Neuroscience
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Comparative Study
The role of the rat prelimbic/infralimbic cortex in working memory: not involved in the short-term maintenance but in monitoring and processing functions.
Contrary to human and primate, working memory in the rodent is usually considered as a simple short term memory buffer and mainly investigated using delayed response paradigms. The aim of the present study was to further investigate the role of the rat prelimbic/infralimbic cortex in different spatial delayed tasks in order to dissociate its involvement in temporary storage from other information processes, such as behavioral flexibility and attention. In experiment 1 rats were trained in a standard elimination win-shift task in a radial-arm maze after which a 1-min delay was inserted mid trial. ⋯ The present findings indicate that prelimbic/infralimbic cortex is not directly involved in the short term maintenance of specific information but is implicated when changes, such as sudden introduction of a delay or exposure to unexpected interfering events, alter the initial situation. It appears that working memory in rodents should be considered, as in humans and primates, to encompass both storage and monitoring functions. The present results along with previous ones strongly suggest that prelimbic/infralimbic cortex is not involved in the temporary on-line storage but rather in the control of information required to prospectively organize the ongoing action.
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Comparative Study
Unique presynaptic and postsynaptic roles of Group II metabotropic glutamate receptors in the modulation of thalamic network activity.
The thalamic reticular nucleus (TRN) is a sheet of GABAergic neurons that project to other TRN neurons and to associated thalamocortical relay nuclei. The TRN receives glutamatergic synaptic inputs from cortex as well as reciprocal inputs from the collaterals of thalamocortical neurons. In addition to ionotropic glutamate receptors, metabotropic glutamate receptors (mGluRs) are present in the TRN circuitry. ⋯ Because strong corticothalamic activation is implicated in abnormal thalamic rhythms, we used extracellular recordings in the lateral geniculate nucleus to study the effect of Group II mGluR agonists upon these slow oscillations. We induced approximately 3 Hz spike-and-wave discharge activity through corticothalamic stimulation, and found that such activity was reduced in the presence of the Group II mGluR agonist, (-)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY379268). These data indicate that Group II mGluR reduce the impact of corticothalamic excitation, and that they may be a useful target in the reduction of absence-like rhythms.
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Comparative Study
Selective mechanisms for complex visual patterns revealed by adaptation.
A great deal is known about the initial steps of visual processing. We know that humans have neural mechanisms selectively tuned to simple patterns of particular spatial frequencies and orientations. ⋯ Very little is known about intermediate levels of visual processing, where early visual signals are presumably combined to represent increasingly complex visual features. Here we show the existence of visual mechanisms in humans, tuned and selective to particular combinations of simple sinusoidal patterns, using a novel method of compound adaptation.
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Comparative Study
Gene expression in the rat cerebral cortex: comparison of recovery sleep and hypnotic-induced sleep.
Most hypnotic medications currently on the market target some aspect of GABAergic neurotransmission. Although all such compounds increase sleep, these drugs differentially affect the activity of the cerebral cortex as measured by the electroencephalogram. Whereas benzodiazepine medications such as triazolam tend to suppress slow wave activity in the cortex, the GABA(B) ligand gamma-hydroxybutyrate greatly enhances slow wave activity and the non-benzodiazepine, zolpidem, which binds to the omega1 site on the GABA(A) receptor/Cl(-) ionophore complex, is intermediate in this regard. ⋯ We find that, although each drug increases the expression of a subset of genes in the panel of biomarkers, no drug fully replicates the molecular changes in the cortex associated with recovery sleep. Furthermore, high levels of slow wave activity in the cortex are correlated with increased expression of fra-2 whereas the expression of grp94 is correlated with body temperature. These results demonstrate that sleep-related changes in gene expression may be affected by physiological covariates of sleep and wakefulness rather than by vigilance state per se.
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Olvanil ((N-vanillyl)-9-oleamide), a non-pungent transient receptor potential vanilloid type 1 agonist, desensitizes nociceptors and alleviates pain. But its molecular targets and signaling mechanisms are little known. Calcium influx through voltage-activated Ca(2+) channels plays an important role in neurotransmitter release and synaptic transmission. ⋯ In addition, double immunofluorescence labeling revealed that olvanil induced a rapid internalization of Ca(V)2.2 immunoreactivity from the membrane surface of dorsal root ganglion neurons. Collectively, this study suggests that stimulation of non-pungent transient receptor potential vanilloid type 1 inhibits voltage-activated Ca(2+) channels through a biochemical pathway involving intracellular Ca(2+)-calmodulin and calcineurin in nociceptive neurons. This new information is important for our understanding of the signaling mechanisms of desensitization of nociceptors by transient receptor potential vanilloid type 1 analogues and the feedback regulation of intracellular Ca(2+) and voltage-activated Ca(2+) channels in nociceptive sensory neurons.