A tachykinin-like factor increases glutamate toxicity in rat cerebellar granule cells

Tachykinins (TKs), which include substance P, neurokinin A and neurokinin B, constitute a group of neuropeptides widely expressed in the CNS where they play several functions connected with neural modulation often in synergy with glutamate excitatory transmission. The aim of this study was to assess whether TKs modulate glutamate response of in vitro cultured cerebellar granule neurons and whether GSA (glutamate-sensitizing activity), a peptide released by these neurons, belongs to the TKs family. Treatment with substance P and other neurokinin 1 receptor (NK1) agonists does not affect the response of cerebellar granule neurons to glutamate toxicity. On the contrary, agonists neurokinin 2 receptor (NK2) and neurokinin 3 receptor (NK3) agonists increase, in a dose and time dependent fashion, the response of the same neurons to glutamate. MEN 10,627, a selective NK2 receptor antagonist, and (Trp(7),betaAla(8)) NKA (4-10), a selective NK3 receptor antagonist inhibit not only the sensitizing action to glutamate of their respective agonists. These antagonists almost equally reduce the glutamate-sensitizing activity of GSA. Such activity is also abolished in the presence of a polyclonal antibody directed against neurokinin B (NKB). These findings indicate that TKs increase glutamate sensitivity in cerebellar granule neurons and that the GSA previously detected in conditioned media of the same cultured neurons belongs to the TK family although its primary structure as compared to known TKs remains to be established.