285 DEVELOPMENT OF THE MONOSYNAPTIC AND POLYSYNAPTIC REFLEXES IN THE CHRONIC FETAL SHEEP PREPARATION

Abstract

We examined the relationship between segmental spinal reflexes and electrocortical activity in fetal lambs from 105-137 days gestational age. Five fetal sheep were studied on 48 occasions. Of these, 4 were older (>120 days) and one was young (105 days onwards). Single shock stimulation (1 to 4mA; 0.1 msec duration; 0.3-0.03 Hz) was used. The mono- and polysynaptic reflexes were elicited by stimulating the sciatic nerve and recording from the peroneal or tibial nerve or vice-versa. The average latency was 3.9 msec for the monosynaptic reflex, and 22 msec for the polysynaptic reflex. In fetuses >120 days gestation both reflexes were reduced or absent in low voltage as compared to high voltage electrocortical activity. In the young fetus (105-115 days) with an undifferentiated electrocorticogram the reflexes were larger during breathing, i.e. in circumstances which correspond to low voltage electrocortical activity later in fetal life. During brief episodes of eye and breathing movements at the transition between high and low voltage electrocortical activity the reflexes were enhanced. It is tempting to speculate that the enhancement of the reflexes during increased eye and breathing movements in low voltage electrocorticogram may indicate wakefulness in utero.