Pre-synaptic histamine H₃ receptors modulate glutamatergic transmission in rat globus pallidus.

The globus pallidus, a neuronal nucleus involved in the control of motor behavior, expresses high levels of histamine H(3) receptors (H(3)Rs) most likely located on the synaptic afferents to the nucleus. In this work we studied the effect of the activation of rat pallidal H(3)Rs on depolarization-evoked neurotransmitter release from slices, neuronal firing rate in vivo and turning behavior. Perfusion of globus pallidus slices with the selective H(3)R agonist immepip had no effect on the release of [(3)H]-GABA ([(3)H]-γ-aminobutyric acid) or [(3)H]-dopamine evoked by depolarization with high (20 mM) K(+), but significantly reduced [(3)H]-d-aspartate release (-44.

Pre-synaptic histamine H3 receptors regulate glutamate, but not GABA release in rat thalamus.

We have investigated the presence of histamine H(3) receptors (H(3)Rs) on rat thalamic isolated nerve terminals (synaptosomes) and the effect of their activation on glutamate and GABA release. N-alpha-[methyl-(3)H]histamine ([(3)H]-NMHA) bound specifically to synaptosomal membranes with dissociation constant (K(d)) 0.78+/-0.

Homologous down-regulation of histamine H3 receptors in rat striatal slices.

Preincubation of striatal slices with the selective histamine H3-receptor agonist immepip (100 nM) decreased the specific binding of N-alpha-[methyl-3H]-histamine ([3H]-NMHA) to membranes obtained from the treated slices. The binding decrease was significant after 5 min, remained at similar reduced levels between 5- and 30-min incubations with agonist, and only a partial recovery was observed after 90-min washout (34, 41, and 44% at 90, 120, and 150 min, respectively). Saturation analysis showed a significant decrease in both receptor density (-44% +/- 9%) and affinity (dissociation constant, Kd 1.