Integrins are a diverse family of heterodimeric (alphabeta) adhesion receptors recently shown to be concentrated within synapses and involved in the consolidation of long-term potentiation. Whether neuronal types or anatomical systems in the adult rat brain are coded by integrin type was studied in the present experiments by mapping the relative densities of mRNAs for nine alpha and four beta subunits. Expression patterns were markedly different and in some regions complementary. General results and areas of notable labeling were as follows: alpha1-limited neuronal expression, neocortical layer V, hippocampal CA3; alpha3 and alpha5-diffuse neuronal and glial labeling, Purkinje cells, hippocampal stratum pyramidale, locus coeruleus (alpha3); alpha4- discrete limbic regions, olfactory cortical layer II, hippocampal CA2; alpha6-most prominently neuronal, neocortical subplate, endopiriform, subiculum; alpha7-discrete, all neocortical layers, hippocampal granule cells and CA3, cerebellar granule and Purkinje cells, all efferent cranial nerve nuclei; alpha8-discrete neuronal, deep cortex, hippocampal CA1, basolateral amygdala, striatum; alphaV-all cortical layers, striatum, Purkinje cells; beta4-dentate gyrus granule cells; beta5-broadly distributed, neocortex, medial amygdala, cerebellar granule and Purkinje cells, efferent cranial nerve nuclei; alpha2, beta2, and beta3-mRNAs not detected. These results establish that brain subfields express different balances of integrin subunits and thus different integrin receptors. Such variations will determine which matrix proteins are recognized by neurons and the types of intraneuronal signaling generated by matrix binding. They also could generate important differences in synaptic plasticity across brain systems.