RETROSPLENIAL PRESUBICULAR CONTINUUM IN PRIMATES - A DEVELOPMENTAL-APPROACH IN FETAL MACAQUES USING NEUROTENSIN AND PARVALBUMIN AS MARKERS/

In spite of numerous hodological and neuropsychological studies emphas izing the multimodal connections and integrative functions of the retr osplenial cortex in primates, the precise fate of its caudoventral ext ent and the composition of the merging area with the hippocampal forma tion remain a matter of debate. We reported previously how the anlage of the retrosplenial cortex merges with the immature presubicular zone in the fetal rhesus monkey at the end of the first trimester of gesta tion. In the present study, this caudal area was further defined on a chemoarchitectonic basis, particularly during the late prenatal and pe rinatal stages, which correspond to the development of the cingulate s ulcus and temporal gyri, and the differentiation of the retrosplenial/ subicular complex. Neurotensin (NT), a pyramidal cell marker in the li mbic cortex, and parvalbumin (PV), a marker of a subset of inhibitory local circuit neurons in the hippocampal formation, were used as immun ocytochemical markers. According to distinct chemoarchitectural patter ns, (1) areas 29l and 29m of the retrosplenial cortex formed a triangl e-shaped ventral expansion which merged with a similar but dorsal expa nsion of the pre/parasubicular fields. A temporal extension of area 29 m down to area TH could not be detected. The pre/parasubiculum contrib uted with area 29m to the lateral bank of the calcarine sulcus as far as the most caudal extent of the hippocampal formation. (2) The lamina principalis interna of the presubiculum was well individualized and d id not appear as a simple horizontal shift of adjoining fields. (3) NT and PV displayed a distinct temporal profile of development. NT was a lready expressed in the pyramidal cells of the prospective retrospleni al cortex and ventral hippocampal formation at E47 (term 165 days). Ma jor pathways of the hippocampal formation and retrosplenial cortex (fi mbria, fornix, angular and cingulum bundles) were progressively labele d indicating early developing projections. A large set of NT-positive afferents reached the retrosplenial cortex between E114 and E120. Thei r laminar distribution was compatible with a thalamic or a subicular o rigin. (4) The development of PV expression was delayed until the last quarter of gestation, supporting its proposal as a signal of function al onset. The developmental fate and the particular connections of the presubiculum suggest that its functional importance should be further investigated during infancy and adulthood. (C) 1997 Elsevier Science B.V.