GROWTH-RELATED AND ANTENNULAR AMPUTATION-INDUCED CHANGES IN THE OLFACTORY CENTERS OF CRAYFISH BRAIN

Freshwater crayfish increase in size throughout their lives, and this growth is accompanied by an increase in the length of the appendages a nd number of mechanoreceptive and chemoreceptive sensilla on them. We find that in the Australian freshwater crayfish Cherax destructor neur opil volumes of the olfactory centers increase linearly with body size over the entice size range of animals found in their natural habitat. The number of cell somata of two groups of interneurons associated wi th the olfactory centers (projection neurons and small local neurons) also increases linearly with the size of the animals. In contrast, axo n counts of interneurons that represent a nonolfactory input to the ol factory centers show that these reach a total number in the very early adult stages that then remains constant regardless of the size of the animal. Only the axon diameter of these interneurons increases linear ly with body size. Amputation of the antennule and olfactory sensilla reduces the number of projection and local interneurons on the amputat ed side. No change in the size of the olfactory centers occurs on the unamputated side. Amputation of the olfactory receptor neurons in cray fish therefore leads not only to a degeneration of the receptor cell e ndings in the olfactory robe but also to a trans-synaptic response in which the number of higher order neurons decreases. Reconstitution of the antennule and olfactory receptor neurons in small adult crayfish i s accompanied by the reestablishment of the normal number of interneur ons and neuropil Volume in the olfactory centers.