Fig 4. Final Calorimetric Assessment during a 60% N₂O Administration for Initially Sensitive and Initially Insensitive Rats.

A calorimetry retest conducted after the self-administration phase revealed that the IS and II groups both became frankly hyperthermic with the onset of 60% N₂O administration but the magnitude was markedly greater and more persistent in the N₂O self administration-prone II rats (A) due primarily to a greater HP response (B). The increases in DHL (C) and EHL (D) likely reflect a durable pharmacological effect of N₂O in addition to the effect of increased body heat content to promote heat loss. The II and IS groups did not differ during the control gas session (E, F, G, H).