Characterization of the h-current in periglomerular dopaminergic neuron of the mouse olfactory bulb.

The properties of the hyperpolarization-activated cation current (Ih) were investigated in mice periglomerular dopaminergic (DA) neurons using patch-clamp recordings in thin slices. A reliable identification of single DA neurons was made possible by use of a transgenic of mice line expressing eGFP under the tyrosine hydroxylase promoter. At 37 °C and minimizing the disturbance of the intracellular milieu with perforated patches, this current shows a midpoint of activation around −82.7 mV, with a significant level of opening already at rest, thereby giving a substantial contribution to the resting potential, and ultimately playing a relevant function in the control of the cell excitability. The blockage of Ih influences the spontaneous firing of these neurons, which results strongly depressed. However the effect is not due to a direct role of the current in the pacemaker process, but to the Ih influence on the resting membrane potential. Ih kinetics is sensitive to the intracellular levels of cAMP, whose increase promotes a depolarizing shift of the activation curve. Application of DA and 5-HT neurotransmitters, physiologically released onto bulbar dopaminergic neurons and known to act on metabotropic receptors coupled to the cAMP pathway, do not modify the Ih amplitude, whereas noradrenaline almost halves the Ih amplitude. Our data indicate that the H-channels do not participate directly to the pacemaker activity of periglomerular (DA) neurones, but influence their resting membrane potential by controlling the excitability profile of these cells, and possibly affecting the processing of sensory information taking place at the entry of the bulbar circuitry.