A comparison of regional somatostatin and neuropeptide Y distribution in rat striatum and brain.

Somatostatin-like immunoreactivity (SLI) and neuropeptide Y-like immunoreactivity (NPYLI) were detected using specific radioimmunoassays in extracts from rat brain. Since we have previously found a topographic distribution of SLI in rat striatum the distribution of NPYLI was examined in the same regions. NPYLI showed an identical distribution to SLI in rat striatum and levels were significantly correlated (r = 0.93, P less than 0.01). Concentrations of both neuropeptides were consistently highest in ventromedial striatum and nucleus accumbens while they were lowest in dorsolateral striatum. These findings provide further evidence of neurochemical heterogeneity in the striatum. Concentrations of NPYLI and SLI were also significantly correlated in cerebral cortex (r = 0.99, P less than 0.01). Concentrations of NPYLI were generally higher than SLI and showed a similar predilection for limbic system nuclei. The present findings support the concept that somatostatin and neuropeptide Y may be co-localized in both striatal and cortical neurons.