5-HT(2A/2C) receptor antagonists in the paraventricular nucleus attenuate the action of DOI on NPY-stimulated eating

Therapeutic modulation of the kynurenine pathway in severe mental illness and comorbidities: A potential role for serotonergic psychedelics

Mounting evidence points towards a crucial role of the kynurenine pathway (KP) in the altered gut-brain axis (GBA) balance in severe mental illness (SMI, namely depression, bipolar disorder, and schizophrenia) and cardiometabolic comorbidities. Preliminary evidence shows that serotonergic psychedelics and their analogues may hold therapeutic potential in addressing the altered KP in the dysregulated GBA in SMI and comorbidities. In fact, aside from their effects on mood, psychedelics elicit therapeutic improvement in preclinical models of obesity, metabolic syndrome, and vascular inflammation, which are highly comorbid with SMI. Here, we review the literature on the therapeutic modulation of the KP in the dysregulated GBA in SMI and comorbidities, and the potential application of psychedelics to address the altered KP in the brain and systemic dysfunction underlying SMI and comorbidities. Psychedelics might therapeutically modulate the KP in the altered GBA in SMI and comorbidities either directly, via altering the metabolic pathway by influencing the rate-limiting enzymes of the KP and affecting the levels of available tryptophan, or indirectly, by affecting the gut microbiome, gut metabolome, metabolism, and the immune system. Despite promising preliminary evidence, the mechanisms and outcomes of the KP modulation with psychedelics in SMI and systemic comorbidities remain largely unknown and require further investigation. Several concerns are discussed surrounding the potential side effects of this approach in specific cohorts of individuals with SMI and systemic comorbidities.

Central 5-HTR2C in the Control of Metabolic Homeostasis

The 5-hydroxytryptamine 2C receptor (5-HTR2C) is a class G protein-coupled receptor (GPCR) enriched in the hypothalamus and the brain stem, where it has been shown to regulate energy homeostasis, including feeding and glucose metabolism. Accordingly, 5-HTR2C has been the target of several anti-obesity drugs, though the associated side effects greatly curbed their clinical applications. Dissecting the specific neural circuits of 5-HTR2C-expressing neurons and the detailed molecular pathways of 5-HTR2C signaling in metabolic regulation will help to develop better therapeutic strategies towards metabolic disorders. In this review, we introduced the regulatory role of 5-HTR2C in feeding behavior and glucose metabolism, with particular focus on the molecular pathways, neural network, and its interaction with other metabolic hormones, such as leptin, ghrelin, insulin, and estrogens. Moreover, the latest progress in the clinical research on 5-HTR2C agonists was also discussed.

Glucagon-Like Peptide-1 (GLP-1) and 5-Hydroxytryptamine 2c (5-HT2c) Receptor Agonists in the Ventral Tegmental Area (VTA) Inhibit Ghrelin-Stimulated Appetitive Reward

Current literature indicates that the orexigenic peptide ghrelin increases appetitive motivation via signaling in the mesolimbic reward system. Another gastric peptide, glucagon-like peptide-1 (GLP-1), and the neurotransmitter 5-hydroxytryptamine (5-HT), are both known to suppress operant responding for food by acting on key mesolimbic nuclei, including the ventral tegmental area (VTA). In order to investigate the interaction effects of ghrelin, GLP-1, and 5-HT within the VTA, we measured operant responding for sucrose pellets after the administration of ghrelin, the GLP-1 receptor agonist exendin-4 (Ex-4), and the 5-HT_2c receptor agonist Ro60-0175 in male Sprague-Dawley rats. Following training on a progressive ratio 3 (PR3) schedule, animals were first injected with ghrelin into the VTA at doses of 3 to 300 pmol. In subsequent testing, separate rats were administered intraperitoneal (IP) Ex-4 (0.1–1.0 µg/kg) or VTA Ex-4 (0.01–0.1 µg) paired with 300 pmol ghrelin. In a final group of rats, the 5-HT_2c agonist Ro60-0175 was injected IP (0.25–1.0 mg/kg) or into the VTA (1.5–3.0 µg), and under both conditions paired with 300 pmol ghrelin delivered into the VTA. Our results indicated that ghrelin administration increased operant responding for food reward and that this effect was attenuated by IP and VTA Ex-4 pretreatment as well as pre-administration of IP or VTA Ro60-0175. These data provide compelling evidence that mesolimbic GLP-1 and serotonergic circuitry interact with the ghrelinergic system to suppress ghrelin’s effects on the mediation of food reinforcement.

