Dexmedetomidine-induced sedation does not mimic the neurobehavioral phenotypes of sleep in Sprague Dawley rat.

STUDY OBJECTIVES: Dexmedetomidine is used clinically to induce states of sedation that have been described as homologous to nonrapid eye movement (NREM) sleep. A better understanding of the similarities and differences between NREM sleep and dexmedetomidine-induced sedation is essential for efforts to clarify the relationship between these two states. This study tested the hypothesis that dexmedetomidine-induced sedation is homologous to sleep. DESIGN: This study used between-groups and within-groups designs. SETTING: University of Michigan. PARTICIPANTS: Adult male Sprague Dawley rats (n = 40). INTERVENTIONS: Independent variables were administration of dexmedetomidine and saline or Ringer's solution (control). Dependent variables included time spent in states of wakefulness, sleep, and sedation, electroencephalographic (EEG) power, adenosine levels in the substantia innominata (SI), and activation of pCREB and c-Fos in sleep related forebrain regions. MEASUREMENTS AND RESULTS: Dexmedetomidine significantly decreased time spent in wakefulness (-49%), increased duration of sedation (1995%), increased EEG delta power (546%), and eliminated the rapid eye movement (REM) phase of sleep for 16 h. Sedation was followed by a rebound increase in NREM and REM sleep. Systemically administered dexmedetomidine significantly decreased (-39%) SI adenosine levels. Dialysis delivery of dexmedetomidine into SI did not decrease adenosine level. Systemic delivery of dexmedetomidine did not alter c-Fos or pCREB expression in the horizontal diagonal band, or ventrolateral, median, and medial preoptic areas of the hypothalamus. CONCLUSIONS: Dexmedetomidine significantly altered normal sleep phenotypes, and the dexmedetomidine-induced state did not compensate for sleep need. Thus, in the Sprague Dawley rat, dexmedetomidine-induced sedation is characterized by behavioral, electrographic, and immunohistochemical phenotypes that are distinctly different from similar measures obtained during sleep.

Buprenorphine disrupts sleep and decreases adenosine concentrations in sleep-regulating brain regions of Sprague Dawley rat.

BACKGROUND: Buprenorphine, a partial µ-opioid receptor agonist and κ-opioid receptor antagonist, is an effective analgesic. The effects of buprenorphine on sleep have not been well characterized. This study tested the hypothesis that an antinociceptive dose of buprenorphine decreases sleep and decreases adenosine concentrations in regions of the basal forebrain and pontine brainstem that regulate sleep. METHODS: Male Sprague Dawley rats were implanted with intravenous catheters and electrodes for recording states of wakefulness and sleep. Buprenorphine (1 mg/kg) was administered systemically via an indwelling catheter and sleep-wake states were recorded for 24 h. In additional rats, buprenorphine was delivered by microdialysis to the pontine reticular formation and substantia innominata of the basal forebrain while adenosine was simultaneously measured. RESULTS: An antinociceptive dose of buprenorphine caused a significant increase in wakefulness (25.2%) and a decrease in nonrapid eye movement sleep (-22.1%) and rapid eye movement sleep (-3.1%). Buprenorphine also increased electroencephalographic delta power during nonrapid eye movement sleep. Coadministration of the sedative-hypnotic eszopiclone diminished the buprenorphine-induced decrease in sleep. Dialysis delivery of buprenorphine significantly decreased adenosine concentrations in the pontine reticular formation (-14.6%) and substantia innominata (-36.7%). Intravenous administration of buprenorphine significantly decreased (-20%) adenosine in the substantia innominata. CONCLUSIONS: Buprenorphine significantly increased time spent awake, decreased nonrapid eye movement sleep, and increased latency to sleep onset. These disruptions in sleep architecture were mitigated by coadministration of the nonbenzodiazepine sedative-hypnotic eszopiclone. The buprenorphine-induced decrease in adenosine concentrations in basal forebrain and pontine reticular formation is consistent with the interpretation that decreasing adenosine in sleep-regulating brain regions is one mechanism by which opioids disrupt sleep.

Activation of orexin/hypocretin projections to basal forebrain and paraventricular thalamus by acute nicotine.

