Development of Muscarinic Receptor Binding in Spinal Cord Cell Cultures and Its Reduction by Glutamic and Kainic Acids

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Abstract
The density of [3H]quinuclidinyl benzilate ([3H]QNB) binding sites in dissociated cell cultures of mouse spinal cord increased almost 4-fold between the 5th and 21st days of maturation in vitro. The mean specific binding of [3H]QNB in 21-day cultures was 340 pmol/g protein. Up to 79% of.[3H]QNB binding sites were lost within a few days after exposure of the cultures to 1 mM glutamate. This neurotoxic action of glutamate showed a steep concentration dependence in the range 0.1–1 mM and did not vary with the duration of exposure of the cultures from 10 min to 24 h. Kainic acid was only moderately more potent than glutamate in reducing [3H]QNB binding. The susceptibility of 8-day cultures to glutamate-induced loss of [3H]QNB binding was less than that of 12- and 19-day cultures. These findings suggest that 80% or more of muscarinic binding sites in the spinal cord cell cultures are on neurons and that the sensitivity of these neurons to the toxic action of glutamate increases with their maturation in vitro.