A systematic investigation of the differential roles for ventral tegmentum serotonin 1- and 2-type receptors on food intake in the rat

Central serotonin (5-HT) pathways are known to influence feeding and other ingestive behaviors. Although the ventral tegmentum is important for promoting the seeking and consumption of food and drugs of abuse, the roles of 5-HT receptor subtypes in this region on food intake have yet to be comprehensively examined. In these experiments, food restricted rats were given 2-h access to rat chow; separate groups of non-restricted animals had similar access to a sweetened fat diet. Feeding and locomotor activity were monitored following ventral tegmentum stimulation or blockade of 5-HT1A, 5-HT1B, 5-HT2A, 5-HT2B, or 5-HT2C receptors. 5-HT1A receptor stimulation transiently inhibited rearing behavior and chow intake in food-restricted rats, and had a biphasic effect on non-restricted rats offered the palatable diet. 5-HT1B receptor agonism transiently inhibited feeding in restricted animals, but did not affect intake of non-restricted rats. In contrast, 5-HT1B receptor antagonism decreased palatable feeding. Although stimulation of ventral tegmental 5-HT2B receptors with BW723C86 did not affect hunger-driven food intake, it significantly affected palatable feeding, with a trend for an increasing intake at 2.0µg/side but not at 5.0µg/side. Antagonism of the same receptor modestly but significantly inhibited feeding of the palatable diet at 5.0µg/side ketanserin. Neither stimulation nor blockade of 5-HT2A or 5-HT2C receptors caused prolonged effects on intake or locomotion. These data suggest that serotonin's effects on feeding within the ventral tegmentum depend upon the specific receptor targeted, as well as whether intake is motivated by food restriction or the palatable nature of the offered diet.

Endogenous 5-HT2C Receptors Phosphorylate the cAMP Response Element Binding Protein via Protein Kinase C-Promoted Activation of Extracellular-Regulated Kinases-1/2 in Hypothalamic mHypoA-2/10 Cells

Serotonin 5-HT2C receptors (5-HT2CR) activate Gq proteins and are expressed in the central nervous system (CNS). 5-HT2CR regulate emotion, feeding, reward, or cognition and may serve as promising drug targets to treat psychiatric disorders or obesity. Owing to technical difficulties in isolating cells from the CNS and the lack of suitable cell lines endogenously expressing 5-HT2CR, our knowledge about this receptor subtype in native environments is rather limited. The hypothalamic mHypoA-2/10 cell line was recently established and resembles appetite-regulating hypothalamic neurons of the paraventricular nucleus (PVN), where 5-HT2CR have been detected in vivo. Therefore, we tested mHypoA-2/10 cells for endogenous 5-HT2CR expression. Serotonin or the 5-HT2CR preferential agonist WAY-161,503 initiated cAMP response element (CRE)-dependent gene transcription with EC50 values of 15.5 ± 9.8 and 1.1 ± 0.9 nM, respectively. Both responses were blocked by two unrelated 5-HT2CR-selective antagonists (SB-242,084, RS-102,221) but not by a 5-HT2AR (EMD-281,014) or 5-HT2BR (RS-127,455) antagonists. By single-cell calcium imaging, we found that serotonin and WAY-161,503 induced robust calcium transients, which were also blunted by both 5-HT2CR antagonists. Additionally we revealed, first, that 5-HT2CR induced CRE activation via protein kinase C (PKC)-mediated engagement of extracellular-regulated kinases-1/2 and, second, that intrinsic activity of WAY-161,503 was in the range of 0.3-0.5 compared with serotonin, defining the frequently used 5-HT2CR agonist as a partial agonist of endogenous 5-HT2CR. In conclusion, we have shown that hypothalamic mHypoA-2/10 cells endogenously express 5-HT2CR and thus are the first cell line in which to analyze 5-HT2CR pharmacology, signaling, and regulation in its natural environment.

