Subcortical waking and sleep during lateral hypothalamic "somnolence" in rats

Distinct lateral hypothalamic CaMKIIα neuronal populations regulate wakefulness and locomotor activity

For nearly a century, evidence has accumulated indicating that the lateral hypothalamus (LH) contains neurons essential to sustain wakefulness. While lesion or inactivation of LH neurons produces a profound increase in sleep, stimulation of inhibitory LH neurons promotes wakefulness. To date, the primary wake-promoting cells that have been identified in the LH are the hypocretin/orexin (Hcrt) neurons, yet these neurons have little impact on total sleep or wake duration across the 24-h period. Recently, we and others have identified other LH populations that increase wakefulness. In the present study, we conducted microendoscopic calcium imaging in the LH concomitant with EEG and locomotor activity (LMA) recordings and found that a subset of LH neurons that express Ca2+/calmodulin-dependent protein kinase IIα (CaMKIIα) are preferentially active during wakefulness. Chemogenetic activation of these neurons induced sustained wakefulness and greatly increased LMA even in the absence of Hcrt signaling. Few LH CaMKIIα-expressing neurons are hypocretinergic or histaminergic while a small but significant proportion are GABAergic. Ablation of LH inhibitory neurons followed by activation of the remaining LH CaMKIIα neurons induced similar levels of wakefulness but blunted the LMA increase. Ablated animals showed no significant changes in sleep architecture but both spontaneous LMA and high theta (8 to 10 Hz) power during wakefulness were reduced. Together, these findings indicate the existence of two subpopulations of LH CaMKIIα neurons: an inhibitory population that promotes locomotion without affecting sleep architecture and an excitatory population that promotes prolonged wakefulness even in the absence of Hcrt signaling.

How REM sleep shapes hypothalamic computations for feeding behavior

The electrical activity of diverse brain cells is modulated across states of vigilance, namely wakefulness, non-rapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep. Enhanced activity of neuronal circuits during NREM sleep impacts on subsequent awake behaviors, yet the significance of their activation, or lack thereof, during REM sleep remains unclear. This review focuses on feeding-promoting cells in the lateral hypothalamus (LH) that express the vesicular GABA and glycine transporter (vgat) as a model to further understand the impact of REM sleep on neural encoding of goal-directed behavior. It emphasizes both spatial and temporal aspects of hypothalamic cell dynamics across awake behaviors and REM sleep, and discusses a role for REM sleep in brain plasticity underlying energy homeostasis and behavioral optimization.

Control of wakefulness by lateral hypothalamic glutamatergic neurons in male mice

The lateral hypothalamus (LH) plays a key role in the maintenance of cortical activation and wakefulness. In the LH, the two main neuronal cell populations consist of excitatory glutamatergic neurons and inhibitory GABAergic neurons. Recent studies have shown that inhibitory LH GABAergic neurons are wake-promoting. However, the mechanism by which excitatory LH glutamatergic neurons contribute to sleep-wake regulation remains unclear. Using fiber photometry in male mice, we demonstrated that LH glutamatergic neurons exhibited high activities during both wakefulness and rapid eye movement sleep. Chemogenetic activation of LH glutamatergic neurons induced an increase in wakefulness that lasted for 6 hr, whereas suppression of LH glutamatergic neuronal activity caused a reduction in wakefulness. Brief optogenetic activation of LH glutamatergic neurons induced an immediate transition from slow-wave sleep to wakefulness, and long-lasting optogenetic stimulation of these neurons maintained wakefulness. Moreover, we found that LH-locus coeruleus/parabrachial nucleus and LH-basal forebrain projections mediated the wake-promoting effects of LH glutamatergic neurons. Taken together, our data indicate that LH glutamatergic neurons are essential for the induction and maintenance of wakefulness. The results presented here may advance our understanding of the role of LH in the control of wakefulness.

Does the perigestational exposure to chlorpyrifos and/or high-fat diet affect respiratory parameters and diaphragmatic muscle contractility in young rats?

The perinatal period is characterized by developmental stages with high sensitivity to environmental factors. Among the risk factors, maternal High-Fat Diet (HFD) consumption and early-life pesticide exposure can induce metabolic disorders at adulthood. We established the effects of perigestational exposure to Chlorpyrifos (CPF) and/or HFD on respiratory parameters, sleep apnea and diaphragm contractility in adult rats. Four groups of female rats were exposed starting from 4 months before gestation till the end of lactation period to CPF (1 mg/kg/day vs. vehicle) with or without HFD. Sleep apnea and respiratory parameters were measured by whole-body plethysmography in male offspring at postnatal day 60. Then diaphragm strips were dissected for the measurement of contractility, acetylcholinesterase (AChE) activity, and gene expression. The perigestational exposure to CPF and/or HFD increased the sleep apnea index but decreased the respiratory frequency. The twitch tension and the fatigability index were also increased, associated with reduced AChE activity and elevated mRNA expression of AChE, ryanodine receptor, and myosin heavy chain isoforms. Therefore, the perigestational exposure to either CPF and/or HFD could program the risks for altered ventilatory parameters and diaphragm contractility in young adult offspring despite the lack of direct contact to CPF and/or HFD.

