Pierrick Poisbeau, Christine Patte-Mensah, Anne Florence Keller, Michel Barrot, Jean-Didier Breton, Oliva Erendira Luis-Delgado, Marie José Freund-Mercier, Ayikoe Guy Mensah-Nyagan, and Rémy Schlichter
This week, Poisbeau et al. report that 3α,5α-reduced neurosteroids (5αNS) modulate inflammatory pain in the rat spinal cord. The authors found that a rapid increase in GABAA-mediated inhibition in lamina II after hindpaw injection of carageenan was prevented by finasteride (FIN), a blocker of 5αNS production. FIN had no effect in control adult rats, indicating that levels of endogenous 5αNS were not sufficient to alter basal synaptic inhibition. The inflammatory stimulus increased sensitivities to thermal and mechanical stimuli, but FIN delivery before inflammation reduced only thermal hyperalgesia. The upregulation of neurosteroids by peripheral inflammation provides support for separate thermal and mechanical pain processing pathways.
2. A Cubic Millimeter of Sweetness inthe Accumbens
Susana Peciña and Kent C. Berridge
Sweets and opiate drugs have powerful reward properties, mediated by μ-opioid accumbens (Nacc). This week, Peciña and Berridge pinpoint the location at which μ-opioids contribute to hedonic impact. With oral infusion of a sugary solution, injections of the μ-opioid agonist D-Ala2-N-Me-Phe4-Glycol5-enkephalin (DAMGO) doubled hedonic reactions in a cubic millimeter hotspot in the rostromedial shell of the Nacc. Aversive reactions to quinine were significantly reduced. In contrast, sites at whichmDAMGO increased food intake were spread throughout the medial shell.