Neuroscience
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The α2 adrenergic receptor antagonist yohimbine (YO) is a sympathomimetic drug that crosses the blood-brain barrier after systemic administration. YO promotes increased transmitter release from noradrenergic (NA) axon terminals in the central nucleus of the amygdala (CEA), bed nucleus of the stria terminalis (BST), hypothalamus, and other brain regions implicated in physiological and behavioral responses to stressful and threatening stimuli. YO is potently anxiogenic in humans and experimental animals, including rats. ⋯ The ability of YO to increase anxiety-like behavior in the EPMZ was similarly robust in rats with sham lesions or ipsilateral CEA-algBST lesions. Conversely, YO anxiogenesis in the EPMZ was disrupted in rats with asymmetric lesions designed to bilaterally disconnect the CEA and algBST, whereas neither unilateral nor bilateral disconnecting lesions altered EPMZ behavior in rats after i.p. saline. We conclude that the anxiogenic effects of increased NA signaling in rats after YO require direct CEA-algBST interactions that do not shape EPMZ behavior under baseline conditions.
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Beside its role in development and maturation of synapses, brain-derived neurotrophic factor (BDNF) is suggested to play a critical role in modulation and plasticity of glutamatergic as well as GABAergic synaptic transmission. Here, we used heterozygous BDNF knockout (BDNF(+/-)) mice, which chronically lack approximately 50% of BDNF of wildtype (WT) animals, to investigate the role of BDNF in regulating synaptic transmission in the ventrobasal complex (VB) of the thalamus. Excitatory transmission was characterized at glutamatergic synapses onto relay (TC) neurons of the VB and intrathalamic inhibitory transmission was characterized at GABAergic synapses between neurons of the reticular thalamic nucleus (RTN) and TC neurons. ⋯ However, the glutamatergic drive onto RTN neurons, as revealed by the percentage reduction in frequency of sIPSCs after application of AMPA and NMDA receptor blockers, was not significantly different. Together, the present findings suggest that a chronically reduced level of BDNF to ∼50% of WT levels in heterozygous knock-out animals, strongly attenuates glutamatergic and GABAergic synaptic transmission in thalamic circuits. We hypothesize that this impairment of excitatory and inhibitory transmission may have profound consequences for the generation of rhythmical activity in the thalamocortical network.
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According to the simulation theory, the internal simulation of a movement (imagined movement, IM) and its execution (actual movement, AM) are based on the same motor representations. The brain uses these representations for controlling action. The specific objective of this study was to investigate the updating process of internal models of action in adults, through massive environmental changes involved by microgravity (0G). 0G has multiple effects on motor control, including short-term adaptations with respect to the planification and performance of actions. ⋯ Furthermore, IM durations in 0G were similar to the 1G value. These results show that although the planification and execution of action were immediately adapted to the 0G condition, the storage of afferent information was inadequate to recalibrate the predictive model. These results suggest that sudden change in gravity was not considered for updating internal models of action, and that forward model probably required more practice in order to integrate the modification of the sensorial feedback generated by the new environmental constraints.
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The Drosophila melanogaster gustatory system consists of several neuronal pathways representing diverse taste modalities. The two predominant modalities are a sweet-sensing pathway that mediates attraction, and a bitter-sensing pathway that mediates avoidance. A central question is how flies integrate stimuli from these pathways and generate the appropriate behavioral response. ⋯ Spatially restricted stimulation indicates that the conditioning stimulus is indeed a signal from the bitter neurons in the proboscis and it is independent of postingestive feedback. The coincidence of temporally specific activation of bitter-sensing neurons with fructose presentation is crucial for memory formation, establishing aversive taste learning in Drosophila as associative learning. Taken together, this optogenetic system provides a powerful new tool for interrogation of the central brain circuits that mediate memory formation.