Functionally refined encoding of threat memory by distinct populations of basal forebrain cholinergic projection neurons

Neurons of the basal forebrain nucleus basalis and posterior substantia innominata (NBM/SIp) comprise the major source of cholinergic input to the basolateral amygdala (BLA). Using a genetically-encoded acetylcholine (ACh) sensor in mice, we demonstrate that BLA-projecting cholinergic neurons can "learn" the association between a naïve tone and a foot shock (training) and release ACh in the BLA in response to the conditioned tone 24h later (recall). In the NBM/SIp cholinergic neurons express the immediate early gene, Fos following both training and memory recall. Cholinergic neurons that express Fos following memory recall display increased intrinsic excitability. Chemogenetic silencing of these learning-activated cholinergic neurons prevents expression of the defensive behavior to the tone. In contrast, we show that NBM/SIp cholinergic neurons are not activated by an innately threatening stimulus (predator odor). Instead, VP/SIa cholinergic neurons are activated and contribute to defensive behaviors in response to predator odor, an innately threatening stimulus. Taken together, we find that distinct populations of cholinergic neurons are recruited to signal distinct aversive stimuli, demonstrating functionally refined organization of specific types of memory within the cholinergic basal forebrain of mice.

The anterior perforated substance (APS) revisited: Commented anatomical and imagenological views

INTRODUCTION

Since 2002, when we published our article about the anterior perforated substance (APS), the knowledge about the region has grown enormously.

OBJECTIVE

To make a better description of the anatomy of the zone with new dissection material added to the previous, to sustain the anatomical analysis of the MRI employing the SPACE sequence, interacting with our imagenology colleagues. Especially, we aim to identify and topographically localize by MRI the principal structures in APS-substantia innominata (SI).

METHOD

The presentation follows various steps: (1) location and boundaries of the zone and its neighboring areas; (2) schematic description of the region with simple outlines; (3) cursory revision of the SI and its three systems; (4) serial images of the dissections of the zone and its vessels, illustrated and completed when possible, by MRI images of a voluntary experimental subject (ES).

RESULTS

With this method, we could expose most of the structures of the region anatomically and imagenologically.

DISCUSSION

The zone can be approached for dissection with magnification and the habitual microsurgical instruments with satisfactory results. We think that fibers in this region should be followed by other anatomical methods in addition to tractography. The principal structures of ventral striopallidum and extended amygdala (EA) can be identified with the SPACE sequence. The amygdala and the basal ganglion of Meynert (BGM) are easily confused because of their similar signal. Anatomical clues can orient the clinician about the different clusters of the BGM in MRI.

CONCLUSIONS

The dissection requires a previous knowledge of the zone and a good amount of patience. The APS is a little space where concentrate essential vessels for the telencephalon, "en passage" or perforating, and neural structures of relevant functional import. From anatomical and MRI points of view, both neural and vascular structures follow a harmonious and topographically describable plan. The SPACE MRI sequence has proved to be a useful tool for identifying different structures in this area as the striatopallidal and EA. Anatomical knowledge of the fibers helps in the search of clusters of the basal ganglion.

Corticotropin Releasing Factor (CRF) Coexpression in GABAergic, Glutamatergic, and GABA/Glutamatergic Subpopulations in the Central Extended Amygdala and Ventral Pallidum of Young Male Primates

