Effect of dopamine receptor-related compounds on naïve common marmosets for auditory steady-state response.

Abnormalities of auditory steady-state responses (ASSRs) and the effects of antipsychotic drugs on ASSRs have been investigated in patients with schizophrenia. It is presumed that drugs do not directly affect ASSRs because its abnormalities are associated with schizophrenia. Therefore, to investigate the direct effect of drugs on ASSRs, we established an ASSR evaluation system for common marmosets in a naïve state. Dopamine D1 receptor stimulation (SKF-81297, 2 mg/kg ip) significantly increased evoked power (EP) at 40 Hz. The phase locking factor (PLF) was increased significantly at 20, 30, 40, and 80 Hz. However, administration of a dopamine D1 receptor antagonist (SCH-39166, 0.3 mg/kg ip) resulted in a significant decrease in EP and PLF at 30 Hz. Dopamine D2 receptor stimulation (quinpirole, 1 mg/kg im) tended to increase EP and induced power (IP) at all frequencies, and a significant difference was observed at 30 Hz IP. There was no change in PLF at all frequencies. In addition, dopamine D2 receptor blockade (raclopride, 3 mg/kg ip) reduced EP and PLF at 30 Hz. Subcutaneous administration of the serotonin dopamine antagonist, risperidone (0.3 mg/kg), tended to increase IP and decrease PLF, but not significantly. Taken together, it is possible to compare the differences in the mode of action of drugs on ASSRs using naïve nonhuman primates.NEW & NOTEWORTHY We measured the effects of dopamine receptor-related compounds on ASSR in marmosets. D1 receptor stimulation increased the phase locking factor (PLF) and evoked power (EP), and reduced the induced power (IP). D2 receptor stimulation increased the IP. D1 and D2 receptor blockers reduced the PLF and EP at 30 Hz. Different modes of action of various drugs related to psychiatric disorders were evaluated by administering antipsychotic drugs to naïve marmosets.

Risperidone on apomorphine-induced stereotyped behavior and auditory sensory gating in rhesus monkeys.

The ameliorating effect of risperidone on apomorphine-induced stereotyped behavior and inhibition of auditory sensory gating was investigated using rhesus monkeys. The total duration of the stereotyped behavior observed in the control group was 43.7 ± 23.0 s (n = 3) between 10 and 25 min after vehicle administration, whereas the duration in the apomorphine-treated (0.1 or 0.15 mg/kg i.m., n = 3) group was observed to be significantly prolonged to 413.0 ± 150.6 s. Administration of 0.01, 0.03, 0.1 mg/kg of risperidone 60 min before apomorphine, significantly reduced the duration of this apomorphine-induced stereotyped behavior to 327 ± 104.9 s (n = 3), 8.3 ± 4.2 s (n = 3), and 0.0 ± × 0.0 s (n = 3, t-test: p < 0.05), respectively. Next, the auditory sensory gating test/conditioning (T/C) ratio was used as a bio-marker. The T/C ratio was 0.598 ± 0.0802 in the vehicle-administered control group (n = 4) and was significantly increased to 2.098 ± 0.254 (n = 4) by apomorphine (0.15 mg/kg, i.m.). Administering of risperidone (0.1 mg/kg, s.c.) 30 min before apomorphine treatment significantly restricted the T/C ratio to 0.571 ± 0.0886 (n = 4), compared to the T/C ratio in the vehicle-administered control group. The above results demonstrate, not only behaviorally but also electrophysiologically, the ameliorating effect of risperidone on the induction of schizophrenia-like symptoms by apomorphine in non-human primates.

The atypical antipsychotic blonanserin reverses (+)-PD-128907- and ketamine-induced deficit in executive function in common marmosets.

Antagonism of the dopamine D3 receptor is considered a promising strategy for the treatment of cognitive impairment associated with schizophrenia. We have previously reported that the atypical antipsychotic blonanserin, a dopamine D2/D3 and serotonin 5-HT2A receptor antagonist, highly occupies dopamine D3 receptors at its antipsychotic dose range in rats. In the present study, we evaluated the effects of blonanserin on executive function in common marmosets using the object retrieval with detour (ORD) task. The dopamine D3 receptor-preferring agonist (+)-PD-128907 at 1mg/kg decreased success rate in the difficult trial, but not in the easy trial. Since the difference between the two trials is only cognitive demand, our findings indicate that excess activation of dopamine D3 receptors impairs executive function in common marmosets. Blonanserin at 0.1mg/kg reversed the decrease in success rate induced by (+)-PD-128907 in the difficult trial. This finding indicates that blonanserin has beneficial effect on executive function deficit induced by activation of the dopamine D3 receptor in common marmosets. Next, and based on the glutamatergic hypothesis of schizophrenia, the common marmosets were treated with the N-methyl-d-aspartate (NMDA) receptor antagonist ketamine. Ketamine at sub-anesthetic doses decreased success rate in the difficult trial, but not in the easy trial. Blonanserin at 0.1mg/kg reversed the decrease in success rate induced by ketamine in the difficult trial. The findings of this study suggest that blonanserin might have beneficial effect on executive dysfunction in patients with schizophrenia.

