Characterization of opioid dependence of isolated ileum of morphine dependent and of chronically stressed Wistar-Kyoto (WKY)-rats.

The opioid antagonist naloxone induced tonic contraction ("gut dependence") of isolated ilia of both morphine dependent WKY-rats and WKY-rats chronically stressed by immobilization. Morphine and met-enkephalin but neither dynorphine nor leu-enkephalin antagonized the naloxone induced "gut dependence" of isolated ilia obtained from morphine dependent WKY-rats. Met-enkephalin as well as dynorphine inhibited the "gut dependence" of chronically stressed rats; morphine and leu-enkephalin had no inhibitory effect.

Modulation of spinal synaptic transmission by beta-melanocyte stimulating hormone (beta-MSH).

Synaptic modulation refers to altered excitability of a synapse by a substance that does not produce a spike potential at the synapse. Available evidence points to the conclusion that beta-melanocyte stimulating hormone (beta-MSH) modulates synaptic transmission through monosynaptic pathways in the cat spinal cord. Earlier evidence is reviewed, and new data are presented.

A fragment of substance P with specific central activity: SP(1-7).

Amino-terminal fragments of substance P (SP), SP(1-7) and SP(1-8), were found to produce naloxone-reversible antinociception in the mouse similar to that produced by SP. Similar to SP, these peptides produce antinociception only within a narrow dose range. They have no activity on smooth muscle or blood pressure.