[5-HT(1A) receptors are involved in the modulation of respiratory rhythmical discharge activity in the medulla oblongata slice preparation of neonatal rats].

The present study was carried out to determine the role of 5-HT(1A) receptors in the generation and modulation of basic respiratory rhythm. Neonatal (aged 0-3 d) Sprague-Dawley rats of either sex were used. The medulla oblongata slice was prepared and the surgical procedure was performed in the modified Kreb's solution (MKS) with continuous carbogen (95% O2 and 5% CO2), and ended in 3 min. In cold MKS, a 600-700 microm single transverse slice was cut, which was rostral to the edge of area postrema and retained the hypoglossal nerve roots and some parts of the ventral respiratory group. The preparation was quickly transferred to a recording chamber and continuously perfused with carbogen-saturated MKS at a rate of 4-6 mL/min at 27-29 degrees C. Glass adsorb-electrodes containing Ag-AgCl needle were attached to the ventral roots of the hypoglossal nerve. Respiratory rhythmical discharge activity (RRDA) of the rootlets of hypoglossal nerve was recorded. Ten medulla oblongata slice preparations were divided into two groups. In group I, 5-HT(1A) receptor specific agonist (+/-)-8-hydroxy-2-(di-N-propylamino)tetralin hydrobromide (8-OHDPAT, 20 micromol/L) was added into the perfusion solution for 10 min first, after washing out, the 5-HT(1A) antagonist [4-iodo-N-[2-[4-methoxyphenyl]-1-piperazinyl]ethyl]-N-2-pyridynyl-benzamide hydrochloride] (PMPPI, 10 micromol/L) was applied to the perfusion solution for 10 min. In group II, after application of 8-OHDPAT for 10 min, additional PMPPI was added into the perfusion solution for 10 min. The discharges of the rootlets of hypoglossal nerve were recorded. Signals were amplified and band-pass filtered (100-3.3 kHz). Data were sampled (1-10 kHz) and stored in the computer via BL-420 biological signal processing system. Our results showed that 8-OHDPAT increased the respiratory cycle (RC) and expiratory time (TE) as well as reduced the integral amplitude (IA), but the changes of the inspiratory time (TI) were not statistically significant. PMPPI induced a significant decrease in RC, TE and TI, but the changes of IA were not statistically significant. The effect of 8-OHDPAT on the respiratory rhythm was partially reversed by additional application of PMPPI. Taken together with previous results, 5-HT(1A) receptors may play an important role in the modulation of RRDA in the medulla oblongata slice preparation of neonatal rats.