Figure 6.

β₃ receptors are expressed on neural precursors, and mediate the norepinephrine-dependent activation. A, Neither the α₁-adrenergic receptor antagonist prazosin nor the α₂-adrenergic receptor blocker yohimbine had any effect on the norepinephrine-stimulated increase in neurosphere numbers. Only the β-adrenergic receptor blocker, propranolol, completely inhibited the norepinephrine-stimulated increase in neurosphere numbers. Note that treatment with propranolol alone had no toxic effect on neurosphere production. A slight but significant increase in the number of neurospheres was also observed in the presence of yohimbine alone. B, The selective β₃ blocker SR59230A completely inhibited the norepinephrine-mediated increase in neurosphere numbers. In contrast, the β₁ receptor antagonist CGP20712 had no effect, whereas the β₂ receptor antagonist ICI118,551 significantly increased neurosphere numbers both in the presence and absence of norepinephrine. C, Expression of β-adrenergic receptors in the sorted population of Hes5-GFP-positive and -negative cells by reverse transcriptase-PCR showed the presence of the β₃-adrenergic receptor exclusively in the Hes5-positive population, whereas β₁- and β₂-adrenergic receptor transcripts were expressed predominantly in the Hes5-negative population. Note that a small amount of β₂ receptor mRNA was also detected in the Hes5-positive population. D, A similar increase in neurosphere numbers was observed in the presence of a selective β₃-adrenergic receptor agonist BRL37344 at 1 and 10 μm, compared with treatment with norepinephrine (mean ± SEM; *p < 0.05; **p < 0.01; ***p < 0.001).