Simultaneous determination of leu-enkephalin localization and [3H] gamma-aminobutyric acid uptake in rat striatal cell cultures

The expression of gamma-aminobutyric acid and Leu-enkephalin immunoreactivity in primary monolayer cultures of rat striatum

Primary monolayer cultures of rat striatum were examined for gamma-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.

Simultaneous immunofluorescence and autoradiography: a useful technique for investigating neurotransmitter uptake by neurons and glia in primary central nervous system culture

Previous studies on the localization of radiolabelled neurotransmitters in cultured cells of neural origin have relied on the comparison of cell morphology, as determined by immunocytochemistry, with the patterns of labelling on autoradiograms. We present here a method combining simultaneously autoradiography, following the uptake of tritium-labelled amino acid transmitters, with indirect immunofluorescence using antibodies against both surface and intracellular antigens. Using a fixative containing only a low concentration of glutaraldehyde (4% paraformaldehyde, 0.1% glutaraldehyde), a similar retention of gamma-[3H]aminobutyric acid (GABA) and D-[3H]aspartate was achieved as with the higher concentrations commonly used, with the advantage that the autofluorescence associated with glutaraldehyde fixed tissue was eliminated, and the immunoreactivity of the antigens to be localized was not destroyed. Using this method GABA and D-aspartate accumulating cells, in dissociated mouse central nervous system (CNS) cultures, could be reliably identified as oligodendrocytes, and some multiprocessed astrocytes, by anti-galactocerebroside (GC) and anti-glial fibrillary acidic protein (GFAP) immunofluorescence respectively. GABA-accumulating neuron-specific enolase (NSE) positive neurons could be clearly identified but no D-aspartate accumulating neurons were found. This technique should have a wide application in the investigation of whether selective transport mechanisms coexist with antigens characteristic of a certain cell type or sub-type.

The effects of barbiturates upon the hemodynamic responses to intravenous methionine-enkephalin in dogs: modulation by the GABA complex

In conscious animals, the intravenous administration of enkephalins increases heart rate (HR) and mean systemic arterial blood pressure (MAP); however, when given during barbiturate anesthesia, enkephalins reduce HR and MAP. We have investigated the potential role of the gamma-aminobutyric acid (GABA) complex (consisting of chloride-ion channel and binding sites for GABA, benzodiazepine, and barbiturate/picrotoxin) as the site of modulation of enkephalin responses by certain anesthetic agents in our chronically instrumented dog model. In our model, methionine-enkephalin (Met5-ENK) (35 micrograms/kg intravenously) increased HR and MAP, but following induction of general anesthesia with barbiturate (pentobarbital) or of sedation with benzodiazepine (diazepam), Met5-ENK produced vasodepressor responses despite differing levels of consciousness in the treated animals. Subsequent administration of picrotoxin restored pressor responses to Met5-ENK in the barbiturate-treated dogs, but not in those treated with benzodiazepine; picrotoxin did not alter the level of consciousness. Picrotoxin had no effect upon Met5-ENK responses in the conscious state. In contrast, alpha-chloralose, a convulsive anesthetic agent which does not appear to alter GABA complex activity, blunted but did not reverse pressor responses to Met5-ENK, despite causing a level of anesthesia similar to that produced by barbiturate. The observed pressor response to Met5-ENK during alpha-chloralose anesthesia was totally inhibited by naloxone, indicating that this response was still mediated by opiate receptors. Our data are compatible with modulation of enkephalin responses by GABA complex activity. Systemic enkephalins may generate afferent signals which may subsequently undergo GABA complex processing; the state of activation of the GABA complex may then determine whether systemic enkephalin signals are translated as vasopressor or vasodepressor responses.