Nogo-A downregulation impairs place avoidance in the Carousel maze but not spatial memory in the Morris water maze.

Nogo-A protein is an important inhibitor of axonal growth, which also regulates neuronal plasticity in the CNS. Mutations in the gene encoding Nogo-A or abnormalities in Nogo-A expression are linked to neuropsychiatric disorders such as schizophrenia. The present study assesses the impact of constitutively reduced expression of Nogo-A on place navigation in a novel transgenic rat model. Two spatial paradigms were used: (1) A battery of tests in the Carousel maze requiring continuous processing of spatial information with increasing demands for the segregation of reference frames and behavioral flexibility and (2) a delayed-matching-to-place version of the Morris water maze (MWM), which requires place navigation and is sensitive to deficits in one-trial-encoded place representation. The Carousel maze testing revealed a subtle but significant impairment in management of reference frames. Matching-to-place learning in the Morris water maze was unaffected, suggesting an intact representation of an unmarked goal. Our results show that Nogo-A deficiency leads to cognitive deficit in processing of the reference frames. Such a deficit may be the result of neuro-developmental alterations resulting from Nogo-A deficiency.

Nogo-A-deficient Transgenic Rats Show Deficits in Higher Cognitive Functions, Decreased Anxiety, and Altered Circadian Activity Patterns.

Decreased levels of Nogo-A-dependent signaling have been shown to affect behavior and cognitive functions. In Nogo-A knockout and knockdown laboratory rodents, behavioral alterations were observed, possibly corresponding with human neuropsychiatric diseases of neurodevelopmental origin, particularly schizophrenia. This study offers further insight into behavioral manifestations of Nogo-A knockdown in laboratory rats, focusing on spatial and non-spatial cognition, anxiety levels, circadian rhythmicity, and activity patterns. Demonstrated is an impairment of cognitive functions and behavioral flexibility in a spatial active avoidance task, while non-spatial memory in a step-through avoidance task was spared. No signs of anhedonia, typical for schizophrenic patients, were observed in the animals. Some measures indicated lower anxiety levels in the Nogo-A-deficient group. Circadian rhythmicity in locomotor activity was preserved in the Nogo-A knockout rats and their circadian period (tau) did not differ from controls. However, daily activity patterns were slightly altered in the knockdown animals. We conclude that a reduction of Nogo-A levels induces changes in CNS development, manifested as subtle alterations in cognitive functions, emotionality, and activity patterns.

Two learning tasks provide evidence for disrupted behavioural flexibility in an animal model of schizophrenia-like behaviour induced by acute MK-801: a dose-response study.

Schizophrenia is a chronic and devastating illness. Exact causes of the disease remain elusive; however, neurodevelopmental changes in the brain glutamate system are recognized to play an important role. Several animal models of the disease are induced by a systemic blockade of N-methyl-d-aspartate (NMDA) receptors. This study examined the animal model of schizophrenia-like behaviours induced by acute treatment with MK-801, a non-competitive NMDA-receptor antagonist. Behavioural flexibility is an ability to adapt to the changes in environment, and schizophrenia is often accompanied by its decrease. The study tested the effect of MK-801 on behavioural flexibility in an active place avoidance task and the Morris water maze (MWM). Flexibility was tested under reversal conditions, i.e., after changing the location of the target. Each spatial task addressed different functions; continuous coordinate-frame segregation was present in the active place avoidance and precise place representation in the MWM. Results showed that reversal was altered in both tasks by MK-801 at doses of 0.10-0.15 mgkg(-1). Some impairment was observed in the active place avoidance task at 0.08 mgkg(-1). Swimming towards a visible platform was impaired only by the highest dose (0.15 mgkg(-1)). The results demonstrate that a significant impairment of behavioural flexibility accompanies this acute animal model of schizophrenia-like behaviours, and that active place avoidance had higher sensitivity for such deficits than the MWM. This suggests the usefulness of the reversal paradigm in both tasks for examining novel drugs with antipsychotic and procognitive actions.

Synergistic effects of dopamine D2-like receptor antagonist sulpiride and ß-blocker propranolol on learning in the carousel maze, a dry-land spatial navigation task.

Spatial navigation attracts the attention of neuroscientists as an animal analogue of human declarative memory. The Carousel maze is a dry-land navigational paradigm, which proved to be useful in studying neurobiological substrates of learning. The task involves avoidance of a stable sector on a rotating arena and is highly dependent upon the hippocampus. The present study aims at testing hypothesis that sulpiride (a centrally-active dopamine D2-like receptor antagonist) and propranolol (a beta-blocker) impair spatial learning in the Carousel maze after combined systemic administration. These doses were previously shown to be subthreshold in this task. Results showed that both substances affected behavior and significantly potentiated their negative effects on spatial learning. This suggests central interaction of both types of receptors in influencing acquisition of this dynamic-environment task.

Combined administration of alpha1-adrenoceptor antagonist prazosin and beta-blocker propranolol impairs spatial avoidance learning on a dry arena.

Spatial learning is a widely studied type of animal behavior often considered as a model of higher human cognitive functions. Noradrenergic receptors play a modulatory role in many nerve functions, including vigilance, attention, reward, learning and memory. The present study aimed at studying the effects of separate or combined systemic administration of the alpha1-adrenergic antagonist prazosin (1 and 2 mg/kg) and beta-blocker propranolol (5 and 20 mg/kg) on the hippocampus-dependent learning in the active allothetic place avoidance (AAPA) task. Both centrally active drugs impaired spatial learning when administered together, exerting no effect in separate applications. Locomotion was impaired only in a combined application of higher doses of both drugs (2 mg/kg prazosin and 20 mg/kg propranolol). These results suggest an in vivo interaction between these two types of receptors in spatial navigation regulation.