Parallel Arousal Pathways in the Lateral Hypothalamus

Until recently, hypocretin (Hcrt) neurons were the only known wake-promoting neuronal population in the lateral hypothalamus (LH), but subpopulations of inhibitory neurons in this area and glutamatergic neurons in the nearby supramammillary nucleus (SuM) have recently been found that also promote wakefulness. We performed chemogenetic excitation of LH neurons in mice and observed increased wakefulness that lasted more than 4 h without unusual behavior or EEG anomalies. The increased wakefulness was similar in the presence or absence of the dual orexin receptor blocker almorexant (ALM). Analysis of hM3Dq transfection and c-FOS expression in LH inhibitory neurons and in the SuM failed to confirm that the increased wakefulness was due to these wake-promoting populations, although this possibility cannot be completely excluded. To evaluate the relationship to the Hcrt system, we repeated the study in Orexin-tTA mice in the presence or absence of dietary doxycycline (DOX), which enabled us to manipulate the percentage of Hcrt neurons that expressed hM3Dq. In DOX-fed mice, 18% of Hcrt neurons as well as many other LH neurons expressed hM3Dq; these mice showed a profound increase in wake after hM3Dq activation even in the presence of ALM. In mice switched to normal chow, 62% of Hcrt neurons expressed hM3Dq along with other LH cells; chemogenetic activation produced even more sustained arousal which could be reduced to previous levels by ALM treatment. Together, these results indicate an LH neuron population that promotes wakefulness through an Hcrt-independent pathway that can act synergistically with the Hcrt system to prolong arousal.

Behavioural and neuronal activation after microinjections of AMPA and NMDA into the perifornical lateral hypothalamus in rats

The perifornical lateral hypothalamic area (PeFLH), which houses orexin/hypocretin (OX) neurons, is thought to play an important role in arousal, feeding, and locomotor activity. The present study examined behavioural effects of activating PeFLH neurons with microinjections of ionotropic glutamate receptor agonists. Three separate unilateral microinjections of either (1) AMPA (1 and 2mM in 0.1 μL artificial cerebrospinal fluid, ACSF) and ACSF, or (2) NMDA (1 and 10mM in 0.1 μL ACSF), and ACSF were made into the PeFLH of adult male rats. Following each injection, the rats were placed into an open field for behavioural scoring for 45 min. Rats were perfused after the third injection for immunohistochemistry for c-Fos and OX to assess the level of activation of OX neurons. Behavioural analyses showed that, as compared to ACSF conditions, AMPA injections produced a dose-dependent increase in locomotion and rearing that persisted throughout the 45 min recording period, and an increase in drinking. Injection of NMDA at 10mM, but not 1mM, induced a transient increase in locomotion and an increase in feeding. Histological analyses showed that while both agonists increased the number of neurons immunoreactive for c-Fos in the PeFLH, only AMPA increased the number of neurons immunoreactive for both c-Fos and OX. There were positive correlations between the number of c-Fos/OX-immunoreactive neurons and the amounts of locomotion, rearing, and drinking. These results support the role of ionotropic glutamate receptors on OX and other neurons in the PeFLH in the regulation of locomotor and ingestive behaviours.

Effect of high-fat diet and metformin treatment on ventilation and sleep apnea in non-obese rats

We investigated the effect of insulin resistance on ventilation and the incidence of sleep apnea in non-obese rats and determined whether metformin could change ventilation and occurrence of sleep apneas. Five groups of rats were studied: (1) standard chow; (2) high-fat groups, with 1 with metformin; (2) had type 2 diabetes induced by streptozotocin, with 1 with metformin. Compared to standard rats, ventilatory parameters remained unchanged in the high-fat fed diet as well as in diabetic rats. However, their oxygen consumption was reduced (p<or=0.01). They had a lower ventilatory response to CO2 challenge (p<or=0.01), and their sleep apnea scores increased markedly (p<or=0.001). These results suggest that insulin resistance could impair the ventilation control. Metformin treatment, known to reduce insulin resistance, got sleep apnea scores back to their basic levels, reinforcing the idea that insulin resistance is a major factor in the occurrence of apneas in this rat model.

Effects of hypocretin2-saporin and antidopamine-beta-hydroxylase-saporin neurotoxic lesions of the dorsolateral pons on sleep and muscle tone

The hypocretin neurons have been implicated in regulating sleep-wake states as they are lost in patients with the sleep disorder narcolepsy. Hypocretin (HCRT) neurons are located only in the perifornical region of the posterior hypothalamus and heavily innervate pontine brainstem neurons, such as the locus coeruleus (LC), which have traditionally been implicated in promoting arousal. It is not known how the hypocretin innervation of the pons regulates sleep-wake states as pontine lesions have never been shown to increase sleep. It is likely that in previous studies specific neurons were not lesioned. Therefore, in this study, we applied saporin-based neurotoxins to the dorsolateral pons and monitored sleep in rats. Anti-dopamine-beta-hydroxylase-saporin killed the LC neurons but sleep was affected only during a two hour light-dark transition period. Application of hypocretin2-saporin killed fewer LC neurons relative to other adjacent neurons. This occurred because the LC neurons possess the hypocretin receptor 1 but the ligand hypocretin 2 binds to this receptor with less affinity relative to the hypocretin receptor 2. The hypocretin2-saporin lesioned rats compared to controls had increased sleep during the dark period and displayed increased limb movements during REM sleep. None of the lesioned rats had sleep onset REM sleep periods or cataplexy. We conclude that the hypocretin innervation to the pons functions to awaken the animal when the lights turn off (via its innervation of the LC), sustains arousal and represses sleep during the rest of the night (via a wider innervation of other pontine neurons), and modulates muscle tone.