The central extended amygdala (CEA) and ventral pallidum (VP) are involved in diverse motivated behaviors based on rodent models. These structures are conserved, but expanded, in higher primates, including human. Corticotropin releasing factor (CRF), a canonical "stress molecule" associated with the CEA and VP circuitry across species, is dynamically regulated by stress and drugs of abuse and misuse. CRF's effects on circuits critically depend on its colocation with primary "fast" transmitters, making this crucial for understanding circuit effects. We surveyed the distribution and colocalization of CRF-, VGluT2- (vesicular glutamate transporter 2), and VGAT- (vesicular GABA transporter) mRNA in specific subregions of the CEA and VP in young male monkeys. Although CRF-containing neurons were clustered in the lateral central bed nucleus (BSTLcn), the majority were broadly dispersed throughout other CEA subregions, and the VP. CRF/VGAT-only neurons were highest in the BSTLcn, lateral central amygdala nucleus (CeLcn), and medial central amygdala nucleus (CeM) (74%, 73%, and 85%, respectively). In contrast, lower percentages of CRF/VGAT only neurons populated the sublenticular extended amygdala (SLEAc), ventrolateral bed nucleus (BSTLP), and VP (53%, 54%, 17%, respectively), which had higher complements of CRF/VGAT/VGluT2-labeled neurons (33%, 29%, 67%, respectively). Thus, the majority of CRF-neurons at the "poles" (BSTLcn and CeLcn/CeM) of the CEA are inhibitory, while the "extended" BSTLP and SLEAc subregions, and neighboring VP, have a more complex profile with admixtures of "multiplexed" excitatory CRF neurons. CRF's colocalization with its various fast transmitters is likely circuit-specific, and relevant for understanding CRF actions on specific target sites.SIGNIFICANCE STATEMENT The central extended amygdala (CEA) and ventral pallidum (VP) regulate multiple motivated behaviors through differential downstream projections. The stress neuropeptide corticotropin releasing factor (CRF) is enriched in the CEA, and is thought to "set the gain" through modulatory effects on coexpressed primary transmitters. Using protein and transcript assays in monkey, we found that CRF neurons are broadly and diffusely distributed in CEA and VP. CRF mRNA+ neurons colocalize with VGAT (GABA) and VGluT2 (glutamate) mRNAs in different proportions depending on subregion. CRF mRNA was also coexpressed in a subpopulation of VGAT/VGluT2 mRNA ("multiplexed") cells, which were most prominent in the VP and "pallidal"-like parts of the CEA. Heterogeneous CRF and fast transmitter coexpression across CEA/VP subregions implies circuit-specific effects.

Altered Cortical Cholinergic Network in Parkinson's Disease at Different Stage: A Resting-State fMRI Study

The cholinergic system is critical in Parkinson’s disease (PD) pathology, which accounts for various clinical symptoms in PD patients. The substantia innominata (SI) provides the main source of cortical cholinergic innervation. Previous studies revealed cholinergic-related dysfunction in PD pathology at early stage. Since PD is a progressive disorder, alterations of cholinergic system function along with the PD progression have yet to be elucidated. Seventy-nine PD patients, including thirty-five early-stage PD patients (PD-E) and forty-four middle-to-late stage PD patients (PD-M), and sixty-four healthy controls (HC) underwent brain magnetic resonance imaging and clinical assessments. We employed seed-based resting-state functional connectivity analysis to explore the cholinergic-related functional alterations. Correlation analysis was used to investigate the relationship between altered functional connectivity and the severity of motor symptoms in PD patients. Results showed that both PD-E and PD-M groups exhibited decreased functional connectivity between left SI and left frontal inferior opercularis areas and increased functional connectivity between left SI and left cingulum middle area as well as right primary motor and sensory areas when comparing with HC. At advanced stages of PD, functional connectivity in the right primary motor and sensory areas was further increased. These altered functional connectivity were also significantly correlated with the Unified Parkinson’s Disease Rating Scale motor scores. In conclusion, this study illustrated that altered cholinergic function plays an important role in the motor disruptions in PD patients both in early stage as well as during the progression of the disease.

