The anatomy of neurons projecting to the corpus cardiacum from the larval brain of the tobacco hornworm, Manduca sexta (L.)

Retrograde cobalt filling followed by silver intensification revealed new features of the anatomy of neurons which project from the brain to the corpus cardiacum (CC) of the fifth instar larva of Manduca sexta. Filling via the fused nervi corporis cardiaci (NCC) I+II demonstrated four groups of cell bodies (Ia, Ib, II, and III) previously described by Nijhout (1975), plus three major axonal tracts (A, B, and C), and four previously unobserved areas of dendritic branching, dendritic fields (DF) 1, 2, 3, and 4. Tract C is unusual in that it originates from cell bodies on the side contralateral to the filled nerve, travels ventrally and crosses over to the ipsilateral side where it turns dorsally, forming a hook in the center of the brain. It then turns ventrally again to join with tract A. DF 1 and 2 are located ventrally on the ipsilateral and contralateral sides of the brain respectively. DF 3 and 4 are situated in the dorsal protocerebrum, on the ipsilateral and contralateral sides respectively. Fills via the NCC III revealed one cell group (IV) and a fifth dendritic field (DF 5). Simultaneous fills of both the fused NCC I+II and the NCC III showed an overlapping of DF 1 and 5, indicating the possibility of synaptic connections between these two fields.