Short-term nerve stimulation increases enkephalin production and content in the guinea pig myenteric plexus.

Methionine-enkephalin content in the guinea pig myenteric plexus was determined before and after acute, short-term electrical or chemical stimulation. Stimulation at 20 Hz for 30 s or exposure to high potassium, the calcium channel agonist, CGP28 392, or the narcotic antagonist, (-)-naloxone, resulted in a significant increase in the content of myenteric methionine-enkephalin. The increase produced by electrical stimulation is dependent upon functional sodium channels and the presence of extracellular calcium.

The effects of etorphine on the carboxylmethylation of synaptosomal proteins of rat striatum.

The stimulation of protein carboxylmethyl transferase (PCMT) activity in rat striatal synaptosomes by the dopamine agonist, apomorphine, and a PCMT substrate, calmodulin, was measured in normal and opioid-treated rats to see if inactivation of calmodulin by methylation is a factor in opioid action. Total carboxyl methyl acceptors were measured in preparations from alkaline homogenates, while those already occupied in vivo were measured in acidic homogenates, since the carboxylmethyl group is stable in acid. The administration of etorphine acutely increased the number of already occupied acceptors while chronic morphine treatment decreased this number.

Effects of delta and mu opiopeptides on the turnover and release of dopamine in rat striatum.

Two mu and two delta opiopeptides were administered intracisternally and morphine was administered systemically to rats. The level of dopamine (DA) and its catabolites, homovanillic acid, dihydroxyphenylacetic acid and 3-methoxytramine were measured by high-pressure liquid chromatography with electrical detector in rat striatum to determine: 1) whether opioids alter the release of DA from striatal neuron (which would be indicated by changes in the level of 3-methoxytramine, the extraneuronal catabolite) and 2) whether delta or mu ligands have a greater effect on DA turnover. We found that the levels of 3-methoxytramine did not rise in response to the administration of any opiopeptide or morphine.