GABAergic and cholinergic basal forebrain and preoptic-anterior hypothalamic projections to the mediodorsal nucleus of the thalamus in the cat

Dopamine Supersensitivity: A Novel Hypothesis of Opioid-Induced Neurobiological Mechanisms Underlying Opioid-Stimulant Co-use and Opioid Relapse

Emergent harms presented by the co-use of opioids and methamphetamine highlight the broader public health challenge of preventing and treating opioid and stimulant co-use. Development of effective therapeutics requires an understanding of the physiological mechanisms that may be driving co-use patterns, specifically the underlying neurobiology of co-use and how they may facilitate (or be leveraged to prevent) continued use patterns. This narrative review summarizes largely preclinical data that demonstrate clinically-meaningful relationships between the dopamine and opioid systems with direct implications for opioid and stimulant co-use. Synthesized conclusions of this body of research include evidence that changes in the dopamine system occur only once physical dependence to opioids develops, that the chronicity of opioid exposure is associated with the severity of changes, and that withdrawal leaves the organism in a state of substantive dopamine deficit that persists long after the somatic or observed signs of opioid withdrawal appear to have resolved. Evidence also suggests that dopamine supersensitivity develops soon after opioid abstinence and results in increased response to dopamine agonists that increases in magnitude as the abstinence period continues and is evident several weeks into protracted withdrawal. Mechanistically, this supersensitivity appears to be mediated by changes in the sensitivity, not quantity, of dopamine D2 receptors. Here we propose a neural circuit mechanism unique to withdrawal from opioid use with implications for increased stimulant sensitivity in previously stimulant-naïve or inexperienced populations. These hypothesized effects collectively delineate a mechanism by which stimulants would be uniquely reinforcing to persons with opioid physical dependence, would contribute to the acute opioid withdrawal syndrome, and could manifest subjectively as craving and/or motivation to use that could prompt opioid relapse during acute and protracted withdrawal. Preclinical research is needed to directly test these hypothesized mechanisms. Human laboratory and clinical trial research is needed to explore these clinical predictions and to advance the goal of developing treatments for opioid-stimulant co-use and/or opioid relapse prevention and withdrawal remediation.

Dynamic Subcortical Modulators of Human Default Mode Network Function

The brain’s “default mode network” (DMN) enables flexible switching between internally and externally focused cognition. Precisely how this modulation occurs is not well understood, although it may involve key subcortical mechanisms, including hypothesized influences from the basal forebrain (BF) and mediodorsal thalamus (MD). Here, we used ultra-high field (7 T) functional magnetic resonance imaging to examine the involvement of the BF and MD across states of task-induced DMN activity modulation. Specifically, we mapped DMN activity suppression (“deactivation”) when participants transitioned between rest and externally focused task performance, as well as DMN activity engagement (“activation”) when task performance was internally (i.e., self) focused. Consistent with recent rodent studies, the BF showed overall activity suppression with DMN cortical regions when comparing the rest to external task conditions. Further analyses, including dynamic causal modeling, confirmed that the BF drove changes in DMN cortical activity during these rest-to-task transitions. The MD, by comparison, was specifically engaged during internally focused cognition and demonstrated a broad excitatory influence on DMN cortical activation. These results provide the first direct evidence in humans of distinct BF and thalamic circuit influences on the control of DMN function and suggest novel mechanistic avenues for ongoing translational research.

Lateral preoptic area neurons signal cocaine self-administration behaviors

The lateral preoptic area is implicated in numerous aspects of substance use disorder. In particular, the lateral preoptic area is highly sensitive to the pharmacological properties of psychomotor stimulants, and its activity promotes drug-seeking in the face of punishment and reinstatement during abstinence. Despite the lateral preoptic area's complicity in substance use disorder, how precisely lateral preoptic area neurons signal the individual components of drug self-administration has not been ascertained. To bridge this gap, we examined how the firing of single lateral preoptic area neurons correlates with three discrete elements of cocaine self-administration: (1) drug-seeking (pre-response), (2) drug-taking (response) and (3) receipt of the cocaine infusion. A significant subset of lateral preoptic area neurons responded to each component with a mix of increases and decreases in firing-rate. A majority of these neurons signal the operant response with increases in spiking, though responses during the drug-seeking, taking and reciept windows were highly correlated.

The Medial Septum as a Potential Target for Treating Brain Disorders Associated With Oscillopathies

The medial septum (MS), as part of the basal forebrain, supports many physiological functions, from sensorimotor integration to cognition. With often reciprocal connections with a broad set of peers at all major divisions of the brain, the MS orchestrates oscillatory neuronal activities throughout the brain. These oscillations are critical in generating sensory and emotional salience, locomotion, maintaining mood, supporting innate anxiety, and governing learning and memory. Accumulating evidence points out that the physiological oscillations under septal influence are frequently disrupted or altered in pathological conditions. Therefore, the MS may be a potential target for treating neurological and psychiatric disorders with abnormal oscillations (oscillopathies) to restore healthy patterns or erase undesired ones. Recent studies have revealed that the patterned stimulation of the MS alleviates symptoms of epilepsy. We discuss here that stimulus timing is a critical determinant of treatment efficacy on multiple time scales. On-demand stimulation may dramatically reduce side effects by not interfering with normal physiological functions. A precise pattern-matched stimulation through adaptive timing governed by the ongoing oscillations is essential to effectively terminate pathological oscillations. The time-targeted strategy for the MS stimulation may provide an effective way of treating multiple disorders including Alzheimer's disease, anxiety/fear, schizophrenia, and depression, as well as pain.

Assessment of the septal area neuronal activity during penile erections in rapid eye movement sleep and waking in the rats

To understand the central mechanism of penile erections during rapid eye movement (REM) sleep and waking, single units were recorded from the septal area in un-anesthetized head-restrained rats simultaneous with erections. Erectile events were assessed by pressure in the bulb of the corpus spongiosum of the penis and bulbospongiosus-muscle activity. Of 143 recorded neurons, 36% showed increased activity (E-type) and 24% decreased activity (I-type) during different phases of erection in REM sleep, while 10% were E-type and 35% were I-type during erections in waking. Most E-type neurons were recorded from the dorsal and intermediate part of lateral septum, whereas I-type neurons were from the medial septum. The findings illustrate the extensive network of various types of neurons in the septal area that fire in concert in relation to erection during REM sleep and waking. This study provides a unique prospective of the septal area for perpetuation of erectile circuitry during sleep.

Thalamocortical synchronization during induction and emergence from propofol-induced unconsciousness

General anesthesia (GA) is a reversible drug-induced state of altered arousal required for more than 60,000 surgical procedures each day in the United States alone. Sedation and unconsciousness under GA are associated with stereotyped electrophysiological oscillations that are thought to reflect profound disruptions of activity in neuronal circuits that mediate awareness and cognition. Computational models make specific predictions about the role of the cortex and thalamus in these oscillations. In this paper, we provide in vivo evidence in rats that alpha oscillations (10-15 Hz) induced by the commonly used anesthetic drug propofol are synchronized between the thalamus and the medial prefrontal cortex. We also show that at deep levels of unconsciousness where movement ceases, coherent thalamocortical delta oscillations (1-5 Hz) develop, distinct from concurrent slow oscillations (0.1-1 Hz). The structure of these oscillations in both cortex and thalamus closely parallel those observed in the human electroencephalogram during propofol-induced unconsciousness. During emergence from GA, this synchronized activity dissipates in a sequence different from that observed during loss of consciousness. A possible explanation is that recovery from anesthesia-induced unconsciousness follows a "boot-up" sequence actively driven by ascending arousal centers. The involvement of medial prefrontal cortex suggests that when these oscillations (alpha, delta, slow) are observed in humans, self-awareness and internal consciousness would be impaired if not abolished. These studies advance our understanding of anesthesia-induced unconsciousness and altered arousal and further establish principled neurophysiological markers of these states.

