The possible involvement of lymphokines in the glial reaction/proliferation that follows brain injury has been investigated by measuring the density of omega 3 (peripheral type benzodiazepine) binding sites associated to glial cells and macrophages after local injection of lymphokines in the rat cerebral cortex and striatum. omega 3 Site densities were measured either by quantitative autoradiography in brain sections or by conventional binding in membrane using [3H]PK 14105 or [3H]PK 11195 as ligands. Intracortical or intrastriatal infusion of interleukin-1 (10 and 20 units) caused a marked increase in the density of omega 3 sites (+83% and +80%, respectively, when compared to saline-infused animals) around the injection site at 7 days postinjection. There was a good spatial correspondence between the autoradiographic distribution of omega 3 sites and the distribution of reactive astrocytes (as assessed by GFAP immunostaining) or acid phosphatase rich cells (phagocytes). Significant increases in omega 3 site densities were also observed in striatal homogenates 1 week after local administration of tumor necrosis factor-alpha (TNF-alpha). The maximal increase (+80%) was observed after the administration of 3 units, higher and lower doses resulting in smaller increases. Intrastriatal injection of E. coli lipopolysaccharide (LPS), a bacterial endotoxin known to stimulate interleukin-1 and TNF-alpha production by microglial cells in culture, also resulted in significant increases in omega 3 site densities in striatal homogenates (maximal increase, +170% 1 week after the injection of 200 ng).(ABSTRACT TRUNCATED AT 250 WORDS)