Acute and delayed restraint stress-induced changes in nitric oxide producing neurons in limbic regions

• Published in: Neuroscience 2004, Vol.125 (4), p.981-993
• Main Authors: Echeverry, M.B, Guimarães, F.S, Del Bel, E.A
• Format: Article
• Language: English
• Subjects: amygdala; Animals; antinociception; Biological and medical sciences; entorhinal cortex; Enzyme Inhibitors - administration & dosage; Fundamental and applied biological sciences. Psychology; hippocampus; Immunohistochemistry; Injections, Intraventricular; Limbic System - physiology; Male; Microinjections; NADPH Dehydrogenase - metabolism; NADPH-diaphorase; Neurons - metabolism; NG-Nitroarginine Methyl Ester - administration & dosage; Nitric Oxide - metabolism; nitric oxide synthase; Nitric Oxide Synthase - metabolism; Nitric Oxide Synthase Type I; Pain - physiopathology; Rats; Rats, Wistar; Reaction Time; Restraint, Physical; Stress, Psychological - physiopathology; Vertebrates: nervous system and sense organs
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/j.neuroscience.2003.12.046

Rationale: Microinjection into the dentate gyrus of the hippocampus of N ω-nitro- l-arginine methyl ester hydrochloride ( l-NAME), a nitric oxide synthase (NOS) inhibitor, induces antinociceptive effect 5 days after a single restraint episode. The mechanisms of this stress-antinociceptive modulatory effect have not been investigated but may involve plastic changes in the hippocampal formation (HF). Objective: The objective of the present study was to investigate possible mechanisms of the stress-modulating effect on antinociception induced by NOS inhibition in the hippocampus. We analyzed the effects of restraint stress on neuronal NOS (nNOS) expression and nicotinamide adenine dinucleotide phosphate-diaphorase histochemical activity (NADPH-d) in the HF and related brain regions. Methods: Male Wistar rats ( n=6–11/group) were submitted to a single (acute stress) or repeated (5 days) episodes of 2-h restraint. Control animals remained in their home cages being all animals daily handled during this period. In the fifth day, animals received unilateral microinjection of l-NAME (150 nmol/0.2 μl) or saline (control) into the dentate gyrus of the dorsal hippocampus (DG). Immediately before and after drug microinjection tail-flick reflex latency or hotplate licking reaction was measured. Animals were killed i. immediately; ii. 5 days after acute stress; or iii. after repeated stress. NADPH-d and nNOS expression were quantified in the HF, caudate-putamen, secondary somatosensorial, entorhinal and piriform cortices and amygdaloid complex. Results: Five days after one or five restraint episodes l-NAME microinjection into the DG elicited antinociceptive effect (analysis of variance [ANOVA], P