Primary rat astrocyte cultures were used to isolate a macrophage population that does not adhere to the confluent glial cells. The cells multiplied vigorously in coculture with astrocytes during the 14 d culture period, provided that functionally active lipopolysaccharide (LPS) was either absent or present in very low concentrations. Based on morphological, immunocytochemical, and pharmacological data, it was concluded that the isolated cells were microglia, the resident macrophages of the brain. The findings characterized them as a distinct cell population that shares features both of peritoneal macrophages and of astroglial cells. Like peritoneal macrophages, the isolated cells were able to phagocytize as shown by their ingestion of latex beads and uptake of L-leucyl methylester. Furthermore, they were immunocytochemically stainable by a specific monoclonal antibody (ED 1) against a macrophage-specific antigen (Dijkstra et al., 1985). They also synthesized prostaglandin E2 (PGE2) and secreted interleukin 1 (IL-1) upon stimulation with LPS. Upon stimulation with the ionophore A23187, PGD2, the predominant prostaglandin of the brain, was the major PG metabolite released by these cells. In contrast to peritoneal macrophages, microglial cells were able to multiply. Proliferation of microglial cells in coculture with astrocytes was suppressed when 2 ng LPS/ml or higher concentrations were added to astroglial culture media. These astrocyte cultures, which contained approximately 1% microglia, were used to investigate the influence of LPS on prostaglandin and IL-1 secretion in order to compare astroglial and microglial features. Increasing LPS concentrations induced increased PGE2 secretion, whereas PGD2 secretion was essentially unaffected by LPS. The critical influence of LPS contaminations in most of the commercially available animal sera used for astrocyte cultures on cellular composition in general and on metabolism of hormones and growth factors in particular is discussed.

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Adenosine triphosphate (ATP) is one of the cotransmitters that are commonly released at catecholaminergic and cholinergic nerve terminals. The glial cell type most closely associated with the synapse is the astrocyte and, thus, is the next cellular element beside the postsynaptic neuron to face the transmitters released. This report gives evidence of P2-purinoceptors on cultured astroglial cells. Upon stimulation with nucleoside triphosphates and nucleoside diphosphates, the cells respond with synthesis of prostaglandins of the D2 type, which is the predominant prostaglandin made in rat brain. Nucleoside triphosphate analogues, such as 5'-adenyl-imido diphosphate, beta,gamma-methylene, or alpha,beta-methylene ATP were less effective than ATP or its non-hydrolysable analogue ATP [gamma S]. The receptor was desensitized by ATP [gamma S] within 15 min, whereas desensitization by alpha,beta-methylene ATP was significantly delayed. 8-phenyl-theophylline (10(-4) M) had no influence on ATP-stimulated prostaglandin synthesis. Adenosine 5'-monophosphate (AMP) and adenosine were unable to stimulate prostaglandin D2 formation. According to the common nomenclature for purinoceptors, the described astroglial receptor would fulfill the characteristics of a P2-purinoceptor. Furthermore, it is shown that pertussis toxin sensitive G-proteins influence some early step in prostaglandin synthesis. The inactivation of these proteins results in reduced prostaglandin formation. It is assumed that ATP serves as an important mediator in the cross-talk between neurons and astroglial cells at the synaptic cleft.