The distribution of the incubation period for the acquired immunodeficiency syndrome (AIDS)

Abstract

The abdominal cerci of immature crickets are regenerated repeatedly after loss. The developmental sequence of cercal regeneration depends on the instar and the time within the instar that cerci are removed. Initial regenerates in early instars lack sensilla, which appear at the second moult, and subsequently increase in number in a definite order as in normal development, with filiform hairs appearing first, followed by large numbers of appressed hairs. Initial regenerates of later instars may bear filiform hairs. If one of the cerci is removed at hatching and all subsequent regenerates are removed as soon as they appear, a maximally asymmetric animal is produced. The general dimensions of the giant interneurons carrying cercal information anteriorly are not altered, but the volume of the terminal abdominal ganglion neuropile on the deprived side is reduced by 30%. At least three important changes in connectivity accompany unilateral deprivation: (a) responses to air puffs in the largest interneurons (l.g.i. and m.g.i.) contralateral to the intact cercus are 20 times greater than in control animals, where responses are virtually completely ipsilateral; (b) responses to substrate vibration, detected by non-cercal receptors, are about 10 times greater than normal on the deprived side; and (c) contralaterally projecting axons from cercal receptors are found, which is never the case in normal animals. Responses on the intact side are normal. Animals which are deprived of both cerci for six instars and then regenerate only one show all these changes but to a lesser degree. In particular, the non-cercal, vibration sensitive input to the continuously deprived side is not enhanced as much as with the former treatment. Animals permanently deprived of both their cerci similarly do not acquire as greatly enhanced a vibration input as does the deprived side of continuously asymmetric animals. None of these rearrangements occur in animals which are deprived of both their cerci for six instars and then regenerate both; these symmetrically deprived and symmetrically regenerating animals resemble normals in all measured respects even though a period of deprivation lasting for two thirds of postembryonic development has intervened between the initial amputation and regeneration. We conclude that the capacity for correct neuronal circuit assembly is maintained throughout postembryonic development; that removal of a major input to the giant interneurons leads to a relative strengthening of the remaining inputs; and that additional rearrangements, beyond the effects of simple deprivation, occur as a result of asymmetry during cercal development.