The Cholinergic Basal Forebrain Links Auditory Stimuli with Delayed Reinforcement to Support Learning

Animals learn to fear conditioned sound stimuli (CSs) that accompany aversive unconditioned stimuli (USs). Auditory cortex (ACx) circuits reorganize to support auditory fear learning when CS-evoked activity temporally overlaps with US-evoked acetylcholine release from the basal forebrain. Here we describe robust fear learning and acetylcholine-dependent ACx plasticity even when the US is delayed by several seconds following CS offset. A 5-s CS-US gap was not bridged by persistent CS-evoked spiking throughout the trace period. Instead, within minutes following the start of conditioning, optogenetically identified basal forebrain neurons that encode the aversive US scaled up responses to the CS and increased functional coupling with the ACx. Over several days of conditioning, bulk imaging of cholinergic basal forebrain neurons revealed sustained sound-evoked activity that filled in the 5-s silent gap preceding the US. These findings identify a plasticity in the basal forebrain that supports learned associations between sensory stimuli and delayed reinforcement.

Structural grey matter changes in the substantia innominata in Alzheimer's disease and dementia with Lewy bodies: a DARTEL-VBM study

OBJECTIVES

Several cholinergic nuclei, and in particular the nucleus basalis of Meynert, are localised to the substantia innominata in the basal forebrain. These nuclei provide major cholinergic innervation to the cerebral cortex and hippocampus, and have an essential role in cognitive function. The aim of this study was to investigate volumetric grey matter (GM) changes in the substantia innominata from structural T1 images in Alzheimer's disease (AD), dementia with Lewy bodies (DLB) and healthy older participants using voxel-based morphometry.

METHODS

Participants (41 DLB, 47 AD and 39 controls) underwent 3 T T1 magnetic resonance imaging and cognitive assessments. Voxel-based morphometry analysis used SPM8 with a substantia innominata brain mask to define the subspace for voxel GM analyses. Group differences, and selected behavioural and clinical correlates, were assessed.

RESULTS

Compared with that in controls, bilateral GM loss in the substantia innominata was apparent in both AD and DLB. Relative to controls, significant bilateral GM loss in the substantia innominata was observed in DLB and AD. In DLB, significant associations were also observed between substantia innominata GM volume loss, and the levels of cognitive impairment and severity of cognitive fluctuations.

CONCLUSIONS

Relative to that controls, atrophy of the substantia innominata was apparent in DLB and AD, and is associated with specific clinical manifestations in DLB. © 2016 The Authors. International Journal of Geriatric Psychiatry Published by John Wiley & Sons Ltd.

Descending projections from the basal forebrain to the orexin neurons in mice

The orexin (hypocretin) neurons play an essential role in promoting arousal, and loss of the orexin neurons results in narcolepsy, a condition characterized by chronic sleepiness and cataplexy. The orexin neurons excite wake-promoting neurons in the basal forebrain (BF), and a reciprocal projection from the BF back to the orexin neurons may help promote arousal and motivation. The BF contains at least three different cell types (cholinergic, glutamatergic, and γ-aminobutyric acid (GABA)ergic neurons) across its different regions (medial septum, diagonal band, magnocellular preoptic area, and substantia innominata). Given the neurochemical and anatomical heterogeneity of the BF, we mapped the pattern of BF projections to the orexin neurons across multiple BF regions and neuronal types. We performed conditional anterograde tracing using mice that express Cre recombinase only in neurons producing acetylcholine, glutamate, or GABA. We found that the orexin neurons are heavily apposed by axon terminals of glutamatergic and GABAergic neurons of the substantia innominata (SI) and magnocellular preoptic area, but there was no innervation by the cholinergic neurons. Channelrhodopsin-assisted circuit mapping (CRACM) demonstrated that glutamatergic SI neurons frequently form functional synapses with the orexin neurons, but, surprisingly, functional synapses from SI GABAergic neurons were rare. Considering their strong reciprocal connections, BF and orexin neurons likely work in concert to promote arousal, motivation, and other behaviors. J. Comp. Neurol. 525:1668-1684, 2017. © 2016 Wiley Periodicals, Inc.

