Neuroscience
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The present study intended to investigate the involvement of dopaminergic and glutamatergic systems of the basolateral amygdala in amnesia induced by the stimulation of dorsal hippocampal cannabinoid receptors in male Wistar rats. The animals were stereotaxically implanted with guide cannulas in the CA1 region of the dorsal hippocampus and basolateral amygdala (BLA), trained in a step-through type passive avoidance task, and tested 24 h after training to measure memory retrieval. Post-training intra-CA1 microinjection of the nonselective CB1/CB2 receptor agonist WIN55,212-2 (WIN) (0.1-0.5 μg/rat) dose-dependently induced amnesia. ⋯ Furthermore, the inhibitory effect of 0.5 μg/rat of intra-CA1 microinjection of WIN on memory formation was significantly decreased by pre-treatment with intra-BLA microinjection of the NMDA receptor antagonist d-2-amino-5-phosphonopentanoic acid (d-AP5; 0.1 and 0.5 μg/rat, intra-BLA). Intra-BLA microinjection of the same doses of NMDA or d-AP5 by itself did not induce any response on memory retrieval. Taken together, these findings support the existence of a functional interaction between dorsal hippocampal and basolateral amygdaloid neural circuits during processing cannabinoid-induced amnesia.
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Hypoxic respiratory and cardiovascular responses in mammals are mediated by peripheral chemoreceptor afferents which are relayed centrally via the solitary tract nucleus (NTS) in dorsomedial medulla to other cardiorespiratory-related brainstem regions such as ventrolateral medulla (VLM). Here, we test the hypothesis that peripheral chemoafferents could also be relayed directly to the Kölliker-Fuse/parabrachial complex in dorsolateral pons, an area traditionally thought to subserve pneumotaxic and cardiovascular regulation. Experiments were performed on adult Sprague-Dawley rats. ⋯ Extracellular recordings from the commissural and medial NTS subnuclei revealed that some hypoxia-excited NTS neurons could be antidromically activated by electrical stimulations at the dorsolateral pons. These findings demonstrate that hypoxia-activated afferent inputs are relayed to the Kölliker-Fuse/parabrachial complex directly via the commissural and medial NTS and indirectly via the ventrolateral NTS subnucleus, VLM and A5 region. These pontine-projecting peripheral chemoafferent inputs may play an important role in the modulation of cardiorespiratory regulation by dorsolateral pons.
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While the basic pathways mediating vestibulo-ocular, -spinal, and -collic reflexes have been described in detail, little is known about vestibular projections to central autonomic sites. Previous studies have primarily focused on projections from the caudal vestibular region to solitary, vagal and parabrachial nuclei, but have noted a sparse innervation of the ventrolateral medulla. Since a direct pathway from the vestibular nuclei to the rostral ventrolateral medulla would provide a morphological substrate for rapid modifications in blood pressure, heart rate and respiration with changes in posture and locomotion, the present study examined anatomical evidence for this pathway using anterograde and retrograde tract tracing and immunofluorescence detection in brainstem sections of the rat medulla. ⋯ In the rostral ventrolateral medulla, these processes are highly branched and extremely varicose, primarily directed toward the somata and proximal dendrites of non-catecholaminergic neurons, with minor projections to the distal dendrites of catecholaminergic cells. In the caudal ventrolateral medulla, the axons of vestibular nucleus neurons are more modestly branched with fewer varicosities, and their endings are contiguous with both the perikarya and dendrites of catecholamine-containing neurons. These data suggest that vestibular neurons preferentially target the rostral ventrolateral medulla, and can thereby provide a morphological basis for a short latency vestibulo-sympathetic pathway.
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Compensated respiratory acidosis has been observed in a significant number of patients with active vestibular disease. We therefore hypothesized that the inner ear may play an unrecognized integral role in respiratory control. To test this premise, we investigated whether mice with induced inner ear injury demonstrated any alteration in their respiratory response to inhaled carbon dioxide (CO(2)). ⋯ Inner ear damage significantly reduces the respiratory response to CO(2) inhalation. In addition to the established role of the inner ear organ in hearing and balance, this alludes to an unidentified function of the inner ear and its interconnecting neuronal pathways in respiratory regulation. This finding may offer valuable new clues for disease states with abnormal respiratory control where inner ear dysfunction may be present.
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It is unclear how haptic touch with a stable surface reduces postural sway. We hypothesized that haptic input enhances postural stability due to alterations in axial postural tone. We measured the influence of heavy and light touch (LT) of the hands on a stable bar on axial postural tone and postural sway during stance in 14 healthy adults. ⋯ This is the first study showing that axial postural tone can be modified by remote somatosensory input and provides a potential explanation for how light touch improves postural stability. Changes in subjects' perception from trunk to surface rotation when changing from no touch (NT) to haptic touch, suggests that the CNS changes from using a global, to a local, trunk reference frame for control of posture during touch. The increase of hip postural tone during touching and gripping can be explained as a suppression of hip muscle shortening reactions that normally assist axial rotation.