Elsevier

Neuroscience

Volume 91, Issue 1, June 1999, Pages 211-219
Neuroscience

Corticosterone and phenytoin reduce neuronal nitric oxide synthase messenger RNA expression in rat hippocampus

https://doi.org/10.1016/S0306-4522(98)00615-0Get rights and content

Abstract

The production and release of the corticosteroids, namely the glucocorticoids and the mineralocorticoids, are regulated by various stimuli, including stress. Previous studies from our laboratory have shown that chronic exposure to stress or to stress levels of glucocorticoids produces atrophy of the apical dendrites of CA3 pyramidal neurons in the hippocampus. This stress-induced dendritic remodeling is blocked by the anti-epileptic drug phenytoin, which suppresses glutamate release, and also by N-methyl-d-aspartate receptor antagonists. These results suggest an interaction between glucocorticoids and excitatory amino acids in the development of stress-induced atrophy of CA3 pyramidal neurons. Since nitric oxide is proposed to play an important role in mediating both the physiological and pathophysiological actions of excitatory amino acids, we examined the regulation of neuronal nitric oxide synthase messenger RNA expression by corticosterone and phenytoin in the rat hippocampus. The expression of neuronal nitric oxide synthase messenger RNA in hippocampal pyramidal neurons and granule neurons of the dentate gyrus was unaffected by 21-day administration of corticosterone (40 mg/kg), phenytoin (40 mg/kg) or the combination of corticosterone and phenytoin. However, in hippocampal interneurons, corticosterone/phenytoin co-administration led to a significant reduction in neuronal nitric oxide synthase messenger RNA levels when compared with vehicle controls.

These results suggest that, during exposure to stress levels of corticosterone, phenytoin inhibits glucocorticoid-induced atrophy of CA3 pyramidal neurons by reducing neuronal nitric oxide synthase expression in hippocampal interneurons. Moreover, these results may provide another example of synaptic plasticity in the hippocampus mediated by nitric oxide synthase.

Section snippets

Experimental animals

Adult, male Sprague–Dawley rats from Charles River Laboratories (Wilmington, MA), weighing 225–250 g at the beginning of the study, were housed under a 12-h/12-h light–dark cycle. Animals were maintained in a temperature-controlled room with ad libitum access to food and water. Animals were housed in accordance with all guidelines and regulations of The Rockefeller University Animal Care and Use Committee. Rats were divided into four groups. Group 1 received corticosterone (40 mg/kg) dissolved in

Characterization of neuronal nitric oxide synthase riboprobe

In order to examine the underlying molecular mechanisms involved in glucocorticoid-induced neuronal atrophy of CA3 pyramidal neurons, rats were administered stress levels of corticosterone (40 mg/kg) or phenytoin (40 mg/kg), or were co-administered both corticosterone and phenytoin for 21 days. Vehicle-injected rats served as controls. Following this 21-day treatment paradigm, in situ hybridization histochemistry for nNOS was performed to determine the regulation of this enzyme during

Stress, glucocorticoids and hippocampal neuronal remodeling

Previous studies from our laboratory have shown that 21-day restraint stress60 or 21-day administration of stress levels of glucocorticoids63 produces atrophy of CA3 pyramidal cell apical dendrites, an effect which requires an interaction between glucocorticoids and glutamate.33., 59. In an attempt to determine the underlying molecular events which contribute to the morphological changes produced by glucocorticoids, we examined the regulation of nNOS mRNA expression under conditions which

Conclusions

In summary, these results confirm the expression of nNOS mRNA in pyramidal neurons of the rat hippocampus, as well as in granule neurons of the dentate gyrus and hippocampal interneurons. In addition, nNOS mRNA expression in hippocampal pyramidal neurons and granule neurons of the dentate gyrus is not affected by 21-day administration of corticosterone or phenytoin, or co-administration of corticosterone and phenytoin. However, expression of nNOS mRNA expression is significantly reduced in

Acknowledgements

We would like to thank Dr Tsutomu Oguri for graciously providing the nNOS riboprobe. We would also like to thank Dr Helen Chao, Dr Louis Lucas, Dr Ana Maria Magariños and Dr Nick Hastings for helpful comments and discussions. This work was supported by NIH grant numbers DK09443 (L.P.R.), GM07524-19 (C.R.M.) and MH42156 (B.S.M.).

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