Blockade of NMDA receptors and nitric oxide synthesis in the dorsolateral periaqueductal gray attenuates behavioral and cellular responses of rats exposed to a live predator

Abstract

Innate fear stimulus induces activation of neurons containing the neuronal nitric oxide synthase enzyme (nNOS) in defensive-related brain regions such as the dorsolateral periaqueductal gray (dlPAG). Intra-dlPAG administration of nitric oxide synthase (NOS) inhibitors and glutamate antagonists induce anxiolytic-like responses. We investigated the involvement of nitric oxide (NO) and glutamate neurotransmission in defensive reactions modulated by dlPAG. We tested if intra-dlPAG injections of the selective nNOS inhibitor, N-propyl-L-arginine (NP), or the glutamate antagonist, AP7 (2-amino-7-phosphonoheptanoic acid), would attenuate behavioral responses and cellular activation induced by predator exposure (cat). Fos-like immunoreactivity (FLI) was used as a marker of neuronal functional activation, whereas nNOS immunohistochemistry was used to identify NOS neurons. Cat exposure induced fear responses and an increase of FLI in the dlPAG and dorsal premammillary nucleus (PMd). NP and AP7 attenuated the cat-induced behavioral responses. Whereas NP tended to attenuate FLI in the dlPAG, AP7 induced a significant reduction in cellular activation of this region. The latter drug, however, increased FLI and double-labeled cells in the PMd. Cellular activation of this region was significantly correlated with time spent near the cat (r = 0.7597 and 0.6057 for FLI and double-labeled cells). These results suggest that glutamate/NO-mediated neurotransmission in the dlPAG plays an important role in responses elicit by predator exposure. Blocking these neurotransmitter systems in this brain area impairs defensive responses. The longer time spent near the predator that follows AP7 effect could lead to an increased cellular activation of the PMd, a more rostral brain area that has also been related to defensive responses.

Neuronal NOS Inhibitor and Conventional Antidepressant Drugs Attenuate Stress-induced Fos Expression in Overlapping Brain Regions

“…The identification method of stained cells was similar to that described in previous studies (Aguiar and Guimaraes 2009;Lino-de-Oliveira et al 2001). The number of FLI was counted from a fixed area size with the help of a computerized image analysis system (Image-Pro Plus, Media Cybernetics, Silver Spring, MD, USA).…”

“…Coronal sections (40 lm) were obtained in duplicate in a cryostat. The sections were processed for c-Fos immunohistochemistry as previously described (Aguiar and Guimaraes 2009;de Oliveira et al 2000b). In brief, tissue sections were washed and incubated overnight at room temperature with rabbit IgG (1/1000 into TBS, sc 52, Santa Cruz Biotechnology Inc., Santa Cruz, CA, USA), which was raised against an amino-acid sequence of the N-terminal region of the peptide and specifically recognizes Fos.…”

Brain Pathways Involved in the Modulatory Effects of Noradrenaline in Lateral Septal Area on Cardiovascular Responses

“…Coronal sections (40 lm) were obtained in duplicate in a cryostat. After this, the sections were processed for c-Fos immunohistochemistry as previously described (Aguiar and Guimaraes 2009;Beijamini and Guimaraes 2006). Briefly, tissue sections were washed and incubated overnight at room temperature with rabbit IgG (1/1,000 into TBS 0.01 M, sc 52, Santa Cruz Biotechnology Inc., Santa Cruz, CA, USA), which was raised against an amino-acid sequence of the N-terminal region of the peptide an specifically recognizes c-Fos.…”

“…The identification method of stained cells was similar to that described in previous works (Aguiar and Guimaraes 2009;Lino-de-Oliveira et al 2001). The number of FLI was counted with the help of a computerized image analysis system (Image-Pro Plus, Media Cybernetics, Silver Spring, MD, USA).…”

The endocannabinoid, endovanilloid and nitrergic systems could interact in the rat dorsolateral periaqueductal gray matter to control anxiety-like behaviors

“…In the brain, NO has been shown to mediate synaptic plasticity and facilitate defensive responses [26,27,28]. In this sense, the present study evaluated the hypothesis that high and ineffective doses of AEA lose its anxiolytic-like effects by facilitating the release of NO in the dlPAG, probably via activation of TRPV 1 receptors.…”