Brain research
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(1) In chloralose anesthetized dogs, effects of the left and the right atrial stretch were studied in the same animal. Stretch of the sino-atrial region of the right atrium produced acceleration of the heart rate during, and reversal of response at the termination of, the stretch. Stretch of the left pulmonary vein-atrial junctional region evoked an initial decrease followed by an increase in heart rate. ⋯ Vagal activity which was greatly augmented by sinus distension was decreased by atrial stretch, while previously inhibited sympathetic activity due to sinus distension was augmented by stretch of the atrium. The effect of stretch on vagal activity seems to depend to a degree on the prestimulus level. It is of interest that the powerful baroreceptor reflexes do not mask the cardiac reflexes studied. (6) The relative importance of sympathetic and vagal efferents to atrial stretch reflexes was discussed.
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Changes in the activity and amount of the neurotransmitter synthesizing enzyme tyrosine hydroxylase (TH) were measured in dopaminergic (DA) neurons of the A10-mesolimbic system of the rat following electrolytic lesions of their axons. Unilateral hypothalamic lesions in close proximity to the cell bodies resulted, within 24--48 h, in a permanent anterograde reduction of TH to 10--20% of control in the ipsilateral olfactory tubercle and nucleus accumbens. The retrograde reaction in the A10-DA nerve cell bodies was characterized by an initial increase in TH activity to 133% by 24--48 h followed by a gradual and permanent fall to 50% of control by day 14 due to retrograde cell death of DA neurons. ⋯ The reduction in TH activity in the A10 was demonstrated by immunochemical titration with a specific antibody to TH to be entirely due to reduced amounts of enzyme protein. We conclude that in mesolimbic DA neurons; (a) the anterograde reaction is characterized by a rapid and permanent decline of TH in degenerating terminals; (b) the retrograde reaction is dependent upon the proximity of the lesion to the nerve cell body, and (c) a reversible reduced accumulation of TH characterizes the retrograde reaction in response to lesions of distal axons. The reaction of DA neurons of the mesolimbic system to axonal injury is comparable to that of the nigrostriatal system.
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The effect of cerebellar lesions upon the pupillary light reflex was examined in anesthetized cats. The pupillary response elicited by a step and sinusoidally modulated light stimulus was used. In acute cerebellectomized cats, the high frequency cutoff of the frequency response of the pupillary reflex was moved to a lower level after cerebellar lesions. ⋯ The fastigial lesions produced the most prominent change in the frequency responses. Electrical stimulation of the deep cerebellar nuclei, especially the fastigial nuclei, induced pupillary dilatation. Thus the cerebellum appears to participate in the control of the pupillary light reflex by improving the frequency responses of the pupil so that it can follow changing light stimuli better, and this control is exerted via the bilateral fastigial nuclei.