Abstract
Addiction to morphine is a problem widely studied but not yet solved. One of the difficulties of this problem is that it involves physical and psychic factors and it is believed that these signs can be demonstrated only in vertabrates with highly developed cerebral hemispheres.
Consequently, addiction experiments in animals have been carried out with higher animals, such as man, monkey, chimpanzee and dog. However, it has been recently reported that rats dosed morphine at 12 hours intervals for several weeks show signs of physical dependence to morphine (1-5). However, we have as yet very little information as to the possibility that similar signs can be also demonstrated in mice. A study of addiction or physical dependence in mice as compared with rats, namely the species difference between mice and rats in their response to morphine, is of great importance for the elucidation of the mechanism of the action of analgesics.
The present paper deals with the development of tolerance to and the occurrence of physical dependence to morphine in mice.
