Age-dependent susceptibility of CNS glial populations in situ to the antimetabolite 6-aminonicotinamide.

Intraperitoneal injections of the nicotinamide antagonist 6-amino-nicotinamide (6-AN) were used to determine if there are regional differences in putative glial energy metabolism between the developing and adult rat CNS. 6-AN shuts down the hexose monophosphate pathway, which is used preferentially by astrocytes and oligodendrocytes. These cells subsequently undergo cytotoxic edema and cell death. Adult rats and pups ranging in age from 7 to 31 d received a single injection of 6-AN and were sacrificed after 24 h. As demonstrated wit immunocytochemical staining for the astroglia-specific markers GFAP and S-100 beta, the 7-9-d-old animals exhibited a uniform appearance with edematous glial cells located throughout the CNS. However, with advancing age, a consistent pattern of progressively decreasing amounts of injured glia, which has not been previously described, occurred in cerebral and cerebellar structures. After 3 wk postnatal, the adult pattern was manifested in which glial degeneration occurred only in specific regions of the spinal cord, cerebellum, medulla, and thalamus, whereas the remainder of the CNS appeared normal. The results suggest the presence of heterogeneous populations of glia whose preferred use of the hexose monophosphate pathway is predicated on both the age of the animal and their location in the CNS.