RESUMO
Activation of muscarinic acetylcholine receptors (mAChRs) inhibits spinal nociceptive transmission by potentiation of GABAergic tone through M(2), M(3), and M(4) subtypes. To study the signaling mechanisms involved in this unique mAChR action, GABAergic spontaneous inhibitory postsynaptic currents (sIPSCs) of lamina II neurons were recorded using whole-cell patch clamp techniques in rat spinal cord slices. The mAChR agonist oxotremorine-M caused a profound increase in the frequency of GABAergic sIPSCs, which was abolished in the Ca(2+)-free solution. Inhibition of voltage-gated Ca(2+) channels with Cd(2+) and Ni(2+) largely reduced the effect of oxotremorine-M on sIPSCs. Blocking nonselective cation channels (NSCCs) with SKF96365 or 2-APB also largely attenuated the effect of oxotremorine-M. However, the KCNQ channel blocker XE991 and the adenylyl cyclase inhibitor MDL12330A had no significant effect on oxotremorine-M-induced increases in sIPSCs. Furthermore, the phosphoinositide-3-kinase (PI3K) inhibitor wortmannin or LY294002 significantly reduced the potentiating effect of oxotremorine-M on sIPSCs. In the spinal cord in which the M(3) subtype was specifically knocked down by intrathecal small interfering RNA (siRNA) treatment, SKF96365 and wortmannin still significantly attenuated the effect of oxotremorine-M. In contrast, SKF96365 and wortmannin both failed to alter the effect of oxotremorine-M on sIPSCs when the M(2)/M(4) mAChRs were blocked. Therefore, our study provides new evidence that activation of mAChRs increases synaptic GABA release through Ca(2+) influx and voltage-gated Ca(2+) channels. The PI3K-NSCC signaling cascade is primarily involved in the excitation of GABAergic interneurons by the M(2)/M(4) mAChRs in the spinal dorsal horn.
Assuntos
Potenciais Pós-Sinápticos Inibidores/fisiologia , Neurônios/fisiologia , Receptores Muscarínicos/fisiologia , Transdução de Sinais/fisiologia , Medula Espinal/citologia , Ácido gama-Aminobutírico/metabolismo , Animais , Antracenos/farmacologia , Biofísica , Cádmio/farmacologia , Cálcio/metabolismo , Interações Medicamentosas , Estimulação Elétrica/métodos , Inibidores Enzimáticos/farmacologia , Regulação da Expressão Gênica/efeitos dos fármacos , Regulação da Expressão Gênica/fisiologia , Técnicas In Vitro , Potenciais Pós-Sinápticos Inibidores/efeitos dos fármacos , Ativação do Canal Iônico/efeitos dos fármacos , Ativação do Canal Iônico/fisiologia , Masculino , Agonistas Muscarínicos/farmacologia , Inibição Neural/efeitos dos fármacos , Inibição Neural/fisiologia , Neurônios/efeitos dos fármacos , Níquel/farmacologia , Oxotremorina/análogos & derivados , Oxotremorina/farmacologia , Técnicas de Patch-Clamp/métodos , Bloqueadores dos Canais de Potássio/farmacologia , RNA Mensageiro/metabolismo , RNA Interferente Pequeno/farmacologia , Ratos , Ratos Sprague-Dawley , Receptores Muscarínicos/classificação , Receptores Muscarínicos/genética , Transdução de Sinais/efeitos dos fármacosRESUMO
Palivizumab is a new anti-RSV monoclonal antibody product indicated for the prevention of serious lower respiratory tract disease caused by RSV in pediatric patients at high risk of developing RSV disease ("Synagis," 1998). Palivizumab was evaluated in a single, large clinical trial (IMpact) (Connor et al., 1998). In this trial, RSV hospital admissions were reduced by 55% in children 24 months of age with BPD or in infants born prematurely (35 weeks gestation). Additionally, the severity of illness was also reduced as evidenced by a decrease in total days of RSV hospitalization and decreased incidence of RSV intensive care unit admissions. Palivizumab is expensive--with an estimated cost for a season ranging from $3,500-$10,700 per infant, depending on the child's weight and length of RSV season in the area where the child resides. Although palivizumab prophylaxis has been shown to reduce hospital admissions, the cost effectiveness of using this product needs to be formally evaluated. The AAP has provided guidance to determine the best candidates for RSV prophylaxis.