Midbrain raphe 5-HT1A receptor activation alters the effects of ghrelin on appetite and performance in the elevated plus maze

Prior research suggests that midbrain serotonergic signaling and hypothalamic ghrelinergic signaling both play critical roles in appetitive and emotional behaviors. In the present study, we investigated the effects of median raphe nucleus (MRN) somatodentritic 5-HT1A receptor activation on the feeding-stimulant and anxiogenic action of paraventricular nucleus (PVN) ghrelin. In an initial experiment, adult male Sprague-Dawley rats were injected with either ghrelin (200-800 pmol) into the PVN or 8-OH-DPAT (2.5-10 nmol), a 5-HT1A receptor agonist, into the MRN. Performance on the elevated plus maze (EPM) was then assessed. In separate rats, MRN 8-OH-DPAT (2.5-5 nmol) was administered 5 min prior to PVN injection of ghrelin (400 pmol) followed by EPM testing. The orexigenic effects of MRN 8-OH-DPAT (0.1-1.6 nmol) paired with PVN ghrelin (50 pmol) were also examined. When administered alone into the PVN, ghrelin significantly decreased the number of entries and time spent in the open arms of the EPM. This anxiogenic effect was blocked if rats were allowed to eat immediately after ghrelin administration and then tested in the plus maze. MRN injections of 8-OH-DPAT were anxiolytic, and when rats were pretreated with 8-OH-DPAT prior to ghrelin, the anxiogenic action of the peptide was attenuated. In contrast, MRN administration of 8-OH-DPAT potentiated the eating-stimulant effect of PVN ghrelin. Overall, our findings demonstrate that ghrelinergic and serotonergic circuits interact in the neural control of eating and anxiety-like behaviors, with 5-HT1A receptor mechanisms potentiating the orexigenic action of ghrelin while inhibiting ghrelin-induced anxiogenesis as measured via the EPM.

Weight gain in risperidone therapy: investigation of peripheral hypothalamic neurohormone levels in psychotic patients

The use of antipsychotic drugs has started a new era in the treatment of psychotic disorders. Nevertheless, they cause complications in the long-term treatment, which is mainly weight gain. In this study, we investigated circulating levels of hypothalamic neuropeptides, which are related to appetite regulation, neuropeptide Y (NPY), α-melanocyte-stimulating hormone (α-MSH), cocaine- and amphetamine-regulated transcript (CART), and leptin, in first-attack psychotic patients who were treated with an atypical antipsychotic drug, risperidone, for 4 weeks. We used a case-control association design to compare the neuropeptides in the control group versus before and after treatment of the patient group. Samples were obtained from psychotic patients who were admitted to the Psychiatry Outpatient Clinics, Gulhane School of Medicine, Ankara, Turkey. When compared with the control group, NPY and α-MSH plasma levels of psychotic patients were severely reduced, and the CART levels were substantially increased when they were first diagnosed (before treatment). However, the patients' body mass index and circulating leptin levels were markedly high after the treatment. Circulating levels of those neurohormones were not significantly changed between before and after treatment of the patients. These data demonstrate that peripheral α-MSH and NPY, although reflecting only secretion from peripheral organs, nevertheless, may provide an insight into the patients sympathetic tone and also suggest change of their appetite regulation. α-Melanocyte-stimulating hormone, NPY, and CART plasma levels may be used as a predictor of weight gain in the early treatment of the patients along with the leptin levels.

