Table1.

Effects of acute and chronic morphine treatment on the spontaneous firing rates of PGi neurons

	Pre-infusion		After infusion(Tolerance /Dependence)
	Baseline	Acute morphine	Baseline	Withdrawal
Excitation site(18)	1.86±0.29	2.87±0.57a	1.98±0.17	1.42±0.20c
Inhibition site(11)	1.97±0.33	1.41±0.23b	2.48±0.49	2.98±0.58b
Non-response site(14)	5.45±1.17	5.40±1.16	3.51±0.51	3.19±0.49

Data are presented as mean ± S.E.D (spike/s).

The responses of PGi neurons to acute and chronic morphine treatment were recorded from 42 wires from 6 rats.

‘Excitatory site’, i.e., the recording sites (wire) that showed excitatory response to acute morphine injection.

‘Inhibitory site’, i.e., the recording sites (wire) that showed inhibitory response to acute morphine injection.

‘Non-response site’, i.e., the recording sites (wire) that did not show no significant response to acute morphine injection.

Numbers in parentheses refer to the number of wires.

^aP< 0.005,

^bP≤0.002,

^cP<0.0005, compared to baseline values (paired t-test).