Table 2.

Data summary for the cross-sensitization challenge, acquisition of self-administration, FR response rate, responding on the non-reinforced lever and PR break points for each separate experiment.

Experiment 1: Heroin Self-Administration
	Walking after heroin challenge (frequency, 5–10 min post-inj.)	Time to acquire FR1(hours)	FR3 Rate during maintenance (resp/min)		Responding on non-reinforced lever during FR3 (resp/min)	PR break point (infusions obtained)
Controls (n=10)	18.3±3.7	11.0±3.8	0.33±0.07		0.08±0.03	12.9±1.4
Social Defeat (14)	37.4±6.9**	11.1±2.1	0.39±0.10		0.02±0.01	9.9±1.3
Experiment 2: Heroin+Cocaine Self-Administration
	Walking after cocaine challenge (frequency, 5–10 min post-inj.)	Time to acquire FR1(hours)	FR5 Rate during maintenance (resp/min)	Responding on non-reinforced lever during FR5 (resp/min)	PR break point (infusions obtained)
					0.025 mg/kg/inf Heroin + 0.25 Cocaine	0.013 mg/kg/inf Heroin + 0.25 Cocaine
Controls (11)	40.7±6.2	10.9±1.5	0.69±0.08	0.11±0.05	14.4±1.2	14.2±0.9
Social Defeat (13)	64.1±7.1*	9.6±1.3	0.70±0.09	0.06±0.02	14.1±0.9	14.0±0.9
Experiment 3: Cocaine Self-Administration
	Walking after cocaine challenge (frequency, 5–10 min post-inj.)	Time to acquire FR1(hours)	FR5 Rate during maintenance (resp/min)		Responding on non-reinforced lever during FR5 (resp/min)	PR break point (infusions obtained)
Controls (11)	37.3±6.3	19.1±4.4	1.62±0.75		0.04±0.02	10.8±0.6
Social Defeat (12)	68.9±4.6**	17.9±2.5	1.03±0.09		0.02±0.01	11.0±0.5

Asterisks and bold type indicate significant group differences (*p<0.05, **p<0.01).