Heteromorphic antennules protect the olfactory midbrain from atrophy following chronic antennular ablation in...

Posthatch larval crayfish (Procambarus clarkii) were unilaterally antennulectomized and maintained in the laboratory for a 6-month period, during which time all regenerating antennular stumps were periodically excised. In another group of animals at a similar developmental stage a heteromorphic antennule was induced on the side of the head ipsilateral to the chronically sectioned normal antennule. After 6 months, all experimental animals were sacrificed and their brains were fixed and sectioned. Computer-aided quantitative measurements were obtained for the volumes of the olfactory lobes on both the experimental and control sides of the brains of both groups of crayfish. In the brains of the crayfish group in which only chronic antennualectomy had been performed, the olfactory lobe ipsilateral to the lesion was reduced in volume by about 80% compared to the olfactory lobe on the control side. In animals in which the normal antennule had been chronically ablated, but which possessed a heteromorphic antennule on the same side, the olfactory lobe on the lesioned side differed in volume from the control side by a mean value of only 28%. We conclude that afferent fibers from a heteromorphic antennule ipsilateral to a chronically lesioned normal antennule can assume some of the central trophic functions of the afferents from the normal antennule; thus, the presence of a heteromorphic antennule offers some measure of protection from the dystrophic effects of chronic ablation of the normal antennule during development and growth in crayfish.