Removal of a major non-catecholaminergic output from the olfactory bulb elicits sprouting of dopaminergic axons in the olfactory tubercle. The functional consequences of this increased dopaminergic innervation are presently not known. This study examined the question of whether lesion- induced sprouting of dopaminergic axons is associated with changes in dopamine-sensitive adenylate cyclase and dopamine receptor density in the partially denervated olfactory tubercle. The results indicate that dopamine- and NaF-stimulated adenylate cyclase activity increased as early as 7 d, while forskolin-sensitive activity increased at 3 d and persisted up to 20 d after lesioning; higher levels of GTP- and NaF- stimulated enzyme activity were found in detergent extracts of olfactory tubercle membranes from 20 d lesioned rats; higher levels of 3H-forskolin binding were found in membranes from 14 and 20 d lesioned rats; and there was an increase in dopamine receptor density, but not affinity, in olfactory tubercle membranes from lesioned rats. The data indicate that lesion-induced dopaminergic sprouting in the olfactory tubercle is temporally coordinated with the increased formation of dopamine receptors, both D1 and D2, the stimulatory guanine nucleotide regulatory protein (Ns) and the catalytic subunit (C) of adenylate cyclase in the postsynaptic membrane.
Monoclonal antibodies (Mabs) to the stimulatory (Ns) and inhibitory (Ni) guanine nucleotide regulatory proteins associated with adenylate cyclase have been developed. Two Mabs (2A3 and 5G12), which are of the IgG2b subclass, recognize the beta-subunits (beta) of Ns, Ni and transducin. Iodinated beta can be immunoprecipitated by either Mab coupled to Affi-Gel 10 and this can be decreased by prior incubation of the Mabs with excess unlabelled beta. The Mabs stabilize the activated state of Ns while decreasing the rate of deactivation of activated Ns in the presence of beta.
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