The h-Current in Periglomerular Dopaminergic Neurons of the Mouse Olfactory Bulb

Abstract

The properties of the hyperpolarization-activated cation current (Ih) were investigated in rat periglomerular dopaminergic neurons using patch-clamp recordings in thin slices. A reliable identification of single dopaminergic neurons was made possible by use of a transgenic line of mice 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 has a profound influence on the spontaneous firing of these neurons, which result as 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 shift of the activation curve towards more positive potentials. The direct 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 modifythe Ih amplitude. On the contrary, noradrenaline almost halves the Ih amplitude. Our data indicate that the HCN channels do not participate directly to the pacemaker activity of periglomerular dopaminergic neurons, 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.

Spiking and Membrane Properties of Rat Olfactory Bulb Dopamine Neurons

“…The I H can act as a pacemaker current for neurons that experience spontaneous, rhythmic spiking ). In mouse OB DA neurons, pharmacological blockade of I H /HCN did hyperpolarize their resting membrane potential, but this did not cause these neurons to stop their spontaneous spiking (Pignatelli et al, 2013). We did not test the importance of the I H in the firing properties of rat OB DA neurons.…”

“…The I H (a non-specific cation current activated during hyperpolarization) is produced by the hyperpolarizationactivated cyclic nucleotide-gated (HCN) channels Wahl-Schott and Biel, 2009). Because the I H has been shown to indirectly influence the resting membrane potential of OB DA neurons (Pignatelli et al, 2013), and because it influences several spiking frequencies in the hippocampus , we analyzed its strength as a possible metric that could contribute to spiking differences between Large and Small DA OB neurons (Figure 3Gii). The presence of I H in our recordings was identified by depolarizing voltage sags in the membrane potential when a sufficiently large hyperpolarizing current is applied.…”

“…Therefore, another focus of this study was to determine the firing and gating properties of OB DA neurons in response to evoked current step stimuli. Further, the ionic currents that directly and indirectly contribute to spiking properties -I Na and the non-specific cation I H , respectively (Pignatelli et al, 2013;Iseppe et al, 2016) -were examined in these neurons. To potentially further distinguish between types of OB DA neurons, these properties were also studied in neurons categorized according to laminar (GL) localization and neuronal area.…”

“…As many previous studies have characterized OB DA neurons in transgenic mice (Pignatelli et al, 2005(Pignatelli et al, , 2009(Pignatelli et al, , 2013Puopolo et al, 2005), the last goal of this study was to determine these properties in the rat. Rats offer some clear advantages over mice (e.g., easier to handle, lower susceptibility to stress, larger brain size facilitates brain surgery and imaging) and are better models for the study of some human behaviors and conditions (Ellenbroek and Youn, 2016).…”

On the properties of identified dopaminergic neurons in the mouse substantia nigra and ventral tegmental area

“…The pharmacological blockade of I h with Zd7288 had an inhibitory effect in the spontaneous firing of TH‐GFP + neurons in the most lateral areas, although it did not completely abolish firing. This is in agreement with the notion that I h is a depolarizing current that participates, but is not responsible, for the firing discharge and probably accounts for the higher firing frequency rates observed in the SNpc cells (Pignatelli et al ., ; Masi et al ., ). In the VTA, the effects of Zd7288 strongly depended on cell location along the medial–lateral axis and on the magnitude of the I h current in each region.…”