CHOLINERGIC MODULATION THROUGH BIOGENIC-AMINES DURING DEVELOPMENT OF THE CHICK SPINAL-CORD

Our previous analyses of the functional maturation of cholinergic neur otransmission in the chick embryo spinal cord showed that 12 days of d evelopment represents a crucial stage in the maturation of cholinergic neurotransmission. Since supraspinal inputs are essential for the mod ulation of motoneuron activity in the embryo, we studied, using a phar macological approach, the regulatory effects of biogenic amines on the developing cholinergic neurotransmission. We show that, in spite of t he early occurrence of serotonin and norepinephrine in the developing spinal cord, the modulatory influences of these biogenic amines on mot oneurons can only be effective from 12 days of incubation onwards. It also appears that the inputs of biogenic amines on cholinergic activit y is a sequential event. Whereas serotonin (5-HT) begins to stimulate cholinergic activity from 12 days of incubation, norepinephrine inputs are only observed at later stages (17 days of development). These obs ervations underline the specific turning point in the functional matur ation of motoneurons, we noted in our previous studies. At the end of embryonic life a specific interrelationship between the biogenic amine s was noted. its effect on the cholinergic system may lead to a more p recise motor control, preparing the chick embryo for hatching.