THE DEVELOPMENTAL EXPRESSION OF SEROTONIN-IMMUNOREACTIVITY IN THE BRAIN OF THE PUPAL HONEYBEE

The biogenic amine serotonin is a neurotransmitter and modulator in bo th vertebrates and invertebrates. In the CNS of insects, serotonin is expressed by identifiable subsets of neurons. In this paper, we charac terize the onset of expression in the brain and suboesophageal ganglio n of the honeybee during pupal development. Several identified seroton in-immunoreactive neurons are present in the three neuromeres of the s uboesophageal ganglion, the dorsal protocerebrum, and the deutocerebru m at pupal ecdysis. Further immunoreactive neurons are incorporated in to the developing pupal brain in two characteristic developmental phas es. During the first phase, 5 days after pupal ecdysis, serotonin immu noreactivity is formed in the protocerebral central body, the lamina a nd lobula, and the deutocerebral antennal lobe. During the second phas e, 2 days later, immunoreactivity appears in neurons of the protocereb ral noduli of the central complex, the medulla, and the pedunculi and lobes of the mushroom bodies. Three novel serotonin-immunoreactive neu rons that innervate the central complex and the mushroom bodies can be individually identified.