Behavioral measures of anxiety during opiate withdrawal

Heightened anxiety is a major component of the withdrawal syndromes associated with ethanol and sedative hypnotic medications. Because of similarities between the opiate and sedative-hypnotic withdrawal syndromes as well as data implicating heightened noradrenergic tone with opiate withdrawal, we investigated changes in anxiety measures identified by plus-maze and social interaction testing during opiate withdrawal. Because Sprague Dawley rats had very low levels of entry into plus-maze open arms, further studies were conducted using the Long-Evans strain. Long-Evans rats received continuous infusions of morphine sulfate at 44 mg/kg per day delivered by osmotic pump over 7 days while control animals received inert implants. During the first 3 days of withdrawal, the number and time of entries into open and closed arms of a plus-maze was recorded. Both social and aggressive behaviors were scored durings pairings of groups of two socially naive animals. Body weight was significantly reduced in morphine-treated animals prior to and during withdrawal. Both the number of entries into open plus-maze arms and the time spent in open areas increased over the 3 days of testing. However, no difference in plus-maze activity was detected between morphine-treated and control subjects. On the third day of withdrawal, social interaction time was greater in pairs of withdrawn and control subjects compared to pairs of two control subjects. In conclusion, behavioral measures of anxiety are not increased during opiate withdrawal.