receptor mRNA expression and binding in euthermic and hibernating ground squirrel brains. Coronal sections of ground squirrel brains showing H3 receptor expression revealed by in situ hybridization using [35S]-labeled oligonucleotide probe complementary to H3 mRNA (A-F) and [3H]NAMH binding to histamine H3 receptors (G-L). The H3 mRNA expression is higher in the cortex, caudatus and putamen but not in the globus pallidus and substantia nigra during hibernation (B and E) than during interbout euthermia (A and D). The signal was blocked with excess cold H3 oligonucleotide probe (C and F). [3H]NAMH binding to histamine H3 receptors is higher in the cortex, globus pallidus and substantia nigra during hibernation (H and K) compared to interbout euthermic brains (G and J). The specific H3 receptor antagonist clobenpropit completely blocked the [3H]NAMH binding (I and L).