Fig. 4.
Example of the effects of a series of unilateral DAMGO microinjections (diamond symbols with pontine R-C/lateral coordinates). Note the progressive increases in TI and TE and decrease in fB and subsequent apnea. An IV bolus of NAL (10 μg/kg) partially antagonized the apnea. Larger subsequent doses were required to fully antagonize the DAMGO effects. A moderate increase in peak PNG is entirely due to the increase in TI without changes in drive (see Fig. 5 and text for further explanation).