Redirected perforant and commissural of connections of eutopic and ectopic neurons in the hippocampus of methylazoxymethanol-acetate treated rats.

In an earlier study, it was reported that clusters of ectopic neurons developed postnatally in the hippocampus of rats which were exposed to Methylazoxymethanol acetate (MAMac) during fetal development (Singh, 1977b). This paper describes the perforant tract and commissural connections of hippocampal eutopic and ectopic neurons. These connections were traced with a reduced-silver method (Eager, 1970). Two observations of significance were made: (i) Ectopic neurons misplaced in stratum radiatum received terminals from axons in the perforant tract. The upper boundary for these redirected fibers was stratum pyramidale--approximately 350 mu outside the normal boundary which is situated near the hippocampal fissure. (ii) Ectopic neurons received a dramatically reduced commissural projection, compared with eutopic pyramidal neurons in Ammon's horn. Eutopic neurons in the hippocampus were found to receive afferent perforant tract and commissural fibers in the same way--i.e., density and distribution, as in control rats.