BILATERAL GLIOSIS IN UNILATERALLY LESIONED SEPTOHIPPOCAMPAL SYSTEM - CHANGES IN GFAP IMMUNOREACTIVITY AND CONTENT

Unilateral damage to the lateral fimbria led to a bilateral gliosis in the septum and hippocampus, The gliosis was manifested by an increase in GFAP staining, accompanied by an increased number of glial fibrill ary acidic protein (GFAP)(+) cells and GFAP content; the latter howeve r was not visible in the contralateral septum, In general, the contral ateral reaction appeared weaker than the ipsilateral one. The pattern of contralateral increase in GFAP-immunoreactivity (IR) matched almost exactly that observed on the ipsilateral side in the hippocampus (the most evident increase was seen in the oriens and pyramidal layers of cornu Ammonis 3 and in polymorphic area of gyrus dentatus), In the sep tum the bilateral increase in GFAP-IR was mainly visible in the dorsol ateral quadrant of the structure; however in the ipsilateral side it s pread over the whole half of the structure. The astrocytic responses i n the septum and hippocampus were not equivalent: they differed mainly with regard to the increase of GFAP(+) cells (over 300% of control in the anterior part of the septum and only about 120% in the dorsal hip pocampus), The differences between astrocytic response in the septum a nd hippocampus were also manifested by different relations between the percentage increases of other gliotic indices: GFAP-IR and GFAP conte nt. Various possibilities that may account for the occurrence of contr alateral gliosis are discussed, the most plausible being the contribut ion of interhemispheric and intraseptal links and the action of some d iffusible agents. We suggest that bilateral gliosis may have an impact on compensatory postlesion processes, possibly by providing trophic s upport to impaired neurons. (C) 1995 Wiley-Liss, Inc.