Hypothalamic Ahi1 mediates feeding behavior through interaction with 5-HT2C receptor

It is indicated that there are important molecules interacting with brain nervous systems to regulate feeding and energy balance by influencing the signaling pathways of these systems, but relatively few of the critical players have been identified. In the present study, we provide the evidence for the role of Abelson helper integration site 1 (Ahi1) protein as a mediator of feeding behavior through interaction with serotonin receptor 2C (5-HT(2C)R), known for its critical role in feeding and appetite control. First, we demonstrated the co-localization and interaction between hypothalamic Ahi1 and 5-HT(2C)R. Ahi1 promoted the degradation of 5-HT(2C)R through the lysosomal pathway. Then, we investigated the effects of fasting on the expression of hypothalamic Ahi1 and 5-HT(2C)R. Fasting resulted in an increased Ahi1 expression and a concomitant decreased expression of 5-HT(2C)R. Knockdown of hypothalamic Ahi1 led to a concomitant increased expression of 5-HT(2C)R and a decrease of food intake and body weight. Last, we found that Ahi1 could regulate the expression of neuropeptide Y and proopiomelanocortin. Taken together, our results indicate that Ahi1 mediates feeding behavior by interacting with 5-HT(2C)R to modulate the serotonin signaling pathway.

Fish oil promotes survival and protects against cognitive decline in severely undernourished mice by normalizing satiety signals

Severe malnutrition resulting from anorexia nervosa or involuntary starvation leads to low weight, cognitive deficits and increased mortality rates. In the present study, we examined whether fish oil supplementation, compared with that of canola oil, would ameliorate the morbidity and mortality associated with these conditions by normalizing endocannabinoid and monoaminergic systems as well as other systems involved in satiety and cognitive function within the hypothalamus and hippocampus. Female Sabra mice restricted to 40% of their daily food intake exhibited decreased body weight, were sickly in appearance, displayed cognitive deficits and had increased mortality rates. Strikingly, fish oil supplementation that contains high omega-3 fatty acids levels decreased mortality and morbidity, and normalized the expression of genes and neurotransmitters in the hippocampus and hypothalamus. Fish oil supplementation, but not canola oil, increased survival rates, improved general appearance and prevented cognitive decline, despite the facts that both diets contained an equivalent number of calories and that there were no differences in weight between mice maintained on the two diets in 100% but decrease in the 40%. In the hypothalamus, the beneficial effects of fish oil supplementation were related to normalization of the endocannabinoid 2-arachidonylglycerol, serotonin (5-HT) (P<.056), dopamine, neuropeptide Y (NPY) and Ca(2+)/calmodulin (CaM)-dependent protein kinase (Camkk2). In the hippocampus, fish oil supplementation normalized 5-HT, Camkk2, silent mating type information regulation 1 and brain-derived neurotrophic factor. In conclusion, dietary supplements of fish oil, as source of omega-3 fatty acids, may alleviate cognitive impairments associated with severe diet restriction and prolong survival independently of weight gain by normalizing neurochemical systems.

Contrasting effects of systemic and central sibutramine administration on the intake of a palatable diet in the rat

Sibutramine hydrochloride monohydrate is the only centrally active weight-modifying agent currently approved by the FDA for long-term use in the treatment of obesity. Systemic sibutramine treatment has been shown to reduce food intake in humans and rodent models in a manner that is consistent with the enhancement of satiety mechanisms. Although it is generally assumed that the hypophagic effects of the drug are mediated by actions within the brain, the locus or loci of these effects remains unclear. These experiments compared the effects of systemic and intracranial injections of sibutramine on the intake of a palatable diet in non-deprived animals. Consistent with prior reports, systemic injections of sibutramine hydrochloride (at 0, 0.5, 1.0, or 3.0mg/kg sibutramine i.p.) dose-dependently reduced feeding on a high fat/high sucrose diet across a 2-h feeding session, but did not alter water intake or locomotor activity. In contrast, bilateral injections of sibutramine (at 0.0, 2.0, 4.0 and 10.0μg/0.5μl/side) into either the paraventricular nucleus of the hypothalamus (PVN) or the medial nucleus accumbens shell (ACb) significantly and dose-dependently increased food intake of the sweetened fat diet. ACb treatment also modestly inhibited locomotor behavior; intracranial injections had no effect on water consumption. These experiments are the first to suggest that sibutramine treatment may have distinct actions upon separate neural circuits that modulate food intake behavior in the rat.

