Neuroscience
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The cortical information flow via the perforant path represents a major excitatory projection to the hippocampus. Lesioning this projection leads to massive degeneration and subsequently to reorganization in its termination zones as well as in primary non-affected subfields of the hippocampus. The molecular mechanisms and factors which are involved in the postlesional events are poorly defined. ⋯ In the hippocampus, the control level was reached again at 21 dal, whereas the cortex reached the control level at 10 dal. In comparison, the mRNA transcripts of the receptors CCK(A) and CCK(B) remained unchanged. Since CCK-containing neurons are involved in the modulation of pyramidal and granule cell excitability, our data indicate a time course correlation between CCK mRNA expression and postlesional axonal sprouting response in the hippocampus.
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A large body of evidence suggests that nitric oxide (NO) and ATP act as neurotransmitters in the regulatory mechanisms concerning several autonomic functions at the level of both the hypothalamus and the brain stem. In the present study, we investigated whether neuronal NO synthase containing neurones also express P2X(2) receptor subunit of the ATP-gated ion channel via double-labelling fluorescence immunohistochemistry. Our data demonstrate that a high percentage of neuronal NO synthase-immunoreactive neurones are also P2X(2)-immunoreactive in the rostral ventrolateral medulla (98%) and supraoptic nucleus of the hypothalamus (92%). ⋯ In contrast to the supraoptic nucleus, there was a lower percentage of co-localisation between NO synthase and P2X(2) receptor subunit in the paraventricular nucleus of the hypothalamus. In summary, this study demonstrates for the first time that there is a widespread co-localisation of neuronal NO synthase and P2X(2) receptor subunit in the hypothalamus and brain stem of the rat. Further studies are required to elucidate whether NO and ATP functionally interact within the hypothalamus and the brain stem.
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Comparative Study
Gonadal hormones differentially modulate cocaine-induced conditioned place preference in male and female rats.
There is accumulating evidence that suggests there are sex differences in behavioral and subjective responses to cocaine. However, it is not known whether differences in cocaine reward contribute to sex differences in these responses or whether gonadal hormones affect the rewarding properties of cocaine. In the present study, conditioned place preference (CPP), a measure of non-contingent reward, was used to determine the effects of endogenous gonadal hormones and of estrogen and progesterone replacement on cocaine reward. ⋯ While no effects of castration were observed, ovariectomy decreased levels of dopamine and serotonin in the ventral tegmental area. In females, progesterone replacement increased levels of serotonin and dopamine in the ventral tegmental area, while estrogen plus progesterone replacement increased dopamine levels in the nucleus accumbens. Collectively, these results indicate that ovarian hormones may influence cocaine reward by altering monoaminergic systems, which, in turn, may contribute to the current sex disparities in overall cocaine use.
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Comparative Study
Constant light housing attenuates circadian rhythms of mPer2 mRNA and mPER2 protein expression in the suprachiasmatic nucleus of mice.
Constant light (LL) or constant dark (DD) environmental lighting conditions cause a free-running period and activity reduction in the rodent behavioral circadian rhythm. In order to understand the molecular process underlying behavioral rhythms in LL or DD housing conditions, we examined the circadian profile of mPer2 mRNA and mPER2 in the suprachiasmatic nucleus (SCN), a main oscillator, of free-running mice. The circadian expression rhythm of mPer2 in the SCN was dampened under 7-day LL conditions, whereas that of mPER2 protein was moderately attenuated and its expression peak delayed. ⋯ On the other hand, LL or DD housing did not affect the mPer2 gene and its product in the cerebral cortex. The present results suggest that mPER2 circadian expression in the SCN corresponds well with behavioral circadian oscillation under LL or DD conditions. Thus, the behavioral circadian rhythm seems to correlate with molecular clock works in the SCN.
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Comparative Study
A change in the pattern of activity affects the developmental regression of the Purkinje cell polyinnervation by climbing fibers in the rat cerebellum.
Pattern of activity during development is important for the refinement of the final architecture of the brain. In the cerebellar cortex, the regression from multiple to single climbing fiber innervation of the Purkinje cell occurs during development between postnatal days (P) 5 and 15. However, the regression is hampered by altering in various ways the morpho-functional integrity of the parallel fiber input. ⋯ Thus, a change in the pattern of activity during a narrow developmental period may affect climbing fiber-Purkinje cell synapse competition resulting in occurrence of multiple innervation at least up to 3 months of age. Our results extend the current view on the role of the pattern of activity in the refinement of neuronal connections during development. They suggest that many similar results obtained by different gene or receptor manipulations might be simply the consequence of disrupting the pattern of activity.