Sleep deprivation increases the activation of nuclear factor kappa B in lateral hypothalamic cells

Sleep deprivation increases sleep propensity in rats and mice as well as the production of several sleep-regulatory substances. Nuclear factor kappa B (NF-kappa B) is a transcription factor implicated in the activation of many of these sleep-promoting substances. A unique population of neurons immunoreactive for the p65 subunit of NF-kappa B was previously localized within the caudal dorsolateral hypothalamus of rats. Therefore, we evaluated the effect of sleep deprivation on NF-kappa Bp65-immunoreactivity (IR) in cells of this region in rats as well as its nuclear translocation in a kappa B-lacZ transgenic mouse line. In rats after 6 h of sleep deprivation beginning at light onset, the number of neurons with NF-kappa Bp65-IR increased significantly in the caudal lateral hypothalamus, specifically the magnocellular lateral hypothalamus adjacent to the subthalamus. Sleep deprivation also significantly increased the number of cells expressing NF-kappa B-dependent beta-galactosidase in the magnocellular lateral hypothalamus, zona incerta dorsal, as well as the adjacent subthalamus in the transgenic mice. These results suggest that NF-kappa B expressing cells within the lateral hypothalamus may be important in the maintenance of the sleep-wake cycle.

State-dependent activity of neurons in the perifornical hypothalamic area during sleep and waking

Neurons containing orexins are located in the perifornical hypothalamic area and are considered to have a role in sleep-wake regulation. To examine how this area is involved in the regulation of sleep and wakefulness, we recorded neuronal activity in undrugged, head-restrained rats across sleep-waking cycles. Recordings were made in the perifornical hypothalamic area where orexin-immunoreactive neurons are distributed (PFH), and in the area dorsal to the PFH, including the zona incerta and subincertal nucleus (collectively referred to as ZI). The 40 neurons recorded from in the PFH were divided into five groups: (1) neurons most active during paradoxical sleep (PS, n=14, 35%), (2) neurons active during both waking (W) and PS (n=12, 30%), (3) neurons most active during W (n=7, 18%), (4) neurons most active during slow-wave sleep (SWS, n=3, 7.5%), and (5) neurons whose activity had no correlation with sleep-waking states (n=4, 10%). Of 30 neurons recorded from in the ZI, the corresponding numbers were 13 (43%), seven (23%), six (20%), three (10%), and one (3.3%). In both areas, neuronal activity fluctuated more during PS than during W. Waking-specific neurons (group 3) in the PFH generated action potentials with longer durations than those produced by other types of neurons. About half of the neurons in the PFH that were classified in groups 1, 2, and 3 increased their firing rate after the transition from one state to another, while higher percentages of neurons of groups 1 and 2 in the ZI than those in the PFH increased their firing rate prior to the state shift from SWS to PS. In these ZI neurons, however, the firing rate varied considerably at the state shift. These results suggest that the PFH and ZI are involved in the regulation of PS or W, especially the regulation of phasic events during PS or the maintenance of W. The ZI appears to be more closely involved than the PFH in the induction of PS or some phasic phenomena associated with PS.

Effects of lateral hypothalamic lesion with the neurotoxin hypocretin-2-saporin on sleep in Long-Evans rats

Narcolepsy, a disabling neurological disorder characterized by excessive daytime sleepiness, sleep attacks, sleep fragmentation, cataplexy, sleep-onset rapid eye movement sleep periods and hypnagogic hallucinations was recently linked to a loss of neurons containing the neuropeptide hypocretin. There is considerable variability in the severity of symptoms between narcoleptic patients, which could be related to the extent of neuronal loss in the lateral hypothalamus. To investigate this possibility, we administered two concentrations (90 ng or 490 ng in a volume of 0.5 microl) of the neurotoxin hypocretin-2-saporin, unconjugated saporin or saline directly to the lateral hypothalamus and monitored sleep, the entrained and free-running rhythm of core body temperature and activity. Neurons stained for hypocretin or for the neuronal specific marker were counted in the perifornical area, dorsomedial and ventromedial nucleus of the hypothalamus. More neuronal nuclei (NeuN) cells were destroyed by the higher concentration of hypocretin-2-saporin (-55%) compared with the lower concentration (-34%) in the perifornical area, although both concentrations lesioned the hypocretin neurons almost equally well (high concentration=91%; low concentration=88%). The high concentration of hypocretin-2-saporin also lesioned neurons in the dorsomedial nucleus of the hypothalamus and ventromedial nucleus of the hypothalamus. Narcoleptic-like sleep behavior was produced by both concentrations of the hypocretin-2-saporin. The high concentration produced a larger increase in non-rapid eye movement sleep amounts during the normally active night cycle than low concentration. Neither concentration of hypocretin-2-saporin disrupted the phase or period of the core temperature or activity rhythms. The low concentration of unconjugated saporin did not significantly lesion hypocretin or neurons and did not alter sleep. The high concentration of unconjugated saporin produced some loss of neuronal nuclei-immunoreactive (NeuN-ir) neurons and hypocretin immunoreactive neurons, but only a transient increase in non-rapid eye movement sleep. These results led us to conclude that the extent of hypocretin neuronal loss together with an accompanying loss of cells in the lateral hypothalamus may explain the differences in severity of symptoms seen in human narcolepsy.