Hypothalamic paraventricular 5-hydroxytryptamine inhibits the effects of ghrelin on eating and energy substrate utilization

Ghrelin microinjections into discrete regions of the hypothalamus, including the paraventricular nucleus (PVN), stimulate eating and promote carbohydrate oxidation, effects similar to PVN microinjection of neuropeptide Y (NPY). We have also reported that NPY's orexigenic and metabolic effects are antagonized by pretreatment with 5-hydroxytryptamine (5-HT) or 5-HT receptor agonists. In order to determine whether 5-HT also inhibits ghrelin's orexigenic and metabolic actions, the present study examined the effects of 5-HT pretreatment on ghrelin-induced alterations in eating and energy substrate utilization following direct injections into the hypothalamic PVN. Both 5-HT (5-20 nmol) and ghrelin (100 pmol) were administered at the onset of the dark cycle. Food intake was measured 2h postinjection. A separate group of rats (n=8) was injected with 5-HT paired with ghrelin and respiratory quotient (RQ; VCO(2)/VO(2)) was measured over 2h using an open circuit calorimeter. PVN injections of ghrelin increased food intake and increased RQ, reflecting a shift in energy substrate utilization in favor of carbohydrate oxidation. 5-HT effectively blocked the effects of ghrelin on both food intake and RQ. We then administered the 5-HT(2A/2C), receptor agonist, DOI, immediately prior to ghrelin. Similar to 5-HT, PVN DOI blocked ghrelin-induced eating and inhibited the peptide's effect on substrate utilization. These data are in agreement with other evidence suggesting that ghrelin functions as a gut-brain peptide in the control of food intake and energy metabolism, and indicate that 5-HT acts within the PVN to modulate ghrelin's orexigenic and metabolic signaling.

Ghrelin is an orexigenic and metabolic signaling peptide in the arcuate and paraventricular nuclei

Ghrelin is a 28-amino acid acylated peptide and is the endogenous ligand for the growth hormone secretagogue receptor (GHS-R). The GHS-R is expressed in hypothalamic nuclei, including the arcuate nucleus (Arc) where it is colocalized with neuropeptide Y (NPY) neurons. In the present study, we examined the effects of ghrelin on feeding and energy substrate utilization (respiratory quotient; RQ) following direct injections into either the arcuate or the paraventricular nucleus (PVN) of the hypothalamus. Ghrelin was administered at the beginning of the dark cycle at doses of 15–60 pmol to male and female rats. In feeding studies, food intake was measured 2 and 4 h postinjection. Separate groups of rats were injected with ghrelin, and the RQ (V̇co2/V̇o2) was measured using an open circuit calorimeter over a 4-h period. Both Arc and PVN injections of ghrelin increased food intake in male and female rats. Ghrelin also increased RQ, reflecting a shift in energy substrate utilization in favor of carbohydrate oxidation. Because these effects are similar to those observed after PVN injection of NPY, we then assessed the impact of coinjecting ghrelin with NPY into the PVN. When rats were pretreated with very low doses of ghrelin (2.5–10 pmol), NPY's (50 pmol) effects on eating and RQ were potentiated. Overall, these data are in agreement with evidence suggesting that ghrelin functions as a gut-brain endocrine hormone implicated in the regulation of food intake and energy metabolism. Our findings are also consistent with a possible interactive role of hypothalamic ghrelin and NPY systems.

Integration of hypothalamic feeding and metabolic signals: focus on neuropeptide Y

Research is reviewed on effects of neuropeptide Y (NPY) on energy substrate utilization and central interactions among NPY, serotonin and urocortin, particularly in neurons of the paraventricular nucleus of the hypothalamus.

Serotonergic and histaminergic mechanisms involved in intralipid drinking?

