PHAR 562 Lecture Notes - Lecture 19: Visual Analogue Scale, Rat Park, Johann Hari
13 Nov 2017
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**but first, we need to finish off lecture 18 material. Rats receive multiple injections of amphetamine or saline. Progressive ratio (pr) schedule requires an increasing number of lever presses to obtain successive infusions. Amphetamine pre-exposed rats worked for longer before giving up. The mere exposure to a drug repeatedly can sensitise the bran to the effects of the drug. Not all saing rats sensitise to reinforcing drug effects. Sa was tested with different doses of heroin. Before (open circles) and after (closed circles) multiple injections of morphine. We see that they are not becoming sensitised since they will press the lever even more over time. Drug abuse is determined by more than initial reinforcing effects. The initial exposure to the drug may not even be pleasant: morphine can produce dysphoria initially, must take it a few times before it becomes euphoric, same for smoking. Subjects could make 8 choices between a capsule and 1 dollar.
