Abstract
Red tears (chromodacryorrhea) in rats are due to porphyrin pigments secreted by Harder's glands and are believed to involve muscarinic mechanisms. Chromodacryorrhea was observed in rats treated with pilocarpine, oxotremorine and neostigmine and this response was blocked by anticholinergic drugs. However, in rats deprived of rapid eye movement (REM) sleep (REMd) for 3 days, through the watertank technique, chromodacryorrhea did not develop even when cholinergic agonists were given in doses severalfold higher than those active in non-REMd animals. Decrease of chromodacryorrhea also was obtained in rats previously treated with neostigmine; conversely, previous treatment with atropine induced an increased chromodacryorrhea when the rats were further challenged with pilocarpine and oxotremorine. It is proposed that the absence of red tears in REMd rats might be due to a down regulation of peripheral cholinergic receptors.
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