The role of hippocampal nitric oxide (NO) on learning and immediate, short- and long-term memory retrieval in inhibitory avoidance task in male adult rats

Effects of intrahippocampal L-NAME treatment on the behavioral long-term potentiation in dentate gyrus

Using a combination of electrophysiological recordings, behavioral tests and local pharmacological administration in hippocampus, we investigated in the present study the effects of nitric oxide (NO) synthase inhibitor N-nitro-l-arginine methyl ester (l-NAME) on the behavioral long-term potentiation (LTP) and maze learning performance in freely moving rats. The results showed as follows: (1) intrahippocampal l-NAME administration led to a defect in maze learning performance of the animals; (2) l-NAME treatment also substantially impaired the induction of the behavioral LTP in perforant pathway to dentate gyrus (PP-DG) pathway induced by maze learning task, while it had no significant effects on basic synaptic transmission in PP-DG pathway; Collectively, these results indicate that NO synthesis may be critical for the behavioral LTP in PP-DG pathway and maze learning performance.

Correlation between hippocampal levels of neural, epithelial and inducible NOS and spatial learning skills in rats

In the present study, to better understand the role of different nitric oxide synthase (NOS) isoforms in hippocampus-dependent forms of learning, we examined the expression of neural, endothelial, and inducible NOS in the hippocampus of young-adult rats classified as "poor" and "good" learners on the basis of their performance in the partially baited 12-arm radial maze. Taking into consideration strain-dependent differences in learning skills and NOS expression, experiments were performed on two different lines of laboratory rats: the inbred Wistar (W) and the outcrossed Wistar/Spraque-Dawley (W/S) line. The hippocampal levels of NOS proteins were assessed by Western Blotting. In the present study, genetically more homogenous W rats showed a slower rate of learning compared to the genetically less homogenous outcrossed W/S rats. The deficient performance in the W rat group compared to outcrossed W/S rats, and in "poor" learners of both groups compared to "good" learners was due to a higher percentage of reference memory errors. The overall NOS levels were significantly higher in W group compared to outcrossed W/S rats. In both rat lines, the rate of learning positively correlated with hippocampal levels of nNOS and negatively correlated with iNOS levels. Hippocampal eNOS levels correlated negatively with animals' performance but only in the W rats. These results suggest that all 3 NOS isoforms are implemented but play different roles in neural signaling.

A functional promoter polymorphism of neuronal nitric oxide synthase moderates prefrontal functioning in schizophrenia

Cognitive deficits in tasks involving the prefrontal cortex such as working memory or verbal fluency are a key component of schizophrenia. This led to the hypofrontality hypothesis of schizophrenia, which is widely accepted even though molecular underpinnings are elusive. While disturbances of glutamatergic neurotransmission might play a role, other components have rarely been investigated. Recently, the promoter region of nitric oxide (NO) synthase-I (NOS-I, encoded by the gene NOS1), impacting on prefrontal glutamate transmission, has repeatedly been associated with schizophrenia. We thus tested whether an associated schizophrenia risk variant (rs41279104), leading to reduced expression of the transcript, influences prefrontal brain functioning. Forty-three patients suffering from chronic schizophrenia and 44 controls were genotyped for NOS1 rs41279104 and investigated by means of functional near-infrared spectroscopy (fNIRS), while completing a working-memory task (2-back test) and a verbal fluency test (VFT). After matching for genotype, behavioural and brain activation data of 26 patients and 28 comparable controls were correlated to rs41279104. Healthy controls showed significant activation of large parts of the lateral prefrontal cortex during both tasks, whereas task-related changes in oxygenation were significantly reduced in patients. Schizophrenia patients also performed worse in both tasks. The NOS1 schizophrenia risk genotype rs41279104 AA/AG was associated with slower reaction time in the 2-back task, as well as with reduced right-hemispheric activation of the frontal cortex for VFT in patients only. Our fNIRS data extend previous studies suggesting disturbed prefrontal functioning in schizophrenia and suggest that genetic variation of NOS1 has a role in cognitive dysfunction, probably by mediating glutamatergic tone.

Mitochondria and neuroplasticity

The production of neurons from neural progenitor cells, the growth of axons and dendrites and the formation and reorganization of synapses are examples of neuroplasticity. These processes are regulated by cell-autonomous and intercellular (paracrine and endocrine) programs that mediate responses of neural cells to environmental input. Mitochondria are highly mobile and move within and between subcellular compartments involved in neuroplasticity (synaptic terminals, dendrites, cell body and the axon). By generating energy (ATP and NAD(+)), and regulating subcellular Ca(2+) and redox homoeostasis, mitochondria may play important roles in controlling fundamental processes in neuroplasticity, including neural differentiation, neurite outgrowth, neurotransmitter release and dendritic remodelling. Particularly intriguing is emerging data suggesting that mitochondria emit molecular signals (e.g. reactive oxygen species, proteins and lipid mediators) that can act locally or travel to distant targets including the nucleus. Disturbances in mitochondrial functions and signalling may play roles in impaired neuroplasticity and neuronal degeneration in Alzheimer's disease, Parkinson's disease, psychiatric disorders and stroke.

Role of ventral hippocampal nitric oxide/cGMP pathway in anxiety-related behaviors in rats submitted to the elevated T-maze

The L-arginine/nitric oxide (NO)/cGMP pathways have been implicated in the control of a variety of physiological mechanisms and are believed to participate in the modulation of anxiety in the CNS. The aim of this study was to investigate the effects of N(G)-nitro-L-arginine-methyl-ester (L-NAME), a non-selective inhibitor of NO synthase (NOS); 7-nitroindazole (7-NI), a preferential inhibitor of neuronal NOS; and sodium nitroprusside (SNP), an NO donor, administered into the ventral hippocampus (VH) of rats submitted to the elevated T-maze (ETM). The ETM, an animal model derived from the elevated plus-maze, allows the measurement of two defensive behavioral responses in the same rat: inhibitory avoidance and escape. Results showed that L-NAME and 7-NI impaired the acquisition of inhibitory avoidance and prolonged escape latency in the ETM, suggesting an anxiolytic-like and panicolytic-like effect, respectively. SNP facilitated the acquisition of inhibitory avoidance without interfering with escape performance, suggesting an anxiogenic-like effect. Treatment with methylene blue did not alter per se any of the behavioral responses measured in the ETM, but blocked the effect promoted by SNP. Thus, altogether these results suggest that NO in the VH is critically involved in the modulation of defensive behavior of rats exposed to the ETM.