Table 1. Groups of animals used in each experiment (total n = 54).

Code	Group name	Drug injection	No. of animals
I	I. Control	None	4
II-1	II. Electrical stimulation	None	5
II-2		Injection of naloxone in the ARC (central antagonism)	4
II-3		Injection of saline in the ARC (central blank)	4
II-4		Peripheral subconjunctival injection of 0.2 ml naloxone (peripheral antagonism)	4
II-5		Peripheral subconjunctival injection of 0.2 ml saline (peripheral blank)	4
III-1	III. DAMGO injection	Injection of DAMGO in the ARC (2 µmol/µl)	4
III-2		Injection of DAMGO in the ARC (4 µmol/µl)	4
III-3		Subconjunctival injection of 0.2 ml naloxone+injection of DAMGO in the ARC (2 µmol/µl)	4
		(peripheral antagonism)
III-4		Subconjunctival injection of 0.2 ml saline+injection of DAMGO in the ARC (2 µmol/µl) (peripheral blank)	3
IV-1	IV. DPDPE injection	Injection of DPDPE in the ARC (2 µmol/µl)	4
IV-2		Injection of DPDPE in the ARC (4 µmol/µl)	4
IV-3		Subconjunctival injection of 0.2 ml naloxone+injection of DPDPE in the ARC (2 µmol/µl)	3
		(peripheral antagonism)
IV-4		Subconjunctival injection of 0.2 ml saline+injection of DPDPE in the ARC (2 µmol/µl) (peripheral blank)	3