Responses of cholinergic markers to a pre- or a postsynaptic pharmacological blockage in the developing chick embryo spinal cord.

The response of cholinergic markers to pre- or postsynaptic blockage was followed during development of the chick embryo spinal cord, to understand better the maturation sequence of the developing cholinergic synapse. It has been shown that the developing neurotransmitter system is able to react to pre- or postsynaptic disturbances by compensatory mechanisms, as early as 7.5 days of incubation. From 12.5 days of incubation the synaptic reactivity to such blockage changes in complexity as well as in nature. At this developmental stage muscarinic receptors show capacity for intrinsic regulation, similar to that of the adult nervous system. These results together with our previous studies clearly demonstrate that 12.5-15.5 days of embryonic life appears to be a crucial period in ontogenesis of the cholinergic neurotransmission in the chick embryo spinal cord.