Massage-like stroking of rats (2007)

Holst, S.

Abstract

Massage is an ancient treatment that still is commonly used in humans. Massage is reported to have several beneficial effects including activation of the relaxation and growth response that is proposed to be mediated by oxytocin (OT). In the present thesis the effects of repeated massage-like stroking (stroking) in rats has been studied. The experimenter restraints the rat with one hand and with the other hand the abdomen of the rat was firm but gently stroked at a speed of 30-40 strokings/min for 5 minutes. In order to analyze the individual behavioral treatment response the stroking sessions were video recorded (paper III and IV). In paper I, the effects of stroking on plasma levels of gastrin, insulin, CCK, somatostatin and glucose were investigated. Plasma levels of gastrin and insulin decreased after 14 stroking sessions, whereas plasma levels of glucose and body weight increased.In paper II, rats were treated postnatally with either stroking early in life or with OT injections. Both postnatal stroking and OT-treatment decreased the diastolic blood pressure measured with the tail-cuff method in adulthood in these rats.In paper III, female rats surgically prepared with telemetric blood pressure equipment were used. The rats were their own controls and the experiment started with a 5 days control period followed by 10 days with stroking. Each stroking session was video recorded and blood pressure measured with telemetry. Blood pressure increased during stroking and was maintained high during the 10 days stroking period compared to the control period. Latency time to relaxation decreased during the stroking period.In paper IV, the effects of stroking on social interaction were studied. Stroking in male rats did not alter the social interaction or the plasma levels of OT and corticosterone. However, home-cage dominance as well as interaction between dominance and stroking altered the social behavior.In conclusion, most of the results indicate that the rat experiences distress rather than anti-stress during stroking. Since rats had to be restrained during stroking, the sympathetic nervous system probably was activated. This might have hidden the suggested stroking induced reflex activation of the parasympathetic nervous system. For future studies another animal model that can be stroked without restraint, i.e. dog is recommended.