Differential effects of persistent nociceptive stimulation on sleep stages.

The purpose of this work was to investigate the sequence of modifications of sleep and pain parameters in a condition of persistent nociceptive stimulation. In freely moving cats carrying implanted electrodes, continuous polygraphic and behavioral recordings were collected 24 h a day for several consecutive days before and after treatment. Injection of formalin (2 ml, 37%) elicited continuous wakefulness (1-6 h) associated with behavioral manifestations of pain. This insomnia was followed by the delayed appearance of LS (light, slow wave sleep) DS (deep slow wave sleep) and REM (rapid eye movement sleep). On days 1 and 2 after injection, pain manifestations displayed a gradual decrease, while total sleep time (LS + DS + REM) slowly returned to normal levels. On day 1, the amount of LS was not modified, but DS and REM were greatly decreased. For 12 h after the first REM episode, REM was decreased while DS was already at the basal levels. Formalin elicited a long-lasting increase in EMG activity of the tibialis anterior muscle which was suppressed during REM and returned to higher levels afterwards. Prolonged wakefulness and delay in sleep stage appearance were also recorded when a 24-h sleep deprivation preceded formalin injection. In this condition, LS, DS and REM amount were at basal levels from their first reappearance, and a rebound in total sleep time and DS occurred on day 2 after the injection. After injection of smaller doses of formalin (0.5 ml, 8%), the amount of LS, DS and REM was at control levels since day 1. The results suggest that (1) the amount of sleep depends on sleep debt and on the level of pain intensity and (2) sleep stages are differentially sensitive to persistent pain.

Central and peripheral endocrine correlates of the immobility reaction in the toad Bufo bufo.

The immobility reaction, which may be regarded as an innate fear response, has been observed in several animal species including Amphibians. Its endocrine correlates were established in the newt Triturus cristatus and in the toad Bufo bufo, in which the duration of immobility is influenced by sex and mating. The aim of the present study was to investigate the possibility of a relation between immobility reaction and central hormonal receptors. Testosterone (T) binding capacity in the brain and plasma sex steroids were studied in four groups of male and female sexually active and inactive toads in which the immobility reaction was induced by inversion (A) and by inversion +pressure (B). Females were found to be more susceptible than males to immobility A, whereas males were more susceptible to B. Sexually active animals with higher plasma levels of sex steroids were less susceptible than inactive ones. Lower T binding capacity in the brain and higher affinity is associated with sexual activity. Susceptibility to the immobility was negatively correlated with plasma sex steroids and positively correlated with T binding capacity. A reciprocal effect was found to exist between endocrine parameters at central and peripheral level, both controlling immobility behaviour. Mating may influence susceptibility to immobility through an endocrine mechanism.