Peripheral tackykinin and excitatory amino acid receptors mediate hyperalgesia induced by Phoneutria nigriventer venom

Abstract

The generation of hyperalgesia by Phoneutria nigriventer venom was investigated in rats using the paw pressure test, through the intraplantar injection of the venom. Hyperalgesia was significantly inhibited by N-[2-(4-chlorophenyl) ethyl]-1,3,4,5-tetrahydro-7,8-dihydroxy-2H-2-benzazepine-2-carbothioamide (capsazepine), a vanilloid receptor antagonist, by the local administration of pGlu-Ala-Asp-Pro-Asn-Lys-Phe-Tyr-Pro (spiro-γ-lactam) Leu-Trp-NH₂ (GR82334) or of Phenyl-CO-Ala-Ala-d-Trp-Phe-d-Pro-Pro-Nle-NH₂ (GR94800), inhibitors of tachykinin NK₁ and NK₂ receptors, respectively, or by the local injection of dizocilpine (MK 801), (±)-2-amino-5-phosphonopentanoic acid ((±)-AP-5), or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), antagonists of NMDA and non-NMDA excitatory amino acid receptors. The correlation between hyperalgesia and the inflammatory response induced by the venom was also investigated. The venom-induced edematogenic response was not modified by the pharmacological treatments. These results suggest that hyperalgesia induced by P. nigriventer venom is mediated by stimulation of capsaicin-sensitive neurons, with activation of peripheral tachykinin NK₁ and NK₂ receptors and of both the NMDA and AMPA receptors. Distinct mechanisms are involved in the development of hyperalgesia and edema induced by the venom.

Introduction

The Phoneutria nigriventer spider represents the most important cause of arachnid envenomization in Brazil (Ministério da Saúde, 1998). The main local clinical manifestation of such envenomization is intense pain that may be followed by local swelling and erythema (Bucharetchi, 1992). The inflammatory response has usually been studied in rats and rabbits. The skin edema formation in rabbits is independent of the histamine and 5-hidroxytryptamine (5-HT, serotonin) components of the venom and is at least partially mediated by the tissue kallikrein–kinin system (Marangoni et al., 1993). In rats, the venom acts as a potent stimulant of capsaicin-sensitive sensory neurons (Costa et al., 1997), resulting in the local release of substance P and activation of tachykinin NK₁ receptors as well as activation of mast cells and release of biogenic amines Palframan et al., 1996, Costa et al., 2001 that act on post-capillary venules eliciting plasma extravasation and edema formation Palframan et al., 1996, Costa et al., 2001. Despite the clear involvement of neurogenic mechanisms in the inflammatory response induced by P. nigriventer venom, no information is available concerning the contribution of these mechanisms to the algogenic activity of this venom.

It was properly demonstrated that tachykinins and excitatory amino acids comprised the main neurotransmitters in pain transmission (reviewed in Yaksh, 1999); additionally to their central action, these neurotransmitters influence nociception in the periphery Carlton et al., 1995, Carlton et al., 1996, Carlton et al., 1998, Heppelmann and Pawlak, 1997, Kessler et al., 1992, Davidson et al., 1997, Prioleau et al., 1996. Tachykinins are released from both central and peripheral endings of primary afferent capsaicin-sensitive neurons Otsuka and Yoshioka, 1993, Holzer, 1988 and, when delivered from peripheral endings of primary sensory neurons, induce neurogenic inflammation (Holzer, 1998). This local response may contribute to the generation of pain. Furthermore, peripheral application of substance P sensitizes afferent neurons, causing painful states. The effect of substance P on these cells involves the activation of tachykinin NK₁ receptors, localized on peripheral terminals of unmyelinated axons Carlton et al., 1996, Heppelmann and Pawlak, 1997. Concerning the peripheral algogenic effect of excitatory amino acids, experimental findings have demonstrated that glutamate, through an action on NMDA and non-NMDA receptors, acts as mediator of inflammatory or thermal hyperalgesia Davidson et al., 1997, Jackson et al., 1995. The possibility of a peripheral action of glutamate on unmyelinated sensory axons was also supported by the demonstration that these sensory fibers immunostain for NMDA, AMPA or kainate receptors Carlton et al., 1995, Coggeshall and Carlton, 1998. Several lines of evidence indicate that, in the case of C fibers, glutamate coexists with substance P (De Biasi and Rustioni, 1988). These neurotransmitters interact synergistically for the pain frame Rusin et al., 1993, Liu et al., 1997, Dougherty et al., 1993, Dougherty and Willis, 1991, Ma and Woolf, 1995, Carlton et al., 1998; this synergism being important for the generation of central sensitization Dougherty et al., 1993, Ma and Woolf, 1995. Recently, Carlton et al. (1998) showed a similar interaction among glutamate and substance P in the periphery, suggesting that primary afferent neurons may be under the same control as are the neurons in the dorsal horn.

In the light of these observations, the aim of the present study was to investigate: (a) the hyperalgesic response induced by P. nigriventer spider venom; (b) the contribution of capsaicin-sensitive neurons to this phenomenon; (c) the involvement of peripheral tachykinin NK₁ and NK₂ receptors and peripheral NMDA and AMPA glutamate receptors in the hyperalgesic manifestation and (d) the possible correlation between hyperalgesia and edematogenic response induced by the venom.