Table 1.

Sensitizing stimuli and expressions. HPA, hypothalamic–pituitary–adrenocortical axis activity.

stimulus type	example	sensitized response
addictive	stimulants [32,33]	increased locomotor response, self-administration, autonomic and rewarding effects
	alcohol [38]
	nicotine [39]
stress-trauma	inescapable stress [40]	increased HPA, autonomic and behaviour responses to stressors; stress-induced arousal and anhedonia
episode-related or endogenous	recurrent episodes [41–44]	increased frequency/severity
	inflammation [45]	increased sensitivity to the same stimulus type
cross-sensitization	addictive × addictive [46]	increased sensitivity to both stimulus classes stress-induced arousal, anhedonia and/or drug sensitivity
	stressor × addictive [37]
	episode × addictive or stressor [16,43]