Sleep and wakefulness modulation of the neuronal firing in the auditory cortex of the guinea pig.

Sleep-related changes-including modification in sensory processing-that influence brain and body functions, occur during both slow wave and paradoxical sleep. Our aim was to investigate how cortical auditory neurons behave during the sleep/waking cycle, and to study cell firing patterns in relation to the processing of auditory information without the interference of anesthetic drugs. We recorded single cells in the A region of the auditory cortex in restrained, chronically-implanted guinea pigs, and compared their evoked and spontaneous activity during sleep stages and quiet wakefulness. A new classification of the unit's responses to simple sound during wakefulness is presented. Moreover, a number of the neurons in the primary auditory cortex exhibited significant quantitative changes in their evoked or spontaneous firing rates. These changes could be correlated to sleep stages or wakefulness in 42.2% to 58.3% of the sampled neurons. A similar population did not show behavioral related changes in firing rates. Our results indicate that the responsiveness of the auditory system during sleep may be considered partially preserved. An important result was that spontaneous and evoked activity may vary in opposite directions, i.e. , the evoked activity could increase while the spontaneous activity decrease or vice versa. Then, a general question was proposed: is the increased spontaneous activity in the auditory cortex, particularly during PS, related to auditory hypnic 'images'? The studied cortical auditory neurons exhibit changes in their firing rates in correlation to stages of sleep and wakefulness. This is consistent with the hypothesis that a general shift in the neuronal networks involved in sensory processing occurs during sleep.

Les manifestations articulaires de la lèpre / Articular manifestations in leprosy

Articular manifestations occur in approximately 1% of cases of leprosy, sometimes at onset. They consist in a highly inflammatory polyarthritis, fairly similar to that seen in rheumatoid polyarthritis. They often herald a reactive leprous exacerbation and are dependent upon immunologic disturbances in brittle leprosy (mainly lepromatous). Joint pain should be differentiated from neurologic pain resulting from peripheral neuropathy which is often concomitant. Leprosy should be considered among the causes of polyarthritis, especially in immigrants, but also in residents who have travelled to areas where leprosy is endemic.