EFFECTS OF INTRACISTERNAL MONOAMINES ON BREATHING MOVEMENTS IN FETAL SHEEP

The effects of intracisternal administration of tyramine on fetal brea thing movements (FBM), electrocortical (ECoG) and nuchal muscle activi ties, and cerebrospinal fluid (CSF) monoamine concentrations have been studied in unanesthetized fetal sheep (124-140 days gestation) in ute ro. In 18 trials (8 fetuses) infusion of 50 or 100 mug/kg tyramine inc reased the incidence of FBM from 32.2 +/- 2.0 to 79.4 +/- 4.7 %/h (P < 0.05) and increased mean breath amplitude from 6.4 +/- 0.4 to 11.8 +/ - 1.6 mmHg (P < 0.05). FBM incidence during high-voltage ECoG activity increased from 3.3 +/- 0.6 to 22.5 +/- 3.6 %/h (P < 0.05). Tyramine i nfusion (100 mug/kg) significantly increased (P < 0.05) the CSF concen trations of dopamine from 129.5 +/- 26.2 to 10,222.4 +/- 1,103.6 pg/ml , of norepinephrine from 74.7 +/- 11.0 to 2,238.6 +/- 143.5 pg/ml, and of serotonin from 1,824.5 +/- 340.7 to 3,888.7 +/- 1,335.2 pg/ml. Int racisternal injection of dopamine or norepinephrine (10-20 mug) caused the rapid onset of large-amplitude FBM, which often continued through out high-voltage ECoG activity. In contrast, serotonin (20-40 mug) cau sed cessation of FBM and change of the ECoG from low- to high-voltage activity. These results indicate that neuronal release of catecholamin es in the CNS has excitatory effects on FBM.