Orexin/hypocretin neurons of the lateral hypothalamus/perifornical area project to a diverse array of brain regions and are responsive to a variety of psychostimulant drugs. It has been shown that orexin neurons are activated by systemic nicotine administration suggesting a possible orexinergic contribution to the effects of this drug on arousal and cognitive function. The basal forebrain and paraventricular nucleus of the dorsal thalamus (PVT) both receive orexin inputs and have been implicated in arousal, attention and psychostimulant drug responses. However, it is unknown whether orexin inputs to these areas are activated by psychostimulant drugs such as nicotine. Here, we infused the retrograde tract tracer cholera toxin B subunit (CTb) into either the basal forebrain or PVT of adult male rats. Seven to 10 days later, animals received an acute systemic administration of (-) nicotine hydrogen tartrate or vehicle and were euthanized 2h later. Triple-label immunohistochemistry/immunofluorescence was used to detect Fos expression in retrogradely-labeled orexin neurons. Nicotine increased Fos expression in orexin neurons projecting to both basal forebrain and PVT. The relative activation in lateral and medial banks of retrogradely-labeled orexin neurons was similar following basal forebrain CTb deposits, but was more pronounced in the medial bank following PVT deposits of CTb. Our findings suggest that orexin inputs to the basal forebrain and PVT may contribute to nicotine effects on arousal and cognition and provide further support for the existence of functional heterogeneity across the medial-lateral distribution of orexin neurons.

Nitric oxide modulates the discharge rate of basal forebrain neurons.

RATIONALE: During prolonged wakefulness, the concentrations of nitric oxide (NO) and adenosine (AD) increase in the basal forebrain (BF). AD inhibits neuronal activity via adenosine (A1) receptors, thus providing a potential mechanism for sleep facilitation. Although NO in the BF increases adenosine and promotes sleep, it is not clear whether the sleep promotion by NO is mediated through adenosine increase, or NO independently of adenosine could modulate sleep. OBJECTIVE: The objective of the study was to clarify whether NO modulates the discharge rate of BF neurons and whether this effect is mediated via AD. MATERIALS AND METHODS: We measured the discharge rates of BF neurons in anesthetized rats during microdialysis infusion of NO donor alone or in combination with A1 receptor antagonist, 8-cyclopentyl-1,3-dimethylxanthine. RESULTS: NO dose dependently modulated the discharge rate of BF neurons. NO donor (0.5 mM) increased the discharge rates in 48% of neurons and decreased it in 22%. A 1-mM dose decreased it in 55% and increased in 18%. Tactile stimulus affected the discharge rates of most neurons: 60% increased (stimulus-on) it and 14% decreased it (stimulus-off). A 1-mM NO donor predominantly inhibited neurons of both stimulus related types. A small proportion of stimulus-on (23%) neurons but none of the stimulus-off neurons were activated by NO donor. The blockade of A1 receptors partly prevented the inhibitory effect of NO on most of the neurons. This response was more prominent in stimulus-on than in stimulus-off neurons. CONCLUSION: NO modulates the BF neuronal discharge rates in a dose-dependent manner. The inhibitory effect is partly mediated via adenosine A1 receptors.

Prediction of response to donepezil in Alzheimer's disease: combined MRI analysis of the substantia innominata and SPECT measurement of cerebral perfusion.

OBJECTIVE: We performed combined studies of magnetic resonance imaging (MRI) analysis of the substantia innominata and single photon emission CT (SPECT) measurement of cerebral perfusion with the goal of predicting which patients with Alzheimer's disease are most likely to respond to donepezil treatment. METHODS: Ninety-one patients treated with donepezil were divided into responders and non-responders on the basis of changes in their MMSE scores from baseline to study endpoint. The thickness of the substantia innominata was measured on the coronal T2-weighted MRI through the anterior commissure. SPECT data were analysed using three-dimensional stereotactic surface projections. RESULTS: Responders had significantly greater atrophy of the substantia innominata, but less prominent frontal hypoperfusion than non-responders. Receiver operating characteristic analysis revealed that combined MRI and SPECT examination showed an overall discrimination rate of 70% between responders and non-responders. DISCUSSION: Our results suggest that responder patients have more severe damage in the cholinergic system and/or less prominent frontal cortical dysfunction. Combined MRI analysis of the substantia innominata and SPECT measurement of frontal perfusion at baseline may help to predict response to donepezil treatment in patients with Alzheimer's disease.

GABA receptor agonism in the sublenticular central extended amygdala impairs medial forebrain bundle self-stimulation but GABA blockade does not enhance it.

