title: NMDA receptor blockade impairs the muscarinic conversion of sub-threshold transient depression into long-lasting LTD in the hippocampus-prefrontal cortex pathway in vivo: correlation with γ oscillations.
abstract: Cholinergic fibers from the brainstem and basal forebrain innervate the medial prefrontal cortex (mPFC) modulating neuronal activity and synaptic plasticity responses to hippocampal inputs. Here, we investigated the muscarinic and glutamatergic modulation of long-term depression (LTD) in the intact projections from CA1 to mPFC in vivo. Cortical-evoked responses were recorded in urethane-anesthetized rats for 30 min during baseline and 4 h following LTD. In order to test the potentiating effects of pilocarpine (PILO), independent groups of rats received either a microinjection of PILO (40 nmol; i.c.v.) or vehicle, immediately before or 20 min after a sub-threshold LTD protocol (600 pulses, 1 Hz; LFS600). Other groups received either an infusion of the selective NMDA receptor antagonist (AP7; 10 nmol; intra-mPFC) or vehicle, 10 min prior to PILO preceding LFS600, or prior to a supra-threshold LTD protocol (900 pulses, 1 Hz; LFS900). Our results show that PILO converts a transient cortical depression induced by LFS600 into a robust LTD, stable for at least 4 h. When applied after LFS600, PILO does not change either mPFC basal neurotransmission or late LTD. Our data also indicate that NMDA receptor pre-activation is essential to the muscarinic enhancement of mPFC synaptic depression, since AP7 microinjection into the mPFC blocked the conversion of transient depression into long-lasting LTD produced by PILO. In addition, AP7 effectively blocked the long-lasting LTD induced by LFS900. Therefore, our findings suggest that the glutamatergic co-activation of prefrontal neurons is important for the effects of PILO on mPFC synaptic depression, which could play an important role in the control of executive and emotional functions.
authors.affiliation: Department of Neuroscience and Behavioral Science, Ribeirão Preto School of Medicine, University of São Paulo, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Cleiton
authors.initials: C
authors.lastname: Lopes-Aguiar
authors.forename: Lezio Soares
authors.initials: LS
authors.lastname: Bueno-Junior
authors.forename: Rafael Naime
authors.initials: RN
authors.lastname: Ruggiero
authors.forename: Rodrigo Neves
authors.initials: RN
authors.lastname: Romcy-Pereira
authors.forename: João Pereira
authors.initials: JP
authors.lastname: Leite
mesh_terms: D000818:Animals; D058256:Brain Waves / Q000187:drug effects / Q000502:physiology*; D018691:Excitatory Amino Acid Antagonists / Q000008:administration & dosage; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D036881:Long-Term Synaptic Depression / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008845:Microinjections; D018721:Muscarinic Agonists / Q000008:administration & dosage*; D009434:Neural Pathways / Q000187:drug effects / Q000502:physiology; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology; D010862:Pilocarpine / Q000008:administration & dosage; D017397:Prefrontal Cortex / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000502:physiology*; D013997:Time Factors
chemical_list: D018691:Excitatory Amino Acid Antagonists; D018721:Muscarinic Agonists; D016194:Receptors, N-Methyl-D-Aspartate; D010862:Pilocarpine