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.

The distribution and morphological characteristics of cholinergic cells in the brain of monotremes as revealed by ChAT immunohistochemistry

The present study employs choline acetyltransferase (ChAT) immunohistochemistry to identify the cholinergic neuronal population in the central nervous system of the monotremes. Two of the three extant species of monotreme were studied: the platypus (Ornithorhynchus anatinus) and the short-beaked echidna (Tachyglossus aculeatus). The distribution of cholinergic cells in the brain of these two species was virtually identical. Distinct groups of cholinergic cells were observed in the striatum, basal forebrain, habenula, pontomesencephalon, cranial nerve motor nuclei, and spinal cord. In contrast to other tetrapods studied with this technique, we failed to find evidence for cholinergic cells in the hypothalamus, the parabigeminal nucleus (or nucleus isthmus), or the cerebral cortex. The lack of hypothalamic cholinergic neurons creates a hiatus in the continuous antero-posterior aggregation of cholinergic neurons seen in other tetrapods. This hiatus might be functionally related to the phenomenology of monotreme sleep and to the ontogeny of sleep in mammals, as juvenile placental mammals exhibit a similar combination of sleep elements to that found in adult monotremes.

Hypocretin-2-saporin lesions of the lateral hypothalamus produce narcoleptic-like sleep behavior in the rat

Hypocretins (Hcrts) are recently discovered peptides linked to the human sleep disorder narcolepsy. Humans with narcolepsy have decreased numbers of Hcrt neurons and Hcrt-null mice also have narcoleptic symptoms. Hcrt neurons are located only in the lateral hypothalamus (LH) but neither electrolytic nor pharmacological lesions of this or any other brain region have produced narcoleptic-like sleep, suggesting that specific neurons need to be destroyed. Hcrt neurons express the Hcrt receptor, and to facilitate lesioning these neurons, the endogenous ligand hypocretin-2/orexin B (Hcrt2) was conjugated to the ribosome-inactivating protein saporin (SAP). In vitro binding studies indicated specificity of the Hcrt2-SAP because it preferentially bound to Chinese hamster ovary cells containing the Hcrt/orexin receptor 2 (HcrtR2/OX(2)R) or the Hcrt/orexin receptor 1 (HcrtR1/OX(1)R) but not to Kirsten murine sarcoma virus transformed rat kidney epithelial (KNRK) cells stably transfected with the substance P (neurokinin-1) receptor. Administration of the toxin to the LH, in which the receptor is known to be present, eliminated some neurons (Hcrt, melanin-concentrating hormone, and adenosine deaminase-containing neurons) but not others (a-melanocyte-stimulating hormone), indicating specificity of the toxin in vivo. When the toxin was administered to the LH, rats had increased slow-wave sleep, rapid-eye movement (REM) sleep, and sleep-onset REM sleep periods. These behavioral changes were negatively correlated with the loss of Hcrt-containing neurons but not with the loss of adenosine deaminase-immunoreactive neurons. These findings indicate that damage to the LH that also causes a substantial loss of Hcrt neurons is likely to produce the multiple sleep disturbances that occur in narcolepsy.

The posterior hypothalamic area: chemoarchitecture and afferent connections

This study provides an analysis of the chemoarchitecture of the posterior hypothalamic area (PHA) and a retrograde transport analysis of inputs to the PHA in the rat. The chemoarchitectural analysis reveals that the majority of PHA neurons contain glutamate. Hypocretin, melanin concentrating hormone, tyrosine hydroxylase, neuropeptide Y and gamma-aminobutyric acid are also found in subsets of PHA neurons, and fibers immunoreactive for these substances as well as for serotonin, dopamine-beta-hydroxylase and met-enkephalin are observed in the area and aid in the delineation of its borders. The retrograde tracing study demonstrates that the PHA receives input from multiple, diverse neuron populations. Descending projections to the PHA arise from the limbic forebrain (cingulate cortex and lateral septum) and both the medial and lateral hypothalamus. Subcortical visual nuclei, including the ventral lateral geniculate nucleus and intergeniculate leaflet, pretectal area, and superior colliculus, and the subthalamus (zona incerta, fields of Forel) also project to the PHA. Ascending projections to the PHA arise from brainstem cholinergic nuclei, the reticular formation, midbrain raphe nuclei, periaqueductal gray and parabrachial nucleus. Retrograde transport studies using the psuedorabies virus (PRV) demonstrate that the PHA receives input indirectly from the hippocampus, amygdala and suprachiasmatic nucleus through circuits including nuclei in the limbic forebrain and hypothalamus. These data suggest that the PHA is important in the neural control of behavioral state, modulating aspects of hippocampal, autonomic and cortical function as they relate to the elaboration of adaptive behavior.

