—In his letter, Zeeberg questions whether the radioiodinated 3-quinuclidinyl-4-iodobenzilate (IQNB) single photon emission computed tomographic (SPECT) images in normal subjects and in patients with dementia described in our article1 reflect primarily muscarinic receptor binding or regional cerebral blood flow (rCBF). We discussed this issue extensively in our article and spoke directly and repeatedly to the concern raised in this letter. Nevertheless, the author of this letter ignores most of our discussion and most of the in vivo data about IQNB, choosing instead to challenge a "straw man" of his own construction. He focuses on our observation regarding the cerebellum and uses this to build his case for an rCBF phenomenon. The cerebellum observation, as clearly discussed in our article, served only to demonstrate that the SPECT images at prolonged times after IQNB administration were distinctly different from, and in marked contrast to, rCBF images, and they indicated
Weinberger DR, Jones DW, Coppola R, Berman KF, Gibson R, Reba RC. Concerning the Distribution of Cerebral Muscarinic Acetylcholine Receptors in Alzheimer's Disease-Reply. Arch Neurol. 1991;48(11):1118. doi:10.1001/archneur.1991.00530230025012
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