Optogenetic astrocyte activation evokes BOLD fMRI response with oxygen consumption without neuronal activity modulation.

Functional magnetic resonance imaging (fMRI) based on the blood oxygenation level-dependent (BOLD) signal has been used to infer sites of neuronal activation in the brain. A recent study demonstrated, however, unexpected BOLD signal generation without neuronal excitation, which led us to hypothesize the presence of another cellular source for BOLD signal generation. Collective assessment of optogenetic activation of astrocytes or neurons, fMRI in awake mice, electrophysiological measurements, and histochemical detection of neuronal activation, coherently suggested astrocytes as another cellular source. Unexpectedly, astrocyte-evoked BOLD signal accompanied oxygen consumption without modulation of neuronal activity. Imaging mass spectrometry of brain sections identified synthesis of acetyl-carnitine via oxidative glucose metabolism at the site of astrocyte-, but not neuron-evoked BOLD signal. Our data provide causal evidence that astrocytic activation alone is able to evoke BOLD signal response, which may lead to reconsideration of current interpretation of BOLD signal as a marker of neuronal activation.

Endogenous nociceptin modulates diet preference independent of motivation and reward.

Previous studies show that the opioid peptide nociceptin stimulates food intake. Here, we studied nociceptin receptor knockout (NOP KO) mice in various behavioral paradigms designed to differentiate psychological and physiological loci at which endogenous nociceptin might control feeding. When presented a choice under food restriction, NOP KO mice displayed reduced preference for high sucrose diet, but lower intake of high fat diet under no-choice conditions. These responses were absent under ad libitum feeding conditions. Conditioned place preference to high fat diet under food-deprived conditions was unaltered in NOP KO mice, suggesting no difference in reward responses. Furthermore, operant food self-administration under a variety of conditions showed no genotype-dependent differences, suggesting no differences in the motivational properties of food. Taste reactivity to sucrose was unchanged in NOP KO mice, though NOP KO mice had altered aversive reactions to quinine solutions under ad libitum feeding, suggesting minor differences in the affective impact of palatable and unpalatable tastants. Although NOP KO mice re-fed following food-deprivation showed normal increases in plasma glucose and insulin, multidimensional scaling analysis showed that the relationship between these measures, body weight and plasma leptin was substantially disrupted in NOP KO, particularly in fasted mice. Additionally, the typical positive relationship between body weight and plasma leptin was considerably weaker in NOP KO mice. Together, these findings suggest that endogenous nociceptin differentially modulates diet preference depending on macronutrient content and homeostatic state, independently of the motivating, rewarding or orosensory properties of food, but may involve metabolic or postingestive processes.

Striatonigral direct pathway activation is sufficient to induce repetitive behaviors.

Pharmacological intervention in the substantia nigra is known to induce repetitive behaviors in rodents, but a direct causal relationship between a specific neural circuit and repetitive behavior has not yet been established. Here we demonstrate that optogenetic activation of dopamine D1 receptor-expressing MSNs terminals in the substantia nigra pars reticulata resulted in sustained and chronic repetitive behaviors. These data show for the first time that activation of the striatonigral direct pathway is sufficient to generate motor stereotypies.

Increased body weight in mice lacking mu-opioid receptors.

Opioids have been suggested to affect feeding behaviour. To clarify the role of mu-opioid receptors in feeding, we measured several parameters relating to food intake in mu-opioid receptor knockout mice. Here, we show that the knockout mice had increased body weight in adulthood, although the intake amount of standard food was similar between the wild-type and knockout littermates. Serum markers for energy homeostasis were not significantly altered in the knockout mice. Hypothalamic neuropeptide Y mRNA, however, was higher in knockouts than in wild-type mice. Our results suggest that the up-regulated expression of neuropeptide Y mRNA might contribute to the increased weights of adult mu-opioid receptor knockout mice.

Vitamin C impacts anxiety-like behavior and stress-induced anorexia relative to social environment in SMP30/GNL knockout mice.

The role of endogenous vitamin C (VC) in emotion and psychiatric measures has long been uncertain. We aimed to investigate how an individual's VC status impacts his or her mental health. Our hypothesis is that body VC levels modulate anxiety, anorexia, and depressive phenotypes under the influence of psychosocial rearing environments and sex. The VC status of senescence marker protein-30/gluconolactonase knockout mice, which lack the ability to synthesize VC, were continuously shifted from adequate (VC+) to depleted (VC-) by providing a water with or without VC. Despite weight loss in both sexes, suppressed feeding was specifically seen in males only during the VC- phase. Anxiety responses in the novelty-suppressed feeding paradigm were worse during the VC-, especially in females. Sensitivity to the forced swim test as determined by the initial latency was significantly shorter in the socially stable animals compared with socially unstable animals during the VC+ condition. The stress coping underlying depressive phenotypes was assessed by immobility duration in a series of forced swim tests. No significant differences were apparent between contrasting VC status. Homeostatic symptoms following stressful behavioral tests consisted of a great loss of appetite during the VC-. It should be noted that anorexia is extremely serious for the females. We conclude that endogenous VC status is critical for determining vulnerability to anxiety and anorexia in a sex-specific manner.

