Hypothalamic GABAergic influences on treadmill exercise responses in rats.
Microinjection of GABAergic antagonists in the posterior hypothalamus (PH) produces exercise-like adjustments in cardiovascular function. To test the hypothesis that a hypothalamic GABAergic mechanism within the PH modulates the cardiovascular adjustments to dynamic exercise in conscious animals, Sprague-Dawley rats (n = 10) were instrumented with bilateral guide cannula directed at the pH, an arterial cannula, and Doppler flow probes on the iliac and mesenteric arteries. Saline (100 nl) or the GABAA receptor agonist muscimol (125 ng.100 nl-1) was bilaterally injected into the PH during treadmill exercise (20 m.min-1). Microinjection of saline had no effect on mean arterial pressure (MAP), heart rate (HR), mesenteric vascular resistance (MR), or iliac vascular resistance (IR) during exercise. Microinjection of muscimol during exercise produced no significant changes in MAP (mean change +/- SE; +0 +/- 1 mmHg), HR (+17 +/- 12 b.min-1), or MR (+7 +/- 13%). However, microinjection of muscimol produced a significant increase in IR during exercise (16 +/- 6%). In addition, muscimol significantly decreased treadmill run time (saline = 19.6 +/- 0.4 min; muscimol = 17.8 +/- 0.6 min) and produced behavioral effects (including mild sedation) that were most evident after exercise. The results of these experiments suggest that while the posterior hypothalamic GABAergic system may modulate iliac blood flow during exercise in rats, this system does not modulate HR and MR responses to dynamic exercise.
Overton
J M
JM
Department of Nutrition, Food, and Movement Sciences, College of Human Sciences, Florida State University, Tallahassee 32306-4079.
Redding
M W
MW
Yancey
S L
SL
Stremel
R W
RW
D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D001835:Body Weight / Q000502:physiology; D018756:GABA Antagonists; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006439:Hemodynamics / Q000187:drug effects / Q000502:physiology; D007031:Hypothalamus / Q000033:anatomy & histology / Q000502:physiology*; D007034:Hypothalamus, Posterior / Q000033:anatomy & histology / Q000502:physiology; D008297:Male; D009118:Muscimol / Q000494:pharmacology; D005082:Physical Exertion / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D014655:Vascular Resistance / Q000187:drug effects / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D018756:GABA Antagonists; D009118:Muscimol; D005680:gamma-Aminobutyric Acid