The incubation of murine thymocytes for 24 hr in the presence of cholinergic agonists induces selective proliferation of PNA- cells as measured by thymidine incorporation. The response of PNA- cells is mediated by the activation of nicotinic receptors. This conclusion is suggested by the inability of the muscarinic agonist, oxotremorine, to induce cell proliferation and by the inhibition exerted by the nicotinic antagonist, d-tubocurarine. The presence of cholinergic axons in the murine thymus adds biological interest to the selective expression of functional cholinergic receptors on mature thymocytes.

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