Increase of paradoxical sleep induced by microinjections of ibotenic acid into the ventrolateral part of the posterior hypothalamus in the cat.

In order to study putative hypothalamic mechanisms of sleep-waking cycle regulation we injected a neural cell body toxin--ibotenic acid (IBO), 40 to 200 micrograms--into the ventrolateral part of the posterior hypothalamus (HVL). This injection induced a dramatic biphasic and transient hypersomnia immediately after the disappearance of the anesthesia (14 to 24 hours after the injection). The duration of hypersomnia was dose dependent. Its first period was characterized by an increase in paradoxical sleep (PS) (300%). Then, during the second phase, PS disappeared and there was a subsequent increase of slow sleep (SWS) (60%). Finally, on the third day, all cats recovered control level of PS and SWS while, 3 weeks later, the histological analysis revealed the great loss of cell bodies in the HVL in all cats.