-resistant (TTX-r) current. TTX-s late current was found in approximately 28% (10/36) of small-diameter neurons and was recorded only in neurons exhibiting TTX-s transient current. ⋯ We suggest that TTX-s late sodium current results from channel openings different from those generating transient current. As in large-diameter sensory neurons, TTX-s channels generating late openings may play a key role in controlling membrane excitability. In contrast, a single population of high-threshold TTX-r channels may account for both transient and late TTX-r currents.
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The suprachiasmatic nucleus (SCN), the dominant circadian pacemaker in mammalian brain, sends axonal projections to the hypothalamic paraventricular nucleus (PVN), a composite of magno- and parvocellular neurons. This neural network likely offers SCN output neurons a means to entrain diurnal rhythmicity in various autonomic and neuroendocrine functions. Earlier investigations using patch-clamp recordings in slice preparations have suggested differential innervation by SCN efferents to magnocellular versus parvocellular PVN cells. ⋯ At 1 microM where baclofen had no significant postsynaptic effect, evidence of activation of presynaptic GABA(B) receptors included reduction in SCN-evoked IPSCs and EPSCs with no change in their kinetics, and paired-pulse depression that was sensitive to both baclofen and saclofen. Baclofen also induced significant reductions in frequency but not amplitudes of miniature IPSCs and EPSCs. These observations suggest that levels of synaptically released GABA from the terminals of SCN output neurons can influence the relative contribution of pre- versus postsynaptic GABA(B) receptors in modulating both excitatory and inhibitory SCN innervation to parvocellular PVN neurons.
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Alpha subunits of the inhibitory glycine receptor (GlyR) display genetic heterogeneity in mammals and zebrafish. This diversity is increased in mammals by the alternative splicing mechanism. We report here in zebrafish, the characterization of a new alphaZ1 subunit likely arising from alphaZ1 gene by an alternative splice process (alphaZ1L). ⋯ Embryonic and adult alphaZ1 and alphaZ1L mRNA expressions are restricted to the CNS. Embryonic alphaZ1L mRNA anatomical pattern of expression is, however, highly restrained and strictly limited to the rostral part of the brain revealing a highly regionalized function of alphaZ1L in the CNS. This report contributes to the characterization of the diversity of glycine receptor isoforms in zebrafish and emphasizes the common mechanism used among vertebrates for creating GlyR variety and specificity.