Author Question: What are two actions induced by psychotropic drugs that may lead to receptor up-regulation? What ... (Read 58 times)

melina_rosy · **on:** Jun 22, 2018

What are two actions induced by psychotropic drugs that may lead to receptor up-regulation?

What will be an ideal response?

Question 2

Two groups of rats have a small pellet implanted under the skin. In Group A rats the pellet contains morphine, which is slowly absorbed over a 72 hour period.

In Group B rats the pellet contains an inert substance. The rats are kept in their home cages for the three days after the pellet implantation. Both groups are then tested for analgesia by being injected intraperitoneally with a small dose of morphine. This test consists of the rats being placed on a hot surface and they are timed to see how long it takes them to lick their paws. (It is assumed that the longer it takes the rats to lick their paws, the more the analgesia.) Group A rats display much less of an analgesic response than Group B rats. Is this tolerance phenomenon more compatible with a pharmacodynamic or a context specific mechanism for tolerance development? Explain your reasoning.

What will be an ideal response?

joanwhite · **Reply #1 on:** Jun 22, 2018

Answer to Question 1

Any drug action that results in a lower than normal activity at receptors for an extended period of time (generally on the order of several hours) may lead to receptor up-regulation, e.g., a drug antagonist may bind to them and prevent neurotransmitter (NT) activation or the drug may increase the levels of the NTs for those receptors by reducing the NT reuptake, by enhancing NT release, by reducing NT metabolic degradation, by activating autoreceptors (which reduces NT release or synthesis), by decreasing the firing of neurons that release the NT, etc.

Answer to Question 2

The fact that the Group A rats, which had been exposed to morphine prior to their exposure in the analgesia test, exhibited less analgesia than Group B rats indicates the development of tolerance to morphine's analgesic properties. Because the Group A rats given the morphine pellet (1) were tested for morphine analgesia in a context totally different from that in which they experienced the effects of morphine and (2) never practiced the paw-licking behavior in response to heat while under the influence of morphine, it is unlikely that this is a context-specific form of tolerance, e.g., the development of a compensatory CR to the contextual/conditioned stimuli (CS) or an instrumental compensatory behavior. On the other hand, three days of chronic exposure to the morphine should be sufficient to induce some pharmacodynamic neuroadaptations in the Group A rats.