Sleep-waking discharge of neurons in the posterior lateral hypothalamus of the albino rat

The sleep-waking discharge patterns of neurons in the posterior lateral hypothalamus (PLH) were investigated in the rat. Previous studies in the cat demonstrated that this region contained neurons that fired tonically at low rates (2-4 Hz) during waking, decreased firing in non-rapid eye-movement (NREM) sleep and nearly ceased firing during rapid eye-movement (REM) sleep. These "REM-off" neurons were proposed to be histaminergic neurons of the tuberomammillary nucleus (TM). Since many anatomical and physiological studies are performed in the rat, we sought to examine the sleep-waking discharge of these neurons in this animal. We found three main types of discharge patterns among PLH neurons. Waking-related neurons decreased their discharge in NREM sleep, and remained at low rates during REM sleep. A subpopulation of these neurons discharged very little during REM sleep (<0.2 Hz) (REM-off neurons). Waking/REM-related neurons decreased their discharge in NREM sleep and returned to waking rates in REM sleep. REM-related neurons decreased their discharge in NREM sleep and increased their discharge during REM sleep higher than waking rates. No NREM-related discharge patterns were recorded. Waking-related and waking/REM-related neurons were similar in location within the PLH and action potential duration. Some REM-off and other waking-related neurons were recorded within the boundaries of the histaminergic TM, however, not all waking-related and REM-off neurons were found within this region. Furthermore, neurons with waking/REM-related and state-indifferent discharge patterns were localized within the TM. These results suggest that waking-related and/or REM-off neurons may not be exclusively histaminergic in rats.

Regulation of posterior lateral hypothalamic arousal related neuronal discharge by preoptic anterior hypothalamic warming

The posterior lateral hypothalamus (PLH) is a brain region involved in cortical activation and maintenance of behavioral arousal. Spontaneous and evoked neuronal activities were recorded in the PLH of cats before and during local warming of the preoptic-anterior hypothalamus (POAH). Forty-six percent of PLH neurons recorded in awake cats decreased spontaneous discharge during POAH warming. In the absence of POAH warming, these same cells exhibited significantly lower discharge rates in non-rapid eye movement (NREM) sleep compared to waking. Responses of PLH neurons to POAH warming were also investigated in sleeping cats to determine whether hypothalamic thermosensitive neurons modulated sleep-wake regulation across arousal states. POAH warming had no influence on spontaneous activities of PLH neurons during NREM sleep, but suppressed activity of a small subset of neurons during rapid eye movement (REM) sleep. Thus, during wakefulness or REM sleep, hypothalamic thermosensitive neurons may modulate behavioral state via inhibition or disfacilitation of arousal systems.

The lateral hypothalamic area revisited: neuroanatomy, body weight regulation, neuroendocrinology and metabolism

This article reviews findings that have accumulated since the original description of the syndrome that follows destruction of the lateral hypothalamic area (LHA). These data comprise the areas of neuroanatomy, body weight regulation, neuroendocrinology, neurochemistry, and intermediary metabolism. Neurons in the LHA are the largest in the hypothalamus, and are topographically well organized. The LHA belongs to the parasympathetic area of the hypothalamus, and connects with all major parts of the brain and the major hypothalamic nuclei. Rats with LHA lesions regulate their body weight set point in a primary manner and not because of destruction of a "feeding center". The lower body weight is not due to finickiness. In the early stages of the syndrome, catabolism and running activity are enhanced, and so is the activity of the sympathetic nervous system (SNS) as shown by increased norepinephrine excretion that normalizes one mo later. The LHA plays a role in the feedback control of body weight regulation different from ventromedial (VMN) and dorsomedial (DMN). Tissue preparations from the LHA promote glucose utilization and insulin release. Although it does not belong to the classical hypothysiotropic area of the hypothalamus, the LHA does affect neuroendocrine secretions. No plasma data on growth hormone are available following electrolytic lesions LHA but electrical stimulation fails to elicit GH secretion. Nevertheless, antiserum raised against the 1-37 fragment of human GHRF stains numerous perikarya in the dorsolateral LHA. The plasma circadian corticosterone rhythm is disrupted in LHA lesioned rats, but this is unlikely due to destruction of intrinsic oscillators. Stimulation studies show a profound role of the LHA in glucose metabolism (glycolysis, glycogenesis, gluconeogenesis), this mechanism being cholinergic. Its role in lipolysis appears not to be critical. In general, stimulation of the VMN elicits opposite effects. Lesion studies in rats show altered in vitro glucose carbon incorporation into several tissue fractions both a few days, and one mo after lesion production. Several of these changes may be due to the reduced food intake, others appear to be due to a "true" lesion effect.

Effects of locus coeruleus lesions on vigilance and attentive behaviour in cat

Previous data have suggested that in the cat, expectancy behaviour (waiting for a target to appear) and associated electrocortical, focal, synchronized activity ('mu' rhythms) are modulated by a noradrenergic system possibly originating from the locus coeruleus (LC). To test the latter hypothesis, we have examined the behavioural and ECoG changes induced after bilateral LC lesions. Our results demonstrated that destruction of the anterior 3/4th of the LC (A6 noradrenergic cell group) resulted in a considerable increase of mu rhythms and expectancy behaviour, without episodes of drowsiness that normally occur. Destruction of the posterior fourth of LC (A4 noradrenergic group) only increased the duration of slow sleep. Extending the A6 lesion to include the dorsal ascending noradrenergic bundle also increased the expectancy behaviour and mu rhythms. Finally, when the nucleus subcoeruleus was also involved, the duration of slow sleep and the frequency of paradoxical sleep episodes increased. These findings indicate that the LC exerts an inhibitory effect on structures involved in the induction and persistence of expectancy behaviour with accompanying mu rhythms.