Optogenetic Dissection of the Basal Forebrain Neuromodulatory Control of Cortical Activation, Plasticity, and Cognition

The basal forebrain (BF) houses major ascending projections to the entire neocortex that have long been implicated in arousal, learning, and attention. The disruption of the BF has been linked with major neurological disorders, such as coma and Alzheimer's disease, as well as in normal cognitive aging. Although it is best known for its cholinergic neurons, the BF is in fact an anatomically and neurochemically complex structure. Recent studies using transgenic mouse lines to target specific BF cell types have led to a renaissance in the study of the BF and are beginning to yield new insights about cell-type-specific circuit mechanisms during behavior. These approaches enable us to determine the behavioral conditions under which cholinergic and noncholinergic BF neurons are activated and how they control cortical processing to influence behavior. Here we discuss recent advances that have expanded our knowledge about this poorly understood brain region and laid the foundation for future cell-type-specific manipulations to modulate arousal, attention, and cortical plasticity in neurological disorders.

SIGNIFICANCE STATEMENT

Although the basal forebrain is best known for, and often equated with, acetylcholine-containing neurons that provide most of the cholinergic innervation of the neocortex, it is in fact an anatomically and neurochemically complex structure. Recent studies using transgenic mouse lines to target specific cell types in the basal forebrain have led to a renaissance in this field and are beginning to dissect circuit mechanisms in the basal forebrain during behavior. This review discusses recent advances in the roles of basal forebrain cholinergic and noncholinergic neurons in cognition via their dynamic modulation of cortical activity.

Basal forebrain dynamics during nonassociative and associative olfactory learning

Cholinergic and GABAergic projections from the horizontal diagonal band (HDB) and medial preoptic area (MCPO) of the basal forebrain to the olfactory system are associated with odor discrimination and odor learning, as well as modulation of neural responses in olfactory structures. Whereas pharmacological and lesion studies give insights into the functional role of these modulatory inputs on a slow timescale, the response dynamics of neurons in the HDB/MCPO during olfactory behaviors have not been investigated. In this study we examined how these neurons respond during two olfactory behaviors: spontaneous investigation of odorants and odor-reward association learning. We observe rich heterogeneity in the response dynamics of individual HDB/MCPO neurons, with a substantial fraction of neurons exhibiting task-related modulation. HDB/MCPO neurons show both rapid and transient responses during bouts of odor investigation and slow, long-lasting modulation of overall response rate based on behavioral demands. Specifically, baseline rates were higher during the acquisition phase of an odor-reward association than during spontaneous investigation or the recall phase of an odor reward association. Our results suggest that modulatory projections from the HDB/MCPO are poised to influence olfactory processing on multiple timescales, from hundreds of milliseconds to minutes, and are therefore capable of rapidly setting olfactory network dynamics during odor processing and learning.

Pedunculopontine arousal system physiology - Deep brain stimulation (DBS)

This review describes the wake/sleep symptoms present in Parkinson׳s disease, and the role of the pedunculopontine nucleus in these symptoms. The physiology of PPN cells is important not only because it is a major element of the reticular activating system, but also because it is a novel target for deep brain stimulation in the treatment of gait and postural deficits in Parkinson׳s disease. A greater understanding of the physiology of the target nuclei within the brainstem and basal ganglia, amassed over the past decades, has enabled increasingly better patient outcomes from deep brain stimulation for movement disorders.

Turning a Negative into a Positive: Ascending GABAergic Control of Cortical Activation and Arousal

Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the brain. Recent technological advances have illuminated the role of GABAergic neurons in control of cortical arousal and sleep. Sleep-promoting GABAergic neurons in the preoptic hypothalamus are well-known. Less well-appreciated are GABAergic projection neurons in the brainstem, midbrain, hypothalamus, and basal forebrain, which paradoxically promote arousal and fast electroencephalographic (EEG) rhythms. Thus, GABA is not purely a sleep-promoting neurotransmitter. GABAergic projection neurons in the brainstem nucleus incertus and ventral tegmental nucleus of Gudden promote theta (4-8 Hz) rhythms. Ventral tegmental area GABAergic neurons, neighboring midbrain dopamine neurons, project to the frontal cortex and nucleus accumbens. They discharge faster during cortical arousal and regulate reward. Thalamic reticular nucleus GABAergic neurons initiate sleep spindles in non-REM sleep. In addition, however, during wakefulness, they tonically regulate the activity of thalamocortical neurons. Other GABAergic inputs to the thalamus arising in the globus pallidus pars interna, substantia nigra pars reticulata, zona incerta, and basal forebrain regulate motor activity, arousal, attention, and sensory transmission. Several subpopulations of cortically projecting GABAergic neurons in the basal forebrain project to the thalamus and neocortex and preferentially promote cortical gamma-band (30-80 Hz) activity and wakefulness. Unlike sleep-active GABAergic neurons, these ascending GABAergic neurons are fast-firing neurons which disinhibit and synchronize the activity of their forebrain targets, promoting the fast EEG rhythms typical of conscious states. They are prominent targets of GABAergic hypnotic agents. Understanding the properties of ascending GABAergic neurons may lead to novel treatments for diseases involving disorders of cortical activation and wakefulness.

Thalamic neuromodulation and its implications for executive networks

The thalamus is a key structure that controls the routing of information in the brain. Understanding modulation at the thalamic level is critical to understanding the flow of information to brain regions involved in cognitive functions, such as the neocortex, the hippocampus, and the basal ganglia. Modulators contribute the majority of synapses that thalamic cells receive, and the highest fraction of modulator synapses is found in thalamic nuclei interconnected with higher order cortical regions. In addition, disruption of modulators often translates into disabling disorders of executive behavior. However, modulation in thalamic nuclei such as the midline and intralaminar groups, which are interconnected with forebrain executive regions, has received little attention compared to sensory nuclei. Thalamic modulators are heterogeneous in regards to their origin, the neurotransmitter they use, and the effect on thalamic cells. Modulators also share some features, such as having small terminal boutons and activating metabotropic receptors on the cells they contact. I will review anatomical and physiological data on thalamic modulators with these goals: first, determine to what extent the evidence supports similar modulator functions across thalamic nuclei; and second, discuss the current evidence on modulation in the midline and intralaminar nuclei in relation to their role in executive function.

