Separate distribution of deutocerebral projection neurons in the mushroom bodies of the cricket brain.

Deutocerebral projection neurones in the brain of the cricket (Gryllus bimaculatus) have been investigated by experimental dextran staining, viewed by light and electron microscopy. These neurones of two separate somata clusters innervate two separate primary glomerular neuropils of the deutocerebral segment, either the antennal lobe receiving only antennal nerve sensory input, or the glomerular lobe, receiving input from sensory neurones of lower segmental origin, including chemosensory fibres from mouth parts. Projection neurones of the antennal lobe only invade the anterior calyx of the mushroom body neuropil via the inner antenno glomerular tract, while glomerular relay neurones of the glomerular lobe innervate only the posterior calyx via the tritocerebral tract. All types of projection neurones give rise to presynaptic boutons. forming the central core of microglomeruli with patterned distribution. These projection neurons are cholinergic. The results are discussed in view of maintained segregated modal information, first processed in the separated primary deutocerebral neuropiles and further on in the second order input neuropils of the mushroom bodies. The large posterior calyces are proposed as a compartment for gustatory information.