AC-3933, a benzodiazepine partial inverse agonist, improves memory performance in MK-801-induced amnesia mouse model.

AC-3933, a novel benzodiazepine receptor partial inverse agonist, is a drug candidate for cognitive disorders including Alzheimer's disease. We have previously reported that AC-3933 enhances acetylcholine release in the rat hippocampus and ameliorates scopolamine-induced memory impairment and age-related cognitive decline in both rats and mice. In this study, we further evaluated the procognitive effect of AC-3933 on memory impairment induced by MK-801, an N-methyl-d-aspartate receptor antagonist, in mice. Unlike the acetylcholinesterase inhibitor donepezil and the benzodiazepine receptor inverse agonist FG-7142, oral administration of AC-3933 significantly ameliorated MK-801-induced memory impairment in the Y-maze test and in the object location test. Interestingly, the procognitive effects of AC-3933 on MK-801-induced memory impairment were not affected by the benzodiazepine receptor antagonist flumazenil, although this was not the case for the beneficial effects of AC-3933 on scopolamine-induced memory deficit. Moreover, the onset of AC-3933 ameliorating effect on scopolamine- or MK-801-induced memory impairment was different in the Y-maze test. Taken together, these results indicate that AC-3933 improves memory deficits caused by both cholinergic and glutamatergic hypofunction and suggest that the ameliorating effect of AC-3933 on MK-801-induced memory impairment is mediated by a mechanism other than inverse activation of the benzodiazepine receptor.

Circulating AIM prevents hepatocellular carcinoma through complement activation.

Hepatocellular carcinoma (HCC) is a widespread fatal disease and the third most common cause of cancer deaths. Here, we show the potent anti-HCC effect of the circulating protein AIM. As in adipocytes, AIM is incorporated into normal hepatocytes, where it interferes with lipid storage. In contrast, AIM accumulates on the HCC cell surface and activates the complement cascade via inactivating multiple regulators of complement activation. This response provokes necrotic cell death specifically in AIM-bound HCC cells. Accordingly, AIM(-/-) mice were highly susceptible to steatosis-associated HCC development, whereas no AIM(+/+) mouse developed the disease despite comparable liver inflammation and fibrosis in response to a long-term high-fat diet. Administration of AIM prevented tumor development in AIM(-/-) mice, and HCC induction by diethylnitrosamine was more prominent in AIM(-/-) than wild-type mice. These findings could be the basis for novel AIM-based therapeutic strategies for HCC.

Obesity-associated autoantibody production requires AIM to retain the immunoglobulin M immune complex on follicular dendritic cells.

Natural immunoglobulin M (IgM) is reactive to autoantigens and is believed to be important for autoimmunity. Blood pentameric IgM loaded with antigens forms a large immune complex (IC) that contains various elements, including apoptosis inhibitor of macrophage (AIM). Here we demonstrate that this IgM-AIM association contributes to autoantibody production under obese conditions. In mice fed a high-fat diet, natural IgM increased through B cell TLR4 stimulation. AIM associated with IgM and protected AIM from renal excretion, increasing blood AIM levels along with the obesity-induced IgM augmentation. Meanwhile, the AIM association inhibited IgM binding to the Fcα/µ receptor on splenic follicular dendritic cells, thereby protecting the IgM IC from Fcα/µ receptor-mediated internalization. This supported IgM-dependent autoantigen presentation to B cells, stimulating IgG autoantibody production. Accordingly, in obese AIM-deficient (AIM(-/-)) mice, the increase of multiple IgG autoantibodies observed in obese wild-type mice was abrogated. Thus, the AIM-IgM association plays a critical role in the obesity-associated autoimmune process.

Modification of N-glycosylation modulates the secretion and lipolytic function of apoptosis inhibitor of macrophage (AIM).

