Changes in serotoninergic receptors 1A and 2A in the piglet brainstem after intermittent hypercapnic hypoxia (IHH) and nicotine

Abstract We studied the effects of intermittent hypercapnic hypoxia (IHH) and/or nicotine on the immunoreactivity of serotoninergic (5-HT) receptors 1A and 2A in the piglet brainstem. These exposures were developed to mimic two common risk factors for Sudden Infant Death Syndrome (SIDS); prone sleeping (IHH) and cigarette smoke exposure (nicotine). Immunoreactivity for 5-HT 1A R and 5-HT 2A R were studied in four nuclei of the caudal medulla. Three exposure groups were compared to controls ( n  = 14): IHH ( n  = 10), nicotine ( n  = 14), and nicotine + IHH ( n  = 14). In control piglets, the immunoreactivity of 5-HT 1A R was highest in the hypoglossal nucleus (XII), followed by inferior olivary nucleus (ION), nucleus of the solitary tract (NTS) and dorsal motor nucleus of the vagus (DMNV), whereas for 5-HT 2A R, the immunoreactivity was highest in DMNV/NTS and then ION. Compared to controls, IHH reduced 5-HT 1A R immunoreactivity in all studied nuclei ( p 2A R immunoreactivity. Nicotine reduced 5-HT 1A R immunoreactivity in the DMNV, ION and NTS ( p 2A R immunoreactivity in DMNV/NTS ( p 1A R in DMNV, ION and NTS ( p 2A R immunoreactivity. Effects of nicotine on the DMNV were more significant in males compared to the females. These results show for the first time that IHH and/or nicotine can reduce 5-HT receptor immunoreactivity within functionally important nuclei of the piglet medulla. The findings support our hypothesis that 5-HT receptor abnormalities may be caused by postnatal exposures to clinically-relevant stimuli such as cigarette smoke exposure and/or prone sleeping.