Development before and after hatching of non-cholinergic excitatory innervation to the rectum via Remak's nerve in the fowl.

1. Development of the excitatory innervation to the rectal region of the intestine via Remak's nerve has been investigated in the rectum with Remak's nerve supply isolated from chicken embryos and young chicks aged less than two weeks. 2. Electrical stimulation of Remak's nerve produced a small contraction of the rectum isolated from chicken embryos on the 14th day of incubation (the earliest time examined). The contractile response was inhibited partially or totally by atropine (0.1 micrograms ml-1) but enhanced by physostigmine (0.01 to 0.05 micrograms ml-1), indicating its cholinergic nature. 3. During the embryonic stage, the proportion of the atropine-resistant component in the contractile response increased, and the contractile response became almost entirely atropine-resistant within the first week after hatching. 4. Later after hatching, the contractile response was increased in magnitude by atropine and reduced by physostigmine. 5. It is concluded that the excitatory innervation to the chicken rectum via Remak's nerve is cholinergic at the 14-16th day of incubation and is gradually replaced by a non-cholinergic innervation during embryonic development.