Sensorimotor gating in neurotensin-1 receptor null mice.

BACKGROUND: Converging evidence has implicated endogenous neurotensin (NT) in the pathophysiology of brain processes relevant to schizophrenia. Prepulse inhibition of the startle reflex (PPI) is a measure of sensorimotor gating and considered to be of strong relevance to neuropsychiatric disorders associated with psychosis and cognitive dysfunction. Mice genetically engineered to not express NT display deficits in PPI that model the PPI deficits seen in schizophrenia patients. NT1 receptors have been most strongly implicated in mediating the psychosis relevant effects of NT such as attenuating PPI deficits. To investigate the role of NT1 receptors in the regulation of PPI, we measured baseline PPI in wildtype (WT) and NT1 knockout (KO) mice. We also tested the effects of amphetamine and dizocilpine, a dopamine agonist and NMDA antagonist, respectively, that reduce PPI as well as the NT1 selective receptor agonist PD149163, known to increase PPI in rats. METHODS: Baseline PPI and acoustic startle response were measured in WT and NT1 KO mice. After baseline testing, mice were tested again after receiving intraperatoneal (IP) saline or one of three doses of amphetamine (1.0, 3.0 and 10.0 mg/kg), dizocilpine (0.3, 1.0 and 3.0 mg/kg) and PD149163 (0.5, 2.0 and 6.0 mg/kg) on separate test days. RESULTS: Baseline PPI and acoustic startle response in NT1 KO mice were not significantly different from NT1 WT mice. WT and KO mice exhibited similar responses to the PPI-disrupting effects of dizocilpine and amphetamine. PD149163 significantly facilitated PPI (P < 0.004) and decreased the acoustic startle response (P < 0.001) in WT but not NT1 KO mice. CONCLUSIONS: The data does not support the regulation of baseline PPI or the PPI disruptive effects of amphetamine or dizocilpine by endogenous NT acting at the NT1 receptor, although they support the antipsychotic potential of pharmacological activation of NT1 receptors by NT1 agonists.

Unveiling the molecular mechanisms behind selenium-related diseases through knockout mouse studies.

Selenium (Se), in the form of the 21st amino acid selenocysteine, is an integral part of selenoproteins and essential for mammals. While a large number of health claims for Se has been proposed in a diverse set of diseases, little is known about the precise molecular mechanisms and the physiological roles of selenoproteins. With the recent and rigorous application of reverse genetics in the mouse, great strides have been made to address this on a more molecular level. In this review, we focus on results obtained from the application of mouse molecular genetics in mouse physiology and discuss these insights into the physiological actions of selenoproteins in light of evidence from human genetics.

Behavioral analysis of Ste20 kinase SPAK knockout mice.

SPAK/STK39 is a mammalian protein kinase involved in the regulation of inorganic ion transport mechanisms known to modulate GABAergic neurotransmission in the both central and the peripheral nervous systems. We have previously shown that disruption of the gene encoding SPAK by homologous recombination in mouse embryonic stem cells results in viable mice that lack expression of the kinase. With the exception of reduced fertility, these mice do not exhibit an overt adverse phenotype. In the present study, we examine the neurological phenotype of these mice by subjecting them to an array of behavioral tests. We show that SPAK knockout mice displayed a higher nociceptive threshold than their wild-type counterparts on the hot plate and tail flick assays. SPAK knockout mice also exhibited a strong locomotor phenotype evidenced by significant deficits on the rotarod and decreased activity in open-field tests. In contrast, balance and proprioception was not affected. Finally, they demonstrated an increased anxiety-like phenotype, spending significantly longer periods of time in the dark area of the light/dark box and increased thigmotaxis in the open-field chamber. These results suggest that the kinase plays an important role in CNS function, consistent with SPAK regulating ion transport mechanisms directly involved in inhibitory neurotransmission.

Elevated anxiety-like and depressive behavior in Desert hedgehog knockout male mice.

To investigate the functional role of Desert hedgehog (Dhh) gene in the nervous system, we examined motor, sensory, learning and memory functions as well as mood in Dhh knockout (KO) mice. Dhh KO male mice exhibited prolonged immobility time compared with wild-type male mice in the forced swimming test, and showed enhanced inhibition in the Vogel's conflict model. These findings suggest that Dhh KO male mice exhibited enhanced anxiety and depressive behavior compared with wild-type male mice. In contrast, Dhh KO female mice did not show any significant difference compared to wild-type female mice. These behavioral abnormalities of Dhh KO male mice may be due to lower testosterone levels with abnormal development of the testes caused by Dhh-null mutation.

Behavioral and biochemical characterization of a mutant mouse strain lacking D-amino acid oxidase activity and its implications for schizophrenia.

D-amino acid oxidase (DAO) degrades D-serine, a co-agonist at the NMDA receptor (NMDAR). Hypofunction of the NMDAR has been suggested to contribute to the pathophysiology of schizophrenia. Intriguingly, DAO has been recently identified as a risk factor for schizophrenia through genetic association studies. A naturally occurring mouse strain (ddY/DAO-) has been identified which lacks DAO activity. We have characterized this strain both behaviorally and biochemically to evaluate DAO as a target for schizophrenia. We have confirmed that this strain lacks DAO activity and shown for the first time it has increased occupancy of the NMDAR glycine site due to elevated extracellular D-serine levels and has enhanced NMDAR function in vivo. Furthermore, the ddY/DAO- strain displays behaviors which suggest that it will be a useful tool for evaluation of the clinical benefit of DAO inhibition in schizophrenia.