Distribution and intrinsic membrane properties of basal forebrain GABAergic and parvalbumin neurons in the mouse

The basal forebrain (BF) strongly regulates cortical activation, sleep homeostasis, and attention. Many BF neurons involved in these processes are GABAergic, including a subpopulation of projection neurons containing the calcium-binding protein, parvalbumin (PV). However, technical difficulties in identification have prevented a precise mapping of the distribution of GABAergic and GABA/PV+ neurons in the mouse or a determination of their intrinsic membrane properties. Here we used mice expressing fluorescent proteins in GABAergic (GAD67-GFP knock-in mice) or PV+ neurons (PV-Tomato mice) to study these neurons. Immunohistochemical staining for GABA in GAD67-GFP mice confirmed that GFP selectively labeled BF GABAergic neurons. GFP+ neurons and fibers were distributed throughout the BF, with the highest density in the magnocellular preoptic area (MCPO). Immunohistochemistry for PV indicated that the majority of PV+ neurons in the BF were large (>20 μm) or medium-sized (15-20 μm) GFP+ neurons. Most medium and large-sized BF GFP+ neurons, including those retrogradely labeled from the neocortex, were fast-firing and spontaneously active in vitro. They exhibited prominent hyperpolarization-activated inward currents and subthreshold "spikelets," suggestive of electrical coupling. PV+ neurons recorded in PV-Tomato mice had similar properties but had significantly narrower action potentials and a higher maximal firing frequency. Another population of smaller GFP+ neurons had properties similar to striatal projection neurons. The fast firing and electrical coupling of BF GABA/PV+ neurons, together with their projections to cortical interneurons and the thalamic reticular nucleus, suggest a strong and synchronous control of the neocortical fast rhythms typical of wakefulness and REM sleep.

Sleep, its regulation and possible mechanisms of sleep disturbances

The state of sleep consists of different phases that proceed in successive, tightly regulated order through the night forming a physiological program, which for each individual is different but stabile from one night to another. Failure to accomplish this program results in feeling of unrefreshing sleep and tiredness in the morning. The program core is constructed by genetic factors but regulated by circadian rhythm and duration and intensity of day time brain activity. Many environmental factors modulate sleep, including stress, health status and ingestion of vigilance-affecting nutrients or medicines (e.g. caffeine). Acute sleep loss results in compromised cognitive performance, memory deficits, depressive mood and involuntary sleep episodes during the day. Moreover, prolonged sleep curtailment has many adverse health effects, as evidenced by both epidemiological and experimental studies. These effects include increased risk for depression, type II diabetes, obesity and cardiovascular diseases. In addition to voluntary restriction of sleep, shift work, irregular working hours, jet lag and stress are important factors that induce curtailed or bad quality sleep and/or insomnia. This review covers the current theories on the function of normal sleep and describes current knowledge on the physiologic effects of sleep loss. It provides insights into the basic mechanisms of the regulation of wakefulness and sleep creating a theoretical background for understanding different disturbances of sleep.

GABA-to-ACh ratio in basal forebrain and cerebral cortex varies significantly during sleep

STUDY OBJECTIVES

GABAergic and cholinergic transmission within the basal forebrain and cerebral cortex contribute to the regulation of sleep and wakefulness. In contrast to levels of acetylcholine (ACh), levels of endogenous GABA in basal forebrain and cortex during sleep and wakefulness have not previously been quantified. This study (1) tested the hypothesis that there are differential, state-specific changes in GABA levels within the substantia innominata (SI) region of the basal forebrain and somatosensory cortex; and (2) quantified the ratio of GABAergic to cholinergic transmission in the SI, cortex, and pontine reticular formation during rapid eye movement sleep (REM), non-REM sleep (NREM), and wakefulness.

DESIGN

Within/between subjects.

SETTING

University of Michigan.

PATIENTS OR PARTICIPANTS

Adult, male, purpose bred cats (n = 5).

INTERVENTIONS

In vivo microdialysis, high performance liquid chromatography, electrophysiological recordings.

MEASUREMENTS AND RESULTS

In the SI, GABA levels were significantly greater during NREM (17%) than during REM. In the cortex, GABA levels were significantly greater during NREM than during wakefulness (39%) and REM (63%). During prolonged wakefulness, there was a linear increase in cortical GABA levels, and the amount of time spent awake accounted for 87% of the variance in GABA. The GABA-to-ACh ratio was largest during NREM for all brain regions. REM was characterized by a 68% decrease in the GABA-to-ACh ratio across brain regions, always due to a decrease in GABA levels.

CONCLUSION

Three of the brain regions that comprise the anatomically distributed, sleep-generating network have in common a GABA-mediated, sleep-dependent decrease in the GABA-to-ACh ratio.

The associative and limbic thalamus in the pathophysiology of obsessive-compulsive disorder: an experimental study in the monkey

Obsessive-compulsive disorder (OCD) is a frequent psychiatric disorder characterized by repetitive intrusive thoughts and severe anxiety, leading to compulsive behaviors. Although medical treatment is effective in most cases, resistance is observed in about 30% of patients. In this context, deep brain stimulation (DBS) of the caudate or subthalamic nuclei has been recently proposed with encouraging results. However, some patients were unimproved or exhibited awkward side effects. Therefore, exploration of new targets for DBS remains critical in OCD. In the latter, functional imaging studies revealed overactivity in the limbic and associative cortico-subcortical loops encompassing the thalamus. However, the role of the thalamus in the genesis of repetitive behaviors and related anxiety is unknown. Here, we tested the hypothesis that pharmacological-induced overactivity of the medial thalamus could give rise to abnormal behaviors close to that observed in OCD. We modulated the ventral anterior (VA) and medial dorsal (MD) nuclei activity by in situ bicuculline (GABA(A) antagonist) microinjections in subhuman primates and assessed their pharmacological-induced behavior. Bicuculline injections within the VA caused significant repetitive and time-consuming motor acts whereas those performed within the MD induced symptoms of dysautonomic dysregulation along with abnormal vocalizations and marked motor hypoactivity. These findings suggest that overactivation of the VA and MD nuclei of the thalamus provokes compulsive-like behaviors and neurovegetative manifestations usually associated with the feeling of anxiety in OCD patients. In further research, this translational approach should allow us to test the effectiveness and side effects of these thalamic nuclei DBS in monkey and perhaps, in a second step, to propose a transfer of this technique to severely disabled OCD patients.

Temporal relationship between awakening and seizure onset in nocturnal partial seizures

Clinical awakening can be seen just before or after seizure onsets. In this study we determined the time between onset of seizures and awakening in patients with frontal lobe epilepsy (FLE) and temporal lobe epilepsy (TLE). Sixty-eight patients who underwent video-EEG monitoring with simultaneous PSG were retrospectively examined. TLE or FLE patients having seizures during sleep were included. Seizure onset and awakening onset were marked according to clinical and electrophysiological features. The duration between awakening and seizure onset was compared in patients with TLE and FLE. Twenty-five patients who had been diagnosed with TLE (17) or FLE (8) had a total of 75 seizures during sleep. All seizures except one, occurred during NREM sleep in both TLE and FLE patients. The seizure onsets were before awakening in 49 seizures (FLE: 20, TLE: 29) and the awakening preceded the seizure onsets in 12 seizures (FLE: 3, TLE: 9). The duration between seizure onset and the awakening was shorter in FLE, either in seizures with preceding awakening or not (p=0.014, p=0.015). Awakening was mostly seen after onset of seizures rather than before, especially in TLE. But in patients with FLE the duration between seizure onset and awakening was shorter. The localization of epileptic activity may play a role for the timing of awakening mechanisms during nocturnal partial seizures.

