ENHANCED NOCICEPTIVE RESPONDING IN TWO RAT MODELS OF DEPRESSION IS ASSOCIATED WITH ALTERATIONS IN MONOAMINE LEVELS IN DISCRETE BRAIN REGIONS

Altered pain responding in depression is a widely recognized but poorly understood phenomenon The present study investigated nociceptive responding to acute (thermal and mechanical) and persistent (inflammatory) noxious stimuli in two animal models of depression the olfactory bulbectomized (OB) and the Wistar Kyoto (WKY) rat In addition, this study examined if altered nociceptive behaviour was associated with changes in monoamine levels in discrete brain regions OB rats exhibited mechanical allodynia (von Frey test) but not thermal hyperalgesia (hot plate and tail-flick tests) when compared to sham operated counterparts For maim induced nociceptive behaviour was both heightened and prolonged in OB versus sham operated controls An inverse correlation was observed between 5 hydroxyindoleacetic acid (5 HIAA) concentration in the hippocampus and amygdaloid cortex and nociceptive behaviour in the for maim test In comparison, WKY rats exhibited thermal hyper algesia in the hot plate test, while behaviour in the tail flick and von Frey tests did not differ between WKY and Sprague Dawley rats Furthermore, WKY rats exhibited enhanced for maim evoked nociceptive responding up to 40 min post ad ministration, an effect inversely correlated with serotonin and 5 HIAA levels in the hypothalamus In conclusion these findings demonstrate that altered pain responding observed in clinically depressed patients can be modelled pre-clinically, providing a means of investigating the neurochemical basis of, and possible treatments for, this phenomenon (C) 2010 IBRO Published by Elsevier Ltd All rights reserved