The expression of γ-aminobutyric acid and leu-enkephalin immunoreactivity in primary monolayer cultures of rat striatum

Primary monolayer cultures of rat striatum were examined for γ-aminobutyric acid (GABA) and leucine-enkephalin (L-ENK) immunoreactivity. Cultures were established on polycation-treated glass coverslips from the striata of gestational day 17 rat embryos using a serum and insulin-supplemented medium. The proportion of GABA-immunoreactive (GABA-IR) neurons increased during the first week in vitro from approximately one third to nearly one half and remained relatively constant thereafter. On the other hand, the proportion of L-ENK-IR neurons increased gradually over the culturing period, increasing from about one-fifth of the neurons initially to one-half after 3-4 weeks in vitro. The changes in the proportions of GABA- and L-ENK-IR neurons appeared to be largely a consequence of the death of non-immunoreactive neurons, not delayed expression or induction of GABA or L-ENK traits. Light microscopic analysis of somatic-proximal neuritic morphology led to a partitioning of the neuronal population into 4 groups. GABA- and L-ENK-IR groups were heterogeneous in this regard and differed only modestly.