Sleep disorders in neurodegenerative diseases

The aim of this review is to provide data on sleep disturbances in three categories of neurodegenerative disorders: synucleinopathies, tauopathies, and other diseases (this heterogeneous group includes also spinocerebellar degeneration and amyotrophic lateral sclerosis). Analysing and knowing sleep disorders in neurodegenerative diseases may offer important insights into the pathomechanism of some of these diseases and calls attention to the still insufficiently known 'sleep neurology'. The identification of sleep disorders in some neurodegenerative conditions may make their diagnosis easier and earlier; for example, rapid eye movements sleep behaviour disorder may precede any other clinical manifestation of synucleinopathies by more than 10 years.

c-Fos protein expression is increased in cholinergic neurons of the rodent basal forebrain during spontaneous and induced wakefulness

It has been proposed that cholinergic neurons of the basal forebrain (BF) may play a role in vigilance state control. Since not all vigilance states have been studied, we evaluated cholinergic neuronal activation levels across spontaneously occurring states of vigilance, as well as during sleep deprivation and recovery sleep following sleep deprivation. Sleep deprivation was performed for 2h at the beginning of the light (inactive) period, by means of gentle sensory stimulation. In the rodent BF, we used immunohistochemical detection of the c-Fos protein as a marker for activation, combined with labeling for choline acetyl-transferase (ChAT) as a marker for cholinergic neurons. We found c-Fos activation in BF cholinergic neurons was highest in the group undergoing sleep deprivation (12.9% of cholinergic neurons), while the spontaneous wakefulness group showed a significant increase (9.2%), compared to labeling in the spontaneous sleep group (1.8%) and a sleep deprivation recovery group (0.8%). A subpopulation of cholinergic neurons expressed c-Fos during spontaneous wakefulness, when possible confounds of the sleep deprivation procedure were minimized (e.g., stress and sensory stimulation). Double-labeling in the sleep deprivation treatment group was significantly elevated in select subnuclei of the BF (medial septum/vertical limb of the diagonal band, horizontal limb of the diagonal band, and the magnocellular preoptic nucleus), when compared to spontaneous wakefulness. These findings support and provide additional confirming data of previous reports that cholinergic neurons of BF play a role in vigilance state regulation by promoting wakefulness.

Inactivation of median preoptic nucleus causes c-Fos expression in hypocretin- and serotonin-containing neurons in anesthetized rat

The median preoptic nucleus (MnPN) of the hypothalamus contains sleep-active neurons including sleep-active GABAergic neurons and is involved in the regulation of nonREM/REM sleep. The hypocretinergic (HCRT) neurons of the perifornical-lateral hypothalamic area (PF-LHA) and serotonergic (5-HT) neurons of the dorsal raphe nucleus (DRN) are mostly active during waking and have been implicated in the regulation of arousal. MnPN GABAergic neurons project to the PF-LHA and DRN. It is hypothesized that MnPN promotes sleep by inhibiting multiple arousal systems including HCRT and other wake-active neurons within the PF-LHA and 5-HT neurons in the DRN. We examined the effects of inactivation of MnPN neurons by locally microinjecting 0.2 microl of 1 mM or 10 mM solutions of a GABA(A) receptor agonist, muscimol, into the MnPN on Fos expression (Fos-IR) in the PF-LHA neurons including HCRT neurons and 5-HT neurons in the DRN in anesthetized rats. Compared to artificial cerebrospinal fluid control, microinjection of muscimol into the MnPN resulted in significantly higher percentages of HCRT and non-HCRT neurons in the PF-LHA and 5-HT neurons in the DRN that exhibited Fos-IR. The percentage of melanin-concentrating hormone (MCH)+/Fos+ neurons in the PF-LHA did not change after muscimol treatments. These results support a hypothesis that the activation of MnPN neurons contributes to the suppression of wake-promoting systems including HCRT and other unidentified neurons in the PF-LHA and 5-HT neurons in the DRN. These results also suggest that MCH neurons may not be under MnPN inhibitory control. These findings are consistent with a hypothesized role of MnPN in sleep regulation.

The presence and absence of prosencephalic cell groups relaying striatal information to the medial and lateral thalamus in tenrec

Although there are remarkable differences regarding the output organization of basal ganglia between mammals and non-mammals, mammalian species with poorly differentiated brain have scarcely been investigated in this respect. The aim of the present study was to identify the pallidal neurons giving rise to thalamic projections in the Madagascar lesser hedgehog tenrec (Afrotheria). Following tracer injections into the thalamus, retrogradely labelled neurons were found in the depth of the olfactory tubercle (particularly the hilus of the Callejal islands and the insula magna), in subdivisions of the diagonal band complex, the peripeduncular region and the thalamic reticular nucleus. No labelled cells were seen in the globus pallidus. Pallidal neurons were tentatively identified on the basis of their striatal afferents revealed hodologically using anterograde axonal tracer substances and immunohistochemically with antibodies against enkephalin and substance P. The data showed that the tenrec's medial thalamus received prominent projections from ventral pallidal cells as well as from a few neurons within and ventral to the cerebral peduncle. The only regions projecting to the lateral thalamus appeared to be the thalamic reticular nucleus (RTh) and the dorsal peripeduncular nucleus (PpD). On the basis of immunohistochemical data and the topography of its thalamic projections, the PpD was considered to be an equivalent to the pregeniculate nucleus in other mammals. There was no evidence of entopeduncular (internal pallidal) neurons being present within the RTh/PpD complex, neuropils of which did not stain for enkephalin and substance P. The ventrolateral portion of RTh, the only region eventually receiving a striatal input, projected to the caudolateral rather than the rostrolateral thalamus. Thus, the striatopallidal output organization in the tenrec appeared similar, in many respects, to the output organization in non-mammals. This paper considers the failure to identify entopeduncular neurons projecting to the rostrolateral thalamus in a mammal with a little differentiated cerebral cortex, and also stresses the discrepancy between this absence and the presence of a distinct external pallidal segment (globus pallidus).

GABAergic and non-GABAergic thalamic, hypothalamic and basal forebrain projections to the ventral oral pontine reticular nucleus: their implication in REM sleep modulation

The ventral part of the oral pontine reticular nucleus (vRPO) is a demonstrated site of brainstem REM-sleep generation and maintenance. The vRPO has reciprocal connections with structures that control other states of the sleep-wakefulness cycle, many situated in the basal forebrain and the diencephalon. Some of these connections utilize the inhibitory neurotransmitter GABA. The aim of the present work is to map the local origin of the basal forebrain and diencephalon projections to the vRPO whether GABAergic or non-GABAergic. A double-labelling technique combining vRPO injections of the neuronal tracer, cholera-toxin (CTB), with GAD-immunohistochemistry, was used for this purpose in adult cats. All of the numerous CTB-positive neurons in the reticular thalamic and dorsocaudal hypothalamic nuclei were double-labelled (CTB/GAD-positive) neurons. Approximately 15%, 14% and 16% of the CTB-positive neurons in the zona incerta and the dorsal and lateral hypothalamic areas are, respectively, CTB/GAD-positive neurons. However, only some double-labelled neurons were found in other hypothalamic nuclei with abundant CTB-positive neurons, such as the paraventricular nucleus, perifornical area and H1 Forel field. In addition, CTB-positive neurons were abundant in the central amygdaline nucleus, terminal stria bed nuclei, median preoptic nucleus, medial and lateral preoptic areas, dorsomedial and ventromedial hypothalamic nuclei, posterior hypothalamic area and periventricular thalamic nucleus. The GABAergic and non-GABAergic connections described here may be the morphological pillar through which these prosencephalic structures modulate, either by inhibiting or by exciting, the vRPO REM-sleep inducing neurons during the different sleep-wakefulness cycle states.

