Effects of locus coeruleus lesions upon sleeping and waking in the rabbit

The effects of radiofrequency lesions in the region of the locus coeruleus (LC) upon sleep--waking states and behaviors were investigated in chronically implanted New Zealand White rabbits. Polygraphic recordings were taken prior to and at 5- and 14-day intervals following lesioning. In animals exhibiting absence of paradoxical sleep and the presence of bizarre motor behavior, additional recordings were taken 30 days postlesion. Prelesion sleep-wakefulness pattern data were comparable to those previously observed in intact rabbits, including the recently reported absence of sustained PS-related nuchal muscle atonia. Lesions histologically localized to the area of the locus coeruleus were of two types, i.e., those effecting bilateral destruction of greater than or equal to 80% (n = 11) or 30-50% (n = 11) of the LC. A transient period of inactivity was present immediately following lesioning, but by two weeks postlesion animals had generally regained normal waking behavioral and physiological functioning, e.g., eating, drinking and grooming behaviors had returned and respiration, micturition and general urological functioning were normal. The more extensive LC lesions were followed by increases in the proportion of total recording time spent in wakefulness, but primarily in quiet rather than active wakefulness. Sleep was fragmented by phasic muscular activation in proportion to the amount of LC destroyed. In animals with the most extensive lesions, slow wave sleep was interrupted by brief, abrupt episodes of twitching, and episodes of marked phasic muscular activation, often violent in nature, occurred following periods of slow wave sleep. The postlesion occurrence of PS was inversely related to the degree of LC destruction and, accordingly, to the presence of episodes of phasic motor activation. These results did not confirm earlier reports in other species implicating the LC in urogenital functioning and respiration, but do corroborate previous findings indicating that neural elements in the LC regions are essential to the integrity of sleep and are especially important to the control of motor mechanisms during sleep.