Steven J. Henriksen

Neuropeptide S: a neuropeptide promoting arousal and anxiolytic-like effects.

Arousal and anxiety are behavioral responses that involve complex neurocircuitries and multiple neurochemical components. Here, we report that a neuropeptide, neuropeptide S (NPS), potently modulates wakefulness and could also regulate anxiety. NPS acts by activating its cognate receptor (NPSR) and inducing mobilization of intracellular Ca2+. The NPSR mRNA is widely distributed in the brain, including the amygdala and the midline thalamic nuclei. Central administration of NPS increases locomotor activity in mice and decreases paradoxical (REM) sleep and slow wave sleep in rats. NPS was further shown to produce anxiolytic-like effects in mice exposed to four different stressful paradigms. Interestingly, NPS is expressed in a previously undefined cluster of cells located between the locus coeruleus (LC) and Barringtons nucleus. These results indicate that NPS could be a new modulator of arousal and anxiety. They also show that the LC region encompasses distinct nuclei expressing different arousal-promoting neurotransmitters.

Electrophysiological Characterization of GABAergic Neurons in the Ventral Tegmental Area

GABAergic neurons in the ventral tegmental area (VTA) play a primary role in local inhibition of mesocorticolimbic dopamine (DA) neurons but are not physiologically or anatomically well characterized. We used in vivo extracellular and intracellular recordings in the rat VTA to identify a homogeneous population of neurons that were distinguished from DA neurons by their rapid-firing, nonbursting activity (19.1 ± 1.4 Hz), short-duration action potentials (310 ± 10 μsec), EPSP-dependent spontaneous spikes, and lack of spike accommodation to depolarizing current pulses. These non-DA neurons were activated both antidromically and orthodromically by stimulation of the internal capsule (IC; conduction velocity, 2.4 ± 0.2 m/sec; refractory period, 0.6 ± 0.1 msec) and were inhibited by stimulation of the nucleus accumbens septi (NAcc). Their firing rate was moderately reduced, and their IC-driven activity was suppressed by microelectrophoretic application or systemic administration of NMDA receptor antagonists. VTA non-DA neurons were recorded intracellularly and showed relatively depolarized resting membrane potentials (−61.9 ± 1.8 mV) and small action potentials (68.3 ± 2.1 mV). They were injected with neurobiotin and shown by light microscopic immunocytochemistry to be multipolar cells and by electron microscopy to contain GABA but not the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH). Neurobiotin-filled dendrites containing GABA received asymmetric excitatory-type synapses from unlabeled terminals and symmetric synapses from terminals that also contained GABA. These findings indicate that VTA non-DA neurons are GABAergic, project to the cortex, and are controlled, in part, by a physiologically relevant NMDA receptor-mediated input from cortical structures and by GABAergic inhibition.

5-HT7 Receptor Inhibition and Inactivation Induce Antidepressantlike Behavior and Sleep Pattern

BACKGROUND The 5-hydroxytryptamine7 receptor (5-HT7) is implicated in circadian rhythm phase resetting, and 5-HT7 receptor-selective antagonists alter rapid eye movement (REM) sleep parameters in a pattern opposite from those in patients with clinical depression. METHODS As sleep, circadian rhythm, and mood regulation are related, we examined 5-HT7 receptor knockout mice in two behavioral models of depression. The forced swim and tail suspension tests are highly predictive for antidepressant drug activity. RESULTS Unmedicated 5-HT7-/- mice showed decreased immobility in both tests, consistent with an antidepressantlike behavior. The selective 5-HT7 receptor antagonist SB-269970 also decreased immobility. The selective serotonin reuptake inhibitor citalopram, a widely used antidepressant, decreased immobility in both 5-HT7+/+ and 5-HT7-/- mice in the tail suspension test, suggesting that it utilizes an independent mechanism. The 5-HT7-/- mice spent less time in and had less frequent episodes of REM sleep, also consistent with an antidepressantlike state. CONCLUSIONS The 5-HT7 receptor might have a role in mood disorders and antagonists might have therapeutic value as antidepressants.

Opiate state controls bi-directional reward signaling via GABAA receptors in the ventral tegmental area

The neural mechanisms that mediate the transition from a drug-naive state to a state of drug dependence and addiction are not yet known. Here we show that a discrete population of GABAA receptors in the mammalian ventral tegmental area (VTA) serves as a potential addiction switching mechanism by gating reward transmission through one of two neural motivational systems: either a dopamine-independent (opiate-naive) or a dopaminergic (opiate-dependent or opiate-withdrawn) system. Bi-directional transmission of reward signals through this GABAA receptor substrate is dynamically controlled by the opiate state of the organism and involves a molecular alteration of the GABAA receptor. After opiate exposure and subsequent withdrawal, the functional conductance properties of the rat VTA GABAA receptor switch from an inhibitory to an excitatory signaling mode.

