Seasonal variation of morphine physical dependence.

The characteristics of morphine physical dependence in ground squirrels (Citellus lateralis) were examined during each of the four annual seasons. The results showed that this rodent hibernator exhibits a strong and characteristic naloxone-precipitated abstinence syndrome during its non-hibernation state, irrespective of the season. Although qualitatively unchanged throughout the year, the abstinence syndrome showed clear quantitative seasonal differences. These differences were evident in terms of both the number of occurrences of particular signs and the percentage of the morphine-dependent population exhibiting them.