The role of sympathetic arousal in discrimination of insulin-produced hypoglycemia.
Hypoglycemia, as produced by insulin administration, elicits counter-regulatory processes including sympathetic nervous system arousal. Humans report that these autonomic responses are salient cues in the recognition of hypoglycemia. The role of these autonomic responses in the recognition of the hypoglycemic state by rats was investigated in this experiment. Nine rats were trained to discriminate the normal state of euglycemia from the hypoglycemia produced by the injection of 2 units/kg insulin, which caused a reduction in blood glucose levels to 66-77% of baseline values. A 'drug discrimination' procedure was used with a food-motivated operant. After extensive training, reliable hypoglycemia discrimination was established, in that the mean percentage of total test-period responses on the 'hypoglycemia' lever was 78% after insulin treatment, compared to 16% after water injection. Tests were then conducted after the injection of epinephrine (and no insulin), and after the injection of insulin plus propranolol, with the intention of eliciting sympathetic activity during euglycemia, and blocking sympathetic responses during hypoglycemia. These manipulations failed to simulate or to block the hypoglycemia cue, with the insulin or non-insulin operant response choice being essentially unchanged. These results indicate that in rats beta-adrenergic sympathetic responses are not critical for the recognition of hypoglycemia. Appropriate discriminative responses were apparently made on the basis of the impairment by hypoglycemia of central nervous system (CNS) function ('neuroglycopenic' effects), although a role for cholinergic activity of the sympathetic nervous system cannot be ruled out.
Duncan
P M
PM
Psychology Department, Old Dominion University, Norfolk, VA 23529-0267, USA.
Hooker
E P
EP
D000322:Adrenergic Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D003463:Cues; D004192:Discrimination, Psychological / Q000187:drug effects / Q000502:physiology*; D004837:Epinephrine / Q000494:pharmacology; D007003:Hypoglycemia / Q000139:chemically induced / Q000503:physiopathology*; D007328:Insulin; D008297:Male; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D020318:Rats, Long-Evans; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*
D000322:Adrenergic Agonists; D000319:Adrenergic beta-Antagonists; D007328:Insulin; D011433:Propranolol; D004837:Epinephrine