RESUMO
RATIONALE: Re-exposing an animal to an environment previously paired with an aversive stimulus evokes large alterations in behavioral and cardiovascular parameters. Dorsal hippocampus (dHC) receives important cholinergic inputs from the basal forebrain, and respective acetylcholine (ACh) levels are described to influence defensive behavior. Activation of muscarinic M1 and M3 receptors facilitates autonomic and behavioral responses along threats. Evidence show activation of cholinergic receptors promoting formation of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) in dHC. Altogether, the action of ACh and NO on conditioned responses appears to converge within dHC. OBJECTIVES: As answer about how ACh and NO interact to modulate defensive responses has so far been barely addressed, we aimed to shed additional light on this topic. METHODS: Male Wistar rats had guide cannula implanted into the dHC before being submitted to the contextual fear conditioning (3footshocks/085 mA/2 s). A catheter was implanted in the femoral artery the next day for cardiovascular recordings. Drugs were delivered into dHC 10 min before contextual re-exposure, which occurred 48 h after the conditioning procedure. RESULTS: Neostigmine (Neo) amplified the retrieval of conditioned responses. Neo effects (1 nmol) were prevented by the prior infusion of a M1-M3 antagonist (fumarate), a neuronal nitric oxide synthase inhibitor (NPLA), a NO scavenger (cPTIO), a guanylyl cyclase inhibitor (ODQ), and a NMDA antagonist (AP-7). Pretreatment with a selective M1 antagonist (pirenzepine) only prevented the increase in autonomic responses induced by Neo. CONCLUSION: The results show that modulation in the retrieval of contextual fear responses involves coordination of the dHC M1-M3/NO/cGMP/NMDA pathway.
Assuntos
N-Metilaspartato , Óxido Nítrico , Acetilcolina , Animais , Colinérgicos/farmacologia , Medo/fisiologia , Fumaratos/farmacologia , Guanosina Monofosfato/farmacologia , Guanilato Ciclase/metabolismo , Guanilato Ciclase/farmacologia , Hipocampo , Masculino , N-Metilaspartato/farmacologia , Neostigmina/farmacologia , Óxido Nítrico/metabolismo , Óxido Nítrico Sintase Tipo I/metabolismo , Pirenzepina/farmacologia , Ratos , Ratos Wistar , Receptores Colinérgicos/metabolismo , Receptores de N-Metil-D-Aspartato , Transmissão SinápticaRESUMO
Intracerebroventricular (icv) administration of leptin facilitates lordosis behavior in ad libitum-fed, estrogen-primed rats. The cellular mechanism involved in this response is unknown. The present study tested the hypothesis that the nitric oxide-guanylyl cyclase, cGMP-dependent protein kinase (PKG) pathway is involved in the facilitation of lordosis behavior induced by the central administration of leptin. We tested the importance of the nitric oxide/cGMP pathway for lordosis stimulation by either icv infusion of a nitric oxide synthase inhibitor (L-NAME) or a nitric oxide-dependent, soluble guanylyl cyclase inhibitor (ODQ) 30 min before leptin administration (1 µg). This dose of leptin reliably induced lordosis behavior in ovariectomized estradiol benzoate treated rats. The lordosis induced by leptin at 1 and 2h after infusion was significantly reduced by the previous injection of either L-NAME or by ODQ. Intracerebroventricular infusion of the PKG inhibitor (KT5823) 30 min before leptin infusion, also significantly inhibited the lordosis behavior induced by leptin at 1 and 2h after hormone administration. These data support the hypothesis that the nitric oxide/cGMP/PKG pathway is involved in the facilitation of lordosis by leptin in estrogen-primed female rats.
Assuntos
Proteínas Quinases Dependentes de GMP Cíclico/metabolismo , Leptina/administração & dosagem , Óxido Nítrico/metabolismo , Comportamento Sexual Animal , Animais , Carbazóis/farmacologia , Proteínas Quinases Dependentes de GMP Cíclico/antagonistas & inibidores , Feminino , Guanilato Ciclase/farmacologia , Leptina/farmacologia , NG-Nitroarginina Metil Éster/farmacologia , Óxido Nítrico/fisiologia , Ovariectomia , Postura , Ratos , Ratos Sprague-Dawley , Receptores Citoplasmáticos e Nucleares/farmacologia , Guanilil Ciclase SolúvelRESUMO
We have shown that the peripheral and spinal cord heme oxygenase (HO)-carbon monoxide (CO)-soluble guanylate cyclase-cGMP pathways play an important role in antinociception in the rat experimental formalin model. Our objective was to determine if there is synergism between peripheral (paw) and spinal HO-CO pathways in nociception. Rats were handled and adapted to the experimental environment for a few days before the formalin test, in which 50 microL of a 1% formalin was injected subcutaneously into the dorsal surface of the right hind paw. The animals were then observed for 1 h and the frequency of flinching behavior was taken to represent the nociceptive response. Thirty minutes before the test, rats were pretreated with intrathecal injections of the HO inhibitor, zinc deuteroporphyrin 2,4-bis glycol (ZnDPBG) or heme-lysinate, which is a substrate of the HO pathway. The paw treatments took place 20 min before the test. Low doses of ZnDPBG did not increase nociception, while a low heme-lysinate dose did not change flinching behavior after paw or spinal injections. Combined subactive spinal (50 nmol) and peripheral (40 nmol) low doses of ZnDPBG induced hypernociception (increase of 80% in the first and 25% in the second phase flinching), whereas combined spinal-peripheral heme-lysinate (50 and 30 nmol) led to second phase antinociception (40% reduction in flinching). These findings suggest a synergy between the peripheral and spinal HO-CO pathways. Local activation of the HO system probably regulates the nociception initiation in peripheral tissue and participates in buffering the emerging nociceptive signals at the peripheral and spinal sites of action. In short, an antinociceptive synergy exists between peripheral and spinal HO pathways, which may reduce the doses required and side effects.
