Korean J Physiol Pharmacol.  1998 Dec;2(6):687-693.

Microinjection of glutamate into the amygdala modulates nociceptive and cardiovascular response in freely moving rats

• Ahn DK
• Kim YS
• Park JS

Abstract

This study was performed to examine the mean arterial pressure and nociceptive jaw opening reflex after microinjection of glutamate into the amygdala in freely moving rats, and to investigate the mechanisms of antinociceptive action of amygdala. Animals were anesthetized with pentobarbital sodium (40 mg/kg, ip). A stainless steel guide cannula (26 gauge) was implanted in the amygdala and lateral ventricle. Stimulating and recording electrodes were implanted into each of the incisor pulp and anterior digastric muscle. Electrodes were led subcutaneously to the miniature cranial connector sealed on the top of the skull with acrylic resin. After 48 hours of recovery from surgery, mean arterial pressure and digastric electromyogram (dEMG) were monitored in freely moving rats. Electrical shocks (200 musec duration, 0.5~2 mA intensity) were delivered at 0.5 Hz to the dental pulp every 2 minutes. After injection of 0.35 M glutamate into the amygdala, mean arterial pressure was increased by 8+/-2 mmHg and dEMG was suppressed to 71+/-5% of the control. Injection of 0.7 M glutamate elevated mean arterial pressure by 25+/-5 mmHg and suppressed dEMG to 20+/-7% of the control. The suppression of dEMG were maintained for 30 minutes. Naloxone, an opioid receptor antagonist, inhibited the suppression of dEMG elicited by amygdaloid injection of glutamate from 28+/-4 to 68+/-5% of the control. Methysergide, a serotonin receptor antagonist, also inhibited the suppression of dEMG from 33+/-5 to 79+/-4% of the control. However, phentolamine, an alpha-adrenergic receptor antagonist, did not affect the suppression of dEMG. These results suggest that the amygdala can modulate both cardiovascular and nociceptive responses and that the antinociception of amygdala seems to be attributed to an augmentation of descending inhibitory influences on nociceptive pathways via serotonergic and opioid pathways.

Keyword

Amygdala; Glutamate; Jaw opening reflex; Antinociception; Freely moving rats

MeSH Terms

Amygdala*
Animals
Arterial Pressure
Catheters
Dental Pulp
Electrodes
Glutamic Acid*
Incisor
Jaw
Lateral Ventricles
Methysergide
Microinjections*
Naloxone
Pentobarbital
Phentolamine
Rats*
Receptors, Opioid
Reflex
Serotonin
Shock
Skull
Stainless Steel
Glutamic Acid
Methysergide
Naloxone
Pentobarbital
Phentolamine
Receptors, Opioid
Serotonin
Stainless Steel