Fields gives a nice summary of work by Schwartz et al., who find a detailed synaptic mechanism for how chronic pain saps our motivations and desires. I pass on the article's abstract and a summary graphic by Schwartz.
Several symptoms associated with chronic pain, including fatigue and depression, are characterized by reduced motivation to initiate or complete goal-directed tasks. However, it is unknown whether maladaptive modifications in neural circuits that regulate motivation occur during chronic pain. Here, we demonstrate that the decreased motivation elicited in mice by two different models of chronic pain requires a galanin receptor 1–triggered depression of excitatory synaptic transmission in indirect pathway nucleus accumbens medium spiny neurons. These results demonstrate a previously unknown pathological adaption in a key node of motivational neural circuitry that is required for one of the major sequela of chronic pain states and syndromes.
Glutamate inputs excite nucleus accumbens medium spiny neurons. Chronic pain reduces AMPA receptor function in the DADR2-expressing class of these neurons, thereby reducing their activation by glutamate input. This decreases the motivation to work for a food reward.