The Nitric Oxide Donor SIN-1-Produced Panic-Like Behaviour And Fear-Induced Antinociception Are Modulated By NMDA Receptors In The Anterior Hypothalamus.

BACKGROUND: An excitatory imbalance in the hypothalamus of rodents caused by local chemical stimulation elicits fear-related defensive reactions such as escape and freezing. In addition, these panic attack-like defensive reactions induced by hypothalamic neurons may cause antinociception. However, there is a shortage of studies showing the participation of the anterior hypothalamic nucleus in these adaptive defensive mechanisms. Nitric oxide (NO) donors have been shown to evoke fear-related defensive responses when microinjected into paralimbic and limbic structures, and this excitatory neuromodulation can recruit the glutamatergic system. AIMS: The aim of this work was to investigate the influence of the glutamatergic system in the nitrergic effects on fear-related defensive responses organised by anterior hypothalamic neurons. METHODS: The present study evaluates the effects of the molsidomine active metabolite SIN-1 NO donor administered into the anterior hypothalamus (AH) of mice at different concentrations (75, 150 and 300 nmol/0.1 µL). Then, we investigated the effects of pre-treatment of the AH with AP-7 (an N-methyl-d-aspartate (NMDA) receptor-selective antagonist; 0.02, 0.2 and 2 nmol/0.1 µL) on the behavioural and antinociceptive effects provoked by AH chemical stimulation with SIN-1 microinjections. RESULTS: The 300 nmol dose of SIN-1 was the most effective at causing panic-like defensive behaviours followed by a significant antinociceptive response. In addition, both of these effects were attenuated or inhibited by AH pre-treatment with AP-7. CONCLUSIONS: These findings suggest that the panicogenic and antinociceptive effects evoked by intra-AH microinjections of SIN-1 depend on NMDA receptor activation.

NOC-9, a selective nitric oxide donor, induces flight reactions in the dorsolateral periaqueductal gray of rats by activating soluble guanylate cyclase.

Previous studies have showed that SIN-1, a nitric oxide (NO) donor, injected into the dorsolateral column of the periaqueductal gray (dlPAG) induces flight reactions. This drug, however, can also produce peroxynitrite, which may interfere in this effect. In addition, it is also unknown if this effect is mediated by local activation of soluble guanylate cyclase (sGC). The aims of this study, therefore, were (1) to investigate if NOC-9 (6-(2-Hydroxy-1-methyl-2-nitrosohydrazino)-N-methyl-1-hexanamine), a NO donor that does not produce peroxynitrite, would produce flight reactions after intra-dlPAG administration similar to those induced by SIN-1; (2) to verify if these responses could be prevented by local injection of a selective guanylate cyclase inhibitor (ODQ). Male Wistar rats (n=5-12) with cannulae aimed at the dlPAG received injections of TRIS (pH 10.0, 0.5 microl), NOC-9 (75 and 150 nmol), saline or SIN-1 (200 nmol) and were placed in an open arena for 10 min. In a subsequent experiment animals (n=7-8) were pretreated with ODQ (1 nmol/0.5 microl) before receiving NOC-9 150 nmol. NOC-9 induced a significant dose-dependent increase in flight reactions in the first minute after injection (% of animals displaying flight: vehicle=0%, NOC 75=67%, NOC 150=75%). SIN-1 had a similar effect (100% of animals showing flight) but the effects lasted longer (10 min) than those of NOC-9. The effect of NOC-9 (150 nmol) was prevented by pretreatment with ODQ (% of animals displaying flight: vehicle+NOC 150=71%, ODQ+NOC 150=37%). The results suggest that NO donors injected into the dlPAG induce defensive responses that are not mediated by secondary peroxynitrite production. Moreover, they also indicate that these defensive responses depend on activation of local sGC. The data strengthen the proposal that NO can modulate defensive reactions in the dlPAG.

The effects of intraspinal L-NOARG or SIN-1 on the control by descending pathways of incisional pain in rats.

