Distribution of serotonergic neurons in the eyestalk and brain of the crab, Cancer antennarius

Abstract

1. Serotonin-containing neurons were localized immunocytochemically in crab cerebral ganglia and their extensions in the eyestalk. 2. Approximately 155 serotonergic cells were found in identifiable regions of the brain, the largest number being localized in the anterior cell cluster (40 reactive cells) and the bilateral anterior olfactory cell clusters (40 cells each). 3. Serotonin immunoreactive cells were found in all three ganglionic divisions of the eyestalk. The medulla terminalis contains up to 15 reactive cells, of which only one occurs in the X-organ (origin of neurosecretory axons in the sinus gland nerve). The m. terminalis also contains three identifiable cells in the mediolateral border adjacent to the sinus gland nerve, of which one is a giant (up to 100 μm diameter), designated MT-1. The axon of MT-1 branches profusely after entering the m. terminalis neuropil. 4. No serotonin immunoreactivity was apparent within the sinus gland, the sinus gland nerve or the organ of Bellonci. 5. These findings are discussed in relation to the known serotonergic control of peptide hormone secretion by the eyestalk X-organ-sinus gland complex.