Inducible and neuronal nitric oxide synthases (NOS) have complementary roles in recovery sleep induction

Sleep homeostasis is the process by which recovery sleep is generated by prolonged wakefulness. The molecular mechanisms underlying this important phenomenon are poorly understood. We have previously shown that nitric oxide (NO) generation increases in the basal forebrain (BF) during sleep deprivation (SD). Moreover, both NO synthase (NOS) inhibition and a NO scavenger prevented recovery sleep induction, while administration of a NO donor during the spontaneous sleep-wake cycle increased sleep, indicating that NO is necessary and sufficient for the induction of recovery sleep. Next we wanted to know which NOS isoform is involved in the production of recovery sleep. Using in vivo microdialysis we infused specific inhibitors of NOS into the BF of rats during SD, and found that an inhibitor of inducible NOS (iNOS), 1400W, prevented non-rapid eye movement (NREM) recovery, while an inhibitor of neuronal NOS (nNOS), L-N-propyl-arginine, decreased REM recovery but did not affect NREM recovery. Using immunoblot analysis we found that iNOS was not expressed during the spontaneous sleep-wake cycle, but was induced by prolonged wakefulness (increased by 278%). A known iNOS inducer, lipopolysaccharide, evoked an increase in sleep that closely resembled recovery sleep, and its effects were abolished by 1400W. These results suggest that the elevation of NO produced by induction of iNOS in the BF during prolonged wakefulness is a specific mechanism for producing NREM recovery sleep and that the two NOS isoforms have a complementary role in NREM and REM recovery induction.

Fatal familial insomnia: a model disease in sleep physiopathology

Fatal Familial Insomnia (FFI) is characterized by loss of sleep, oneiric stupor with autonomic/motor hyperactivity and somato-motor abnormalities (pyramidal signs, myoclonus, dysarthria/dysphagia, ataxia). Positon emission tomography (PET) disclosed thalamic hypometabolism and milder involvement of the cortex; neuropathology severe neuronal loss in the thalamic nuclei variably affecting the caudate, gyrus cinguli and fronto-temporal cortices. Genetic analysis disclosed a mutation in the PRNP gene and FFI was transmitted to experimental animals, thus classifying FFI within the prion diseases. Rare Sporadic Fatal Insomnia (SFI) cases occur without PRNP mutation but with features similar to FFI. FFI represents a model disease for the study of sleep-wake regulation: (I) the profound thalamic hypometabolism/atrophy associated with lack of sleep spindles and delta sleep implicate the thalamus in the origin of slow wave sleep (SWS); (II) loss of SWS is associated with marked autonomic and motor hyperactivity; termed 'agrypnia excitata', this association has been proposed as a useful clinical concept representative of thalamo-limbic dysfunction; (III) lack of SWS occurs with substantial preservation of stage 1 NREM sleep, implying that the latter has mechanisms different from SWS and unaffected by thalamic atrophy; accordingly, conflating stage 1 NREM with SWS into NREM sleep is inappropriate.

Origin and immunolesioning of cholinergic basal forebrain innervation of cat primary auditory cortex

Numerous studies have implicated the cholinergic basal forebrain (cBF) in the modulation of auditory cortical responses. This study aimed to accurately define the sources of cBF input to primary auditory cortex (AI) and to assess the efficacy of a cholinergic immunotoxin in cat. Three anaesthetized cats received multiple injections of horseradish-peroxidase conjugated wheatgerm-agglutin into physiologically identified AI. Following one to two days survival, tetramethylbenzidine histochemistry revealed the greatest number of retrogradely labeled cells in ipsilateral putamen, globus pallidus and internal capsule, and smaller numbers in more medial nuclei of the basal forebrain (BF). Concurrent choline acetyltransferase immunohistochemistry showed that almost 80% of the retrogradely labeled cells in BF were cholinergic, with the vast majority of these cells arising from the more lateral BF nuclei identified above. In the second part of the study, unilateral intraparenchymal injections of the cholinergic immunotoxin ME20.4-SAP were made into the putamen/globus pallidus nuclei of six cats. Immuno- and histochemistry revealed a massive reduction in the number of cholinergic cells in and around the targeted area, and a corresponding reduction in the density of cholinergic fibers in auditory cortex. These results are discussed in terms of their implications for investigations of the role of the cBF in cortical plasticity.

Glutamic acid decarboxylase isoforms are differentially distributed in the septal region of the rat

The septal region of the brain consists of a heterogeneous population of GABAergic neurons that play an important role in the generation of hippocampal theta rhythms. While GABAergic neurons employ two isoforms of the enzyme glutamic acid decarboxylase (GAD) for the synthesis of GABA, distribution of GAD isoforms has not been investigated in the septum. Immunohistochemical techniques were used to investigate the expression of GAD enzymes in medial and lateral septum. GAD65 and GAD67 immunohistochemistry revealed dense fibers and punctuated immunoreactivity in septal regions. While few GAD65-positive neuronal somas were detected in medial septum, a significantly higher number of immunoreactive neurons were detected in lateral septum. GAD65- and GAD67-positive neurons in the lateral septum exhibit higher complexity of dendritic arborizations than in the medial septum where staining was mainly restricted to the soma. Presumptive axon terminals (puncta) showed abundant immunoreactivity predominantly for GAD65 isoforms in all septal regions. This suggests that septal GABAergic neurons differentially express GAD enzymes thereby potentially reflecting functional differences. Differences found between medial and lateral septal GABAergic neuronal populations are in agreement with the concept that medial and lateral septum are brain structures with highly different connectivity and function despite anatomical proximity.

Synaptic relationships between axon terminals from the mediodorsal thalamic nucleus and gamma-aminobutyric acidergic cortical cells in the prelimbic cortex of the rat

Although the reciprocal interconnections between the prefrontal cortex and the mediodorsal nucleus of the thalamus (MD) are well known, the involvement of inhibitory cortical interneurons in the neural circuit has not been fully defined. To address this issue, we conducted three combined neuroanatomical studies on the rat brain. First, the frequency and the spatial distribution of synapses made by reconstructed dendrites of nonpyramidal neurons were identified by impregnation of cortical cells with the Golgi method and identification of thalamocortical terminals by degeneration following thalamic lesions. Terminals from MD were found to make synaptic contacts with small dendritic shafts or spines of Golgi-impregnated nonpyramidal cells with very sparse dendritic spines. Second, a combined study that used anterograde transport of Phaseolus vulgaris leucoagglutinin (PHA-L) and postembedding gamma-aminobutyric acid (GABA) immunocytochemistry indicated that PHA-L-labeled terminals from MD made synaptic junctions with GABA-immunoreactive dendritic shafts and spines. Nonlabeled dendritic spines were found to receive both axonal inputs from MD with PHA-L labelings and from GABAergic cells. In addition, synapses were found between dendritic shafts and axon terminals that were both immunoreactive for GABA. Third, synaptic connections between corticothalamic neurons that project to MD and GABAergic terminals were investigated by using wheat germ agglutinin conjugated to horseradish peroxidase and postembedding GABA immunocytochemistry. GABAergic terminals in the prelimbic cortex made symmetrical synaptic contacts with retrogradely labeled corticothalamic neurons to MD. All of the synapses were found on cell somata and thick dendritic trunks. These results provide the first demonstration of synaptic contacts in the prelimbic cortex not only between thalamocortical terminals from MD and GABAergic interneurons but also between GABAergic terminals and corticothalamic neurons that project to MD. The anatomical findings indicate that GABAergic interneurons have a modulatory influence on excitatory reverberation between MD and the prefrontal cortex.

