Functional in vivo interaction between growth hormone and dopamine systems are correlated to changes in striatal somatostatin levels as detected by voltammetry.
The effects of growth hormone (GH) and somatomedin C (SmC), as well as those of apomorphine, dopamine (DA) agonist, or haloperidol (DA antagonist), upon the size of striatal voltammetric peaks 2 and 5 were investigated. Local intrastriatal injections of GH or SmC were followed by an increase in the height of both peak 2 (corresponding to the oxidation of extracellular dihydrophenylacetic acid, DOPAC, a metabolite of DA) and peak 5 (which may represent the oxidation of striatal extracellular somatostatin, SRIF). Treatment with haloperidol also increased the size of the striatal catechol peak but was responsible for a reduction of the neuropeptidergic signal. By contrast, apomorphine determined a decrease in striatal peak 2 (DOPAC) while increasing the levels of peak 5 (SRIF). The data further support the chemical identification of peak 5 at +800 mV as related to the in vivo oxidation of SRIF; in addition they indicate the presence of a functional relationship between this neuropeptide and the GH and DA systems in the striatum of anaesthetised rats.