Differences in Behavioral Parameters of Long-Term Pain in Formalin Test at the Period of Sex Maturation in Prenatally Stressed Female and Male Rats

Abstract

The effect of immobilization of pregnant rats was studied on parameters of the specific biphasic behavioral response (BBR) (patterns of flexion, shaking, licking, duration of the phases and of the interphase interval), of which the first phase characterizes the acute, while the second, he long-term pain in a nociceptive formalin test in the 40-day old female and male off-spring. The following was found: (1) an increase of intensity of patterns of flexion and shaking in the extremity injected with formalin at the second response phase and of the phase duration both in males and in females, (2) an increase of the licking pattern during the second phase and of the phase duration in males. Thus, the prenatal stress produced an increase of the pain sensitivity only at the long-term BBR phase; this increase was revealed in males from the patterns organized at the spinal and supraspinal levels, whereas in females, only at the spinal level. It was concluded that at the period of sex maturation, before the onset of sex maturity, the prenatally stressed males had more expressed damages in the behavioral parameters of the long-term pain in the formalin test, as compared with the prenatally stressed females. The comparative analysis of the response parameters allows suggesting the greater damage in males, then in females, of the inhibition process in the descending inhibitory system modulating nociceptive signals at the spinal cord level.