The sublenticular central extended amygdala (SLEAc), which is important in medial forebrain bundle (MFB) self-stimulation, is heavily populated with GABAergic medium spiny neurons that intercommunicate via local axon collaterals. This study examines the role of GABAergic communication in the SLEAc in MFB self-stimulation. Male Long-Evans rats were given unilateral MFB stimulation electrodes and bilateral injection guide cannulae aimed at the SLEAc. Changes in the stimulation's reward efficacy and in the animals' ability to respond for stimulation following 0.5 microl injections of saline, 50 ng of muscimol (GABA-A agonist), 75 ng of baclofen (GABA-B agonist), 25 ng of bicuculline methiodide (GABA-A antagonist), and 500 ng of phaclofen (GABA-B antagonist) were assessed using the rate-frequency curve shift paradigm. Injecting the receptor agonists ipsi- and contralateral to the stimulation site substantially decreased stimulation reward efficacy and responding. Baclofen's effects were more anatomically specific to the SLEAc and baclofen was less challenging to response rate than was muscimol. Ipsi- and contralateral injections of the receptor blockers and saline had no effect on either stimulation reward efficacy or response rate, although the blockers, especially phaclofen, sometimes enhanced response rate when injected into the globus pallidus or ventral pallidum. Comparing these results to others' observations about GABAergic communication in the basal forebrain suggests that muscimol may have inhibited endemic SLEAc neurons while baclofen may have impaired the release of glutamate into the SLEAc from cortical and amygdalar afferents. These results also suggest functional differences between the two basal forebrain macrostructures of striatopallidum and extended amygdala.

Effects of estrogens on cholinergic neurons in the rat basal nucleus.

Estrogen replacement in postmenopausal women may help prevent or delay development of Alzheimer's disease. Because loss of basal forebrain cholinergic neurons with reductions in choline acetyltransferase (ChAT) concentration are associated with Alzheimer's disease, we investigated the effect of estradiol (E(2)) and J 861, a non-feminizing estrogen, on cholinergic neurons in the basal forebrain. Ovariectomized rats received E(2), J 861 or vehicle, and basal forebrain sections through the substantia innominata, medial septum, and nucleus of the diagonal band were immunostained for ChAT. ChAT-immunoreactive cells in the basal forebrain were significantly reduced in the ovariectomized rats compared to intact rats, but those ovariectomized rats receiving estrogen replacement with E(2) and J 861 had near normal levels of ChAT-positive neurons. While retrograde tracing experiments with fluorogold injected into the prefrontal cortex showed no significant differences in the number of fluorogold-labeled cells among the groups, ChAT-immunoreactive cells and double-labeled cells were significantly lower in OVX rats than in intact and E(2) rats. Some substantia innominata cells in the J 861 rats were ChAT/estrogen receptor alpha-positive. These results suggest that E(2) and J 861 have positive effects on cholinergic neurons that project from the basal nucleus to the forebrain cortex.

Role of substantia innominata in cerebral blood flow autoregulation.

Ascending projections from the substantia innominata (SI) may have an important role in the regulation of cerebral blood flow (CBF). However, several reports have suggested that unilateral lesion of the SI does not affect CBF autoregulation. On the other hand, it is also reported that several cortical and subcortical functions may be regulated not only by ipsilateral SI, but also by contralateral SI. Thus, the objective of this study is to test the hypothesis that bilateral lesions of the SI affect CBF autoregulation. Experiments were performed on anesthetized male Sprague-Dawley rats. Ibotenic acid or physiological saline was microinjected into bilateral SI. Rats were classified into four groups as follows: bilateral SI lesion rats (ibotenic acid was injected bilaterally), left or right SI lesion rats (ibotenic acid was injected into the unilateral SI and saline into the contralateral SI), and control rats (saline was injected bilaterally). Ten days after injection, CBF in the left frontal cortex was measured by laser-Doppler flowmetry during stepwise controlled hemorrhagic hypotension. In bilateral SI lesion rats, CBF was started to decrease significantly at 80 mm Hg (p<0.01). In the other three groups, CBF was well maintained until 50 mm Hg. Changes in CBF through stepwise hypotension in bilateral SI lesion rats were significantly different from the other groups (p<0.01). These results suggest that bilateral SI regulates cortical vasodilator mechanisms during hemorrhagic hypotension. Under unilateral SI lesion, some compensatory effects from the contralateral SI may maintain CBF autoregulation.

Adenosine inhibits basal forebrain cholinergic and noncholinergic neurons in vitro.