Neural cell adhesion molecule-null mice are not deficient in prepulse inhibition of the startle response.

Mice constitutively deficient in the neural cell adhesion molecule have morphological changes in the brain, which are hallmarks of schizophrenia. Schizophrenic patients are impaired in sensorimotor processing indicated by a deficit in prepulse inhibition of the acoustic startle response. Here we tested whether prepulse inhibition and prepulse facilitation are changed in neural cell adhesion molecule-deficient mice compared with their wild-type littermates. Neither prepulse inhibition nor prepulse facilitation (which occurred only at the lowest prepulse intensity used and was weak) was altered. This result is discussed in the light of the 'two-hit' hypothesis of schizophrenia, suggesting that in neural cell adhesion molecule-deficient mice, a prepulse inhibition deficit may become apparent only after treatment with a 'second hit' (such as increased stress).

Involvement of serotonin in the hypoglycemic response to 2 Hz electroacupuncture of zusanli acupoint (ST36) in rats.

In our previous studies, an insulin-dependent hypoglycemic effect produced by electroacupuncture (EA) was shown to be mediated by endogenous opioid peptides (EOP). In the present study, we applied 2 Hz EA to both zusanli acupoints (ST36) in the test group for 30 min, and to a nonacupoint area in the control group for 30 min to compare the acupoint specific character in the hypoglycemic effect of EA. Assays of plasma beta-endorphin and insulin levels were performed by ELISA kits. The insulin-dependent mechanism of the hypoglycemic effect was also investigated in streptozotocin (STZ)-induced diabetic rats. The mediation of EOP and the role of mu-opioid receptor were examined by naloxone and mu-opioid receptor knockout mice (MOR-KOM). The serotonin depletion was carried out by injecting (i.p.) p-chlorophenylalanine (PCPA); two low doses of serotonin were also injected (i.v.) to analyze the direct effect on plasma glucose levels. The hypoglycemic effect of EA was much greater in rats stimulated at ST36 than in rats receiving the same stimulation at the nonacupoint area. The plasma levels of insulin and beta-endorphin were also significantly elevated after stimulation of both zusanli acupoints, but remained unchanged following stimulation at the nonacupoint area. There was no sharp hypoglycemic response to 2 Hz EA at zusanli acupoint of STZ-induced diabetic rats. However, the hypoglycemic effect of this EA was not totally blocked by the sufficient dose of naloxone (1 mg/kg, i.v.). Additionally, 2 Hz EA at ST36 also showed a sharp decrease in plasma glucose levels of MOR-KOM. Pretreatment with PCPA did not reproduce hypoglycemic response to 2 Hz EA in naloxone-treated rats and MOR-KOM mice. Furthermore, injection of serotonin decreased the plasma glucose levels significantly. Therefore, we suggest that serotonin also involved in the hypoglycemic action of 2 Hz EA at both zusanli acupoints of normal rats.

Type IX collagen knock-out mouse shows progressive hearing loss.

Type IX collagen is one of the important components, together with type II, V, and XI collagens, in the tectorial membrane of the organ of Corti. To confirm the significance of type IX collagen for normal hearing, we assessed the detailed morphological and electrophysiological features of type IX collagen knock-out mice, which have recently been reported as a deafness model. Through assessment by auditory brainstem response (ABR), knock-out mice were shown to have progressive hearing loss. At the light microscopic level, the tectorial membrane of knock-out mice was found to be abnormal in shape. These morphological changes started in the basal turn and were progressive toward the apical turn. Electron microscopy confirmed disturbance of organization of the collagen fibrils. These results suggest that mutations in type IX collagen genes may lead to abnormal integrity of collagen fibers in the tectorial membrane.

Behavioural characterization of vitamin D receptor knockout mice.

Vitamin D (calcitriol) is a nuclear transcription regulator acting via a nuclear hormone receptor (VDR). In addition to its role in the regulation of calcium and phosphate homeostasis and in bone formation, Vitamin D is also thought to be involved in brain function. The aim of this study was to behaviourally phenotype VDR knockout mice. We characterized the behaviour of VDR null mutant mice and wildtype littermate controls by subjecting them to a range of tests including a primary behavioural screen (using the SHIRPA protocol), rotarod, gait analysis, Y-maze, marble burying test, bedding test, holeboard test, elevated plus maze, open field test and prepulse inhibition of the acoustic startle response. There were no effects of genotype on most of the scores from the SHIRPA protocol except that VDR -/- mice had alopecia, were shorter and weighed less than VDR +/+ mice. VDR -/- mice had a shorter gait as well as impairments on the rotarod, in the bedding test and impaired habituation in both the open field and on the acoustic startle response. The VDR -/- mice had normal acoustic startle responses but had impaired PPI at long (256 ms) but not short (64 ms) prepulse to pulse intervals. The VDR -/- mice were less active in the open field and buried fewer marbles in the marble burying test. However, there were no differences in the time spent on the open arms of the elevated plus maze or in working memory as assessed by repeat arm entries on the Y-maze. Therefore, it appears that VDR -/- mice have muscular and motor impairments that significantly affects locomotor behaviour but seemingly no impairments in cognition as indicated by exploration, working memory or anxiety.