Induction of Pathogenic Sets of Genes in Macrophages and Neurons in NeuroAIDS

The etiology of the central nervous system (CNS) alterations after human immunodeficiency virus (HIV) infection, such as dementia and encephalitis, remains unknown. We have used microarray analysis in a monkey model of neuroAIDS to identify 98 genes, many previously unrecognized in lentiviral CNS pathogenesis, whose expression is significantly up-regulated in the frontal lobe of simian immunodeficiency virus-infected brains. Further, through immunohistochemical illumination, distinct classes of genes were found whose protein products localized to infiltrating macrophages, endothelial cells and resident glia, such as CD163, Glut5, and ISG15. In addition we found proteins induced in cortical neurons (ie, cyclin D3, tissue transglutaminase, alpha1-antichymotrypsin, and STAT1), which have not previously been described as participating in simian immunodeficiency virus or HIV-related CNS pathology. This molecular phenotyping in the infected brains revealed pathways promoting entry of macrophages into the brain and their subsequent detrimental effects on neurons. These data support the hypothesis that in HIV-induced CNS disease products of activated macrophages and astrocytes lead to CNS dysfunction by directly damaging neurons, as well as by induction of altered gene and protein expression profiles in neurons themselves which are deleterious to their function.

Mice devoid of prion protein have cognitive deficits that are rescued by reconstitution of PrP in neurons

Prion protein (PrP(C)) is a constituent of most normal mammalian cells and plays an essential role in the pathogenesis of transmissible spongiform encephalopathies (TSE). However, the normal cellular function of PrP(C) remains unclear. Here, we document that mice with a selective deletion of PrP(C) exhibited deficits in hippocampal-dependent spatial learning, but non-spatial learning remained intact. mPrP-/- mice also showed reduction in paired-pulse facilitation and long-term potentiation in the dentate gyrus in vivo. These deficits were rescued in transgenic mPrP-/- mice expressing PrP(C) in neurons under control of the neuron-specific enolase (NSE) promoter indicating that they were due to lack of PrP(C) function in neurons. The deficits were seen in mPrP-/- mice with a homogeneous 129/Ola background and in mPrP-/- mice in the mixed (129/Ola x C57BL/10) background indicating that these abnormalities were unlikely due to variability of background genes or alteration of the nearby Prnd (doppel) gene.

Structural and functional neuropathology in transgenic mice with CNS expression of IFN-α1

Abstract Cytokines belonging to the type I interferon (e.g. interferon-α) family are important in the host response to infection and may have complex and broad ranging actions in the central nervous system (CNS) that may be beneficial or harmful. To better understand the impact of the CNS expression of the type I interferons (IFN), transgenic mice were developed that produce IFN-α1 chronically from astrocytes. In two independent transgenic lines with moderate and low levels of astrocyte IFN-α mRNA expression respectively, a spectrum of transgene dose- and age-dependent structural and functional neurological alterations are induced. Structural changes include neurodegeneration with loss of cholinergic neurons, gliosis, angiopathy with mononuclear cell cuffing, progressive calcification affecting basal ganglia and cerebellum and the up-regulation of a number of IFN-α-regulated genes. At a functional level, in vivo and in vitro electrophysiological studies revealed impaired neuronal function and disturbed synaptic plasticity with pronounced hippocampal hyperexcitability. Severe behavioral alterations were also evident in higher expressor GFAP-IFNα mice which developed fatal seizures around 13 weeks of age precluding their further behavioral assessment. Modest impairments in discrimination learning were measured in lower expressor GFAP-IFNα mice at various ages (7–42 weeks). The behavioral and electrophysiological findings suggest regional changes in hippocampal excitability which may be linked to abnormal calcium metabolism and loss of cholinergic neurons in the GIFN mice. Thus, these transgenic mice provide a novel animal model in which to further evaluate the mechanisms that underlie the diverse actions of type I interferons in the intact CNS and to link specific structural changes with functional impairments.

Profound increase in sensitivity to glutamatergic- but not cholinergic agonist-induced seizures in transgenic mice with astrocyte production of IL-6.

