Contribution of Ih to the relative facilitation of synaptic responses induced by carbachol in the entorhinal cortex during repetitive stimulation of the parasubiculum

Heterosynaptic modulation of evoked synaptic potentials in layer II of the entorhinal cortex by activation of the parasubiculum

“…This is consistent with a potential role of cholinergic inputs to the entorhinal cortex in promoting processing of synaptic afferents that are active during theta and gamma EEG activity (Dickson et al 2000a;Glasgow and Chapman 2007;Mitchell and Ranck 1980). This cholinergic facilitation of rhythmic parasubicular synaptic input to the entorhinal cortex was found to be due, in part, to a reduction in the cationic conductance I h , which also increases input resistance and enhances dendritic integration during repetitive synaptic activation in the hippocampal formation (Carr and Surmeier 2007;Day et al 2005;Dickson et al 2000b;Garden et al 2008;Magee 1998;Rosenkranz and Johnston 2006;Sparks and Chapman 2014).…”

“…We next applied the I h antagonist ZD7288, because reductions in I h contribute to the facilitation of responses during repetitive theta-and gamma-frequency stimulation (Sparks and Chapman 2014), and I h is also known to play an important role in synaptic integration in the hippocampal formation (Carr and Surmeier 2007;Magee 1998). Application of ZD7288 caused an overall increase in the amplitude of EPSPs (118.9 Ϯ 7.4% of baseline for single pulses, n ϭ 6, F 1,10 ϭ 5.7, P ϭ 0.04; Fig.…”

“…Theta EEG activity is associated with strong effects on synaptic transmission in the entorhinal cortex (Fernandez et al 2013;Sparks and Chapman 2014), and we therefore assessed the heterosynaptic effects of theta-frequency stimulation of the parasubiculum on layer I responses. Trains (10 Hz) of stimulation delivered to the parasubiculum led to a strong suppression of layer I inputs, 5 ms after the train, but in contrast to paired-pulse results, the inhibitory effect induced by trains was blocked by bicuculline.…”

“…Paired-pulse suppression induced by single parasubicular stimulation pulses was not affected by ZD7288 (C 1 ), but the facilitation of layer I responses induced by trains of parasubicular stimulation at the 25-ms interval was increased significantly during block of I h (C 2 ), indicating that reduction in I h can contribute to the heterosynaptic facilitation of responses evoked by activation of layer I inputs to the entorhinal cortex. *P Ͻ 0.05. repetitive activation of inputs (Magee 1998;Medinilla et al 2013;Sparks and Chapman 2014).…”

Regulation of cholinergic basal forebrain development, connectivity, and function by neurotrophin receptors

“…However, parvalbumin-positive interneurons can be inhibited by the activation of cholinergic-responsive layer 1 interneurons, which in turn results in somatic disinhibition of pyramidal neurons. Finally, despite sparse expression of nAChRs in layer 5/6 pyramidal neurons, robust mAChR expression is maintained predominantly at the soma [107,108], where the receptors act to suppress single synaptic responses, but facilitate synaptic responses evoked during stimulation trains [111,112]. However M1 mAChRs are also distributed on the extrasynaptic membrane of pyramidal cell dendrites and spines opposed to cholinergic varicosities indicative of volume release sites [113].…”