Histamine-immunoreactive neurons in the midbrain and suboesophageal ganglion of sphinx moth Manduca sexta

This paper describes the distribution of histamine-like immunoreactivity in the midbrain and suboesophageal ganglion of the sphinx moth Manduca sexta. Intense immunocytochemical staining was detected in ten bilateral pairs of neurons in the median protocerebrum and in one pair of neurons in the suboesophageal ganglion. Whereas most areas of the brain and suboesophageal ganglion are innervated by one or more of these neurons, typically no immunoreactive fibers were found in the mushroom bodies, the protocerebral bridge, and the lateral horn of the protocerebrum. The 11 histamine-immunoreactive neurons were reconstructed from serial sections. Ten neurons have bilateral arborizations, often with axonal projections in symmetric areas of both hemispheres. One neuron, whose soma resides in the lateral protocerebrum, has only unilateral projections. Of the 11 neurons, 6 occur in pairs with similar morphological features. In addition to these neurons, weak histamine-like immunoreactivity was detected in 7-13 interneurons that were not reconstructed individually. The central projections of the ocellar nerves from the intracranial ocelli also exhibit histamine-like immunoreactivity. The single-cell reconstructions reveal similarities between the organization of histamine- and serotonin-immunoreactive neurons in the brain and suboesophageal ganglion of this insect.