Dennis McGinty

Dorsal raphe neurons: depression of firing during sleep in cats.

The results of lesion and pharmacological experiments suggest that 5-HT-containing neurons localized in the raphe nuclei of the brain stem participate functionally in the control of slow wave sleep (SWS) 24-27 as well as in a variety of waking (W) behavioral processes s,l°. Studies of neuronal unit discharge of this cell type in unanesthetized chronic animals should provide additional data bearing on their functions in the control of sleep and waking behaviors. The dorsal raphe nucleus of the midbrain is a primary location of neuronal perikarya containing 5-hydroxytryptamine (5-HT) and a major source of axons projecting to forebrain sites 5,xl,z°,2a. This report describes the changes in the rate and pattern of unit discharge of dorsal raphe neurons during the W-SWS-REM cycle in the cat*. Single units were recorded from adult cats through chronically-implanted flexible Formvar insulated nichrome wires with diameters of 32, 45, or 62 #m as described previously in. Under pentobarbital anesthesia, bundles of 6 microwires were stereotaxically lowered into position through the barrel of a mechanical microdrive in. The dorsal raphe nucleus (AP --2 to + 1, H --1 to --3, L 0) was approached through the cerebellum with the microdrive inclined caudally 40 ° from the vertical to avoid the bony tentorium. Each microwire, as well as leads to macroelectrodes for recording cortical and subcortical slow wave activity, eye movements and neck EMG, were soldered to a standard electrical connector which was rigidly attached to the skull with dental cement. Beginning two weeks following surgery, the cat was placed within an insulated, shielded cubicle (each side about 60 cm), and connected to recording amplifiers through a low noise cable. The microdrive was advanced until stable single units with signal to noise ratios exceeding 2:1 were encountered. A continuous recording, in* Preliminary reports describing these results previously presented are: McGINTY, D. J., Neurochemically defined neurons: behavioral correlates of unit activity of serotonin-containing neurons. In M. I. PHILLIPS (Ed), Brain Unit Activity During Behavior, Thomas, Springfield, Ii1., 1973, pp. 244-267. McGINTY, D. J., HARPER, R. M., AND FAIRBANKS, M. K., 5-HT-containing neurons: unit activity in behaving cats. In J. BARCHAS AND E. USmN (Eds.), Serotonin and Behavior, Academic Press, New York, 1973, pp. 267-279.

Sleep suppression after basal forebrain lesions in the cat.

Large bilateral preoptic lesions produced complete sleeplessness in two cats. In eight additional cats, similar but smaller lesions resulted in a significant reduction of quiet (slow-wave) sleep by 55 to 73 percent, and active (paradoxical) sleep by 80 to 100 percent. These values were determined by pre- and postlesion 22-hour continuous observations. Complete sleeplessness was followed by lethal exhaustion within a few days, whereas incomplete sleeplessness persisted at maximum levels for 2 to 3 weeks. The suppression of sleep was characterized by a gradual onset during the first 1 to 2 weeks, and a complete or partial recovery after 6 to 8 weeks. The severity of sleep suppression was found to be related to the size and localization of lesions placed specifically within the preoptic area and not to transient disturbances in feeding and temperature regulation.

Sleep–waking discharge patterns of ventrolateral preoptic/anterior hypothalamic neurons in rats

Numerous lesion, stimulation and recording studies in experimental animals demonstrate the importance of neurons within the preoptic/anterior hypothalamic area (POA) in the regulation of sleep induction and sleep maintenance. Recently, a discrete cluster of cells in the ventrolateral POA (vlPOA) of rats was found to exhibit elevated c-fos gene expression during sleep, indicating that these neurons are strongly activated during nonREM and/or REM sleep stages. We examined neuronal discharge during wakefulness and sleep throughout the dorsal to ventral extent of the lateral POA in rats, using chronic microwire technique. We found that neurons with elevated discharge rates during sleep, compared to waking, were localized to the vlPOA. As a group, vlPOA neurons displayed elevated discharge rates during both nonREM and REM sleep. Discharge of vlPOA neurons reflected the depth of sleep, i.e., discharge rates increased significantly from light to deep nonREM sleep. During recovery sleep following 12-14 h of sleep deprivation, vlPOA neurons displayed increased sleep-related discharge, compared to baseline sleep. Neurons in the vlPOA displaying increased neuronal discharge during sleep were located in the same area where neurons exhibit increased c-fos gene expression during sleep. Such neurons are likely components of a rostral hypothalamic mechanism that regulates sleep onset and sleep maintenance.