The NOP (ORL1) receptor antagonist Compound B stimulates mesolimbic dopamine release and is rewarding in mice by a non-NOP-receptor-mediated mechanism.

1. Compound B (1-[(3R, 4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one, CompB) is a nociceptin/orphanin FQ (N/OFQ) antagonist showing high selectivity for the NOP (ORL1) receptor over classical opioid receptors. We studied the effect of subcutaneous CompB administration on the release of mesolimbic dopamine (DA) and the expression of hedonia in mice. 2. CompB (0.3-30 mg kg(-1)) dose dependently stimulated mesolimbic DA release as measured by in vivo freely moving microdialysis, without any change in locomotor activity. However, intracerebroventricular administered N/OFQ (endogenous agonist of the NOP receptor, 6 nmol) did not influence CompB- (10 mg kg(-1)) induced DA release, despite clearly suppressing release when administered alone. 3. Studies using NOP receptor knockout mice and no-net-flux microdialysis revealed mildly, but not statistically significantly higher endogenous DA levels in mice lacking the NOP receptor compared to wild-type mice. Administration of CompB (10 mg kg(-1)) induced identical increases in mesolimbic DA release in wild-type and NOP receptor knockout mice. 4. CompB was rewarding in approximately the same dose range in which CompB induced major increases in mesolimbic DA release when assayed using a conditioned place preference paradigm. The rewarding effect of CompB (30 mg kg(-1)) was maintained in NOP receptor knockout mice. 5. These results show that CompB stimulates mesolimbic DA release and is rewarding by an action independent of the NOP receptor, the precise site of which is unclear. Consequently, caution should be exercised when interpreting the results of studies using this drug, particularly when administered by a peripheral route.

Pathophysiologic characteristics of the activity-stress paradigm in animal models: inhibitory effect of glucose on these responses.

This review provides a discussion of the pathophysiologic significance of animal models of the activity-stress paradigm and the role of plasma glucose level in the appearance of physical stress responses of those models. Many research reports have demonstrated that animal models exposed to activity-stress are useful as a "symptomatic model" of anorexia nervosa and obsessive-compulsive disorder as well as peptic ulcer. Our findings show that a decrease in plasma glucose concentration is an important factor in determining the activity-stress-induced physical responses. Further investigation of the pathophysiology of activity-stressed animal models may contribute to the development of new therapeutics for diseases such as anorexia nervosa and obsessive-compulsive disorder.

Enterostatin increases extracellular serotonin and dopamine in the lateral hypothalamic area in rats measured by in vivo microdialysis.

The effect of enterostatin injection into the rat lateral hypothalamic area (LHA) on serotonin and dopamine releases in extracellular space was investigated by in vivo microdialysis technique. The primary focus being to understand whether a small amount of enterostatin crossing the blood-brain barrier correlates with activity changes in serotonergic and dopaminergic nervous systems or not. We found a significant elevation in serotonin release in the LHA. The enterostatin perfusion also induced a smaller but significant increase in dopamine level than serotonin one. This result suggests that enterostatin plays some sort of role in the control of feeding of fat through the control serotonergic and dopaminergic satiety mechanism.

Uptake across the blood-brain barrier and tissue distribution of enterostatin after peripheral administration in rats.

Enterostatin, the N-terminal activation pentapeptide of procolipase that is produced by the pancreas, reduces food intake from high-fat diet when injected either peripherally or centrally to rats. We investigated uptake across the blood-brain barrier (BBB) and tissue distribution of enterostatin by giving radioactive-labeled enterostatin (3H-VPDPR) intravenously. Low levels of 3H-VPDPR were detected in many areas of the brain, with greatest radioactivity in the frontal cortex, hippocampus and cerebellum. Radioactivity was found in the plasma and all tissues, with the highest amount detected in the pancreas.

Exogenous, but not endogenous nociceptin modulates mesolimbic dopamine release in mice.

The effect of nociceptin (an endogenous ligand of the ORL1 receptor) on mesolimbic dopamine release and simultaneous horizontal locomotion was studied in freely moving mice undergoing microdialysis of the nucleus accumbens. Intracerebroventricular (i.c.v.) administration of nociceptin (7 nmol) induced a long-lasting suppression of mesolimbic dopamine release and horizontal locomotion in wild-type but not ORL1 knockout mice. I.c.v. administration of the recently reported peptide nociceptin antagonist [Nphe1, Arg14, Lys15] nociceptin-NH(2) (known also as UFP-101, 5 nmol) completely abolished the suppressive effect of nociceptin on mesolimbic dopamine release. However, UFP-101 administration alone induced a mild and lasting suppression of mesolimbic dopamine release in both wild-type and ORL1 knockout mice that was magnified in ORL1 knockout mice by coadministration of nociceptin. UFP-101 administration alone suppressed locomotion in both genotypes. These results confirm that the suppressive action of nociceptin on mesolimbic dopamine release is mediated entirely by the ORL1 receptor, and that UFP-101 effectively antagonizes this action. However, the lack of a stimulatory effect of UFP-101 in wild-type mice indicates that despite being sensitive to exogenous nociceptin action, basal mesolimbic dopaminergic activity is not determined by endogenous nociceptin in mice.