Afferent projections to the cholinergic pedunculopontine tegmental nucleus and adjacent midbrain extrapyramidal area in the albino rat. I. Retrograde tracing studies

The afferent connections of the pedunculopontine tegmental nucleus (PPT) and the adjacent midbrain extrapyramidal area (MEA) were examined by retrograde tracing with wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). Major afferents to the PPT originate in the periaqueductal gray, central tegmental field, lateral hypothalamic area, dorsal raphe nucleus, superior colliculus, and pontine and medullary reticular fields. Other putative inputs originate in the paraventricular and preoptic hypothalamic nuclei, the zona incerta, nucleus of the solitary tract, central superior raphe nucleus, substantia innominata, posterior hypothalamic area, and thalamic parafascicular nucleus. The major afferent to the medially adjacent MEA originates in the lateral habenula, while other putative afferents include the perifornical and lateral hypothalamic area, periaqueductal gray, superior colliculus, pontine reticular formation, and dorsal raphe nucleus. MEA inputs from basal ganglia nuclei include moderate projections from the substantia nigra pars reticulata, entopeduncular nucleus, and a small projection from the globus pallidus, but not the subthalamic nucleus. Dense anterograde labeling was observed in the substantia nigra pars compacta, entopeduncular nucleus, subthalamic nucleus, globus pallidus, and caudate-putamen only following WGA-HRP injections involving the MEA. The results of this study demonstrate that the PPT and MEA share many potential afferents. Remarkable differences were found that support distinguishing between these two nuclei in future studies regarding the functional organization of the midbrain and pons. The results, for example, confirm our previous observations that the largely reciprocal connections between the midbrain and basal ganglia distinguish the MEA from the PPT. Afferents from the lateral habenula and contralateral superior colliculus represent extensions of more traditional basal ganglion circuitry which further delineate the MEA from the PPT. The results are discussed with respect to the important role of the midbrain and pons in behavioral state control and locomotor mechanisms.

Neurotoxic lesion of the mesencephalic reticular formation and/or the posterior hypothalamus does not alter waking in the cat

In order to re-evaluate the role of two putative waking systems, we injected a neural cell body toxin, ibotenic acid (IA) (45 micrograms/microliters), into the mesencephalic reticular formation (MRF) and/or the posterior hypothalamus (PH). On the one hand, when the cell body destruction was only restricted to the MRF, the IA microinjection was followed by a temporary high voltage and slow neocortical electroencephalogram (EEG) during the first 24 postoperative hours and by a subsequent long term increase in waking which lasted 8-12 h. After the first postoperative day, there were no motor disturbances, no aphagia nor adypsia, no alteration of cortical activation and no modification of thermoregulation or of the sleep-waking cycle. On the other hand, the IA microinjection into the PH induced a hypothermia during the first postoperative night and a dramatic transient hypersomnia immediately after the disappearance of the anesthesia (14-24 h after the IA injection). On the third day, all cats recovered control level of paradoxical sleep (PS), slow wave sleep (SWS) and cerebral temperature. They presented normal motor behavior but they were not able to eat by themselves during the first postoperative week. Finally, when the lesions of the MRF and the PH were realized in one single operation, the cats were first motionless in a comatose state for 2-3 days. This state was accompanied by a transitory hypothermia and the suppression of a spontaneous or evoked cortical low voltage fast activity. However, from the 2nd postoperative week, both behavioral and EEG waking re-occurred. By contrast, the two successive operations (MRF followed by PH) did not induce a comatose state. We did not observe any deficit in motor behavior, and the sleep-waking cycle was quite normal as from the second postlesion day. In the MRF-PH-lesioned cats, the injection of alpha-methyl-p-tyrosine (150 mg/kg) induced a large decrease in waking and a moderate increase in PS. In the MRF-lesioned cats, IA produced a large area of cell body loss, centered in the MRF, that extended from levels A2 to A6 of stereotaxic planes and sometimes encroached upon the red nucleus and the substantia nigra. In the PH-lesioned cats, the histological analysis revealed a great loss of cell bodies in the PH extended from levels A8 to A12.5. The damage included the lateral and posterior hypothalamic areas and sometimes the tuberomamillary nucleus. In MRF- and PH-lesioned cats, the cell body loss extended from levels A2 to A12.5.(ABSTRACT TRUNCATED AT 400 WORDS)

Lower brainstem afferents to the cat posterior hypothalamus: a double-labeling study

Using a double-immunostaining technique with cholera toxin (CT) as a retrograde tracer, the authors examined the cells of origin and the histochemical nature of lower brainstem afferents to the cat posterior hypothalamus. The posterior hypothalamus, in particular the lateral hypothalamic area, receives substantial afferent projections from: substantia nigra, peripeduncular nucleus, ventral tegmental area, periaqueductal grey, mesencephalic reticular formation, peribrachial region including the locus coeruleus complex, rostral raphe nuclei and the rostral part of the nucleus magnus. In addition, a moderate number of retrogradely labeled neurons was found in: Edinger-Westphal nucleus, nucleus reticularis pontis oralis, nucleus reticularis magnocellularis, caudal lateral bulbar reticular formation around the nucleus ambiguus and lateral reticular nucleus and the nucleus of the solitary tract. The posterior hypothalamus receives: 1) dopaminergic inputs from A8, A9 and A10 cell groups; 2) noradrenergic inputs from A6 and A7 pontine, as well as A1 and A2 bulbar cell groups; 3) adrenergic inputs from C1 cell group in the caudal medulla; 4) serotoninergic inputs from the rostral raphe nuclei (B6, B7 and B8 cell groups); 5) cholinergic inputs from the peribrachial region of the dorsal pontine tegmentum as well as from the nucleus reticularis magnocellularis of the medulla; 6) peptidergic inputs such as methionine-enkephalin, substance P, corticotropin-releasing factor and galanin that originate mainly in the mesencephalic periaqueductal grey, the dorsal raphe nucleus and the peribrachial region of the dorsal pontine tegmentum.