Some newer antipsychotic agents are associated with weight gain in humans and a hyperphagic response to intralipid solutions in rodents. To examine the possible contribution of serotonin (5-HT) and histamine (H) receptor blockade in antipsychotic-associated hyperphagia, rats were trained to drink a palatable, high-calorie fat emulsion (10% intralipid) during 30-min sessions and were tested following pretreatment with mepyramine (H1 receptor antagonist), metergoline (5-HT(1/2) receptor antagonist), cyproheptadine (H1 and 5-HT(2A/2B/2C) and muscarinic receptor antagonist), SB 242084 (5-HT2C receptor antagonist) and an SB 242084-mepyramine combination. Total intake and ingestive behaviour microstructure were measured. Mepyramine (10 mg/kg) reduced intake, as did metergoline (3.0 mg/kg). Cyproheptadine (0.1-1.0 mg/kg) increased intake and microstructural analysis suggests that this was due to increased numbers of clusters of licking. SB 242084 (3 mg/kg) reduced intake, either when administered alone, or in combination with mepyramine (1 mg/kg). In conclusion, simple antagonism of either H1 (mepyramine) or 5-HT(1/2) receptors (metergoline) alone was not sufficient to increase intake. Furthermore, combined blockade of H1 and 5-HT2C receptors (SB 242084 and mepyramine) was also insufficient to produce hyperphagia. Conversely, simultaneous blockade of H1, 5-HT(2A/2C) and muscarinic receptors (cyproheptadine) led to a substantial hyperphagia and pattern of ingestive behaviour that was similar to that previously observed with some newer antipsychotic agents.

Metachlorophenylpiperazine (m-CPP) induced intracavernous pressure responses in anaesthetized rats

Here we have recorded the effects of metachlorophenylpiperazine (m-CPP) on intracavernous pressure (ICP) in anesthetized rats pretreated with various pharmacological agents in an attempt to determine the mechanism and relevance of the m-CPP induced ICP response to other models of erection. m-CPP elicited consistent and significantly greater increases in ICP (71.5+/-6.6 mmHg) compared with the mixed 5-HT(2a/2c) agonists trifluoromethylphenylpiperazine (3.4+/-1.3 mmHg) and quipazine (10.9+/-1.8 mmHg). Blockade of 5-HT(2a) receptors with ketanserin failed to unmask any stimulatory effect of quipazine (7.2+/-1.0 mmHg). m-CPP induced ICP responses (71+/-7.0 mmHg) were unaffected in the presence of mianserin (63+/-5 mmHg) and ketanserin (51+/-12 mmHg). Spiperone significantly reduced the m-CPP induced increase in ICP (8.0+/-1.0 mmHg). Naloxone, yohimbine and 8-hydroxy-2-(di-n-propylamino)tetralin (8-OHDPAT) failed to elicit increases in ICP on their own. All three drugs significantly reduced the latency to the first m-CPP induced ICP response compared to saline. Yohimbine increased the duration of m-CPP induced ICP responses whereas 8-OHDPAT increased the mean number of m-CPP induced ICP responses compared to saline. The effects of m-CPP on ICP in anesthetized rats may not be mediated by 5-HT(2c) receptors and appears to be similar to erection in copula, but not erection elicited by other drugs or penile sheath retraction.

Intermittent, chronic fenfluramine administration to rats repeatedly suppresses food intake despite substantial brain serotonin reductions

The mechanisms by which fenfluramine suppresses food intake and body weight have been linked to its ability to enhance transmission across serotonin synapses in brain. This drug initially lowers body weight and suppresses food intake, yet after repeated administration food intake soon returns to normal and body weight no longer decreases. Fenfluramine also causes rapid and prolonged reductions in brain serotonin concentrations, which might account for its loss of appetite suppression. This possibility has been evaluated in rats by assessing if intermittent, chronic fenfluramine administration could suppress food intake during each treatment period, and if so, whether such an effect occurs in the presence of reduced brain serotonin levels. Rats were injected once daily with 10 mg/kg D,L-fenfluramine for 5 days, and then received no injections for the next 5 days. Control rats received only vehicle injections. This 10-day sequence was repeated five more times. During each period of fenfluramine administration, daily food intake dropped markedly the first 1-2 days of treatment, but returned to pretreatment values by day 5. Daily food intake was normal or slightly above normal during non-injection periods. Body weight dropped modestly during each period of fenfluramine administration, and rose during each subsequent period when injections had ceased. Serotonin concentrations and synthesis rates in several brain regions were markedly reduced at early, middle, and late periods of the experiment. Despite the long-term reduction in brain serotonin pools produced by fenfluramine, the drug continues to reduce food intake and body weight. Several possible interpretations of these findings are considered, based on the multiple mechanisms through which this drug has been proposed to modify synaptic serotonin transmission.

