Facilitation of baroreflex-induced bradycardia by stimulation of specific hypothalamic sites in the rat

B. J. Pardini, K. P. Patel, P. G. Schmid, D. D. Lund

Research output: Contribution to journalArticle

8 Scopus citations

Abstract

Hypothalamic stimulation generally inhibits baroreflex-induced bradycardia. However, we have noted discrete areas of the rat hypothalamus which facilitate reflex bradycardia. The effects of hypothalamic stimulation on baroreflex-induced changes in heart rate were investigated in urethane-anesthetized rats (1.2 g/kg, i.p.; n = 6) instrumented with femoral arterial and venous catheters. Bipolar electrodes (250 μm diameter) were implanted stereotaxically in the hypothalamus. Baroreflex-induced bradycardia was elicited by phenylephrine (PE) injection (8-20 μg/kg). Responses to stimulation (STIM) (50-150 μA, 80 Hz, 0.5 ms), PE, and Stim + PE were studied for 1 min. In the ventral medial and anterior hypothalamus. STIM caused transient increases in blood pressure and no changes in heart rate. Peak blood pressure was lower during STIM + PE than during PE (144 ± 5 vs 164 ± 3 mm Hg; P < 0.05). However, STIM + PE resulted in a lower heart rate compared to PE (194 ± 22 vs 270 ± 17 bpm; P < 0.05). At 1 min, the heart rate in STIM + PE rats remained lower than in PE rats (205 ± 37 vs 319 ± 16 bpm; P < 0.05). Atropine administration indicated that the facilitation was primarily parasympathetic in nature. These results identify specific hypothalamic regions which facilitate baroreflex-induced bradycardia by parasympathetic mechanisms.

Original languageEnglish (US)
Pages (from-to)274-281
Number of pages8
JournalBrain Research
Volume384
Issue number2
DOIs
StatePublished - Oct 8 1986

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Keywords

  • Anterior hypothalamic area
  • Baroreflex
  • Heart rate
  • Parasympathetic nervous system
  • Ventromedial nucleus of the hypothalamus

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Clinical Neurology
  • Developmental Biology

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