Keeping cool: a hypothesis about the mechanisms and functions of slow-wave sleep.

Current evidence supports a hypothesis that slow-wave sleep (SWS) in mammals and birds is controlled by thermoregulatory mechanisms, and provides brain and body cooling as a primary homeostatic feedback process. Recent work has identified a medial preoptic area anterior hypothalamic and basal forebrain neuronal network which integrates thermoregulatory and hypnogenic controls. This network induces EEG and behavioral deactivation, in part, through suppression of the reticular activating system. Studies have shown that SWS, like other heat loss processes, is facilitated when brain temperature exceeds a threshold level. This threshold is hypothesized to be determined by responses of POAH thermosensitive neurons and to be regulated by both circadian and homeostatic processes. Many known chemomodulators of SWS appear to act on this hypnogenic thermoregulatory system. At a functional level, SWS-induced brain and body cooling would provide several adaptations including lower energy utilization, reduced cerebral metabolism, protection of the brain against the sustained high temperatures of wakefulness, facilitation of immune defense processes and regulation of the timing of behavioral activity relative to the circadian light-dark cycle. This concept provides a comprehensive model for analysis of sleep homeostasis.

Sleep-related neuronal discharge in the basal forebrain of cats.

Although evidence suggests that the basal forebrain contains a hypnogenic mechanism, putative sleep-promoting neural elements within this area have not been identified. We examined basal forebrain neuronal activity during waking, non-rapid-eye-movement (NREM) sleep, REM sleep and various transition states. Based on state-related discharge rates. 3 cell types were defined. Thirty-nine of 83 cells were classified as waking-active, i.e. waking discharge rates were greater than 2 times NREM sleep rates. Twenty-three of 82 cells were classified as state-indifferent (waking and NREM rates differed by a factor of less than 2). NREM sleep discharge rates of the remaining 20 cells were greater than 2 times waking rates. These were labeled sleep-active cells. Discharge rates of these cells during epochs of alert waking were low, averaging less than 1 spike/s. Maximal discharge rates occurred during NREM sleep, averaging 9.44 spikes/s. Increased discharge of sleep-active cells anticipated sleep onset; cells had an average discharge rate of 6.60 spikes/s during transitions between waking and NREM sleep. Sleep-active cells were confined to the ventral basal forebrain, in the horizontal limb of the diagonal bands of Broca, substantia innominata, entopeduncular nucleus and ventral globus pallidus. These areas overlap, in part, with those where chemical, thermal and electrical stimulations evoke sleep, and where lesions suppress sleep. Based on location and discharge pattern we consider sleep-active cells candidates for mediating some of the sleep-promoting functions of the basal forebrain.

Hypothalamic Regulation of Sleep and Arousal

Normal waking is associated with neuronal activity in several chemically defined ascending arousal systems. These include monoaminergic neurons in the brainstem and posterior hypothalamus, cholinergic neurons in the brainstem and basal forebrain, and hypocretin (orexin) neurons in the lateral hypothalamus. Collectively, these systems impart tonic activation to their neuronal targets in the diencephalon and neocortex that is reflected in the low‐voltage fast‐frequency electroencephalogram patterns of wakefulness. Neuronal discharge in these arousal systems declines rapidly at sleep onset. Transitions from waking to sleep, therefore, involve coordinated inhibition of multiple arousal systems. An important source of sleep‐related inhibition of arousal arises from neurons located in the preoptic hypothalamus. These preoptic neurons are strongly activated during sleep, exhibiting sleep/waking state‐dependent discharge patterns that are the reciprocal of that observed in the arousal systems. The majority of preoptic sleep regulatory neurons synthesize the inhibitory neurotransmitter GABA. Anatomical and functional evidence supports the hypothesis that GABAergic neurons in the median preoptic nucleus (MnPN) and ventrolateral preoptic area (VLPO) exert inhibitory control over the monoaminergic systems and the hypocretin system during sleep. Recent findings indicate that MnPN and VLPO neurons integrate homeostatic aspects of sleep regulation and are important targets for endogenous sleep factors, such as adenosine and growth hormone releasing hormone.