Adenosine has been proposed as a homeostatic "sleep factor" that promotes the transition from waking to sleep by affecting several sleep-wake regulatory systems. In the basal forebrain, adenosine accumulates during wakefulness and, when locally applied, suppresses neuronal activity and promotes sleep. However, the neuronal phenotype mediating these effects is unknown. We used whole-cell patch-clamp recordings in in vitro rat brain slices to investigate the effect of adenosine on identified cholinergic and noncholinergic neurons of the magnocellular preoptic nucleus and substantia innominata. Adenosine (0.5-100 microM) reduced the magnocellular preoptic nucleus and substantia innominata cholinergic neuronal firing rate by activating an inwardly rectifying potassium current that reversed at -82 mV and was blocked by barium (100 microM). Application of the A1 receptor antagonist 8-cyclo-pentyl-theophylline (200 nM) blocked the effects of adenosine. Adenosine was also tested on two groups of electrophysiologically distinct noncholinergic magnocellular preoptic nucleus and substantia innominata neurons. In the first group adenosine, via activation of postsynaptic A1 receptors, reduced spontaneous firing via inhibition of the hyperpolarization-activated cation current. Blocking the H-current with ZD7288 (20 microM) abolished adenosine effects on these neurons. The second group was not affected by adenosine. These results demonstrate that, in the magnocellular preoptic nucleus and substantia innominata region of the basal forebrain, adenosine inhibits both cholinergic neurons and a subset of noncholinergic neurons. Both of these effects occur via postsynaptic A1 receptors, but are mediated downstream by two separate mechanisms.

Morphine inhibits acetylcholine release in rat prefrontal cortex when delivered systemically or by microdialysis to basal forebrain.

BACKGROUND: Cortical acetylcholine originates in the basal forebrain and is essential for maintaining normal cognition and arousal. Morphine impairs these cholinergically mediated cortical functions. The current study tested the hypothesis that morphine decreases prefrontal cortical acetylcholine release by acting at the level of the basal forebrain. METHODS: Adult male Sprague-Dawley rats (n = 18) were anesthetized with isoflurane. One microdialysis probe was placed in the substantia innominata region of the basal forebrain and perfused with Ringer's solution (control) followed by one concentration of morphine (1, 10, 100, or 1,000 microm) or morphine (1,000 microm) plus naloxone (100 microm). A second microdialysis probe was placed in the prefrontal cortex for measuring acetylcholine. In a second series of experiments, rats (n = 6) were implanted with electrodes for recording states of arousal, a guide cannula positioned above the prefrontal cortex for inserting a microdialysis probe, and an indwelling jugular vein catheter. The effects of administering intravenous morphine (30 mg/kg) versus normal saline (0.9%) on prefrontal cortical acetylcholine release, cortical electroencephalographic power, and behavior were quantified. RESULTS: Dialysis delivery of morphine to the substantia innominata caused a concentration-dependent, naloxone-sensitive decrease in acetylcholine release within the prefrontal cortex. The maximal decrease in acetylcholine was 36.3 +/- 11.5%. Intravenous morphine administration significantly decreased cortical acetylcholine release, increased electroencephalographic power in the 0.5- to 5-Hz range, and eliminated normal wakefulness. CONCLUSION: Morphine causes obtundation of arousal and may cause cognitive impairment by acting at the level of the substantia innominata to disrupt cortical cholinergic neurotransmission.

Sensitized attentional performance and Fos-immunoreactive cholinergic neurons in the basal forebrain of amphetamine-pretreated rats.

BACKGROUND: The consequences of repeated exposure to psychostimulants have been hypothesized to model aspects of schizophrenia. This experiment assessed the consequences of the administration of an escalating dosing regimen of amphetamine (AMPH) on attentional performance. Fos-like immunoreactivity (Fos-IR) in selected regions of these rats' brains was examined to test the hypothesis that AMPH-sensitized attentional impairments are associated with increased recruitment of basal forebrain cholinergic neurons. METHODS: Rats were trained in a sustained attention task and then treated with saline or in accordance with an escalating dosing regimen of AMPH (1-10 mg/kg). Performance was assessed during the pretreatment and withdrawal periods and following the subsequent administration of AMPH "challenges" (.5, 1.0 mg/kg). Brain sections were double-immunostained to visualize Fos-IR and cholinergic neurons. RESULTS: Compared with the acute effects of AMPH, AMPH "challenges," administered over 2 months after the pretreatment was initiated, resulted in significant impairments in attentional performance. In AMPH-pretreated and -challenged animals, an increased number of Fos-IR neurons was observed in the basal forebrain. The majority of these neurons were cholinergic. CONCLUSIONS: The evidence supports the hypothesis that abnormally regulated cortical cholinergic inputs represent an integral component of neuronal models of the attentional dysfunctions of schizophrenia.

