Alterations in respiratory behavior, brain neurochemistry and receptor density induced by pharmacologic suppression of sleep in the neonatal period

Abstract

The present study examined if drug suppression of active sleep (AS) in the neonate affected the development and expression of respiratory behavior. Secondly, we assessed brain neurochemistry and receptor density in specific supra-medullary brain regions to identify coincident biochemical alterations. Sprague–Dawley newborn rat pups were randomized and divided among six rat mothers ( n=10/mother/group), each mother housed separately. Two untreated control (UC) groups received either no interventions or were fed milk vehicle twice daily and were handled similarly to the drug intervention animals. Pharmacological disruption of sleep was achieved by administration (2 groups of each) of either clonidine (CLO) 100 μm/kg, or scopolamine (SCO) 800 μm/kg, given orally twice daily for the first 7 days of life. On postnatal (P) days P10 and P19 of life, pups were assessed for metabolism, minute ventilation ( V E), tidal volume ( V t) and frequency ( f). On P21 (14 days after the end of drug exposure), pups from each condition were sacrificed and punch biopsies of the frontal cortex, hypothalamus, and hippocampus were examined for hydroxytryptophan (5-HT), and norepinepherine (NE) by HPLC. An equal number of pups were sacrificed and brains examined for muscarinic acetylcholine (mAch), α 2-adrenergic and I 1-imidazoline receptor density. Results: Both CLO and SCO exposed animals had a lower V t and respiratory quotient than UC animals ( p<0.01). CLO animals exhibited a higher f ( p<0.01) and both CLO and SCO exhibited a lower V t ( p<0.05) than the UC groups; V E was reduced in the SCO groups, compared with CLO and UC groups ( p<0.01). Pattern of breathing in response to brief hypoxia exposure was altered for CLO and SCO. The normal decline in V E during sleep was not observed in CLO rats. Both drug exposures resulted in a comparable reduction in hypothalamic NE and 5-HT levels ( p<0.05), while in the frontal cortex, and the hippocampus variable changes in NE and 5-HT, occurred. In CLO and SCO rats mAch receptors were increased in cortex, and reduced in hypothalamus; I 1-imidazoline receptors were increased in hypothalamus and decreased in hippocampus ( p<0.05 for each). In contrast, α 2-adrenergic receptors were increased in cortex for both CLO and SCO, decreased in hypothalamus for CLO, and decreased in hippocampus for SCO ( p<0.05 for each). Conclusions: these data show that drug-induced neonatal sleep suppression will alter ventilatory pattern, metabolism, and site-specific concentrations of adrenergic neurotransmitters and in receptor density, perhaps as a result of suppression of neonatal AS.