Assuntos
Monóxido de Carbono/metabolismo , Guanilato Ciclase/administração & dosagem , Heme Oxigenase (Desciclizante)/metabolismo , Nociceptores/efeitos dos fármacos , Medição da Dor/efeitos dos fármacos , Receptores Citoplasmáticos e Nucleares/administração & dosagem , Medula Espinal/efeitos dos fármacos , Animais , Relação Dose-Resposta a Droga , Sinergismo Farmacológico , Guanilato Ciclase/farmacologia , Heme Oxigenase (Desciclizante)/efeitos dos fármacos , Injeções Espinhais , Masculino , Nociceptores/fisiologia , Ratos , Ratos Wistar , Transdução de Sinais , Guanilil Ciclase Solúvel , Medula Espinal/fisiologiaRESUMO
We have shown that the peripheral and spinal cord heme oxygenase (HO)-carbon monoxide (CO)-soluble guanylate cyclase-cGMP pathways play an important role in antinociception in the rat experimental formalin model. Our objective was to determine if there is synergism between peripheral (paw) and spinal HO-CO pathways in nociception. Rats were handled and adapted to the experimental environment for a few days before the formalin test, in which 50 µL of a 1 percent formalin was injected subcutaneously into the dorsal surface of the right hind paw. The animals were then observed for 1 h and the frequency of flinching behavior was taken to represent the nociceptive response. Thirty minutes before the test, rats were pretreated with intrathecal injections of the HO inhibitor, zinc deuteroporphyrin 2,4-bis glycol (ZnDPBG) or heme-lysinate, which is a substrate of the HO pathway. The paw treatments took place 20 min before the test. Low doses of ZnDPBG did not increase nociception, while a low heme-lysinate dose did not change flinching behavior after paw or spinal injections. Combined subactive spinal (50 nmol) and peripheral (40 nmol) low doses of ZnDPBG induced hypernociception (increase of 80 percent in the first and 25 percent in the second phase flinching), whereas combined spinal-peripheral heme-lysinate (50 and 30 nmol) led to second phase antinociception (40 percent reduction in flinching). These findings suggest a synergy between the peripheral and spinal HO-CO pathways. Local activation of the HO system probably regulates the nociception initiation in peripheral tissue and participates in buffering the emerging nociceptive signals at the peripheral and spinal sites of action. In short, an antinociceptive synergy exists between peripheral and spinal HO pathways, which may reduce the doses required and side effects.
Assuntos
Animais , Masculino , Ratos , Monóxido de Carbono/metabolismo , Guanilato Ciclase/administração & dosagem , Heme Oxigenase (Desciclizante)/metabolismo , Nociceptores/efeitos dos fármacos , Medição da Dor/efeitos dos fármacos , Receptores Citoplasmáticos e Nucleares/administração & dosagem , Medula Espinal/efeitos dos fármacos , Relação Dose-Resposta a Droga , Sinergismo Farmacológico , Guanilato Ciclase/farmacologia , Heme Oxigenase (Desciclizante)/efeitos dos fármacos , Injeções Espinhais , Nociceptores/fisiologia , Ratos Wistar , Transdução de Sinais , Medula Espinal/fisiologiaRESUMO
Previous data from our laboratory have indicated that nitric oxide (NO) acting at the presynaptic level increases the amplitude of muscular contraction (AMC) of the phrenic-diaphragm preparations isolated from indirectly stimulated rats, but, by acting at the postsynaptic level, it reduces the AMC when the preparations are directly stimulated. In the present study we investigated the effects induced by NO when tetanic frequencies of stimulation were applied to in vivo preparations (sciatic nerve-anterior tibial muscle of the cat). Intra-arterial injection of NO (0.75-1.5 mg/kg) induced a dose-dependent increase in the Wedensky inhibition produced by high frequencies of stimulation applied to the motor nerve. Intra-arterial administration of 7.2 micrograms/kg methylene blue did not produce any change in AMC at low frequencies of nerve stimulation (0.2 Hz), but antagonized the NO-induced Wedensky inhibition. The experimental data suggest that NO-induced Wedensky inhibition may be mediated by the guanylate cyclase-cGMP pathway.
Assuntos
Antídotos/farmacologia , Azul de Metileno/farmacologia , Contração Muscular/efeitos dos fármacos , Óxido Nítrico/farmacologia , Tetania/induzido quimicamente , Animais , Gatos , Estimulação Elétrica , Guanilato Ciclase/farmacologia , Músculo Esquelético/efeitos dos fármacos , Condução Nervosa/efeitos dos fármacos , Óxido Nítrico/efeitos adversosRESUMO
Previous data from our laboratory have indicated that nitric oxide (NO) acting at the presynaptic level increases the amplitude of muscular contraction (AMC) of the phrenic-diaphragm preparations isolated from indirectly stimulated rats, but, by acting at the postsynaptic level, it reduces the AMC when the preparations are directly stimulated. In the present study we investigated the effects induced by NO when tetanic frequencies of stimulation were applied to in vivo preparations (sciatic nerve-anterior tibial muscle of the cat). Intra-arterial injection of NO (0.75-1.5 mg/kg) induced a dose-dependent increase in the Wedensky inhibition produced by high frequencies of stimulation applied to the motor nerve. Intra-arterial administration of 7.2 mug/Kg methylene blue did not produce any change in AMC at low frequencies of nerve stimulation (0.22 Hz), but antagonized the NO-induced Wedensky inhibition. The experimental data suggest that NO-induced Wedensky inhibition may be mediated by the guanylate cyclase-cGMP pathway.