Neuromuscular organization of the buccal system in Aplysia californica

The intrinsic muscles and peripheral nerves in the buccal system of the sea hare Aplysia californica were studied to build a foundation on which to base future investigations of feeding in intact animals. A detailed description of the bilaterally paired intrinsic muscles is given identifying previously unreported muscles. Each of the six buccal nerves (n1-n6) and the cerebrobuccal connective (CBC) have been characterized in several respects. Cell bodies in the buccal ganglion with projections into each of the buccal nerves have been identified via the cobalt backfilling technique. All nerves contain axons of cell bodies in the ipsilateral as well as the contralateral ganglia. For each nerve, there is a consistent pattern in the distribution of cell bodies in the paired ganglia with the number of cell bodies in the contralateral ganglion being less than or equal to the number in the ipsilateral ganglion. Although the total number of backfilled cell bodies varies among the nerves, their size ranges are similar with the majority being small. Nerves 1, 2, 4, 5, and 6 provide motor innervation to the intrinsic buccal muscles in varying degrees with nerve 4 supplying all the intrinsic muscles; nerve 2 supplies only one. The axon composition of each nerve was scrutinized and revealed large numbers of axon profiles, the majority of which were less than 2 microns in diameter. The present study provides a framework for analysis of feeding behavior in Aplysia californica.