Somatostatin receptors in the ventral pallidum/substantia innominata modulate rat locomotor activity.

RATIONALE: Somatostatin and its receptors (sst(1) and sst(2)) have been localized in brain nuclei implicated in motor control, such as the nucleus accumbens, ventral pallidum (VP) and substantia innominata (SI). OBJECTIVES: The objective of the study is to investigate the effect of somatostatin and selective sst(1) and sst(2) analogs infused in the VP/SI on the locomotor activity of the rat. METHODS: Somatostatin (15, 30, 60, 120 and 240 ng/0.5 microl/side), CH275 (sst(1) analog; 60, 180, 240 and 480 ng/0.5 microl/side), MK678 (sst(2) analog; 120, 240 and 480 ng/0.5 microl/side), L-809,087 (sst(4) agonist, 240 ng/0.5 microl/side) or saline (vehicle) were infused bilaterally in the VP/SI of the rat and locomotor activity measured for 60 min. The effect of SRA-880 (sst(1) antagonist) and CYN-154806 (sst(2) antagonist) on somatostatin-, CH275- and MK678-mediated locomotor activity was also ascertained. RESULTS: Somatostatin decreased locomotor activity in the first 30 min after its infusion in the VP/SI and in a dose-dependent manner. The sst(1) and sst(2) antagonists, SRA-880 and CYN-154806, respectively, reversed the somatostatin effect. The sst(1) and sst(2) agonists CH275 and MK678, respectively, mimicked somatostatin's actions, while the selective sst(4) agonist L-809,087 had no effect. Moreover, SRA-880 and CYN-154806 reversed the respective agonist action on locomotor activity. CONCLUSION: The present study provides functional evidence for the presence of sst(1) and sst(2) receptors in the VP/SI and their implication in motor control. The mechanism via which somatostatin and agonists mediate the attenuation of locomotor activity is presently being investigated.

A1 receptor and adenosinergic homeostatic regulation of sleep-wakefulness: effects of antisense to the A1 receptor in the cholinergic basal forebrain.

We hypothesized that adenosine, acting via the A1 receptor, is a key factor in the homeostatic control of sleep. The increase in extracellular levels of adenosine during prolonged wakefulness is thought to facilitate the transition to sleep by reducing the discharge activity of wakefulness-promoting neurons in the basal forebrain. Adenosine A1 receptor control of the homeostatic regulation of sleep was tested by microdialysis perfusion of antisense oligonucleotides against the mRNA of the A1 receptor in the magnocellular cholinergic region of the basal forebrain of freely behaving rats. After microdialysis perfusion of A1 receptor antisense in the basal forebrain, spontaneous levels of sleep-wakefulness showed a significant reduction in non-rapid eye movement (REM) sleep with an increase in wakefulness. After 6 hr of sleep deprivation, the antisense-treated animals spent a significantly reduced amount of time in non-REM sleep, with postdeprivation recovery sleep hours 2-5 showing a reduction of approximately 50-60%. There was an even greater postdeprivation reduction in delta power (60-75%) and a concomitant increase in wakefulness. All behavioral state changes returned to control (baseline) values after the cessation of antisense administration. Control experiments with microdialysis perfusion of nonsense (randomized antisense) oligonucleotides and with artificial CSF showed no effect during postdeprivation recovery sleep or spontaneously occurring behavioral states. Antisense to the A1 receptor suppressed A1 receptor immunoreactivity but did not show any neurotoxicity as visualized by Fluoro-Jade staining. These data support our hypothesis that adenosine, acting via the A1 receptor, in the basal forebrain is a key component in the homeostatic regulation of sleep.

Switching to cue-directed behavior: specific for ventral striatal dopamine but not ventral pallidum/substantia innominata gaba as revealed by a swimming-test procedure in rats.

