Effects of pontine tegmental lesions that induce paradoxical sleep without atonia on thermoregulation in cats during wakefulness

REM sleep-suppressing effects of atropine in cats vary with environmental temperature

Because the occurrence of rapid eye movement (REM) sleep is critically dependent upon an animal's thermal balance, acute pharmacological treatments may effect REM sleep through effects on thermoregulation. We describe how manipulating ambient temperature (T(a)) alters the REM sleep-suppressing effects of systemically-administered atropine, a muscarinic receptor antagonist, in adult cats. At a T(a) of 23 degrees C , atropine (0.5 mg/kg) produced a significant reduction in REM sleep time that persisted for about 8 h of a 16 h recording period. Hypothalamic temperature fell below control levels for about 4 h following atropine. At a T(a) of 30 degrees C, the same dose of atropinehad no significant effect on REM sleep time, or hypothalamic temperature. These findings indicate the importance of considering the possible role of thermoregulation in drug-induced effects on REM sleep.

A brain-warming function for REM sleep

During REM sleep, arterial blood flow, neuronal firing rates, metabolism, and temperature increase in many parts of the CNS. Eye muscle tone also increases, and the eyes exhibit bursts of rapid movements. If one of the functions of sleep is to conserve energy, then it is curious that energy is so conspicuously expended in the vicinity of the CNS during REM sleep. The author hypothesizes that homeotherms use REM sleep to produce heat in order to maintain a high, stable temperature in a restricted CNS core during sleep. The fact that several of the active features of REM sleep heat the CNS, and the fact that REM sleep propensity increases when core temperature physiologically decreases, seem consistent with the hypothesis that REM sleep is a regulated mechanism for warming the CNS.

Dissociation of thermoregulation in cats with cytotoxic pontine lesions

Neurons of the pontine tegmentum of the cat were lesioned by microinjection of ibotenic acid into the brainstem. The threshold ambient temperatures for heat-gain (shivering) and for heat-loss (panting) responses, together with brain and skin temperatures, were measured in intact animals and after the neurotoxic lesioning. After the lesioning the shivering threshold was altered but the panting threshold did not change. The results indicate that certain neurons involved in the shivering response reside in the pontine tegmentum. Neurons involved in the panting response, however, may lie outside the lesioned areas.

Effect of ambient temperature on sleep-waking cycle in cats with electrolytic dorsolateral pontine tegmental lesions

The effects of ambient temperature on the sleep-waking cycle were studied in intact cats and those with bilateral electrolytic lesions in the pontine tegmentum. At a room temperature of 23 degrees C, the percentage of time spent in paradoxical sleep was significantly lower in the lesioned cats than in intact animals. The mean duration of paradoxical sleep episodes was also decreased in the lesioned animals. The reduction in slow-wave sleep was not significant. At a slightly warmer ambient temperature of 30 degrees C, both the mean duration of paradoxical sleep episodes and the total duration of paradoxical sleep in the lesioned animals were increased toward normal values. Slow-wave sleep increased slightly but not significantly. At a higher ambient temperature of 35 degrees C, as well as at colder ambient temperatures of 15 and 7 degrees C, the durations of both paradoxical sleep and slow-wave sleep were significantly reduced. Under these thermal loads, the reduction in the duration of sleep was significantly greater in the lesioned cats than in the intact animals. The results suggest that: (i) pontine lesions alter the sleep cycle of cats and ambient temperature influences this alteration; (ii) the effects of thermal loads on the sleep cycle are more severe in the lesioned cats; and (iii) a moderately warm ambient temperature (30 degrees C) improves the sleep of pontine-lesioned cats.

Afferent and efferent connections of the cholinoceptive medial pontine reticular formation (region of the ventral tegmental nucleus) in the cat