Sleep-waking discharge of neurons in the posterior lateral hypothalamic area of cats

Damage to the posterior hypothalamic area produces a syndrome of EEG synchrony and behavioral somnolence. Cells of a recently described projection system within the posterior lateral hypothalamic area (PLHa) are potential candidates for mediating this area's influences on EEG and behavioral arousal. We examined PLHa neuronal activity during sleep and wakefulness in freely moving cats, identifying projection neurons by antidromic activation from stimulation sites in the external capsule, anterior cingulate bundle, or mesencephalic reticular formation. Orthodromic response evoked from these sites were also investigated. Twenty-two cells were found to send axons outside the PLHa; 9 with ascending projections and 13 with descending projections. Projection cells were found to discharge phasically in relation to waking movements. Most seemed to be related to complex head movements, although specific movement correlates were difficult to ascertain. Discharge rates during periods of waking immobility were similar to those occurring during slow-wave sleep. Rates during phasic REM sleep were generally similar to peak waking rates. Cells with ascending and descending projections displayed similar discharge profiles, although the former had somewhat higher rates in all conditions. Seventy-four cells were orthodromically driven from external capsule or anterior cingulate bundle. Responses evoked from these two sites were similar; an initial brief period of excitation, followed by a sustained (mean greater than 100 msec) episode of discharge suppression. Twenty-four cells exhibited orthodromic excitation from the mesencephalic reticular formation, but the duration of the subsequent discharge suppression was comparatively brief (mean less than 30 msec). With few exceptions, the discharge correlates of orthodromically driven cells were identical to those described above for identified projection neurons. These results do not support a role for neurons within the PLHa in the control of tonic EEG arousal. They are consistent with a possible involvement in either motor function, or phasic movement-related aspects of EEG activation.

Forebrain afferents to the cat posterior hypothalamus: a double labeling study

Using a double immunostaining technique with cholera toxin (CT) as a retrograde tracer, we examined the cells of origin and the histochemical nature of afferents to the cat posterior hypothalamus. After injection in the tuberomamillary nucleus, a number of CT-labeled cells were observed in: medial preoptic area, nuclei of the septum and the stria terminalis, amygdaloid complex, anterior hypothalamic, ventromedial hypothalamic and premamillary nuclei. CT injections in the lateral hypothalamic area gave an additional heavy labeling of neurons in: lateral preoptic area, nuclei of the diagonal band of Broca, substantia innominata, and nucleus accumbens. The posterior hypothalamus receives: 1) cholinergic inputs from the septum, the lateral preoptic area and the nuclei of the diagonal band of Broca; 2) dopaminergic afferents from A11, A13, and A14 groups; 3) histaminergic afferents from the posterior hypothalamus; and 4) peptidergic afferents such as methionin-enkephalin, galanin and neurotensin, substance P and corticotropin-releasing factor from the medial preoptic area, the nucleus of the stria terminalis and/or the posterior hypothalamic structures.

A critical role of the posterior hypothalamus in the mechanisms of wakefulness determined by microinjection of muscimol in freely moving cats

In order to determine critical sites within the hypothalamus responsible for the induction and maintenance of wakefulness (W), we performed microinjections of muscimol, a potent gamma-aminobutyric acid (GABA) agonist, in various lateral hypothalamic regions of freely moving cats. We found that bilateral injections of a small amount of muscimol (0.1-1.0 micrograms/0.5 microliters) in the preoptic and anterior hypothalamus and rostral mesencephalic tegmentum resulted in increased vigilance and insomnia. In contrast, microinjections of muscimol in the middle and anterior parts of the posterior hypothalamus induced long-lasting behavioral and electroencephalographic signs of sleep with short latency. The hypersomnia was characterized by a significant increase in both light and deep slow wave sleep (SWS), and a nearly complete suppression of paradoxical sleep (PS). Animals with muscimol microinjections in the ventrolateral part of the posterior hypothalamus, however, exhibited increased SWS followed by a significant increase in PS. When injected into the posterior hypothalamus of insomniac cats pretreated with p-chlorophenylalanine (PCPA), muscimol induced not only SWS but also PS with short latency. The present data thus support the hypotheses that the posterior hypothalamus plays a critical role in the mechanisms of W and that sleep might result from functional blockade of the hypothalamic waking center.

