Cognitive performance in neurokinin 3 receptor knockout mice.

RATIONALE: The neurokinin 3 (NK(3)) receptor is a novel target under investigation for improvement of the symptoms of schizophrenia due to its ability to modulate dopaminergic signaling. However, research on effects of NK(3) antagonism with animal models has been hindered because of species differences in the receptor between humans, rats, and mice. OBJECTIVES: The aim of the present study is to further knowledge on the role of NK(3) in cognitive functioning by testing the effect of knockout of the NK(3) receptor on tests of working memory, spatial memory, and operant responding. MATERIALS AND METHODS: NK(3) knockout mice generated on a C57Bl/6 background were tested in delayed matching to position (DMTP), spontaneous alternation, Morris water maze, and active avoidance tasks. RESULTS: NK(3) knockout mice showed better performance in the DMTP task, though not delay dependently, which points to an effect on operant performance but not on working memory. No differences were seen between the groups in spontaneous alternation, another indication that working memory is not affected in NK(3) knockouts. There was no impairment in knockout mice in Morris water maze training, and the mice also showed faster response latency in the active avoidance task during training. CONCLUSIONS: Collectively, these results support a role for the NK(3) receptor in performance of operant tasks and in spatial learning but not in working memory.

Impact of environmental housing conditions on the emotional responses of mice deficient for nociceptin/orphanin FQ peptide precursor gene.

Nociceptin/orphanin FQ (N/OFQ) is a newly discovered neuropeptide that has been implicated in the neurobiological regulation of the behavioral responses to stress and fear. To investigate the role of this peptide in the expression of stress/anxiety-related behaviors in mice, a gene targeting approach to disrupt N/OFQ in the pre-proN/OFQ gene was used. The impact of environmental housing conditions (single and social housing) was assessed on N/OFQ-knockout male and female mice in different experimental paradigms known to trigger distinctive types of stress and anxiety states. Neurological examination of homozygous mutant adult animals indicated that basic neurological functions (vision, audition, olfaction, tactile and pain sensitivity, motor performances) were normal. When housed individually, N/OFQ-knockout animals displayed responses similar to control animals in behavioral tests of emotional reactivity (behavioral despair, locomotor activity, light-dark preference, and acoustic startle tests). In contrast, increased emotional responses were detected when individually housed mice were crowded together (five per cage) under conditions of competitive access to food, water, space, and social contacts. Under those conditions, male mice deficient for N/OFQ developed greater home-cage aggression and increased fear/anxiety-like behaviors in the light-dark and acoustic startle tests, when compared to their wild-type littermates. Group-housed female mutants also showed higher level of anxiety in the acoustic startle test, but needed additional restrain stress to express detectable levels of anxiety in the light-dark test. These data indicate a clear environment-induced rise in fear reactions of N/OFQ-knockout mice. They further suggest that N/OFQ system is essential for development of adequate coping strategies to acute and chronic stress.

Influence of the selective ORL1 receptor agonist, Ro64-6198, on rodent neurological function.

Identification of synthetic agonists and antagonists at orphan receptors represents an important step for understanding their physiological function and therapeutic potential. Accordingly, we have recently described a non-peptide agonist at the opioid receptor like (ORL1) receptor (1S,3aS)-8-(2,3,3a,4,5,6-hexahydro-1H-phenalen-1-yl)-1-phenyl-1,3,8-triazaspiro[4.5]decan-4-one (Ro64-6198; Jenck et al., PNAS 94 (2000) 4938; Wichmann et al., Eur. J. Med. Chem. 35 (2000) 839). We have investigated the effects of this compound in various tests of rodent neurological function, utilising ORL1 knockout mice to examine the pharmacological specificity of Ro64-6198. In male C57BL/6J mice, effects on balance and motor co-ordination were detected following low doses (0.3-1mg/kg IP) of Ro64-6198. At higher doses (1-3mg/kg IP), effects on swim behaviour and hypothermia was observed. At 10mg/kg, each effect became more profound and a severe neurological disturbance appeared, including loss of righting reflex. These effects of Ro64-6198 (10mg/kg IP) were absent in ORL1 receptor knockout mice. In male, hooded Lister rats, Ro64-6198 (6-10mg/kg IP), produced some disturbance of neurological function, including hypoactivity, rotarod performance, grip strength and mild hypothermia. An impairment of food responding under a variable interval (VI) 20s schedule of reinforcement was noted at 3mg/kg. These results confirm Ro64-6198 to be a highly selective pharmacological tool to investigate ORL1 receptor function in vivo and, furthermore, that activation of this receptor is accompanied by a variety of effects on neurological function.