Topographic organization of the basal forebrain projections to the perirhinal, postrhinal, and entorhinal cortex in rats

Previous studies have shown that the basal forebrain (BF) modulates cortical activation via its projections to the entire cortical mantle. However, the organization of these projections is only partially understood or, for certain areas, unknown. In this study, we examined the topographic organization of cholinergic and noncholinergic projections from the BF to the perirhinal, postrhinal, and entorhinal cortex by using retrograde tracing combined with choline acetyltransferase (ChAT) immunohistochemistry in rats. The perirhinal and postrhinal cortex receives major cholinergic and noncholinergic input from the caudal BF, including the caudal globus pallidus and substantia innominata and moderate input from the horizontal limb of the diagonal band, whereas the entorhinal cortex receives major input from the rostral BF, including the medial septum and the vertical and horizontal limbs of the diagonal band. In the perirhinal cases, cholinergic projection neurons are distributed more caudally in the caudal globus pallidus than noncholinergic projection neurons. Compared with the perirhinal cases, the distribution of cholinergic and noncholinergic neurons projecting to the postrhinal cortex shifts slightly caudally in the caudal globus pallidus. The distribution of cholinergic and noncholinergic neurons projecting to the lateral entorhinal cortex extends more caudally in the BF than to the medial entorhinal cortex. The ratio of ChAT-positive projection neurons to total projection neurons is higher in the perirhinal/postrhinal cases (26-48%) than in the entorhinal cases (13-30%). These results indicate that the organization of cholinergic and noncholinergic projections from the BF to the parahippocampal cortex is more complex than previously described. J. Comp. Neurol. 524:2503-2515, 2016. © 2016 Wiley Periodicals, Inc.

Cognitive Correlates of Basal Forebrain Atrophy and Associated Cortical Hypometabolism in Mild Cognitive Impairment

Degeneration of basal forebrain (BF) cholinergic nuclei is associated with cognitive decline, and this effect is believed to be mediated by neuronal dysfunction in the denervated cortical areas. MRI-based measurements of BF atrophy are increasingly being used as in vivo surrogate markers for cholinergic degeneration, but the functional implications of reductions in BF volume are not well understood. We used high-resolution MRI, fluorodeoxyglucose-positron emission tomography (PET), and neuropsychological test data of 132 subjects with mild cognitive impairment (MCI) and 177 cognitively normal controls to determine associations between BF atrophy, cortical hypometabolism, and cognitive deficits. BF atrophy in MCI correlated with both impaired memory function and attentional control deficits, whereas hippocampus volume was more specifically associated with memory deficits. BF atrophy was also associated with widespread cortical hypometabolism, and path analytic models indicated that hypometabolism in domain-specific cortical networks mediated the association between BF volume and cognitive dysfunction. The presence of cortical amyloid pathology, as assessed using AV45-PET, did not significantly interact with the observed associations. These data underline the potential of multimodal imaging markers to study structure-function-cognition relationships in the living human brain and provide important in vivo evidence for an involvement of the human BF in cortical activity and cognitive function.

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.

Effects of hypocretin and norepinephrine interaction in bed nucleus of the stria terminalis on arterial pressure

