A comparison of the effectiveness of intravenous morphine at attenuating the nociceptive responses of medullary dorsal horn and thalamic neurones.
In anaesthetized rats microelectrode recordings were made of single neurone activity in the medullary dorsal horn and in the thalamus. Ratemeter records were made of responses evoked by peripheral noxious stimuli. When consistent control responses had been obtained, morphine sulphate was administered by intravenous injection, and the total dose necessary to abolish or maximally attenuate nociceptive responses was recorded. For thalamic responses a mean dose of 0.7 +/- 0.18 mg/kg (mean +/- SEM, n = 16) was obtained, whereas for attenuation of medullary dorsal horn responses a mean dose of 2.5 +/- 0.72 mg/kg (mean +/- SEM, n = 13) was required. The greater sensitivity of the thalamic responses suggests that the effect of morphine at this site is not merely a consequence of a spinal action of the opiate and that an important component of the antinociceptive action is supraspinal.
D000818:Animals; D004553:Electric Conductivity; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000502:physiology*; D009020:Morphine / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology*; D009928:Organ Specificity; D051381:Rats; D013788:Thalamus / Q000187:drug effects / Q000502:physiology*
D009020:Morphine