Parallel organization in honey bee mushroom bodies by peptidergic Kenyon cells

Antisera against the neuromodulatory peptides, Phe-Met-Arg-Phe-NH2-amide (F MRF-amide) and gastrin cholecystokinin, demonstrate that the mushroom bodie s of honey bees are subdivided longitudinally into strata. Three-dimensiona l reconstructions demonstrate that these strata project in parallel through the entire pedunculus and through the medial and vertical lobes. Immunosta ining reveals clusters of immunoreactive cell bodies within the calyx cups and immunoreactive bundles of axone that line the inside of the calyx cup a nd lead to strata. Together, these features reveal that immunoreactive stra ta are composed of Kenyon cell axons rather than extrinsic elements, as sug gested previously by some authors. Sorting amongst Kenyon cell axons into t heir appropriate strata already begins in the calyx before these axons ente r the pedunculus. The three main concentric divisions of each calyx (the li p, collar, and basal ring) are divided further into immunoreactive and immu nonegative zones. The lip neuropil is divided into two discrete zones, the collar neuropil is divided into five zones, and the basal ring neuropil is divided into four zones. Earlier studies proposed that the lip, collar, and basal ring are represented by three broad bands in the lobes: axons from a djacent Kenyon cell dendrites in the calyces are adjacent in the lobes even after their polar arrangements in the calyces have been transformed to rec tilinear arrangements in the lobes. The universality of this arrangement is not supported by the present results. Although immunoreactive zones are fo und in all three calycal regions, immunoreactive strata in the lobes occur mainly in the two bands that were ascribed previously to the collar and the basal ring. In the lobes, immunoreactive strata are visited by the dendrit es of efferent neurons that carry information from the mushroom bodies to o ther parts of the brain. Morphologically and chemically distinct subdivisio ns through the pedunculus and lobes of honey bees are comparable to longitu dinal subdivisions demonstrated in the mushroom bodies of other insects, su ch as the cockroach Periplaneta americana. The functional and evolutionary significance of the results is discussed. J. Comp. Neurol. 424:179-195, 200 0. (C) 2000 Wiley-Liss, Inc.