OBJECTIVETo investigate the role of GABA A receptor in nikethamide-induced respiratory enhancement in the medullary slices of neonatal rats.

METHODSEx vivo medullary slices of neonatal rats (1 to 3 days old) containing the medial region of the nucleus retrofacialis with the hypoglossal nerve rootlets were prepared and perfused with modified Kreb's solution to record respiration-related rhythmic discharge activity (RRDA) from the hypoglossal nerve rootlets using suction electrodes. Thirty RRDA-positive slices were randomized into 5 equal groups and perfused with nikethamide (at concentrations of 0.5, 1, 3, 5, 7, and 10 microg/ml with the optimal nikethamide concentration determined), GABA (at 10, 20, 40, and 60 micromol/ to determine the optimal concentration), 10 micromol/ bicuculline, 10 micromol/ bicuculline plus 40 micromol/L GABA, and 5 microg/ml nikethamide followed by 5 microg/ml nikethamide plus 10 micromol/ bicuculline after wash out, respectively.

RESULTSNikethamide increased RRDA at the concentrations of 0.5-7 microg/ml, and 5 microg/ml nikethamide showed the most distinct effect on the inspiratory time (TI), integral amplitude (IA), and respiratory cycle (RC). GABA at 40 micromol/ showed the most effective inhibition of RRDA in terms of TI, IA, and RC. Bicuculline at 10 micromol/ could increase the IA, TI and RC, but the combination of 10 micromol/ bicuculline and 40 micromol/ GABA had no significant effects on RRDA. Compared with nikethamide used alone, nikethamide plus bicuculline significantly increased TI and IA without affecting RC.

CONCLUSIONNikethamide can enhance RRDA of the hypoglossal nerve rootlets in the medullary slices of neonatal rats, and the effect can be partially mediated by the GABA A receptor.

Animals ; Animals, Newborn ; Central Nervous System Stimulants ; pharmacology ; Female ; In Vitro Techniques ; Male ; Medulla Oblongata ; physiology ; Nikethamide ; pharmacology ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Receptors, GABA-A ; physiology ; Respiration ; drug effects ; Respiratory Center ; drug effects ; physiology

To investigate the effects of nikethamide on the generation and modulation of rhythmic respiration of neonatal rats and the role of 5-HT(2A) receptor in this course, experiments were performed on the transverse medullary slices of neonatal rats (both sexes, 1-3 d) in vitro. The slices containing the medial region of the nucleus retrofacialis (mNRF) with the hypoglossal nerve rootlets were prepared in which the respiratory-related rhythmic discharge activity (RRDA) was recorded from the hypoglossal nerve rootlets by suction electrode. The possible role of nikethamide on RRDA was investigated by administration of an agonist of 5-HT(2A) receptor, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), and an antagonist of 5-HT(2A) receptor, ketanserine, dissolved in modified Krebos solution (MKS). Thirty slices were randomly divided into five groups: Group 1: the slices were perfused with different concentrations of nikethamide (0.5, 1, 3, 5, 7, 10 μg/mL), and the most effective concentration was selected; Group 2: the slices were perfused with DOI (40 μmol/L); Group 3: the slices were perfused with ketanserine (40 μmol/L); Group 4: the slices were perfused with ketanserine + DOI; Group 5: the slices were perfused with nikethamide, then perfused with nikethamide + ketanserine after washout of nikethamide. Nikethamide increased RRDA in transverse medullary slices at 0.5-7 μg/mL, and 5 μg/mL was the most effective concentration. DOI increased RRDA with prolonged inspiratory time (TI), increased integral amplitude (IA), and shortened respiratory cycle (RC). Ketanserine decreased RRDA with shortened TI, decreased IA and prolonged RC. Ketanserine + DOI had no significant effects on RRDA. The effects of nikethamide on RC and IA were totally and partially reversed by additional application of ketanserine, but the effect of nikethamide on TI was not influenced by ketanserine. It is proposed that nikethamide increases RRDA partly via 5-HT(2A) receptors.
Animals ; Animals, Newborn ; Female ; In Vitro Techniques ; Male ; Medulla Oblongata ; drug effects ; physiology ; Nikethamide ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptor, Serotonin, 5-HT2A ; metabolism ; Respiration ; drug effects ; Respiratory Center ; physiology ; Serotonin