New neurons in the adult brain: The role of sleep and consequences of sleep loss

Research over the last few decades has firmly established that new neurons are generated in selected areas of the adult mammalian brain, particularly the dentate gyrus of the hippocampal formation and the subventricular zone of the lateral ventricles. The function of adult-born neurons is still a matter of debate. In the case of the hippocampus, integration of new cells in to the existing neuronal circuitry may be involved in memory processes and the regulation of emotionality. In recent years, various studies have examined how the production of new cells and their development into neurons is affected by sleep and sleep loss. While disruption of sleep for a period shorter than one day appears to have little effect on the basal rate of cell proliferation, prolonged restriction or disruption of sleep may have cumulative effects leading to a major decrease in hippocampal cell proliferation, cell survival and neurogenesis. Importantly, while short sleep deprivation may not affect the basal rate of cell proliferation, one study in rats shows that even mild sleep restriction may interfere with the increase in neurogenesis that normally occurs with hippocampus-dependent learning. Since sleep deprivation also disturbs memory formation, these data suggest that promoting survival, maturation and integration of new cells may be an unexplored mechanism by which sleep supports learning and memory processes. Most methods of sleep deprivation that have been employed affect both non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. Available data favor the hypothesis that decreases in cell proliferation are related to a reduction in REM sleep, whereas decreases in the number of cells that subsequently develop into adult neurons may be related to reductions in both NREM and REM sleep. The mechanisms by which sleep loss affects different aspects of adult neurogenesis are unknown. It has been proposed that adverse effects of sleep disruption may be mediated by stress and glucocorticoids. However, a number of studies clearly show that prolonged sleep loss can inhibit hippocampal neurogenesis independent of adrenal stress hormones. In conclusion, while modest sleep restriction may interfere with the enhancement of neurogenesis associated with learning processes, prolonged sleep disruption may even affect the basal rates of cell proliferation and neurogenesis. These effects of sleep loss may endanger hippocampal integrity, thereby leading to cognitive dysfunction and contributing to the development of mood disorders.

Subregional organization of preoptic area/anterior hypothalamic projections to arousal-related monoaminergic cell groups.

Pathways mediating the generation and/or maintenance of sleep reside within the preoptic/anterior hypothalamus (POAH). Reproduction, water balance, thermoregulation, and neuroendocrine functions are also associated with POAH, but it is not fully understood whether sleep is consolidated with these behavioral and physiological functions, or whether sleep‐related circuitry is segregated from other POAH regions. Recent studies indicate that sleep mechanisms may be localized to the ventrolateral preoptic area (VLPO) and that this region sends inhibitory projections to waking/arousal‐related neurons in the histaminergic tuberomammillary nucleus (TM), the noradrenergic locus coeruleus (LC), and the serotonergic dorsal raphe (DR). The present study is a quantitative investigation of preoptic area efferents to these monoaminergic groups. The results demonstrate that biotinylated dextran injections in the VLPO region reveal a robust innervation of TM that was as much as five times greater than innervation derived from other POAH subregions. The innervation of TM originated almost exclusively from injection sites in the region of galanin neurons. VLPO projections to the LC were moderately dense and were greater than in other POAH regions except for equivalent input from the medial preoptic area. Projections to the dorsal raphe were equivalent to LC innervation and were generally two to three times greater from VLPO than from other POAH regions, except for projections from the lateral preoptic region, which were similar in magnitude. The rostral and caudal levels projected more to the TM, whereas the midrostral region of VLPO strongly innervated the LC core. These findings, with recent studies demonstrating medial and lateral extensions of the sleep‐related VLPO neuronal group, indicate that descending arousal state control may be mediated by this specific galaninergic/γ‐aminobutyric acid (GABA)ergic cell group. J. Comp. Neurol. 429:638–653, 2001.