Forebrain neuronal circuits containing hypocretin-1 (hcrt-1) and norepinephrine (NE) are important components of central arousal-related processes. Recently, these two systems have been shown to have an overlapping distribution within the bed nucleus of the stria terminalis (BST), a limbic structure activated by stressful challenges, and which functions to adjust arterial pressure (AP) and heart rate (HR) to the stressor. However, whether hcrt-1 and NE interact in BST to alter cardiovascular function is unknown. Experiments were done in urethane-α-chloralose anesthetized, paralyzed, and artificially ventilated male Wistar rats to investigate the effect of hcrt-1 and NE on the cardiovascular responses elicited by l-glutamate (Glu) stimulation of BST neurons. Microinjections of hcrt-1, NE or tyramine into BST attenuated the decrease in AP and HR to Glu stimulation of BST. Additionally, combined injections of hcrt-1 with NE or tyramine did not elicit a greater attenuation than either compound alone. Furthermore, injections into BST of the α2-adrenergic receptor (α2-AR) antagonist yohimbine, but not the α1-AR antagonist 2-{[β-(4-hydroxyphenyl)ethyl]aminomethyl}-1-tetralone hydrochloride, blocked both the hcrt-1 and NE-induced inhibition of the BST cardiovascular depressors responses. Finally, injections into BST of the GABAA receptor antagonist bicuculline, but not the GABAB receptor antagonist phaclofen, blocked the hcrt-1 and NE attenuation of the BST Glu-induced depressor and bradycardia responses. These data suggest that hcrt-1 effects in BST are mediated by NE neurons, and hcrt-1 likely acts to facilitate the synaptic release of NE. NE neurons, acting through α2-AR may activate Gabaergic neurons in BST, which in turn through the activation of GABAA receptors inhibit a BST sympathoinhibitory pathway. Taken together, these data suggest that hcrt-1 pathways to BST through their interaction with NE and Gabaergic neurons may function in the coordination of cardiovascular responses associated with different behavioral states.

Atrophy of the cholinergic Basal forebrain over the adult age range and in early stages of Alzheimer's disease

BACKGROUND

The basal forebrain cholinergic system (BFCS) is known to undergo moderate neurodegenerative changes during normal aging as well as severe atrophy in Alzheimer's disease (AD). However, there is a controversy regarding how the cholinergic lesion in AD relates to early and incipient stages of the disease. In vivo imaging studies on the structural integrity of the BFCS in normal and pathologic aging are rare.

METHODS

We applied automated morphometry techniques in combination with high-dimensional image warping and a cytoarchitectonic map of basal forebrain cholinergic nuclei to a large cross-sectional data set of high-resolution magnetic resonance imaging scans, covering the whole adult age range (20-94 years; n = 211) as well as patients with very mild AD (Clinical Dementia Rating = .5; n = 69) and clinically manifest AD (AD; Clinical Dementia Rating = 1; n = 28). For comparison, we investigated hippocampus volume using automated volumetry.

RESULTS

Volume of the BFCS declined from early adulthood on, and atrophy aggravated in advanced age. Volume reductions in very mild AD were most pronounced in posterior parts of the nucleus basalis of Meynert, whereas in AD, atrophy was more extensive and included the whole BFCS. In clinically manifest AD, the diagnostic accuracy of BFCS volume reached the diagnostic accuracy of hippocampus volume.

CONCLUSIONS

Our findings indicate that cholinergic degeneration in AD occurs against a background of age-related atrophy and that exacerbated atrophy in AD can be detected at earliest stages of cognitive impairment. Automated in vivo morphometry of the BFCS may become a useful tool to assess BF cholinergic degeneration in normal and pathologic aging.

FoxP2 brainstem neurons project to sodium appetite regulatory sites

The transcription factor Forkhead box protein 2 (FoxP2) is expressed in two cell groups of the brainstem that have been implicated in sodium appetite regulation: the pre-locus coeruleus (pre-LC) and parabrachial nucleus--external lateral-inner subdivision (PBel-inner). Because the connections of these two groups are unknown, neuroanatomical tracing methods were used to define their central projections. The pre-LC outputs were first analyzed using an anterograde axonal tracer--Phaseolus vulgaris leucoagglutinin (PHAL) to construct a brain map. Next, we examined whether the FoxP2 immunoreactive (FoxP2+) neurons of the pre-LC contribute to these projections using a retrograde neuronal tracer--cholera toxin β-subunit (CTb). CTb was injected into selected brain regions identified in the anterograde tracing study. One week later the rats were killed, and brainstem sections were processed by a double immunohistochemical procedure to determine whether the FoxP2+ neurons in the pre-LC and/or PBel-inner contained CTb. FoxP2+ pre-LC neurons project to: (1) ventral pallidum; (2) substantia innominata and bed nucleus of the stria terminalis; (3) paraventricular, central medial, parafascicular, and subparafascicular parvicellular thalamic nuclei; (4) paraventricular (PVH), lateral, perifornical, dorsomedial (DMH), and parasubthalamic hypothalamic nuclei; and (5) ventral tegmental area (VTA), periaqueductal gray matter (PAG), dorsal and central linear raphe nuclei. FoxP2+ PBel-inner neurons project to the PVH and DMH, with weaker connections to the LHA, VTA, and PAG. Both the pre-LC and PBel-inner project to central sites implicated in sodium appetite, and related issues, including foraging behavior, hedonic responses to salt intake, sodium balance, and cardiovascular regulation, are discussed.

