Brain reaggregate cultures in neurotoxicological investigations: adaptational and neuroregenerative processes following lesions.

In vitro neural systems can be predictive for CNS neurotoxicity, except where xenobiotics primarily affect the blood-brain barrier. The wide range of systems now used in neurobiological studies is available for mechanistic neurotoxicological investigations although the choice of system is generally arbitrary. A more rational approach may now be justified. There are many culture systems available including neural cell lines, organotypic explant or reaggregation cultures, and primary monolayer cultures of individual neural cell types: neurons, astrocytes, and oligodendrocytes. Of these models much success has recently been achieved using the organotypic explant culture type. Similarly in our laboratories, using rat whole-brain reaggregate cultures, we have demonstrated good in vitro/in vivo correlations for the cholinergic neurotoxicant ethylcholine mustard aziridinium (ECMA) where specific cholinergic lesions are produced using low concentrations of ECMA (12.5 microM). Higher concentrations (25-50 microM) were more cytotoxic, as shown, for example, by nonspecific effects on cerebellar glutamatergic granule neurons. Treatment of reaggregates lesioned with the cholinotoxin with a neurotrophic factor, nerve growth factor (NGF), did not reverse the lesion but treatment of control cells with NGF (50 ng/ml) elevated both choline acetyltransferase (ChAT) activity and muscarinic receptor binding. The "lesioned" reaggregate culture system may thus be of future value in evaluating potential therapeutic agents that could reverse such lesions in the CNS. By supplementing the information gained in the reaggregate system with tests using primary monolayer cultures of neurons or astrocytes we can propose a stepwise screening system for potential neurotoxicants in vitro. In its simplest form this is (1) screen initially using tumor-derived neural cell line, (2) test selected compounds in whole-brain reaggregates, and (3) supplement information with primary monolayer cultures of individual neural cell types.