title: Heterosynaptic modulation of evoked synaptic potentials in layer II of the entorhinal cortex by activation of the parasubiculum.
abstract: The superficial layers of the entorhinal cortex receive sensory and associational cortical inputs and provide the hippocampus with the majority of its cortical sensory input. The parasubiculum, which receives input from multiple hippocampal subfields, sends its single major output projection to layer II of the entorhinal cortex, suggesting that it may modulate processing of synaptic inputs to the entorhinal cortex. Indeed, stimulation of the parasubiculum can enhance entorhinal responses to synaptic input from the piriform cortex in vivo. Theta EEG activity contributes to spatial and mnemonic processes in this region, and the current study assessed how stimulation of the parasubiculum with either single pulses or short, five-pulse, theta-frequency trains may modulate synaptic responses in layer II entorhinal stellate neurons evoked by stimulation of layer I afferents in vitro. Parasubicular stimulation pulses or trains suppressed responses to layer I stimulation at intervals of 5 ms, and parasubicular stimulation trains facilitated layer I responses at a train-pulse interval of 25 ms. This suggests that firing of parasubicular neurons during theta activity may heterosynaptically enhance incoming sensory inputs to the entorhinal cortex. Bath application of the hyperpolarization-activated cation current (Ih) blocker ZD7288 enhanced the facilitation effect, suggesting that cholinergic inhibition of Ih may contribute. In addition, repetitive pairing of parasubicular trains and layer I stimulation induced a lasting depression of entorhinal responses to layer I stimulation. These findings provide evidence that theta activity in the parasubiculum may promote heterosynaptic modulation effects that may alter sensory processing in the entorhinal cortex.
authors.affiliation: Centre for Studies in Behavioural Neurobiology, Department of Psychology, Concordia University, Montréal, Québec, Canada.
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Sparks
authors.affiliation: Centre for Studies in Behavioural Neurobiology, Department of Psychology, Concordia University, Montréal, Québec, Canada andrew.chapman@concordia.ca.
authors.forename: C Andrew
authors.initials: CA
authors.lastname: Chapman
mesh_terms: D000344:Afferent Pathways / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D001640:Bicuculline / Q000031:analogs & derivatives / Q000494:pharmacology; D002317:Cardiovascular Agents / Q000494:pharmacology; D004558:Electric Stimulation; D018728:Entorhinal Cortex / Q000166:cytology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology*; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology; D006624:Hippocampus / Q000502:physiology*; D008297:Male; D018408:Patch-Clamp Techniques; D010721:Phosphinic Acids / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D051381:Rats; D020318:Rats, Long-Evans; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D014633:Valine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: C102659:CGP 56999A; D002317:Cardiovascular Agents; D018691:Excitatory Amino Acid Antagonists; D058787:GABA-A Receptor Antagonists; D010721:Phosphinic Acids; D011743:Pyrimidines; C082246:ICI D2788; C017069:bicuculline methiodide; C056639:2-amino-5-phosphopentanoic acid; D014633:Valine; D001640:Bicuculline
keywords: Ih; entorhinal cortex; heterosynaptic; parasubiculum; plasticity