Projections from the cat posterior lateral hypothalamus to the ventral part of the oral pontine reticular nucleus contain a GABAergic component

The posterior lateral hypothalamus (PLH) has long been considered crucial to normal wakefulness while the ventral part of the oral pontine reticular nucleus (vRPO) is involved in the generation and maintenance of rapid eye movement (REM) sleep. However, to date, there is no information on the ultrastructure or neurotransmitter content of the hypothalamo-reticular projection. In the present study, we examined the morphology and synaptic organization of PLH terminals in the vRPO using PLH injections of biotinylated dextran amine (BDA) as well as of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Since some PLH neurons are GABAergic, we used a post-embedding immunogold technique to determine whether any anterogradely labeled terminals were GABA-immunopositive. Electron microscope analyses revealed a variety of ultrastructural features in the vRPO anterogradely labeled terminals. Although most labeled terminals (over 63%) formed symmetric synapses on vRPO somata and dendrites, others made asymmetric synapses on vRPO dendrites. The relative percentages of labeled terminals observed on large, medium and small diameter dendrites were 44.3 +/- 5.5%, 35.3 +/- 3.0% and 20.4 +/- 3.1%, respectively. Finally, post-embedding immunogold technique revealed that there are GABA-immunopositive and immunonegative components to this projection, indicating that GABA is one of the transmitters used by the PLH cells that project to the vRPO. Furthermore, most, if not all, of the GABA-labeled axon terminals formed symmetric synapsis. In conclusion, our results suggest that the PLH could modulate the physiological responses of vRPO neurons through a GABAergic pathway as well as by other inhibitory and/or excitatory pathways. Activation of the descending PLH GABAergic projection may inhibit the REM sleep-inducing neurons within the vRPO and thus contribute to the suppression of REM sleep activation during wakefulness.

Rabbit forebrain cholinergic system: morphological characterization of nuclei and distribution of cholinergic terminals in the cerebral cortex and hippocampus

Although the rabbit brain, in particular the basal forebrain cholinergic system, has become a common model for neuropathological changes associated with Alzheimer's disease, detailed neuroanatomical studies on the morphological organization of basal forebrain cholinergic nuclei and on their output pathways are still awaited. Therefore, we performed quantitative choline acetyltransferase (ChAT) immunocytochemistry to localize major cholinergic nuclei and to determine the number of respective cholinergic neurons in the rabbit forebrain. The density of ChAT-immunoreactive terminals in layer V of distinct neocortical territories and in hippocampal subfields was also measured. Another cholinergic marker, the low-affinity neurotrophin receptor (p75(NTR)), was also employed to identify subsets of cholinergic neurons. Double-immunofluorescence labeling of ChAT and p75(NTR), calbindin D-28k (CB), parvalbumin, calretinin, neuronal nitric oxide synthase (nNOS), tyrosine hydroxylase, or substance P was used to elucidate the neuroanatomical borders of cholinergic nuclei and to analyze the neurochemical complexity of cholinergic cell populations. Cholinergic projection neurons with heterogeneous densities were found in the medial septum, vertical and horizontal diagonal bands of Broca, ventral pallidum, and magnocellular nucleus basalis (MBN)/substantia innominata (SI) complex; cholinergic interneurons were observed in the caudate nucleus, putamen, accumbens nucleus, and olfactory tubercule, whereas the globus pallidus was devoid of cholinergic nerve cells. Cholinergic interneurons were frequently present in the hippocampus and to a lesser extent in cerebral cortex. Cholinergic projection neurons, except those localized in SI, abundantly expressed p75(NTR), and a subset of cholinergic neurons in posterior MBN was immunoreactive for CB and nNOS. A strict laminar distribution pattern of cholinergic terminals was recorded both in the cerebral cortex and in CA1-CA3 and dentate gyrus of the hippocampus. In summary, the structural organization and chemoarchitecture of rabbit basal forebrain may be considered as a transition between that of rodents and that of primates.

Functional recovery of cholinergic basal forebrain neurons under disease conditions: old problems, new solutions?

Recognition of the involvement of cholinergic neurons in the modulation of cognitive functions and their severe dysfunction in neurodegenerative disorders, such as Alzheimer's disease, initiated immense research efforts aimed at unveiling the anatomical organization and cellular characteristics of the basal forebrain (BFB) cholinergic system. Concomitant with our unfolding knowledge about the structural and functional complexity of the BFB cholinergic projection system, multiple pharmacological strategies were introduced to rescue cholinergic nerve cells from noxious attacks; however, a therapeutic breakthrough is still awaited. In this review, we collected recent findings that significantly contributed to our better understanding of cholinergic functions under disease conditions, and to the design of effective means to restore lost or damaged cholinergic functions. To this end, we first provide a brief survey of the neuroanatomical organization of BFB nuclei with emphasis on major evolutionary differences among mammalian species, in particular rodents and primates, and discuss limitations of the translation of experimental data to human therapeutic applications. Subsequently, we summarize the involvement of cholinergic dysfunction in the pathogenesis of severe neurological conditions, including stroke, traumatic brain injury, virus encephalitis and Alzheimer's disease, and emphasize the critical role of pro-inflammatory cytokines as common mediators of cholinergic neuronal damage. Moreover, we review leading functional concepts on the limited recovery of cholinergic neurons and their impaired plastic re-modeling, as well as on the hampered interplay of the ascending cholinergic and monoaminergic projection systems under neurodegenerative conditions. In addition, recent advances in the dynamic labeling of living cholinergic neurons by fluorochromated antibodies, referred to as in vivo labeling, and novel neuroimaging approaches as potential diagnostic tools of progressive cholinergic decline are surveyed. Finally, the potential of cell replacement strategies using embryonic and adult stem cells, and multipotent neural progenitors, as a means to recover damaged cholinergic functions, is discussed.

Preoptic area warming inhibits wake-active neurons in the perifornical lateral hypothalamus

Activation of the preoptic area (POA) warm sensitive neurons is known to promote non-REM (NREM) sleep and inhibit neuronal discharge in arousal-related brain structures. The perifornical area of the lateral hypothalamus (PF/LH) was recently recognized to be an additional important arousal promoting region. We studied the behavior of PF/LH neurons in rats during the normal sleep-wake cycle and in response to local POA warming. Most PF/LH neurons were wake-active, and exhibited low discharge throughout NREM. Seventy four percent of these wake-active neurons exhibited moderate or strong activation in REM sleep compared to NREM sleep. A substantial group (26%) exhibited very low discharge in REM as well as NREM sleep. Fifty two percent of units in the PF/LH area were responsive to POA warming; 90% of responsive neurons exhibited a significant reduction (-26.47+/-2.16% for 1 degrees C of POA warming) in their discharge rate. The inhibitory effect of POA warming on PF/LH neurons was not associated with EEG slowing. This study supports the hypothesis that sleep induction by POA warm sensitive neurons is mediated through the inhibition of multiple arousal-related structures.

Muscarinic and GABAA receptors modulate acetylcholine release in feline basal forebrain

Acetylcholine (ACh) release within the basal forebrain changes significantly as a function of sleep and wakefulness, hence identifying the neurochemical modulators of basal forebrain ACh release will contribute to a mechanistic understanding of sleep cycle regulation. This study tested the hypothesis that muscarinic and gamma aminobutyric acid(A) (GABAA) receptors modulate basal forebrain ACh release. Cats were anaesthetized with halothane to hold arousal state constant and a microdialysis probe was aimed stereotaxically for the substantia innominata region of the basal forebrain. Four concentrations of the muscarinic antagonist scopolamine (0.1, 0.3, 1.0, and 10 nm) and five concentrations of the GABAA antagonist bicuculline (3, 10, 30, 100, and 300 micro m) were delivered by reverse dialysis from the same probes used to collect ACh. These results are based on 27 experiments in nine animals. Scopolamine and bicuculline each caused a concentration dependent enhancement of ACh release. Scopolamine increased ACh by 118% above control levels whereas bicuculline was more effective, causing a 287% increase in ACh release. Scopolamine was more potent (EC50 = 0.16 nm) than bicuculline (EC50 > or = 90 micro m) for increasing ACh release. The results support the hypothesis that substantia innominata ACh release is modulated by muscarinic autoreceptors and inhibited by GABAA receptors. These findings are consistent with the interpretation that inhibition of basal forebrain cholinergic neurotransmission by GABA contributes to the generation of sleep.

