A utonomicNervous Tones in Chronic Spinal Rats

Sympathetic and parasympathetic nervous tones and ability of temperature regulation were compared in spinal-intact control rats and in chronic spinal rats. The lower cervical cord of male Wistar rats was transected under pentobarbital anesthesia, and the rats were reared in a room of 30℃.For the experiment, each rat was placed in wire-meshed small cage in the climatic chamber (30℃, 60%, r.h). Ninety minutes after the beginning of recording, atropine sulfate (1mg/kg, i.p.) or propranolol hydrochloride (8mg/kg, i.p.) was injected. Cardiac parasympathetic and sympathetic tones were evaluated by heart rate (HR) change after the medication. Rectal temperature (Tre), tail skin temperature (Ttail) and HR were evaluated for 30 min before the medication. Mean Tre (M. ± S.E.) in control was 38.0±0.1℃, and those in the 1st, 2nd and 3rd week after spinalization were 36.1±0.2℃, 37.0±0.3℃ and 37.3±0.3℃, respectively. Resting HR (HR(norm.)) in control was 369±6 beats/min, and those in the 1st, 2nd and 3rd week after spinalization were 330±19 beats/min, 344±10 beats/min and 341±9 beats/min, respectively. The excess temperatures (dT) of the tail skin over the environmental temperature in the 1st to 3rd week were significantly higher (p<0.05) than in the control. In chronic spinal rats, there was a negative correla- tion between the increase in heart rate by atropine (HR(p)) and HR(norm.), and a positive correlation between the decrease in heart rate by propranolol (HR(s)) and HR(norm.). In control rats, parasympathetic tone (PT) and sympathetic tone (ST) were calculated as 22.5% and 24.4%, while in chronic spinal rats (from 1st to 6th week after spinalization), PT and ST were 16.6% and 15.7%, respectively. From these results it is presumed that the change in parasympathetic tone also may be a contributing factor in the recovery of the autonomic functions in chronic spinal animals.