Striatal neurones displaying substance P (NK1) receptor immunoreactivity in human and non-human primates

The striatum of normal human subjects and that of squirrel monkeys (Saimiri sciureus) was found to contain two distinct types of neurones displaying immunoreactivity for substance P (neurokinin-1) receptor (SPR). Large and medium-sized SPR-immunoreactive neurones, both with aspiny dendrites, were fairly uniformly distributed in the striatum of humans and squirrel monkeys. In humans the proportions of large and medium-sized SPR-positive neurones were 57.2% and 42.8% in putamen, compared with 51.9% and 48.1% in caudate nucleus. These findings suggest that substance P exerts its local influence not only on large cholinergic neurones, as commonly believed, but also on a subset of medium-sized interneurones in the striatum of human and non-human primates.