HCN Channel Modulation of Synaptic Integration in GABAergic Interneurons in Malformed Rat Neocortex

Abstract

Cortical malformations are often associated with pharmaco-resistant epilepsy. Alterations in hyperpolarization-activated, cyclic nucleotide-gated, non-specific cation (HCN) channels have been shown to contribute to malformation associated hyperexcitability. We have recently demonstrated that expression of HCN channels and Ih current amplitudes are reduced in layer (L) 5 pyramidal neurons of rats with freeze lesion induced malformations. These changes were associated with an increased EPSP temporal summation. Here, we examine the effects of HCN channel inhibition on synaptic responses in fast spiking, presumptive basket cells and accommodating, presumptive Martinotti, GABAergic interneurons in slices from freeze lesioned animals. In control animals, fast spiking cells showed small sag responses which were reduced by the HCN channel antagonist ZD7288. Fast spiking cells in lesioned animals showed absent or reduced sag responses. The amplitude of single evoked EPSPs in fast spiking cells in the control group was not affected by HCN channel inhibition with ZD7288. EPSP ratios during short stimulus trains at 25 Hz were not significantly different between control and lesion groups. ZD7288 produced an increase in EPSP ratios in the control but not lesion groups. Under voltage clamp conditions, ZD7288 did not affect EPSC ratios. In the control group, accommodating interneurons showed robust sag responses which were significantly reduced by ZD7288. HCN channel inhibition increased EPSP ratios and area in controls but not the lesioned group. The results indicate that HCN channels differentially modulate EPSPs in different classes of GABAergic interneurons and that this control is reduced in malformed rat neocortex.

Developmental Changes in HCN Channel Modulation of Neocortical Layer 1 Interneurons

“…Using the HCN channel inhibitor ZD7288, we were able to confirm the presence of small amplitude I h in L1 INs (Figure 2D ; Instantaneous—Control: 128.57 ± 23.71 pA, ZD7288: 39.15 ± 12.86 pA; p < 0.01, paired t -test; Steady-state—Control: 132.97 ± 20.19 pA, ZD7288: 38.73 ± 10.92 pA; p = 0.0001, paired t -test). The measured I h amplitude was small compared to currents previously observed in L5 pyramidal neurons (PNs; Albertson et al, 2011 ) and GABAergic INs (Albertson et al, 2017 ). The voltage “sag” response characteristic of I h was also quantified to assess differences in functional HCN channel expression between groups.…”

“…HCN channels have been shown to modulate the excitability of CR cells (Kilb and Luhmann, 2000 ) and affect the intrinsic and synaptic excitability of diverse cortical INs (Albertson et al, 2011 , 2017 ). HCN channels can be active at rest, contributing to the RMP and conductance of the membrane in a cell-type specific manner (Pape, 1996 ; Lupica et al, 2001 ; Nolan et al, 2003 ; Day et al, 2005 ; Meuth et al, 2006 ).…”

LSO:Ce Inorganic Scintillators Are Biocompatible With Neuronal and Circuit Function

“…Due to the age of the mice, a more neuroprotective dissection solution was used during acute hippocampal slice preparation (Tanaka et al, 2008). The brains were rapidly removed and placed in ice-cold dissection solution containing the following (in mM): 135 N-Methyl-D-glucamine, 1.5 KCl, 1.5 KH 2 PO 4 , 0.5 CaCl 2 , 3.5 MgCl 2 , 23 NaHCO 3 , 0.4 L-Ascorbic acid, and 10 glucose, bubbled with 95% O 2 /5% CO 2 , pH 7.35–7.45, and osmolarity 295–305 (Albertson et al, 2017). A vibratome (Campden 7000smz-2, Lafayette Instrument) was used to cut 300 μM thick hippocampal brain slices.…”

LSO:Ce Inorganic Scintillators are Biocompatible with Neuronal and Circuit Function

“…The brains were rapidly removed and placed in ice cold dissection solution containing the following (in mM): 135 N-Methyl-D-glucamine, 1.5 KCl, 1.5 KH 2 PO 4 , 0. 5 CaCl2, 3.5 MgCl 2 , 23 NaHCO3, 0.4 L-Ascorbic acid, and 10 glucose, bubbled with 95% O2/5% CO2, pH 7.35–7.45, and osmolarity 295–305 (Albertson et al, 2017). A vibratome (Campden 7000smz-2, Lafayette Instrument) was used to cut 300 μM thick hippocampal brain slices.…”