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Role of galanin receptor-expressing dorsal horn neurons in operant nocifensive responses.

Lemons LL, Wiley RG (2009) Role of galanin receptor-expressing dorsal horn neurons in operant nocifensive responses. Neuroscience 2009 Abstracts 170.18/X20. Society for Neuroscience, Chicago, IL.

Summary: Selective destruction of galanin receptor-expressing dorsal horn neurons using the targeted cytotoxin, galanin-saporin (gal-sap), reduced reflex nocifensive hotplate responses, particularly at 44° C (see adjacent poster). The antinociceptive effect of gal-sap was additive with morphine (5 mg/kg, s.c.) in reducing hotplate responses. While these findings are provocative, inferences about analgesia also require information on cerebral processing of nociceptive information, such as obtained from operant nocifensive responses. We therefore sought to determine the effects of lumbar intrathecal gal-sap on nocifensive operant responses. Thirteen Long Evans female rats were injected with either 500 ng gal-sap or 500 ng blank-sap and tested on the escape test at several temperatures. The escape task consists of a two-chambered box; one side is dark with a thermal floor while the other side is brightly lit with a room temperature shelf. Gal-sap treated rats escaped from the thermal plate to the escape shelf less than controls. The difference was particularly striking at 25°, 38°, 44°, 45°, and 47°C. Morphine effects on escape responses was tested at 44°C. Thirty minutes before testing, rats were injected subcutaneously with either 0, 0.5, 1.5 or 4.5 mg/kg morphine. The testing was done over four days such that every rat was tested at each dosage in a counterbalanced fashion. 1.5mg/kg of morphine significantly reduced the escape duration of the blank-sap control rats, but not the gal-sap rats. The 4.5mg/kg dosage completely eliminated escape responding in both control and gal-sap rats. In summary, Gal-sap rats showed reduced nocifensive reflex responding on the hotplate tests, which was further reduced in essentially additive fashion by 5mg/kg of morphine. The Gal-sap treated rats also showed reduced escape behaviors at 44°C in the operant escape test, but were less sensitive to 1.5 mg/kg of morphine than the control rats. These results differ from the effects of NPY-saporin and dermorphin-saporin, cytotoxins also targeted at dorsal horn interneurons, suggesting that selective destruction of galanin receptor-expressing superficial dorsal horn neurons is analgesic and that galanin-receptor-expressing dorsal horn interneurons play a unique role in nociceptive processing.

Related Products: Galanin-SAP (Cat. #IT-34)