Uncertainty of histologic classification of experimental tumors.

with 0.2-Hz stimulation before the LTP episode. There was a 10-minute period between the end of the second LTP episode and the conditioning train for the third (wash) episode. During this time, input-output and baseline responses were again obtained. A final series of input-output responses was taken at the end of the experiment. 15. J. V. Levy, Eur. J. Pharmacol. 2, 250 (1968); K. R. Courtney, J. Pharmacol. Exp. Ther. 213, 114 (1980). 16. B. J. Clark, in Beta Adrenoceptor Blocking Agents, P. R. Saxena and R. P. Forsyth, Eds. (North-Holland, Amsterdam, 1976), pp. 45-76. 17. R. D. Hawkins, T. W. Abrams, T. J. Carew, E. R. Kandel, Science 219, 400 (1983); E. T. Walters and J. H. Byrne, ibid. 219, 405 (1983). 18. E. T. Walters and J. H. Byrne, Soc. Neurosci. Abstr. 9, 168 (1983). 19. C. A. Breen and H. L. Atwood, Nature (London) 303, 716 (1983). 20. D. Johnston and T. H. Brown, J. Neurophysiol. 50, 464 (1983); T. H. Brown and D. Johnston, ibid. 50, 487 (1983). 21. We thank F. J. Lebeda, E. T. Walters, and J. H. Byrne for helpful comments on the manuscript. This work was supported by NIH grants NS11535 and NS15772 and a McKnight Foundation Neuroscience Development Award.