In rabbits provided with chronic intracerehroventricular cannula

CaCl_2 or MgC1_2 was injected intraventricularly (ivt) to increase the cerebral content of Ca

(++)

and Mg(++) and Mg

(++)

and CDTA

the cation chelator

was injected ivt to lower the cerebral content of cations including Ca(++)

and CDTA

the cation chelator

was injected ivt to lower the cerebral content of cations including Ca

(++)

and Mg(++) and Mg

(++)

to see its effect on the analgesia induced by electroacupuncture (EA) or by morphine. 1. The effect on EA analgesia: EA of 2-15Hz

1v

10 min was given to hind leg points Zusanli and Qunlun

10 rain after the ivt injection of one of the following chemicals: CaCl_2

MgCl_2 or CDTA in a dose of 0.5 μmol

or 50μl of normal saline as control. Nociception was tested by the latency of the head jerk induced by radiant heat applied on the skin over the snout. It was shown that EA analgesia found in CaCl_2 group(28±8%) was much lower than that of the saline control group(133±13%

p

<

0.001). A decrease in EA analgesia was also observed in rabbits injected with MgCl_2 (47±11% vs 123±15%

p

<

0.001). Ivt injection of the chelator CDTA

on the contrary

resulted in a potentiation of EA analgesia(CDTA group 164±15% vs saline group 104±19%

p

<

0.05). No significant chan- ges in pain threshold were seen when these chemicals were injected alone. The results indicate that Ca(++) to see its effect on the analgesia induced by electroacupuncture (EA) or by morphine. 1. The effect on EA analgesia: EA of 2-15Hz

1v

10 min was given to hind leg points Zusanli and Qunlun

10 rain after the ivt injection of one of the following chemicals: CaCl_2

MgCl_2 or CDTA in a dose of 0.5 μmol

or 50μl of normal saline as control. Nociception was tested by the latency of the head jerk induced by radiant heat applied on the skin over the snout. It was shown that EA analgesia found in CaCl_2 group(28±8%) was much lower than that of the saline control group(133±13%

p

<

0.001). A decrease in EA analgesia was also observed in rabbits injected with MgCl_2 (47±11% vs 123±15%

p

<

0.001). Ivt injection of the chelator CDTA

on the contrary

resulted in a potentiation of EA analgesia(CDTA group 164±15% vs saline group 104±19%

p

<

0.05). No significant chan- ges in pain threshold were seen when these chemicals were injected alone. The results indicate that Ca

(++)

and Mg(++) and Mg

(++)

in brain may exert an antagonis- tic effect on EA analgesia 2. The effect on morphine analgesia: Groups of rabbits were given ivt injection of one of the following chemicals: CaCl_2 4 μmol

MgCl_2 2 μmol

CDTA 1.4 μmol

or normal saline 50 μl

followed 10 min later by iv injection of morphine(3 or 6 mg/kg). Pain threshold changes were monitored for 1 h. A decrease in morphine analgesia was shown both in CaCl_2 group(50±26% vs 197±2%

p

<

0.001) and in MgCl_2 group (54±11% vs 145±19%

p

<

0.001). Ivt injection of CDTA

however

caused a marked potentiation of morphine analgesia (166+20% as compared with 105±10% in control group

p

<

0.05). An antagonistic effect of cerebral Ca(++) in brain may exert an antagonis- tic effect on EA analgesia 2. The effect on morphine analgesia: Groups of rabbits were given ivt injection of one of the following chemicals: CaCl_2 4 μmol

MgCl_2 2 μmol

CDTA 1.4 μmol

or normal saline 50 μl

followed 10 min later by iv injection of morphine(3 or 6 mg/kg). Pain threshold changes were monitored for 1 h. A decrease in morphine analgesia was shown both in CaCl_2 group(50±26% vs 197±2%

p

<

0.001) and in MgCl_2 group (54±11% vs 145±19%

p

<

0.001). Ivt injection of CDTA

however

caused a marked potentiation of morphine analgesia (166+20% as compared with 105±10% in control group

p

<

0.05). An antagonistic effect of cerebral Ca

(++)

and Mg(++) and Mg

(++)

was thus shown also on morphine analgesia. That both EA and morphine analgesia were attenuated by an increase in cerebral Ca(++) was thus shown also on morphine analgesia. That both EA and morphine analgesia were attenuated by an increase in cerebral Ca

(++)

and Mg(++) and Mg

(++)

and augmented by a decrease in brain cations implies a similarity in the mechanisms of action for these two analgesic processes.