Postsynaptic targets of GABAergic basal forebrain projections to the basolateral amygdala

Recent studies indicate that the basolateral amygdala, like the neocortex and hippocampus, receives GABAergic inputs from the basal forebrain in addition to the well-established cholinergic inputs. Since the neuronal targets of these inputs have yet to be determined, it is difficult to predict the functional significance of this innervation. The present study addressed this question in the rat by employing anterograde tract tracing combined with immunohistochemistry at the light and electron microscopic levels of analysis. Amygdalopetal axons from the basal forebrain mainly targeted the basolateral nucleus (BL) of the amygdala. The morphology of these axons was heterogeneous and included GABAergic axons that contained vesicular GABA transporter protein (VGAT). These axons, designated type 1, exhibited distinctive large axonal varicosities that were typically clustered along the length of the axon. Type 1 axons formed multiple contacts with the cell bodies and dendrites of parvalbumin-containing (PV+) interneurons, but relatively few contacts with calretinin-containing and somatostatin-containing interneurons. At the ultrastructural level of analysis, the large terminals of type 1 axons exhibited numerous mitochondria and were densely packed with synaptic vesicles. Individual terminals formed broad symmetrical synapses with BL PV+ interneurons, and often formed additional symmetrical synapses with BL pyramidal cells. Some solitary type 1 terminals formed symmetrical synapses solely with BL pyramidal cells. These results suggest that GABAergic neurons of the basal forebrain provide indirect disinhibition, as well as direct inhibition, of BL pyramidal neurons. The possible involvement of these circuits in rhythmic oscillations related to emotional learning, attention, and arousal is discussed.

Parvalbumin-immunoreactive neurons and GABAergic neurons of the basal forebrain project to the rat basolateral amygdala

The basal forebrain (BF) contains a diffuse array of cholinergic and non-cholinergic neurons that project to the cerebral cortex and basolateral nuclear complex of the amygdala (BLC). Previous studies have shown that the GABAergic subpopulation of non-cholinergic corticopetal BF neurons selectively innervates cortical interneurons. Although several investigations in both rodents and primates have indicated that some BF neurons projecting to the BLC are non-cholinergic, there have been no studies that have attempted to identify the neurochemical phenotype(s) of these neurons. The present study combined Fluorogold retrograde tract tracing with immunohistochemistry for two markers of BF GABAergic neurons, parvalbumin (PV) or glutamic acid decarboxylase (GAD), to determine if a subpopulation of BF GABAergic cells projects to the BLC. Injections of Fluorogold confined to the rat BLC, and centered in the basolateral nucleus, produced extensive retrograde labeling in the ventral pallidum and substantia innominata regions of the BF. Although the great majority of retrogradely labeled neurons were not double-labeled, about 10% of these neurons, located mainly along the ventral aspects of the fundus striati and globus pallidus, exhibited immunoreactivity for PV or GAD. The results of this investigation contradict the long-held belief that there is no extra-amygdalar source of GABAergic inputs to the BLC, and indicate that the cortex-like BLC, in addition to the cortex proper, receives inhibitory inputs from the basal forebrain.