Awakening from sleep

Awakening is a crucial event for the organism. The transition from sleep to waking implies physiological processes which lead to a new behavioural state. Spontaneous awakenings have varying features which may change as a function of several factors. The latter include intrasleep architecture, circadian phase, time awake, age, or disordered sleep. Despite its clear theoretical and clinical importance, the topic of awakening (in humans) has received little attention so far. This contribution focuses on major issues which relate to awakening from both basic (experimental) and clinical research. Recent knowledge on neurophysiological mechanisms is reported. The experimental data which provide in the human suggestions on the regulation of awakening are discussed, mainly those concerning sleep architecture and homeostatic/circadian factors also in a life-span perspective, since age is a powerful factor which may influence awakening. Clinical contributions will examine two main sleep disorders: insomnia and hypersomnia. Daytime functioning is shown in insomniac patients and compared to other pathologies like sleep apnea. A final section evokes links between some types of night waking and psychological factors.

The nitric oxide synthase inhibitor NG-Nitro-L-arginine increases basal forebrain acetylcholine release during sleep and wakefulness

Cholinergic neurotransmission in the basal forebrain changes across the sleep/wake cycle, and considerable data show cortical activation by ACh originating from basal forebrain neurons. These findings have stimulated efforts to elucidate molecular modulators of ACh release within the basal forebrain. Basal forebrain cholinergic neurons contain nitric oxide synthase (NOS), the enzyme that produces the gaseous neuromodulator nitric oxide. This study tested the hypothesis that administration of an NOS inhibitor to the basal forebrain would alter basal forebrain ACh release, sleep, and respiratory rate. Seven cats were instrumented for recording sleep and wakefulness and for in vivo microdialysis and microinjection. Compared with Ringer's solution (control), microdialysis delivery of the NOS inhibitor N(G)-nitro-l-arginine (NLA; 10 mm) increased ACh release during wakefulness (33%), non-rapid eye movement (NREM) sleep (70%), and rapid eye movement (REM) sleep (16%). Mean +/- SEM ACh levels (pmol/10 min) during control and NLA dialysis, respectively, were 0.58 +/- 0.03 and 0.77 +/- 0.06 in wakefulness, 0.36 +/- 0.01 and 0.61 +/- 0.06 in NREM sleep, and 0.68 +/- 0.06 and 0.79 +/- 0.09 in REM sleep. Increases in ACh release were not evoked by dialysis delivery of the less active enantiomer N(G)-nitro-d-arginine. Dialysis administration of NLA did not alter respiratory rate. Sleep-dependent changes in basal forebrain ACh release were localized specifically to lateral basal forebrain regions and did not occur in medial basal forebrain sites. Microinjection of NLA into the lateral basal forebrain did not significantly alter the sleep/wake cycle. In contrast to NLA-induced depression of REM sleep and ACh release in the cat pons, the present results demonstrate that NLA increased ACh release in the cat basal forebrain and had no effect on sleep. The different effects of NLA on ACh release in the cat pons and cat basal forebrain may prove relevant for developing compounds that differentially alter cholinergic neurotransmission in specific brain regions.

Intrapreoptic microinjection of TNF-alpha enhances non-REM sleep in rats

Tumor necrosis factor-alpha (TNFalpha) is involved in sleep regulation. Peripheral or central administration of TNFalpha induces non-rapid eye movement sleep (NREMS) in many species. However, the brain site responsible for TNF-enhanced NREMS remains unclear. Thus, we tested the hypothesis that the preoptic area (POA) of the anterior hypothalamus, a crucial site for sleep regulation, is involved in TNF-induced sleep responses in rats. Unilateral microinjection of TNFalpha (2, 20 and 100 ng) or a TNF receptor fragment (TNFRF; 1.25, 5.0 and 12.5 microg) into the POA was performed at dark onset and light onset, respectively. The two higher doses of TNFalpha increased NREMS and brain temperature with little effect on REMS and EEG slow wave activity. These effects were lost after the heat-treatment of TNFalpha. The two higher doses of the TNFRF decreased NREMS without affecting the other parameters measured. Combined with previous results showing diurnal variations of TNFalpha in the hypothalamus, the present data suggest that POA TNFalpha is involved, in part, in the regulation of physiological sleep.

Functional relationship between subfornical organ cholinergic stimulation and cellular activation in the hypothalamus and AV3V region

The subfornical organ (SFO) has been suggested to be important for water intake and secretion of vasopressin (AVP). However, the role of the SFO cholinergic mechanism in the control of body fluid regulation is not clear. This study determined the effects of local cholinergic stimulation in the SFO produced by administration of physostigmine on drinking and cellular excitation in the anterior third ventricle (AV3V) region and in the supraoptic and paraventricular nuclei (SON and PVN). The results showed that injection of physostigmine into the SFO induced water intake and c-fos expression in the AV3V area as well as in the AVP containing neurons in the hypothalamus. Pretreatment of the SFO with mecamylamine, a nicotinic receptor antagonist, had no effect on physostigmine induced behavioral and c-fos responses. The muscarinic receptor blocker atropine, however, abolished both drinking and cellular activation after injection of physostigmine into the SFO. Immunostaining experiments demonstrated positive acetyltransferase (ChAT) in the SFO. Intensive ChAT immunoreactivity was located in the cholinergic fibers in the SFO. Together, the results indicate that SFO cholinergic mechanisms are important in co-operation with the AV3V and hypothalamic neurons in the control of thirst and AVP-mediated body fluid homeostasis.

Distribution and co-localization of choline acetyltransferase and p75 neurotrophin receptors in the sheep basal forebrain: implications for the use of a specific cholinergic immunotoxin

The basal forebrain cholinergic system is involved in different forms of memory. To study its role in social memory in sheep, an immunotoxin, ME20.4 immunoglobulin G (IgG)-saporin, was developed that is specific to basal forebrain cholinergic neurons bearing the p75 neurotrophin receptor. The distribution of sheep cholinergic neurons was mapped with an antibody against choline acetyltransferase. To assess the localization of the p75 receptor on basal forebrain cholinergic neurons, the distribution of p75 receptor-immunoreactive neurons with ME20.4 IgG was examined, and a double-labeling study with antibodies against choline acetyltransferase and p75 receptor was undertaken. The loss of basal forebrain cholinergic neurons and acetylcholinesterase fibers in basal forebrain projection areas was assessed in ewes that had received intracerebroventricular injections of the immunotoxin (50, 100 or 150 microg) alone, as well as, in some of the ewes treated with the highest dose, with bilateral immunotoxin injections in the nucleus basalis (11 microg/side). Results indicated that choline acetyltransferase- and p75 receptor-immunoreactive cells had similar distributions in the medial septum, the vertical and horizontal limbs of the band of Broca, and the nucleus basalis. The double-labeling procedure revealed that 100% of the cholinergic neurons are also p75 receptor positive in the medial septum and in the vertical and horizontal limbs of the band of Broca, and 82% in the nucleus basalis. Moreover, 100% of the p75 receptor-immunoreactive cells of these four nuclei were cholinergic. Combined immunotoxin injections into ventricles and the nucleus basalis produced a near complete loss (80-95%) of basal forebrain cholinergic neurons and acetylcholinesterase-positive fibers in the hippocampus, olfactory bulb and entorhinal cortex. This study provides the first anatomical data concerning the basal forebrain cholinergic system in ungulates. The availability of a selective cholinergic immunotoxin effective in sheep provides a new tool to probe the involvement of basal forebrain cholinergic neurons in cognitive processes in this species.