Hypothalamic paraventricular nucleus injections of urocortin alter food intake and respiratory quotient

Corticotropin releasing hormone (CRH) acts on the central nervous system to alter energy balance and influence both food intake and sympathetically-mediated thermogenesis. CRH is also reported to inhibit food intake in several models of hyperphagia including neuropeptide Y (NPY)-induced eating. The recently identified CRH-related peptide, urocortin (UCN), also binds with high affinity to CRH receptor subtypes and decreases food intake in food-deprived and non-deprived rats. The present experiment characterized further the feeding and metabolic effects of UCN by examining its impact after direct injections into the paraventricular nucleus (PVN) of the hypothalamus. In feeding tests (n=8), UCN (50-200 pmol) was injected into the PVN at the onset of the dark cycle and food intake was measured 1, 2 and 4 h postinjection. In separate rats (n=8), the metabolic effects of UCN were monitored using an open circuit calorimeter which measured oxygen consumption (V(O2)) and carbon dioxide production (V(CO2)). Respiratory quotient (RQ) was calculated as V(CO2)/V(O2). UCN suppressed feeding at all times studied and reliably decreased RQ within 30 min of infusion. Additional work examined the effect of UCN (50-100 pmol) pretreatment on the feeding and metabolic effects of NPY. NPY, injected at the start of the dark period, reliably increased 2 h food intake. This effect was blocked by PVN UCN administration. Similarly, UCN blocked the increase in RQ elicited by NPY alone. These results suggest that UCN-sensitive mechanisms within the PVN may modulate food intake and energy substrate utilization, possibly through an interaction with hypothalamic NPY.

Mirtazapine for treatment of depression and comorbidities in Alzheimer disease

BACKGROUND

Depression in patients with Alzheimer disease is a treatable cause of functional decline, caregiver burden, and mortality. It is often associated with severe weight loss, insomnia, and anxiety. These symptoms independently and collaboratively further worsen the prognosis of these vulnerable patients. An antidepressant medication with good adverse effect profile and salutary effects on these comorbid symptoms may be of significant therapeutic value in these patients.

OBJECTIVE

To describe the role of mirtazapine in the treatment of depressed Alzheimer patients with comorbid weight loss, insomnia, and anxiety.

CASE SUMMARY

Three patients with dementia and depression complicated by weight loss, insomnia, and anxiety were treated with mirtazapine at an outpatient memory loss clinic of a university hospital.

DISCUSSION

Despite the persistence of memory loss, the patients experienced a prompt and sustained response to mirtazapine. There was a complete remission of poor appetite, weight loss, sleep disturbances, and anxiety. Other depression symptoms, including sad mood, anhedonia, and energy level, were also substantially improved.

CONCLUSIONS

The clinical response of our patients underscores the usefulness of mirtazapine in the treatment of the comorbid symptoms of weight loss, insomnia, and anxiety. The effectiveness of mirtazapine in depressed Alzheimer patents may be a reflection of its enhancement of brain serotonergic and noradrenergic neurotransmission. The usefulness of mirtazapine in depressed Alzheimer patients merits further study in a large randomized, controlled, clinically comparative trial.

Paraventricular nucleus injections of naloxone methiodide inhibit NPY's effects on energy substrate utilization

Microinjection of neuropeptide Y (NPY) into the paraventricular nucleus (PVN) of the hypothalamus stimulates eating and increases respiratory quotient. In contrast, administration of opioid receptor antagonists reduces food intake and suppresses NPY-induced feeding. The present study examined whether naloxone methiodide, an opioid antagonist, would suppress the potentiation of NPY on energy substrate utilization, when injected into the PVN. Naloxone methiodide was injected at doses of 0.1 and 1.0 g, 10 min prior to NPY treatment. NPY was administered immediately prior to the start of the nocturnal period and RQ was determined using an open-circuit calorimeter. Doses of 50 and 100 pmol NPY alone evoked reliable increases in RQ within 30min of treatment. Following naloxone methiodide pretreatment, the stimulatory action of NPY was significantly attenuated. These data indicate that opioid receptors in the PVN influence the action of NPY on energy substrate utilization.