Increase of galanin-like immunoreactivity in rat hypothalamic arcuate neurons after peripheral nerve injury

Galanin and galanin receptors are widely distributed within the central nervous system, and may play important roles in pain signaling and modulation. In the present study, we examined the galanin immunoreactivity (IR) in the hypothalamus and the amygdala following peripheral nerve injury. Four weeks after the operation, the ipsilateral mechanical threshold in the spared nerve injury (SNI) group (0.87 ± 0.33 g) was significantly lower than that in the sham group (12.53 ± 3.41 g; P < 0.05). In the SNI group, the number of galanin-IR neurons per section in the arcuate nucleus (Arc) of the hypothalamus was 10.2 ± 1.7, significantly higher than that in the sham group (5.6 ± 1.0; P < 0.05). These data suggest that the galanin-ergic neurons in the Arc may be involved in the functional modulation of descending pain modulation system following peripheral nerve injury.