Histamine depolarizes neurons in the dorsal vagal complex

We sought to determine whether histamine has effects on single neurons in the dorsal vagal complex of the brainstem since previous studies have suggested a role for histamine receptors in this region. Using whole-cell patch clamp recordings from neurons within the nucleus of the tractus solitarius (NTS) and the dorsal vagal nucleus (DVN), histamine (20 μM) depolarized a small proportion of neurons in these regions accompanied by a decrease in input resistance. Although few neurons were depolarized (21% of NTS neurons and 15% of DVN neurons), those that were affected showed robust depolarizations of 13 mV. These depolarizations were antagonized by the histamine H1 receptor antagonist triprolidine (2 μM) and were subject to a level of desensitization. Neither histamine nor the H3 receptor agonist imetit caused any change in the amplitudes of excitatory or inhibitory postsynaptic potentials elicited in NTS neurons by stimulation of the solitary tract. These data indicate that histamine has a restricted but profound effect on neurons in the dorsal vagal complex.