Dopaminergic and enkephalinergic involvement in the regulation of blood glucose in the red swamp crayfish, Procambarus clarkii.

In in vivo experiments injection of dopamine (DA) or leucine enkephalin (L-Enk) produced hypoglycemia in intact red swamp crayfish, Procambarus clarkii. In contrast, neither compound had a significant effect on the circulating glucose concentration in eyestalkless individuals. With intact crayfish spiperone, a DA receptor blocker, inhibited this hypoglycemic action of DA but not this action of L-Enk. In contrast, in intact crayfish naloxone, a competitive opioid antagonist, inhibited the in vivo hypoglycemic actions of both L-Enk and DA. In vitro, both DA and L-Enk reduced the rate of release of the crustacean hyperglycemic hormone (CHH) from isolated eyestalk neuroendocrine tissue. These results suggest that both DA and L-Enk act to inhibit release of CHH by affecting the eyestalk neuroendocrine complex and that the enkephalinergic inhibitory neuron follows the dopaminergic inhibitory neuron in the chain of neurons which leads to the neuroendocrine cells that secrete CHH.