Agrypnia excitata: clinical features and pathophysiological implications

Fatal familial insomnia, Morvan's chorea and delirium tremens share the same clinical features: severe insomnia and mental confusion with dream enactment, associated with motor and autonomic activation. Polygraphically, they share an inability to generate slow wave sleep. Agrypnia excitata is the term which aptly defines this peculiar medical condition. In fatal familial insomnia, the syndrome is due to a functional imbalance between activating and deactivating structures within the limbic system provoked by the atrophy of the mediodorsal and anteroventral thalamic nuclei. In Morvan's chorea and delirium tremens, a functional imbalance within the thalamolimbic circuits might be explained by the accumulation of some antireceptor antibodies and by a transient prevalence of excitatory over inhibitory synapses, down-regulated by chronic alcohol abuse, respectively. The selective disappearance of slow sleep (i.e. sleep spindles and delta rhythms) characterizing the agrypnia excitata syndrome, together with other clinical and experimental findings, suggests that sleep can be divided into three types. The most archaic form of sleep corresponding to stage 1 non-REM sleep is shared by man and poikilothermic animals and generated within activating and deactivating neuronal poles located in the basal forebrain, hypothalamus and brain stem; the other two forms of sleep, slow wave sleep and paradoxical sleep, confined to homeothermic animals, are generated in the thalamus and pontine reticular formation respectively. 2001 Harcourt Publishers Ltd

Brain site-specificity of extracellular adenosine concentration changes during sleep deprivation and spontaneous sleep: an in vivo microdialysis study

Previous data suggested that increases in extracellular adenosine in the basal forebrain mediated the sleep-inducing effects of prolonged wakefulness. The present study sought to determine if the state-related changes found in basal forebrain adenosine levels occurred uniformly throughout the brain. In vivo microdialysis sample collection coupled to microbore high-performance liquid chromatography measured extracellular adenosine levels in six brain regions of the cat: basal forebrain, cerebral cortex, thalamus, preoptic area of hypothalamus, dorsal raphe nucleus and pedunculopontine tegmental nucleus. In all these brain regions extracellular adenosine levels showed a similar decline of 15 to 20% during episodes of spontaneous sleep relative to wakefulness. Adenosine levels during non-rapid eye movement sleep did not differ from rapid eye movement sleep. In the course of 6h of sleep deprivation, adenosine levels increased significantly in the cholinergic region of the basal forebrain (to 140% of baseline) and, to a lesser extent in the cortex, but not in the other regions. Following sleep deprivation, basal forebrain adenosine levels declined very slowly, remaining significantly elevated throughout a 3-h period of recovery sleep, but elsewhere levels were either similar to, or lower than, baseline. The site-specific accumulation of adenosine during sleep deprivation suggests a differential regulation of adenosine levels by as yet unidentified mechanisms. Moreover, the unique pattern of sleep-related changes in basal forebrain adenosine level lends strong support to the hypothesis that the sleep-promoting effects of adenosine, as well as the sleepiness associated with prolonged wakefulness, are both mediated by adenosinergic inhibition of a cortically projecting basal forebrain arousal system.

Discharge profiles of juxtacellularly labeled and immunohistochemically identified GABAergic basal forebrain neurons recorded in association with the electroencephalogram in anesthetized rats

The basal forebrain ostensibly plays a dual role in the modulation of cortical activation and behavioral state. It is essential for stimulating cortical activation in association with waking (and paradoxical sleep), yet also important for attenuating cortical activation and promoting slow wave sleep. Using juxtacellular recording and labeling of neurons with Neurobiotin followed by immunohistochemical staining for glutamic acid decarboxylase (GAD), we studied the discharge properties of identified GABAergic basal forebrain neurons in relation to electroencephalographic (EEG) activity in urethane-anesthetized rats to determine the part or parts that they may play in this dual role. The GABAergic neurons displayed distinct discharge profiles in relation to somatosensory stimulation-evoked cortical activation. Whereas a significant minority increased its average discharge rate, the majority decreased its average discharge rate in association with cortical activation. Moreover, subgroups displayed distinct discharge patterns related to different cortical activities, including very regular high-frequency tonic spiking within a gamma EEG frequency range and rhythmic cluster spiking within a theta-like frequency range during cortical activation. During irregular slow EEG activity in absence of stimulation, one subgroup displayed spike bursts correlated with cortical slow oscillations. As relatively large in size and also antidromically activated from the cortex, many GABAergic neurons recorded were considered to be cortically projecting and thus capable of directly modulating cortical activity. Subgroups of GABAergic basal forebrain neurons would thus have the capacity to promote cortical activation by modulating gamma or theta activity and others to attenuate cortical activation by modulating irregular slow oscillations that normally occur during slow wave sleep.

Basal forebrain acetylcholine release during REM sleep is significantly greater than during waking

Cholinergic neurons of the basal forebrain supply the neocortex with ACh and play a major role in regulating behavioral arousal and cortical electroencephalographic activation. Cortical ACh release is greatest during waking and rapid eye movement (REM) sleep and reduced during non-REM (NREM) sleep. Loss of basal forebrain cholinergic neurons contributes to sleep disruption and to the cognitive deficits of many neurological disorders. ACh release within the basal forebrain previously has not been quantified during sleep. This study used in vivo microdialysis to test the hypothesis that basal forebrain ACh release varies as a function of sleep and waking. Cats were trained to sleep in a head-stable position, and dialysis samples were collected during polygraphically defined states of waking, NREM sleep, and REM sleep. Results from 22 experiments in four animals demonstrated that means +/- SE ACh release (pmol/10 min) was greatest during REM sleep (0.77 +/- 0.07), intermediate during waking (0.58 +/- 0.03), and lowest during NREM sleep (0.34 +/- 0.01). The finding that, during REM sleep, basal forebrain ACh release is significantly elevated over waking levels suggests a differential role for basal forebrain ACh during REM sleep and waking.

Multiple output pathways of the basal forebrain: organization, chemical heterogeneity, and roles in vigilance

Studies over the last decade have shown that the basal forebrain (BF) consists of more than its cholinergic neurons. The BF also contains non-cholinergic neurons, including gamma-aminobutyric acid-ergic neurons which co-distribute and co-project with the cholinergic neurons. Both types of neuron project, in variable proportions, to the cerebral cortex, hippocampus, thalamus, amygdala, and olfactory bulb, whereas descending projections to the posterior hypothalamus and brainstem nuclei are predominantly non-cholinergic. Some of the cholinergic and non-cholinergic projection neurons contain neuropeptides such as galanin, nitric oxide synthase, and possibly glutamate. To understand better the function of the BF, the organization of the multiple ascending and descending projections of BF neurons is reviewed along with their neurochemical heterogeneity, and possible functions of individual pathways are discussed. It is proposed that BF neurons belong to multiple systems with distinct cognitive, motivational, emotional, motor, and regulatory functions, and that through these pathways, the BF plays a role in controlling both cognitive and non-cognitive aspects of vigilance.