Transgenic mice with glial fibrillary acidic protein (GFAP) promoter driven‐astrocyte production of the cytokines interleukin‐6 (IL‐6) and tumor necrosis factor (TNF) were used to determine whether the pre‐existing production of these cytokines in vivo might modulate the sensitivity of neurons to excitotoxic agents. Low doses of kainic acid (5 mg/kg) that produced little or no behavioral or electroencephalogram (EEG) alterations in wild type or glial fibrillary acidic protein (GFAP)‐TNF animals induced severe tonic‐clonic seizures and death in GFAP‐IL6 transgenic mice of 2 or 6 months of age. GFAP‐IL6 mice were also significantly more sensitive to N‐methyl‐D‐aspartate (NMDA)‐ but not pilocarpine‐induced seizures. Kainic acid uptake in the brain of the GFAP‐IL6 mice was higher in the cerebellum but not in other regions. Kainic acid binding in the brain of GFAP‐IL6 mice had a similar distribution and density as wild type controls. In the hippocampus of GFAP‐IL6 mice that survived low dose kainic acid, there was no change in the extent of either neurodegeneration or astrocytosis. Immunostaining revealed degenerative changes in gamma aminobutyric acid (GABA)‐ and parvalbumin‐positive neurons in the hippocampus of 2‐month‐old GFAP‐IL6 mice which progressed to the loss of these cells at 6 months of age. Thus, GFAP‐IL6 but not GFAP‐TNF mice showed markedly enhanced sensitivity to glutamatergic‐ but not cholinergic‐induced seizures and lethality. This may relate, in part, to a compromise of inhibitory interneuron function. Therefore, pre‐existing IL‐6 production and inflammation in the central nervous system (CNS) not only causes spontaneous neurodegeneration but also synergizes with other neurotoxic insults to induce more severe acute functional neurological impairment.

Highly Activated CD8+ T Cells in the Brain Correlate with Early Central Nervous System Dysfunction in Simian Immunodeficiency Virus Infection

One of the consequences of HIV infection is damage to the CNS. To characterize the virologic, immunologic, and functional factors involved in HIV-induced CNS disease, we analyzed the viral loads and T cell infiltrates in the brains of SIV-infected rhesus monkeys whose CNS function (sensory evoked potential) was impaired. Following infection, CNS evoked potentials were abnormal, indicating early CNS disease. Upon autopsy at 11 wk post-SIV inoculation, the brains of infected animals contained over 5-fold more CD8+ T cells than did uninfected controls. In both infected and uninfected groups, these CD8+ T cells presented distinct levels of activation markers (CD11a and CD95) at different sites: brain > CSF > spleen = blood > lymph nodes. The CD8+ cells obtained from the brains of infected monkeys expressed mRNA for cytolytic and proinflammatory molecules, such as granzymes A and B, perforin, and IFN-γ. Therefore, the neurological dysfunctions correlated with increased numbers of CD8+ T cells of an activated phenotype in the brain, suggesting that virus-host interactions contributed to the related CNS functional defects.

C10 Is a Novel Chemokine Expressed in Experimental Inflammatory Demyelinating Disorders that Promotes Recruitment of Macrophages to the Central Nervous System

Chemokines may be important in the control of leukocytosis in inflammatory disorders of the central nervous system. We studied cerebral chemokine expression during the evolution of diverse neuroinflammatory disorders in transgenic mice with astrocyte glial fibrillary acidic protein-targeted expression of the cytokines IL-3, IL-6, or IFN-alpha and in mice with experimental autoimmune encephalomyelitis. Distinct chemokine gene expression patterns were observed in the different central nervous system inflammatory models that may determine the phenotype and perhaps the functions of the leukocytes that traffic into the brain. Notably, high expression of C10 and C10-related genes was found in the cerebellum and spinal cord of GFAP-IL3 mice with inflammatory demyelinating disease and in mice with experimental autoimmune encephalomyelitis. In both these neuroinflammatory models, C10 RNA and protein expressing cells were predominantly macrophage/microglia and foamy macrophages present within demyelinating lesions as well as in perivascular infiltrates and meninges. Intracerebroventricular injection of recombinant C10 protein promoted the recruitment of large numbers of Mac-1(+) cells and, to a much lesser extent, CD4(+) lymphocytes into the meninges, choroid plexus, ventricles, and parenchyma of the brain. Thus, C10 is a prominent chemokine expressed in the central nervous system in experimental inflammatory demyelinating disease that, we show, also acts as a potent chemotactic factor for the migration of these leukocytes to the brain.