PARENT SESSION
Pregnancy and Parturition

CONTROL OF FETAL NARCOSIS DURING PREGNANCY BY SEROTONIN IN THE BOVINE: ELECTROENCEPHALOGRAPHIC STUDY.

Thomas, William¹, Fecteau, Kellie², Eiler, Hugo², ^{1 2}

ABSTRACT- During pregnancy, fetuses stay "dormant" and express limited movements in the uterus. In contrast and soon after birth, the newborn starts moving and often stand within an hour; the mechanism is not known. We reported a dramatic drop in fetal blood concentrations of serotonin (5-hydroxytryptamine, 5-HT) during partum from 50 to 13.0 M. The objective of this work was to establish whether the "narcotic" effects of 5-HT infusion in newborn calves are associated with sleeping electrical activity of the brain. Six 24 h old calves were used. Recording electrodes were inserted subcutaneously over the left and right frontal, left and right occipital, and ventral regions. A ground electrode was inserted in the dorsal region of the neck. Bipolar electroencephalogram (EEG) recording was performed in an 8-channel polygraph. 5-HT sulfate (1.5 mg/ml/min/calf) was infused via jugular vein attached to an infusion pump. The infusion rate was adjusted to avoid respiratory and intestinal distress. When 5-HT was infused, calves became unconscious, stretched on the floor, leg muscles relaxed, and pain reflex elicited by needle stimulation was abolished. This condition was named "narcosis". It was induced within 8 min and subsided within 8 min of infusion. The EEG before 5-HT infusion and during the saline infusion (control period) contained generalized low-voltage fast activity (20-25 Hz, 15-20 V) waves, similar to the pattern previously reported in alert calves. During the initial infusion of 5-HT, the calves became quiet, during which time the EEG contained generalized high-voltage slow activity (4-5 Hz, 30 V) with superimposed fast activity waves, which was consistent with EEG pattern in relaxed calves. With continued 5-HT infusion, the calves came into the stage of "narcosis" with an EEG pattern containing generalized high-voltage slow activity (3-4 Hz, up to 150 V) waves, similar to that reported for calves during sleep. In support of our hypothesis, infusion of 5-HT caused "narcosis" and EEG sleeping pattern. In contrast, withdrawal of 5-HT caused an awake EEG pattern and ambulatory behavior.

KEY WORDS: fetal narcosis, serotonin