Neuroscience
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Comparative Study
Urocortin expression in the Edinger-Westphal nucleus is down-regulated in transgenic mice over-expressing neuronal corticotropin-releasing factor.
In recent years a large body of evidence has emerged linking chronic stress with increased vulnerability for depression and anxiety disorders. As corticotropin-releasing factor (CRF) is hypersecreted under these psychological conditions, we used our CRF-overexpressing (CRF-OE) mouse line to study underlying brain mechanisms possibly causing these disorders. Urocortin (Ucn), a recently discovered member of the CRF peptide family may play a role in the pathophysiology of stress-induced disorders. ⋯ Our results support this hypothesis as we found weaker immunohistochemical labeling with anti-Ucn and a six times weaker Ucn mRNA signal in E-WN in CRF-OE mice. Moreover, E-WN Ucn-expressing neurons mounted a response to acute challenge in CRF-OE mice too. From these results it is concluded that the CRF and E-WN Ucn neuronal systems work in concert in response to acute challenges, but are inversely regulated in their activities during chronic hyperactivity of the hypothalamo-pituitary-adrenal axis.
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The cortical regions surrounding the suprasylvian sulcus have previously been associated with motion processing. Of the six areas originally described by Palmer et al. [J Comp Neurol 177 (1978) 237], the posteromedial lateral suprasylvian (PMLS) cortex has attracted the greatest attention. Very little physiological information is available concerning other suprasylvian visual areas, and in particular, the anteromedial lateral suprasylvian cortex (AMLS). ⋯ Finally, 45% of 20 neurons were direction selective to a radial optic flow stimulus. Overall, these results suggest that AMLS cortex is involved in higher-order analyses of visual motion. It is possible that the AMLS cortex represents a region between PMLS and the anterior ectosylvian visual area in a functional hierarchy of areas involved in motion integration.
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Using intracellular recording, we studied how several muscarinic antagonists affected the evoked endplate potentials in singly and dually innervated endplates of the levator auris longus muscle from 3 to 6-day-old rats. In dually innervated fibers, a second endplate potential (EPP) may appear after the first one when we increase the stimulation intensity. The lowest and highest EPP amplitudes are designated "small-EPP" and "large-EPP," respectively. ⋯ We observed a graded change from a multichannel involvement (P/Q- N- and L-type voltage-dependent calcium channels) of all muscarinic responses (M1-, M2- and M4-mediated) in the small-EPP to the single channel (P/Q-type) involvement of the M1 and M2 responses in the singly innervated endplates. This indicates the existence of a progressive calcium channels shutoff in parallel with the specialization of the adult type P/Q channel. In conclusion, muscarinic autoreceptors can directly modulate large-EPP generating ending potentiation, and small-EPP generating ending depression through their association with the calcium channels during development.
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Recent in vivo electrophysiological studies suggest that chronic dopamine depletion alters profoundly the firing pattern of basal ganglia neurons. These changes may disrupt the processing of cortical information flow from the striatum to the output nuclei, and presumably underlie the clinical manifestations of Parkinson's disease. We have recently reported that chronic nigrostriatal lesions induce changes in the functional state of striatal medium-spiny neurons (MSNs) that could facilitate spreading of cortical synchronous activity (approximately 1 Hz) to striatal target nuclei. ⋯ Following systemic administration of SKF38393 or SKF81279 the membrane potential of striatal MSNs was upheld into a more hyperpolarized value and action potential firing probability decreased. D1 agonists also increased the latency to the cortically driven plateau depolarization and reduced the peak potential of the short latency depolarizing postsynaptic response to a more hyperpolarized value. The present study provides in vivo evidence indicating that pharmacological stimulation of D1-class dopamine receptors can modulate the flow of cortical information through the striatum in the parkinsonian state.
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While the acute physiological effects of brain-derived neurotrophic factor (BDNF) have been well demonstrated, little is known regarding possible morphological effects that occur within a short period of time. The acute effects of BDNF on dendritic spine morphology were examined in granule cells in cultured main olfactory bulb slices. Organotypic slices prepared from 7-day-old rats were cultured for 1 day, and BDNF was applied at varying time points prior to fixation. ⋯ The changes became detectable as early as 30 min when 50 ng of BDNF was applied. The pretreatment with tetanus toxin or an N-methyl-D-aspartate receptor antagonist abolished the acute effects of BDNF on spine morphology. These results indicate that BDNF can alter spine morphology within a shorter period of time than previously observed and that the effects are mediated by enhanced glutamatergic signaling.