Dopamine-like immunoreactivity in the brain and suboesophageal ganglion of the honeybee.

The distribution of dopamine in the brain and suboesophageal ganglion of the honeybee Apis mellifera was investigated by means of immunocytochemistry with a well-characterized antiserum against dopamine. The binding of the antiserum in paraffin serial sections was studied with the peroxidase-antiperoxidase method. Dopamine-like immunoreactive neurons are present in most parts of the brain and in the suboesophageal ganglion. Only the optic lobes are devoid of label. There are ca. 330 dopamine immunoreactive somata in each brain hemisphere plus respective suboesophageal hemiganglion, which is less than 0.1% of the entire neuronal population. Most of the labelled somata are situated within three clusters: one below the lateral calyx and two in the anterior-ventral protocerebrum. Other labelled somata lie dispersed or in small groups around the protocerebral bridge, below the optic tubercles, proximal to the ventral rim of the lobula, and in the lateral and ventral somatal rind of the suboesophageal ganglion. Similar to neurons that react with an antiserum against serotonin, the fine processes of dopamine immunoreactive fibers have a varicose appearance which is typical for aminergic neurons. In addition to the neuronal staining, dopamine-like immunoreactivity is also present in the sheath surrounding the brain and in the retina, where it is not restricted to any particular cell type. A detailed account is given for those neurons and groups of neurons that could be traced and reconstructed in some detail. A common feature of all dopamine immunoreactive fibers is that each fiber invades large volumes of neuropil, suggesting that dopamine is more important in mediating distant rather than local neural interactions.