Ventral tegmental self-stimulation, sensory reactivity and pain reduction in rats selected for high and low rates of lateral hypothalamic self-stimulation.

Ventral tegmental self-stimulation (VTSS) was studied in 56 male rats of four genetic lines (LC1-Lo, LC1-Hi, LC2-Lo, LC2-Hi), which differed in their inherent tendencies to self-stimulate the lateral hypothalamus. It was found that LC2-Hi rats engage more in VTSS than do rats of the LC2-Lo line. No differences were observed between the LC1-Hi and -Lo lines. In a second experiment, the LC2-Hi and -Lo lines were compared as to peripheral pain thresholds (36 animals) and VT-induced-analgesia (21 animals). Genetically low self-stimulators of the LC2 selection program were found to be more sensitive to acute peripheral pain and to VT analgesic influences than are their high counterparts. Theoretical implications are discussed.