In this study it was investigated whether ventral striatal dopamine-induced changes in switching to cue-directed behavioral patterns were funnelled via the rostral areas of the ventral pallidum/substantia innominata (VP/SI) complex and, if so, whether changes in switching to cue-directed behavioral patterns could be elicited in the VP/SI complex by manipulating GABAergic activity. To this end rats were bilaterally equipped with cannulae directed at the ventral striatum and/or rostral VP/SI complex and subjected to a swimming-test procedure for 6 min. Injections of the dopamine-releasing agent d-amphetamine (10 microg/0.5 microl per side) enhanced the number of different cue-directed behavioral patterns while they had no effect upon the number of different non-cue-directed behavioral patterns in line with previous studies (Life Sci - 1989 1697). This increase was attenuated by a low dose of the GABAa agonist muscimol (1 ng/0.5 microl) into the rostral VP/SI complex. This dose of muscimol when injected alone into the rostral VP/SI complex had no effect upon the number of different cue-directed behavioral patterns. Only the lowest dose of the GABAa antagonist bicuculline (10-25 ng/0.5 microl per side) into the rostral VP/SI complex slightly, and in a non-d-amphetamine-like manner, increased the number of different cue-directed behavioral patterns while none of the doses had an effect on the number of different non-cue-directed behavioral patterns. Both injections of d-amphetamine into the ventral striatum and injections of bicuculline into the rostral VP/SI complex strongly increased motor activity in the 10-min period preceding the swimming test. We conclude from the data that switching to cue-directed behavioral patterns is sensitive to manipulations with the dopaminergic activity in the ventral striatum but not with the GABAergic activity in the VP/SI complex although the VP/SI transmits it to other brain structures. In contrast motor activity is sensitive to manipulations with both ventral striatal dopamine and rostral VP/SI complex GABA.

Compartmentation of alpha 1 and alpha 2 GABA(A) receptor subunits within rat extended amygdala: implications for benzodiazepine action.

The extended amygdala, a morphological and functional entity within the basal forebrain, is a neuronal substrate for emotional states like fear and anxiety. Anxiety disorders are commonly treated by benzodiazepines that mediate their action via GABA(A) receptors. The binding properties and action of benzodiazepines depend on the alpha-subunit profile of the hetero-pentameric receptors: whereas the alpha1 subunit is associated with benzodiazepine type I pharmacology and reportedly mediates sedative as well as amnesic actions of benzodiazepines, the alpha2 subunit confers benzodiazepine type II pharmacology and mediates the anxiolytic actions of benzodiazepines. We determined the localization of alpha1 and alpha2 subunits within the extended amygdala, identified by secretoneurin immunostaining, to define the morphological substrates for the diverse benzodiazepine actions. A moderate expression of the alpha1 subunit could be detected in compartments of the medial subdivision and a strong expression of the alpha2 subunit throughout the central subdivision. It is concluded that the alpha1 and alpha2 subunits are differentially expressed within the extended amygdala, indicating that this structure is compartmentalized with respect to function and benzodiazepine action.

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.

Atrophy of the substantia innominata on magnetic resonance imaging and response to donepezil treatment in Alzheimer's disease.

Atrophy of the substantia innominata on magnetic resonance imaging (MRI), reflecting degeneration of cholinergic neurons in the nucleus basalis of Meynert, may be an in vivo marker of cholinergic damage. We attempted to investigate whether the MRI features of the substantia innominata predict response to donepezil treatment in Alzheimer's patients. The thickness of the substantia innominata was measured on the coronal T2-weighted MRI through the anterior commissure. Seventy-two patients treated with donepezil were divided into the two groups (responders and non-responders) based on changes in Mini-Mental State Examination (MMSE) scores from baseline to study endpoint. Atrophy of the substantia innominata was more pronounced in responders than non-responders. There was a significant inverse correlation between thickness of the substantia innominata and MMSE changes. MRI analysis of the substantia innominata may be a simple and practical method for the selection of possible treatment responders.

Wake-promoting and sleep-suppressing actions of hypocretin (orexin): basal forebrain sites of action.

