Substance P as a neuromodulator of cerebellar cholinergic systems

Substance P in low concentrations (10 -7 M) activates rat cerebellar neurons (in slices), while in high concentrations (10 -6 and 10 -5 M) this compound causes a biphasic response (excitation-inhibition). Substance P probably acts as the excitatory neurotransmitter in the cerebellum and produces modulatory effects (triggering and facilitation) on cerebellar cholinergic structures. Substance P reactivates cholinergic excitatory processes, while acetylcholine prevents substance P-induced inhibitory phase. The data suggest that the modulatory effects of substance P are realized via the feedback mechanisms.