Cathepsin L deficiency as molecular defect of furless: hyperproliferation of keratinocytes and pertubation of hair follicle cycling.

Lysosomal cysteine proteinases of the papain family are involved in lysosomal bulk proteolysis, major histocompatibility complex class II mediated antigen presentation, prohormone processing, and extracellular matrix remodeling. Cathepsin L (CTSL) is a ubiquitously expressed major representative of the papain-like family of cysteine proteinases. To investigate CTSL in vivo functions, the gene was inactivated by gene targeting in embryonic stem cells. CTSL-deficient mice develop periodic hair loss and epidermal hyperplasia, acanthosis, and hyperkeratosis. The hair loss is due to alterations of hair follicle morphogenesis and cycling, dilatation of hair follicle canals, and disturbed club hair formation. Hyperproliferation of hair follicle epithelial cells and basal epidermal keratinocytes-both of ectodermal origin-are the primary characteristics underlying the mutant phenotype. Pathological inflammatory responses have been excluded as a putative cause of the skin and hair disorder. The phenotype of CTSL-deficient mice is reminiscent of the spontaneous mouse mutant furless (fs). Analyses of the ctsl gene of fs mice revealed a G149R mutation inactivating the proteinase activity. CTSL is the first lysosomal proteinase shown to be essential for epidermal homeostasis and regular hair follicle morphogenesis and cycling.

Functional consequences of reduction in NMDA receptor glycine affinity in mice carrying targeted point mutations in the glycine binding site.

We have used site-directed mutagenesis in conjunction with homologous recombination to generate two mouse lines carrying point mutations in the glycine binding site of the NMDAR1 subunit (Grin1). Glycine concentration-response curves from acutely dissociated hippocampal neurons revealed a 5- and 86-fold reduction in receptor glycine affinity in mice carrying Grin1(D481N) and Grin1(K483Q) mutations, respectively, whereas receptor glutamate affinity remained unaffected. Homozygous mutant Grin1(D481N) animals are viable and fertile and appear to develop normally. However, homozygous mutant Grin1(K483Q) animals are significantly lighter at birth, do not feed, and die within a few days. No gross abnormalities in CNS anatomy were detected in either Grin1(D481N) or Grin1(K483Q) mice. Interestingly, in situ hybridization and Western blot analysis revealed changes in the expression levels of NMDA receptor subunits in Grin1(D481N) mice relative to wild type that may represent a compensatory response to the reduction in receptor glycine affinity. Grin1(D481N) mice exhibited deficits in hippocampal theta burst-induced long-term potentiation (LTP) and spatial learning and also a reduction in sensitivity to NMDA-induced seizures relative to wild-type controls, consistent with a reduced activation of NMDA receptors. Mutant mice exhibited normal prepulse inhibition but showed increased startle reactivity. Preliminary analysis indicated that the mice exhibit a decreased natural aversion to an exposed environment. The lethal phenotype of Grin1(K483Q) animals confirms the critical role of NMDA receptor activation in neonatal survival. A milder reduction in receptor glycine affinity results in an impairment of LTP and spatial learning and alterations in anxiety-related behavior, providing further evidence for the role of NMDA receptor activation in these processes.