Hypothermic response to NT in rats treated i.p. with saline, antisense PNA to the NTR (AS-NTR1), mismatch AS-NTR1 PNA, or antisense PNA to the MOR (AS-MOR1) or sense-NTR1 PNA microinjected into the PAG. Animals were treated as described in Fig. 2. Body temperature was measured by use of a thermistor probe inserted 3 cm into the rat’s rectum before and 30 min after NT (18 nmol) microinjection into the PAG. The change in body temperature ± SEM is reported. ∗, P < 0.001 vs. NT alone; †, P = 0.008 vs. NT alone.