1. Gibbs, J., Young, R. C., and Smith, G. P., Nature, 245, 323–325 (1973).
2. Lehr, D., Mallow, J., and Krukowski, M., J. Pharmac. exp. Ther., 158, 150–163 (1967).
3. Fitzsimons, J. T., J. Physiol., Lond., 159, 297–309 (1961).
4. Weiss, C. S., and Almli, C. R., Physiol. Behav., 14, 477–481 (1975).
5. Kozlowski, S., and Drzewiecki, K., Acta Physiol. pol., 24, 325–330 (1973).