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Influence of GABAergic mechanisms on baroreceptor inputs to nucleus tractus solitarii of rats.
No full textThe firing frequency of baroreceptive neurons in the nucleus tractus solitarii (NTS) during microiontophoretic application of muscimol, a γ- aminobutyric acid (GABA)(A) agonist, or baclofen, a GABA(B) agonist, was monitored in anesthetized rats. Muscimol decreased the spontaneous discharge of 69 of 73 (94.5%) NTS baroreceptive neurons without affecting the remaining four neurons (5.5%). The statistical comparison on a bin-by-bin basis of the peri-R wave interval histograms of the discharge of each NTS neuron showed that the inhibitory action of muscimol was always exerted on the whole neuronal discharge independently of its correlation to the cardiac cycle. Baclofen inhibited 60 of 73 (82.2%) NTS neurons without affecting the remaining 13 neurons (17.8%). In 31 of 60 (51.7%) neurons inhibited by baclofen, this substance significantly affected only pulse-synchronous peaks of neuronal discharge without significant inhibition of the neuronal firing between cardiac cycle-related peaks. Fifty-eight of 73 (79.5%) NTS neurons studied were inhibited by both muscimol and baclofen, 11 neurons (15%) only by muscimol, 2 neurons (2.7%) only by baclofen, and 2 neurons (2.7%) were unaffected by both substances. These results demonstrate that both GABA(A) and GABA(B) receptors mediate inhibition of the spontaneous discharge in the great majority of the NTS baroreceptive neurons studied and suggest different functions of the two types of GABA receptors in influencing baroreceptor inputs to the NT
The role of ANF in functional properties of the central pathways of cardiovascular reflexes
No full textSevere insulin resistance does not associate with hypertension in the young homozigote Zucker rat
No full textEnhanced sympathetic reactivity associates with insulin resistance in the young zucker rat
No full textThe direct effect of insulin on barosensitive neurones in the nucleus tractus solitarii of rats
No full textThe present investigation was designed to determine the direct effect of insulin on the spontaneous discharge of barosensitive neurones in the nucleus tractus solitarii (NTS) of rats anaesthetized with urethane. Microinjection of 20 nl insulin (10 IU/ml) into NTS decreased the spontaneous discharge of 38 of the 52 units studied (73.1%), and this decrease was augmented by increasing the concentration to 40 IU/ml. Microinjections of insulin vehicle, glucose, hydralazine or phenylephrine did not elicit significant changes in the spontaneous discharge of NTS barosensitive neurones. These results demonstrate that insulin inhibits the spontaneous discharge of barosensitive NTS neurones. They suggest that insulin increases sympathetic nervous activity via a central neural mechanism and may play a role in the modulation of cardiovascular information within the NTS
Actions of 3 alpha,5 alpha-tetrahydrodeoxycorticosterone on single neurones of the mesencephalic reticular formation in the rat
No full textThe effects of microinjections of 3 alpha,5 alpha-tetrahydrodeoxycorticosterone (3 alpha-THDOC) on single neurones of the mesencephalic reticular formation (MRF) were investigated in rats anaesthetized with urethan. Microinjections of approximately 100 nl of 0.5-2 microM 3 alpha-THDOC inhibited firing of 105 of 112 neurones (94%). Microinjections of approximately 100 nl of 100-250 nM of 3 alpha-THDOC did not alter neuronal activity, but in 52 of 68 cases (76%) it potentiated the inhibitory action of microiontophoretically applied gamma-aminobutyric acid (GABA). The 3 beta-isomer of tetrahydrodeoxycorticosterone did not elicit any changes in neuronal firing. The effects of 3 alpha-THDOC were reversibly antagonized by microiontophoretically applied bicuculline. This 'in vivo' study supports the hypothesis that 3 alpha-THDOC may function as endogenous modulator of GABAA-mediated inhibition in various physiopathological condition
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