Following minor concussive brain injury when there is an otherwise general suppression of CNS activity, the ventral tegmental nucleus of Gudden (VTN) demonstrates increased functional activity (32). Electrical or pharmacological activation of a cholinoceptive region in this same general area of the medial pontine tegmentum contributes to certain components of reversible traumatic unconsciousness, including postural atonia (31, 32, 45). Therefore, in an effort to examine the neuroanatomical basis of the behavioral suppression associated with a reversible traumatic unconsciousness, the afferent and efferent connections of the VTN and putative cholinoceptive medial pontine reticular formation (cmPRF) were studied in the cat using the retrograde horseradish peroxidase (HRP), HRP/choline acetyltransferase (ChAT) double-labeling immunohistochemistry, and anterograde HRP and autoradiographic techniques. Based upon retrograde HRP labeling, the principal afferents to the VTN region of the cmPRF originated from the medial and lateral mammillary nuclei, and lateral habenular nucleus, and to a lesser extent from the interpeduncular nucleus, lateral hypothalamus, dorsal tegmental nucleus, superior central nucleus, and contralateral nucleus reticularis pontis caudalis. Other afferents, which were thought to have been labeled through spread of HRP into the medial longitudinal fasciculus (MLF), adjacent paramedian pontine reticular formation, or uptake by transected fibers descending to the inferior olive, included the nucleus of Darkschewitsch, interstitial nucleus of Cajal, zona incerta, prerubral fields of Forel, deep superior colliculus, nucleus of the posterior commissure, nucleus cuneiformis, ventral periaqueductal gray, vestibular complex, perihypoglossal complex, and deep cerebellar nuclei. In HRP/ChAT double labeling studies, only a very small number of cholinergic VTN afferent neurons were found in the medial parabrachial region of the dorsolateral pontine tegmentum, although the pedunculopontine and laterodorsal tegmental nuclei contained numerous single-labeled ChAT-positive cells. Anterograde HRP and autoradiographic findings demonstrated that the VTN gave rise almost exclusively to ascending projections, which largely followed the course of the mammillary peduncle (16,21) and medial forebrain bundle, or the tegmentopeduncular tract (4). The majority of fibers ascended to terminate in the medial and lateral mammillary nuclei, interpeduncular complex (especially paramedian subnucleus), ventral tegmental area, lateral hypothalamus, and the medial septum in the basal forebrain. Labeling that joined the mammillothalamic tract to terminate in the anterior nuclear complex of the thalamus was thought to occur transneuronally. Some projections were also observed to nucleus reticularis pontis oralis and caudalis, superior central nucleus, and dorsal tegmental nucleus adjacent to the VTN...

Release of heat-loss responses in paradoxical sleep by thermal loads and by pontine tegmental lesions in cats

Thermoregulatory heat-loss responses at high ambient temperatures were studied in intact cats and those with bilateral electrolytic lesions in the pontine tegmentum during wakefulness (W), slow-wave sleep (SWS), paradoxical sleep (PS) and PS without atonia induced by the lesions. Panting (respiratory rate greater than or equal to 90/min) was present during W, SWS, and in some cases, during PS. The percentage of the PS episodes with panting was directly related to ambient temperature. In intact cats at 30 degrees C, panting occurred in 8% of the PS episodes; at 35 degrees C, in 52%, and at 40 degrees C, in 77%. The percentage of PS episodes with panting was higher in the pontine-lesioned cats (90% at 35 degrees C), probably another indication of the altered thermoregulation of such animals. Thermoregulatory responses to heat load, and thermoregulation in general, have previously been shown to be suppressed in PS. Because hypothalamic thermosensitive neurons lack thermal responses during PS, the partial activation of heat-loss responses observed here may depend upon the function of extrahypothalamic brainstem areas.

Descending projections from the gigantocellular tegmental field in the cat: cells of origin and their brainstem and spinal cord trajectories

The trajectories and the cells of origin of the pontobulbar gigantocellular tegmental field descending pathways were studied in the cat using anterograde WGA-HRP and retrograde HRP techniques. Four main descending pathways and cells of origin were delineated: (1) Predominantly large neurons in the pontine gigantocellular tegmental field (average soma diameter = 43.4 microns) and rostral bulbar gigantocellular tegmental field (41.3 microns) gave rise to reticulospinal fibers descending in the ipsilateral medial longitudinal fasciculus and ventral funiculus and distributed in laminae V-X with an ipsilateral predominance. These were primarily large-diameter fibers. (2) Predominantly large neurons (46.9 microns) in the bulbar gigantocellular tegmental field gave rise to reticulospinal fibers descending in the contralateral medial longitudinal fasciculus and ventral funiculus. These were mainly large-diameter fibers. (3) Neurons of predominantly medium size (29.5 microns) in the pontine gigantocellular tegmental field gave rise to reticuloreticular fibers descending directly to and distributed bilaterally in the bulbar reticular formation. These were small-diameter fibers. (4) Neurons of predominantly medium size (28.9 microns) in the bulbar gigantocellular tegmental field gave rise to reticulospinal fibers descending in the ipsilateral reticular formation and lateral funiculus. These were small-diameter fibers.