摘要
We have previously reported,based on systemic studies,that multiple opioid receptors(μ,δandκ) modulate nociceptive and non-nociceptive inputs in the superficial and the deeper dorsal horn of the medulla(trigeminal nucleus caudalis).The effects of iontophoretically applied receptor-selective opioid agonists have not been investigated previously either on the natural stimuli-evoked or the N-methyl-d-aspartate (NMDA)-evoked responses of physiologically characterized neurons in the superficial and the deeper dorsal born of the medulla.The present study was, therefore, designed to investigate the role of mu(DAMGO) and delta(DPDPE)opioid receptor selective agonists in modulating the NMDA-evoked responses of neurons in the trigeminal nucleus caudalis. Extracellular single unit recordings were made with the central barrel of a seven barreled microelectrode in rats anesthetized with urethane (1. 5g/kg, i. p.).The other barrels contained freshly made solutions of[D-Ala2, N-Me-Phe4, Gly5-ol] enkephalin (DAMGO, 25mmol/L, pH 4. 5 ),[D-pen2.5]enkephalin (DPDPE, 10mmol/L,pH4.5 ),NMDA(50mmol/L,pH8. 2), DL-2-Amino-5-phosphonovaleri acid (AP-5, 50 mmol/L,pH 8.0),naloxone hydrochloride (50 mmol/L, PH 4. 5),and NaCl for current balancing. Neurons were characterized nociceptive specific (NS),wide dynamic range (WDR), low threshold (LTH)using natural stimuli (brush,pressure, pinch,squeeze, heat). Opioids were ejected with positive current whereas NMDA and AP-5 were ejected with negative current. DAMGO(40～120nA)nad DPDPE (40～80nA) primarily produced reduction in the NMDA(15～90nA,cycle) evoked responses of NS, WDR,and LTH neurons in the superficial and the deeper dorsal horn of the medulla.However,excitatory or biphasic effects were also observed. It is concluded that mu and delta opioid receptor selective agonists produce modulation of the NMDA-evoked responses of nociceptive and non-nociceptive neurons in the medullary dorsal horn.
We have previously reported,based on systemic studies,that multiple opioid receptors(μ,δandκ) modulate nociceptive and non-nociceptive inputs in the superficial and the deeper dorsal horn of the medulla(trigeminal nucleus caudalis).The effects of iontophoretically applied receptor-selective opioid agonists have not been investigated previously either on the natural stimuli-evoked or the N-methyl-d-aspartate (NMDA)-evoked responses of physiologically characterized neurons in the superficial and the deeper dorsal born of the medulla.The present study was, therefore, designed to investigate the role of mu(DAMGO) and delta(DPDPE)opioid receptor selective agonists in modulating the NMDA-evoked responses of neurons in the trigeminal nucleus caudalis. Extracellular single unit recordings were made with the central barrel of a seven barreled microelectrode in rats anesthetized with urethane (1. 5g/kg, i. p.).The other barrels contained freshly made solutions of[D-Ala2, N-Me-Phe4, Gly5-ol] enkephalin (DAMGO, 25mmol/L, pH 4. 5 ),[D-pen2.5]enkephalin (DPDPE, 10mmol/L,pH4.5 ),NMDA(50mmol/L,pH8. 2), DL-2-Amino-5-phosphonovaleri acid (AP-5, 50 mmol/L,pH 8.0),naloxone hydrochloride (50 mmol/L, PH 4. 5),and NaCl for current balancing. Neurons were characterized nociceptive specific (NS),wide dynamic range (WDR), low threshold (LTH)using natural stimuli (brush,pressure, pinch,squeeze, heat). Opioids were ejected with positive current whereas NMDA and AP-5 were ejected with negative current. DAMGO(40～120nA)nad DPDPE (40～80nA) primarily produced reduction in the NMDA(15～90nA,cycle) evoked responses of NS, WDR,and LTH neurons in the superficial and the deeper dorsal horn of the medulla.However,excitatory or biphasic effects were also observed. It is concluded that mu and delta opioid receptor selective agonists produce modulation of the NMDA-evoked responses of nociceptive and non-nociceptive neurons in the medullary dorsal horn.
