Neuroscience
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Comparative Study
Individual responses to novelty predict qualitative differences in d-amphetamine-induced open field but not reward-related behaviors in rats.
Differences in the locomotor response of rats to a novel environment (high responders [HR] versus low responders [LR]) have been associated with differences in vulnerability to psychostimulants. In the present study we profiled extensively the behavioral repertoire of HR and LR rats (differentiated on the basis of vertical activity) during exposure to a novel environment and in response to d-amphetamine (d-amp; 1.5 mg/kg, i.p.). Moreover, we ascertained whether HR and LR rats differ in the rewarding effects of medial forebrain bundle electrical self-stimulation and in the ability of d-amp to increase the reinforcing efficacy of self-stimulation. ⋯ Additionally, brain stimulation reward thresholds for the two groups were not differentially affected by d-amp. The above results suggest that HR and LR can be further differentiated upon exposure to a novel environment and in response to d-amp. This differentiation is primarily based on qualitative cohorts of their behavioral structure, but not on deviations in the reward processes as assessed by intracranial self-stimulation.
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Cortical gamma oscillations have been associated with neural processes supporting cognition and the state of consciousness but the effect of general anesthesia on gamma oscillations is controversial. Here we studied the concentration-dependent effect of halothane on gamma (20-60 Hz) power of event-related potentials (ERP) in rat primary visual cortex. ERP to light flashes repeated at 5-s intervals was recorded with chronically implanted, bipolar, intracortical electrodes at selected steady-state halothane concentrations between 0 and 2%. gamma-Band power was calculated for 0-1000, 0-300 and 300-1000 ms poststimulus periods and corresponding prestimulus (PS) periods. ⋯ Single-trial gamma power was present also at 300-1000 ms poststimulus, reflecting ERP not phase-locked to the stimulus. In summary, these observations suggest that (1) gamma activity is present in states ranging from waking to deep halothane anesthesia, (2) halothane does not prevent the transfer of visual input to striate cortex even at surgical plane of anesthesia, and (3) anesthetic-induced loss of consciousness, as reflected by the loss of righting reflex, is not correlated with a reduction in gamma power. Variance with other studies may be due to an underestimation of gamma power by ERP signal averaging as compared with single-trial analysis.
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Generation of plateau potentials in spinal motoneurons depends on activation of voltage sensitive L-type Ca(2+) channels. These channels are facilitated by metabotropic receptors known to promote release of Ca(2+) from intracellular stores. The aim of this study is to determine if Ca(2+)-release receptors in the endoplasmic reticulum (ER) that are sensitive to ryanodine (RyRs) and to inositol triphosphate receptors (IP(3)Rs) contribute to the generation of plateau potentials. ⋯ Plateau-related discharge patterns, un-facilitated or facilitated by agonists for group I glutamate metabotropic receptors, muscarine-sensitive cholinergic receptors or L-type Ca(2+) channels were inhibited by blockade of RyRs. In contrast, antagonists of IP(3)Rs or PLC preferentially inhibited plateau-related discharge patterns when facilitated by activation of metabotropic receptors but in only half of the cells when promoted in the absence of metabotropic facilitators. Our findings show that RyRs and IP(3)Rs regulate the generation of plateau potentials in motoneurons and suggest that RyRs may be directly involved with activation of the plateau potential.
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Neurons of the principal nucleus of the bed nuclei of the stria terminalis (BSTp) process pheromonal and viscerosensory stimuli associated with reproduction and relay this information to preoptic and hypothalamic cell groups that regulate reproductive function. The anteroventral periventricular nucleus of the hypothalamus (AVPV), a nucleus involved in the regulation of gonadotropin secretory patterns, receives dense projections from BSTp neurons in males but not in females. ⋯ Treatment of newborn females with testosterone or neonatal orchidectomy of males reversed these sex differences, while GAD65-immunoreactivity in the AVPV was not altered in response to exogenous hormone treatments administered to peripubertal animals. Our results suggest that projections from BSTp neurons constitute a stable, sex-specific GABAergic input to the AVPV that is patterned permanently by perinatal hormone exposure.
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Neurokinins such as substance P and neurokinin A have long been thought to act as neurotransmitters or modulators in the nucleus tractus solitarius. However, the role and location of the receptors for these peptides have remained unclear. We examined the consequences of activation of the neurokinin-1 (NK1) receptor subtype in the rat nucleus tractus solitarius using whole-cell patch clamp recordings in brain slices. ⋯ The increase in GABA release was also shown to be protein kinase C-dependent. The data presented here show NK1 receptors in the rat nucleus tractus solitarius are present both excitatory and inhibitory neurons. Activation of these receptors can result in increases in release of both GABA and glutamate, suggesting a crucial modulatory role for NK1 receptors in the rat nucleus tractus solitarius.