Polygraphic Studies of Normal Infants during the First Six Months of Life. I. Heart Rate and Variability as a Function of State

Extract: This study examined spontaneous heart rate (HR) and variability as a function of age and sleep state in eight normal full term infants from birth to 6 months of age. Heart rates recorded during sleep were lower and less regular at 1 week (quiet sleep (QS) mean rate = 128, interquartile range = 6.4 beats/min; rapid eye movement (REM) = 134.5, 11.6) than at 1 month (QS = 138.6, 3.4; REM 139.6, 4.2). Rate decreased sharply from 1 to 3 months (QS = 118; REM 123.8) and decreased only slightly thereafter (6-month QS = 113.5; REM 118.9). Variability decreased rapidly in REM from 2 to 4 months (from 11.4 to 9.1) and less quickly from 4 to 6 months (from 9.1 to 8.2), while QS variability decreased at 1 month (from 6.4 to 5.7) and became stable from that point (6.0 at 6 months). Waking heart rate and variability were both relatively low at 1 week (163, 11.2 beats/min) and increased from that age to 1 month (167.4, 14.3). Rate decreased rapidly in waking at 3 months (152 beats/min) and more slowly thereafter (152 beats/min at 4 months, 149 beats/min at 6 months), whereas variability remained elevated until after 3 months, becoming stable at a lower level during later infancy (3 months = 14.8, 6 months 11.7). Lowest values of rate and variability were found in QS and the highest values were found in waking at all ages, except at 1 week. Heart rates during REM closely approximated those in QS, whereas variability values more closely resembled those of waking.Speculation: It would appear that, in the normal infant, there are at least three relatively discrete stages in the ontogenetic sequence of cardiac rate and variability characteristics: a newborn period, early infancy (1–3 months), and later infancy. Since regulation of cardiac activity is greatly modified by sleep and waking behavior, the measurement of heart rate and variability must consider state as a factor in such regulation. Moreover, since states undergo both qualitative and quantitative changes during the first 6 months of age, the nature of cardiac regulation during this period may be a function of state maturation.

Sleep-waking discharge patterns of neurons recorded in the rat perifornical lateral hypothalamic area

The perifornical lateral hypothalamic area (PF‐LHA) has been implicated in the control of several waking behaviours, including feeding, motor activity and arousal. Several cell types are located in the PF‐LHA, including projection neurons that contain the hypocretin peptides (also known as orexins). Recent findings suggest that hypocretin neurons are involved in sleep‐wake regulation. Loss of hypocretin neurons in the human disorder narcolepsy is associated with excessive somnolence, cataplexy and increased propensity for rapid eye movement (REM) sleep. However, the relationship of PF‐LHA neuronal activity to different arousal states is unknown. We recorded neuronal activity in the PF‐LHA of rats during natural sleep and waking. Neuronal discharge rates were calculated during active waking (waking accompanied by movement), quiet waking, non‐REM sleep and REM sleep. Fifty‐six of 106 neurons (53 %) were classified as wake/REM‐related. These neurons exhibited peak discharge rates during waking and REM sleep and reduced discharge rates during non‐REM sleep. Wake‐related neurons (38 %) exhibited reduced discharge rates during both non‐REM and REM sleep when compared to that during waking. Wake‐related neurons exhibited significantly higher discharge rates during active waking than during quiet waking. The discharge of wake‐related neurons was positively correlated with muscle activity across all sleep‐waking states. Recording sites were located within the hypocretin‐immunoreactive neuronal field of the PF‐LHA. Although the neurotransmitter phenotype of recorded cells was not determined, the prevalence of neurons with wake‐related discharge patterns is consistent with the hypothesis that the PF‐LHA participates in the regulation of arousal, muscle activity and sleep‐waking states.