Long-lasting insomnia induced by preoptic neuron lesions and its transient reversal by muscimol injection into the posterior hypothalamus in the cat

In order to analyse the role of the anterior hypothalamus in the regulation of the sleep-waking cycle we made bilateral neuronal lesions at different levels of the anterior hypothalamus in cats, by means of microinjections of a cell-specific neurotoxin:ibotenic acid. These lesions resulted in severe insomnia in eight cats. This insomnia was characterized by a large decrease or even disappearance of paradoxical sleep and deep slow wave sleep and, to a lesser extent, by a decrease of light slow wave sleep, for 2-3 weeks. In the other five animals, we observed a large reduction of deep slow wave sleep (0-40% of control level), but a less intensive decrease of time spent in paradoxical sleep (50-75% of control level) and no marked effect on light slow wave sleep. During the first 3-6 postoperative days we also noticed hyperthermia in all cats; thereafter, the animals presented only a slight increase in brain temperature which did not appear to trigger the sleep impairment. Histological analysis of the different lesions revealed that the insomnia could be attributed to neuronal cell body destruction in the mediobasal part of the anterior hypothalamus covering; the medial preoptic area and a narrow portion of the lateral preoptic area as well as a restricted part of the anterior hypothalamic nucleus. In order to investigate the putative role of the posterior hypothalamic structures in the mechanism of insomnia after lesion of the mediobasal preoptic area neurons we injected an agonist of GABA into the ventrolateral part of the posterior hypothalamus to locally depress the neuronal activity. The bilateral intracerebral microinjection of muscimol (0.5-5 micrograms) induced a transient intensive hypersomnia (slow wave sleep and paradoxical sleep). These findings indicate that neuronal cell loss in the mediobasal preoptic area induced a long lasting insomnia. Thus, it may be hypothesized that the integrity of this structure is necessary for sleep appearance. Finally, our data are in keeping with an intrahypothalamic regulation of the sleep-waking cycle.

Organization of cerebral cortical afferent systems in the rat. II. Hypothalamocortical projections

The organization of hypothalamic projections to the cerebral cortex in the rat has been studied using retrograde and anterograde tracer methods. Four separate populations of hypothalamic neurons, which constitute a major source of diffuse cortical innervation, were identified: Tuberal lateral hypothalamic (LHAt) neurons which innervate the cerebral cortex tend to cluster in the perifornical region, in the zona incerta, and along the medial edge of the cerebral peduncle, at levels roughly coextensive with the ventromedial hypothalamic nucleus. Most of these neurons project to the ipsilateral cortex; a small percentage innervate the contralateral cortex, but this varies among cortical terminal fields. The perifornical neurons are organized in a roughly topographic medial-to-lateral relationship with respect to their cortical terminal fields. Field of Forel (FF) neurons, which project primarily to the frontal cortex of the ipsilateral hemisphere, are located just ventral to the medial edge of the medial lemniscus, at the level of the ventromedial basal thalamic nucleus. The more laterally placed neurons innervate the lateral frontal, insular and perirhinal cortex; the more medial neurons, around the mammillothalamic tract, innervate the medial frontopolar, prelimbic, infralimbic, and anterior cingulate cortex. Posterior lateral hypothalamic (LHAp) neurons form a dense cluster spanning the lateral hypothalamus, from the cerebral peduncle to the posterior hypothalamic area at premammillary levels, and extending into the supramammillary nucleus and the adjacent ventral tegmental area. LHAp neurons innervate the entire cerebral cortex, predominantly on the ipsilateral side. Populations of LHAp neurons projecting to different cortical target areas show considerable spatial overlap, but computer plots of the centers of these populations demonstrate a strict topographic relationship with respect to the cerebral cortex. Tuberomammillary (TMN) neurons form a sheet along the ventrolateral surface of the premammillary hypothalamus. About twice as many TMN neurons innervate the ipsilateral, as compared to the contralateral hemisphere; it is not known whether single neurons project to both hemispheres. No topographic organization of the TMN cortical projection is apparent. Injections of different-colored fluorescent dyes into various cortical areas demonstrate that hypothalamic neurons in general have rather restricted cortical terminal fields. Only occasional neurons are found, primarily in LHAt, which are double labeled by injections into different cytoarchitectonic areas.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of clonidine on EEG wavebands associated with sleep in the rat

Clonidine was studied for its effects in rats on the occurrence of several EEG waves that characterize the sleep/waking cycle. Intraperitoneal administration of the drug (0.001-1.0 mg/kg) at the onset of the daily light period induced low frequency (4-7 Hz) rhythmical slow activity (RSA), and suppressed delta-wave occurrence. These effects were more prominent with increasing dose. Clonidine also had a biphasic effect on spindles: at low doses it suppressed, while at high doses it enhanced spindle occurrence. These effects could not be characterized as modifications in any of the classical sleep stages. A clearly non-classical state was induced by the clonidine in these studies. These results suggest that in rat, effects of clonidine cannot simply be interpreted as an alteration in one or more of the classically-defined sleep states.

Methysergide releases locomotion without support in lateral hypothalamic akinesia

Rats made profoundly akinetic by large bilateral electrolytic partial transections of the lateral hypothalamus were released from their akinesia by methysergide maleate (45 mg/kg, IP). When tested as soon as 24 hr postoperatively, lateral hypothalamic rats treated with methysergide displayed vigorous forward locomotion without postural support for as long as an hour and a half. By postoperative day 5, the locomotion elicited by methysergide was integrated with postural support to produce a more normal form of walking. Although atropine sulfate (50 mg/kg, IP) releases excessive walking in akinetic rats treated with 6-hydroxydopamine [53] it did not release locomotion lateral hypothalamic rats. Similarly, apomorphine, clonidine and phentolamine did not do so. Assuming that methysergide in the dose used exerts its effects primarily via the blockade of serotonin systems, we suggest that, in addition to an inhibitory cholinergic system, an independent inhibitory serotonergic system may also exaggerate the akinesia seen following treatments that diminish the action of brain catecholamine systems. Furthermore, the type of locomotion released by methysergide is a fractional form not previously isolated.