The hypocretins (orexins) are a newly identified peptide family comprised of two peptides, hypocretin-1 and hypocretin-2. Recent observations suggest an involvement of these peptides in the regulation of behavioral state. For example, these peptides are found in a variety of brain regions associated with the regulation of forebrain neuronal and behavioral activity states. Furthermore, when infused into the lateral ventricles in awake animals, hypocretin-1 elicits increased duration of waking beyond that observed in vehicle-treated animals. Previous studies have been limited to an examination of the sleep-wake effects of hypocretin-1 in awake animals. Currently, the sleep-wake effects of hypocretin-2 and the extent to which hypocretins can initiate waking in the sleeping animal remain unclear. To better characterize the wake-promoting actions of the hypocretins, the current studies examined the sleep-wake effects of varying doses (0.007, 0.07 and 0.7 nmol) of hypocretin-1 and hypocretin-2 when administered into sleeping rats (e.g. remote-controlled infusions). Infusions of hypocretin-1 and hypocretin-2 into the lateral ventricles elicited a short latency (0.7 nmol hypocretin-1; 93+/-30 s from the start of the 120-s infusion) increase in electroencephalographic, electromyographic, and behavioral indices of waking. These infusions also produced substantial decreases in slow-wave and rapid-eye movement sleep. Hypocretin-1 was more potent than hypocretin-2 in these actions. Interestingly, hypocretin-1 infused into the fourth ventricle elicited less robust waking which occurred with a longer latency than infusions into the lateral ventricles. These latter observations suggest a forebrain site of action participates in hypocretin-1-induced waking. Within the forebrain, a variety of basal forebrain structures, including the medial preoptic area, the medial septal area and the substantia innominata, receive a moderate hypocretin innervation. Therefore, additional studies examined the sleep-wake effects of bilateral hypocretin-1 infusions into these basal forebrain structures. Robust increases in waking were observed following infusions into, but not outside, the medial septal area, the medial preoptic area and the substantia innominata. These results indicate a potentially prominent role of hypocretins in sleep-wake regulation via actions within certain basal forebrain structures and are consistent with studies indicating a prominent role of hypocretins in sleep/arousal disorders.

Zinc inhibition of group I mGluR-mediated calcium homeostasis in auditory neurons.

Zinc is widely distributed in the central nervous system (CNS), it functions normally as a synaptic modulator, and it contributes to neuronal death under pathologic conditions. Zinc colocalizes with glutamate in excitatory synapses, and the presence of zinc is well characterized in the synapses of the auditory system. Since chick cochlear nucleus neurons depend upon synaptic activation of metabotropic glutamate receptors (mGluRs) for maintenance and survival, the goal of this study was to determine (1) if zinc is released from the eighth nerve calyces onto nucleus magnocellularis (NM) neurons in the chick cochlear nucleus, and, if so, (2) what effect it has on group I mGluR-mediated calcium homeostasis of these neurons. Using in vitro slices and a fluorescent dye relatively specific to vesicularized zinc, we show that zinc is indeed localized to the presynaptic calyces and is released upon nerve stimulation or KCl depolarization. Experiments employing fura-2 calcium imaging show that zinc inhibits group I mGluR release of calcium from internal stores of NM neurons and disrupts activity-dependent calcium homeostasis in a manner identical to the mGluR5-specific antagonist 2-methyl-6-(phenylethynyl)pyridine. The mGluR1-specific antagonist 7-hydroxyiminocyclopropan-[b]chromen-la-carboxylic acid ethyl ester did not affect release of calcium from stores by the nonspecific mGluR agonist aminocyclopentane dicarboxylic acid, nor did it affect activity-dependent calcium homeostasis. We conclude that zinc is present in and released from the glutamatergic eighth nerve calcyes. The presence of zinc inhibits mGluR5, a major component of calcium homeostasis of NM neurons, and plays a modulatory role in the activity-dependent, mGluR-mediated calcium homeostasis of auditory neurons.

Differential sensitivity to the wake-promoting actions of norepinephrine within the medial preoptic area and the substantia innominata.

Mapping studies were conducted to delineate the site(s) of action for the arousal-enhancing actions of norepinephrine (NE) within the basal forebrain region encompassing the medial preoptic area (MPOA) and the substantia innominata (SI). Varying doses of NE, the beta-agonist, isoproterenol, or the alpha1-agonist, phenylephrine, were infused into the MPOA or SI in the resting rat. Infusions of NE (4 nmol, 16 nmo/150 nl), isoproterenol (15 nmol/150 nl), and phenylephrine (40 nmol/250 nl) into the MPOA elicited robust increases in waking. In contrast, neither isoproterenol or phenylephrine infusions into the SI altered behavioral state. NE infusions into the SI increased waking only at the highest dose, and at this dose there was an anatomical gradient for NE-induced waking, with infusions placed farther from the MPOA, producing smaller increases in waking. Thus, in contrast to the MPOA, the SI is relatively insensitive to the wake-promoting actions of NE.