Cholinesterase activity:muscarinic receptor ratios in canine and feline brains

In response to findings that brain cholinesterase (ChE): muscarinic cholinergic receptor density (mChR) ratio is highly conserved between bird species (I), this study investigated the conservation of brain ChE:mChR between 2 mammalian species. Whole brains of 7 normal greyhounds, 14 normal non-greyhound dogs, and 8 normal cats, were assayed for ChE, mChR and protein. The same assays were made on cerebrum, cerebellum and brainstem from the greyhounds and 6 of the non-greyhound dogs. The Ellman assay was used to measure serum ChE activity, mChR were labelled with tritiated quinuclidinyl benzilate, and protein was measured by Lowry assay. Brain ChE:mChR was not highly conserved between the species. There was a statistically significant difference in brain mChR between greyhounds and non-greyhounds but this did not translate to a statistically significant difference in mean ChE:mChR. Measurement of ChE:mChR is unlikely to be useful in endangered carnivores for which normal ChE levels are unknown, because it cannot be assumed that endangered species would have the same ChE:mChR as their domestic relatives.