Computer-assisted 3D reconstruction of the human basal forebrain complex

The basal forebrain complex (BFC) is a small but intricate structure. Its organization and function is hard to investigate using conventional methods, especially in humans. By combining new methods of research we present a comprehensive overview of this complex, in order to better understand its function in normal and diseased brains.

Disconnection of the amygdala central nucleus and the substantia innominata/nucleus basalis magnocellularis disrupts performance in a sustained attention task

The basal forebrain cholinergic system is broadly implicated in the regulation of attention. Disruptions in the function of this system produce impairments in many attentional functions, including the performance of well-learned responses under increased attentional load and the surprise-induced enhancement of learning rate. Similarly, lesions of the amygdala central nucleus (CeA) have been found to impair attentional function in some circumstances. In the present article, the effects of lesions that disconnected CeA from the cholinergic substantia innominata/nucleus basalis magnocellularis (SI/nBM) on performance are examined in a modified 5-choice serial reaction time (5CSRT) task, thought to assess selective or sustained attention. The lesions impaired performance under conditions of increased attentional load, suggesting that a circuit that includes CeA and SI/nBM regulates these aspects of attention.

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.

mu-opioid receptor-mediated antinociceptive responses differ in men and women

Sex differences in the experience of clinical and experimental pain have been reported. However, the neurobiological sources underlying the variability in pain responses between sexes have not been adequately explored, especially in humans. The endogenous opioid neurotransmitters and mu-opioid receptors are centrally implicated in responses to stress, in the suppression of pain, and in the action of opiate analgesic drugs. Here we examined sex differences in the activation of the mu-opioid system in response to an intensity-controlled sustained deep-tissue pain challenge with positron emission tomography and a mu-opioid receptor-selective radiotracer. Twenty-eight young healthy volunteers (14 men and 14 women) were studied during saline control and pain conditions using a double-blind, randomized, and counterbalanced design. Women were scanned during the early follicular phase of their menstrual cycles after ovulatory cycles. Significant sex differences in the regional activation of the mu-opioid system in response to sustained pain were detected compared with saline controls. Men demonstrated larger magnitudes of mu-opioid system activation than women in the anterior thalamus, ventral basal ganglia, and amygdala. Conversely, women demonstrated reductions in the basal state of activation of the mu-opioid system during pain in the nucleus accumbens, an area previously associated with hyperalgesic responses to the blockade of opioid receptors in experimental animals. These data demonstrate that at matched levels of pain intensity, men and women during their follicular phase differ in the magnitude and direction of response of the mu-opioid system in distinct brain nuclei.

Masked presentations of emotional facial expressions modulate amygdala activity without explicit knowledge

Functional magnetic resonance imaging (fMRI) of the human brain was used to study whether the amygdala is activated in response to emotional stimuli, even in the absence of explicit knowledge that such stimuli were presented. Pictures of human faces bearing fearful or happy expressions were presented to 10 normal, healthy subjects by using a backward masking procedure that resulted in 8 of 10 subjects reporting that they had not seen these facial expressions. The backward masking procedure consisted of 33 msec presentations of fearful or happy facial expressions, their offset coincident with the onset of 167 msec presentations of neutral facial expressions. Although subjects reported seeing only neutral faces, blood oxygen level-dependent (BOLD) fMRI signal in the amygdala was significantly higher during viewing of masked fearful faces than during the viewing of masked happy faces. This difference was composed of significant signal increases in the amygdala to masked fearful faces as well as significant signal decreases to masked happy faces, consistent with the notion that the level of amygdala activation is affected differentially by the emotional valence of external stimuli. In addition, these facial expressions activated the sublenticular substantia innominata (SI), where signal increases were observed to both fearful and happy faces--suggesting a spatial dissociation of territories that respond to emotional valence versus salience or arousal value. This study, using fMRI in conjunction with masked stimulus presentations, represents an initial step toward determining the role of the amygdala in nonconscious processing.