The modulation by spinal nitric oxide (NO) of descending pathways travelling through the dorsal lateral funiculus (DLF) is a mechanism proposed for the antinociceptive effects of drugs that changes the NO metabolism. In this study we confirm that a surgical incision in the mid-plantar hind paw of rats reduces the threshold to mechanical stimulation with von Frey filaments. The incisional pain was further increased in rats with ipsilateral DLF lesion. Intrathecal L-NOARG (50-300 microg), or SIN-1 (0.1-5.0 microg) reduced, while SIN-1 (10 and 20 microg) intensified the incisional pain in rats with sham or effective lesion of the DLF. Stimulation of the dorsal raphe (DRN) or anterior pretectal (APtN) nuclei with stepwise increased electrical currents (7, 14, 21, 28 and 35 microA r.m.s.) produced a current-related reduction of the incisional pain. These nuclei activate pain inhibitory pathways that descend to the spinal cord mainly through the DLF. Intrathecal SIN-1 (5 microg) reduced, SIN-1 (20 microg) decreased and L-NOARG (150 microg) did not change the EC50 for the DRN or APtN stimulation-induced reduction of incisional pain. We conclude that the antinociceptive effects of L-NOARG or low doses of SIN-1 are independent on the activity of descending pain control pathways travelling via the DLF, but the antinociceptive effect of stimulating electrically the DRN or APtN can be summated to the effect of low dose of SIN-1 or overcome by the high dose of SIN-1.

Benzodiazepine receptor and serotonin 2A receptor modulate the aversive-like effects of nitric oxide in the dorsolateral periaqueductal gray of rats.

RATIONALE: Escape reactions induced by electrical stimulation of the dorsolateral periaqueductal gray (dlPAG) are inhibited by local administration of benzodiazepine (BZ) or serotonin (5-HT) receptor agonists. Nitric oxide (NO) is a gas messenger that may mediate aversive behaviors. NO donors injected into the dlPAG induce escape reactions. OBJECTIVES: To test the hypothesis that the escape reactions induced by a NO donor in the dlPAG would be attenuated by pre-treatment with BZ-receptor or 5-HT-receptor agonists. METHODS: Male Wistar rats with cannulae aimed at the dlPAG received microinjections of vehicle (0.2 microl), the BZ midazolam maleate (80 nmol), the 5-HT(1A)-receptor agonist 8-OH-DPAT (8 nmol or 16 nmol) or the 5-HT(2A/2C)-receptor agonist DOI (16 nmol) 10 min before the administration of the NO donor SIN-1 (150 nmol). Behavioral observation took place immediately after the last injection in an open arena over a 10-min period. RESULTS: SIN-1 induced escape reactions characterized by running and jumps. Pre-treatment with DOI, but not 8-OH-DPAT, partially inhibited the effects of SIN-1. Pre-treatment with midazolam maleate, however, completely prevented the effects of the NO donor. CONCLUSION: The results suggest that the aversive-like effects of NO donor in the dlPAG may be modulated by the BZ and 5-HT(2A/2C) receptors.

Opposite nociceptive effects of the arginine/NO/cGMP pathway stimulation in dermal and subcutaneous tissues.

1. Nitric oxide has been described either as pronociceptive or antinociceptive. In this investigation, using an electronic pressure-metre, the intradermal and the subcutaneous effects of prostaglandin E(2) (PGE(2)) and agents that mimic or inhibit the arginine/NO/cGMP pathway were compared. 2. The hypernociceptive effect of the intradermal injection of PGE(2) (100 ng) was immediate, peaking within 15-30 min and returning to basal values in 45-60 min. The subcutaneous injection of PGE(2) induced a hypernociception with a delayed peak (3 h) plateauing for 4-6 h. 3. Intradermal administration of 3-morpholino-sydnonimine-hydrochloride (SIN-1) enhanced, while its subcutaneous administration inhibited, subcutaneous hypernociception induced by PGE(2). This inhibition was prevented by ODQ (8 micro g) but not by NG-monomethyl-L-arginine (L-NMMA) (50 micro g). 4. Intradermal but not subcutaneous administration of L-arginine (1-100 micro g), SIN-1 (1-100 micro g) and dibutyrylguanosine 3':5'-cyclic monophosphate (db cGMP) (0.1-100 micro g) induced an early (15-30 min) dose-dependent hypernociceptive effect. Intradermal pretreatment with NG-monomethyl-L-arginine (L-NMMA; 50 micro g) inhibited the hypernociception induced by L-Arg (10 micro g), but not that induced by SIN-1 (10 micro g) or db cGMP (10 micro g). 5. Intradermal injection of ODQ (8 micro g) antagonized the hypernociception induced by L-arginine and SIN-1, but not that induced by db cGMP. 6. Considering (a) the different time course of intradermal and subcutaneous PGE(2)-induced hypernociception, (b) the opposite nociceptive effect of intradermal and subcutaneous administration of SIN-1 (db cGMP) as well as the arginine/NO/cGMP pathway, the existence of different subsets of nociceptive primary sensory neurons in which the arginine/NO/cGMP pathway plays opposing roles is suggested. This hypothesis would explain the apparent contradictory observations described in the literature.