Presumed apoptosis and reduced arcuate nucleus neuropeptide Y and pro-opiomelanocortin mRNA in non-coma hypoglycemia

Hypoglycemia reduces sympathoadrenal responses to subsequent hypoglycemic bouts by an unknown mechanism. To assess whether such hypoglycemia-associated autonomic failure is due to actual brain damage, male Sprague-Dawley rats underwent 1-h bouts of insulin-induced (5 U/kg i.v.) hypoglycemia (1.6-2.8 mmol/l) 1 or 3 times on alternate days. Bats remained alert and were rescued with intravenous glucose at 60-80 min. Plasma epinephrine and corticosterone responses were significantly reduced during the second and third bouts. Brains from these rats were processed by the terminal transferase-mediated deoxyuridine triphosphate-biotin nick end-labeling (TUNEL) procedure as an index of apoptotic cell death at 24, 48, or 96 h after their first bout. At 48 h, but not 24 h, TUNEL+ cells were consistently seen only in the arcuate nucleus (arcuate hypothalamic nucleus [ARC]), Hypoglycemic rats had 188% more apoptotic ARC cells (1 bout 39 +/- 5; 3 bouts 37 +/- 4) than euglycemic controls (13 +/- 3; P = 0.001). In situ hybridization for neuropeptide Y (NPY) and proopiomelanocortin (POMC) mRNA mas performed in sections of ARC containing maximal numbers of apoptotic cells as well as in other fresh frozen brains. After 1 bout, NPP (0.041 +/- 0.003) and POMC (0.119 +/- 0.022) mRNA were decreased, respectively, by 52 and 55% vs. controls (NPY 0.076 +/- 0.007; POMC 0.222 +/- 0.030; P = 0.01). NPT (0.029 +/- 0.002) but not POMC (0.093 +/- 0.013) fell 29% further after a third bout. NPY (r = -0.721; P = 0.001) and POMC (r = -0.756; P = 0.001) mRNA levels correlated negatively with the number of apoptotic ARC cells in the same sections, Thus, non-coma hypoglycemia produces apparent apoptotic cell death with reduced NPY and POMC expression selectively in the ARC. This may contribute to the reduced counterregulatory response following repeated bouts of hypoglycemia.