The presence of ionotropic P2X(7) receptor has been studied in mice brain from wild type and P2X(7) receptor knockout animals. Western blot and immunocytochemical assays show the presence of a protein containing the P2X(7) immunogenic epitopes in the brain of knockout model. Reverse transcriptase polymerase chain reaction experiments demonstrate the absence of the disrupted sequence, but other sequences of P2X(7) specific mRNA expression have been detected. Functional calcium imaging experiments in cultured granule neurons from P2X(7) knockout cerebella show the existence of a functional P2X(7)-like receptor that keeps some of the properties of the genuine receptor.