The mouse macrophage-derived apoptosis inhibitor of macrophage (AIM), which is incorporated into adipocytes and induces lipolysis by suppressing fatty acid synthase (FAS) activity, possesses three potential N-glycosylation sites. Inactivation of N-glycosylation sites revealed that mouse AIM contains two N-glycans in the first and second scavenger receptor cysteine-rich domains, and that depletion of N-glycans decreased AIM secretion from producing cells. Interestingly, the lack of N-glycans increased AIM lipolytic activity through enhancing AIM incorporation into adipocytes. Although human AIM contains no N-glycan, attachment of N-glycans increased AIM secretion. Thus, the N-glycosylation plays important roles in the secretion and lipolytic function of AIM.

Apoptosis inhibitor of macrophage (AIM) diminishes lipid droplet-coating proteins leading to lipolysis in adipocytes.

Under fasting conditions, triacylglycerol in adipose tissue undergoes lipolysis to supply fatty acids as energy substrates. Such lipolysis is regulated by hormones, which activate lipases via stimulation of specific signalling cascades. We previously showed that macrophage-derived soluble protein, AIM induces obesity-associated lipolysis, triggering chronic inflammation in fat tissue which causes insulin resistance. However, the mechanism of how AIM mediates lipolysis remains unknown. Here we show that AIM induces lipolysis in a manner distinct from that of hormone-dependent lipolysis, without activation or augmentation of lipases. In vivo and in vitro, AIM did not enhance phosphorylation of hormone-sensitive lipase (HSL) in adipocytes, a hallmark of hormone-dependent lipolysis activation. Similarly, adipose tissue from obese AIM-deficient and wild-type mice showed comparable HSL phosphorylation. Consistent with the suppressive effect of AIM on fatty acid synthase activity, the amount of saturated and unsaturated fatty acids was reduced in adipocytes treated with AIM. This response ablated transcriptional activity of peroxisome proliferator-activated receptor (PPARγ), leading to diminished gene expression of lipid-droplet coating proteins including fat-specific protein 27 (FSP27) and Perilipin, which are indispensable for triacylglycerol storage in adipocytes. Accordingly, the lipolytic effect of AIM was overcome by a PPARγ-agonist or forced expression of FSP27, while it was synergized by a PPARγ-antagonist. Overall, distinct modes of lipolysis appear to take place in different physiological situations; one is a supportive response against nutritional deprivation achieved by enhancing lipase activity, and the other is a pathological consequence of obesity, causing subclinical inflammation and metabolic disorders, mediated by abolishing droplet-coating proteins.

The effects of selective serotonin-reuptake inhibitor on visual evoked potential in rats.

The present study was undertaken to clarify the effects of selective serotonin-reuptake inhibitors (SSRIs) on visual evoked potential (VEP) in rats. To elucidate the mechanism of action of SSRIs, some serotonin (5-HT) agonists were used. SSRIs, fluvoxamine and paroxetine, caused a reduction in the amplitudes of P1-N1, P3-N3, and N3-P4 components of VEP. The amplitude of the P1-N1 component was also reduced by the 5-HT1A agonist 8-OH-DPAT and 5-HT1B agonist anpirtoline. On the other hand, amplitudes of P3-N3 and N3-P4 components were reduced by anpirtoline and the 5-HT2 agonist DOI. These results indicate that the reduction in the amplitude of the P1-N1 component of VEP induced by SSRIs may participate in 5-HT1A and 5-HT1B receptors, and those of P3-N3 and N3-P4 components induced by SSRIs may be closely related with 5-HT1B and 5-HT2 receptors.

The effects of certain H(1)-antagonists on visual evoked potential in rats.

The present study was undertaken to clarify the effects of certain H(1)-antagonists on visual evoked potential (VEP) in rats. Pyrilamine (5 and 10 mg/kg), diphenhydramine (5 and 10 mg/kg) and chlorpheniramine (10 and 20 mg/kg) caused a significant reduction in the amplitude of late VEP components (P(3)-N(3), N(3)-P(4)), although these drugs showed no significant changes in early VEP components (P(1)-N(1), N(1)-P(2)). Cyproheptadine caused a slight enhancement of late components of VEP at a dose of 20 mg/kg. On the other hand, epinastine caused no significant effect on late VEP components even at a dose of 20 mg/kg. The reduction in the late VEP components induced by pyrilamine and diphenhydramine was significantly antagonised by pre-treatment of histidine (200 and 500 mg/kg), but not by physostigmine even at a dose of 0.01 mg/kg. The effect induced by cyproheptadine was significantly potentiated by histidine (500 mg/kg), and significantly reduced by DOI (2 mg/kg). These results indicate that an inhibition of the late VEP components induced by H(1)-antagonist pyrilamine, diphenhydramine and chlorpheniramine may be due to an inhibition of specific sensory system relating the histaminergic mechanisms. In addition, slight enhancement of these components induced by cyproheptadine may be attributable to its anti-serotonergic effects.