Impact of functional synapse clusters on neuronal response selectivity

Clustering of functionally similar synapses in dendrites is thought to affect neuronal input-output transformation by triggering local nonlinearities. However, neither the in vivo impact of synaptic clusters on somatic membrane potential (sVm), nor the rules of cluster formation are elucidated. We develop a computational approach to measure the effect of functional synaptic clusters on sVm response of biophysical model CA1 and L2/3 pyramidal neurons to in vivo-like inputs. We demonstrate that small synaptic clusters appearing with random connectivity do not influence sVm. With structured connectivity, ~10–20 synapses/cluster are optimal for clustering-based tuning via state-dependent mechanisms, but larger selectivity is achieved by 2-fold potentiation of the same synapses. We further show that without nonlinear amplification of the effect of random clusters, action potential-based, global plasticity rules cannot generate functional clustering. Our results suggest that clusters likely form via local synaptic interactions, and have to be moderately large to impact sVm responses

A pH-sensitive chloride current in the chemoreceptor cell of rat carotid body

Cardiorespiratory response to acidosis is initiated by the carotid body.The direct effect of extracellular pH (pHo) on the chloride currents of isolated chemoreceptor cells of the rat carotid body was investigated using the whole-cell patch-clamp technique.On applying intra- and extracellular solutions with a symmetrical high-Cl− content and with the monovalent cations replaced with membrane-impermeant ones, an inwardly rectifying Cl− current was found.The current activated slowly and did not display any time-dependent inactivation. Current activation was present at membrane potentials negative to 0 mV (pHo = 7.0).The current was activated by extracellular acidosis and inhibited by alkalosis in the physiologically relevant pH range of 7.0-7.8.The current was reduced by 0.1 mM Cd2+ to the level of the leak current and by 1 mM anthracene-9-carboxylic acid (9-AC) to about 40 %, while 0.1 mM Ba2+ had no effect.Application of 1 mM 9-AC caused a slow but statistically significant increase in the resting pHi (from a mean of 7.29 to 7.37 in 5 min) in clusters of chemoreceptor cells in CO2/HCO3−-buffered media as measured with carboxy-SNARF-1.When membrane potential changes were estimated in the cell-attached mode, 1 mM 9-AC hyperpolarized three out of five tested cells (by 14 mV in average) incubated in CO2/HCO3−-buffered media.In summary, chemoreceptor cells express an inwardly rectifying Cl− current, which is directly regulated by pHo. The current may participate in intracellular acidification and membrane depolarization during acidic challenge

Involvement of nitric oxide in depolarization-induced suppression of inhibition in hippocampal pyramidal cells during activation of cholinergic receptors.

Several types of neurons are able to regulate their synaptic inputs via releasing retrograde signal molecules, such as endocannabinoids or nitric oxide (NO). Here we show that, during activation of cholinergic receptors, retrograde signaling by NO controls CB1 cannabinoid receptor (CB1R)-dependent depolarization-induced suppression of inhibition (DSI). Spontaneously occurring IPSCs were recorded in CA1 pyramidal neurons in the presence of carbachol, and DSI was induced by a 1-s-long depolarization step. We found that, in addition to the inhibition of CB1Rs, blocking the NO signaling pathway at various points also disrupted DSI. Inhibitors of NO synthase (NOS) or NO-sensitive guanylyl cyclase (NO-sGC) diminished DSI, whereas a cGMP analog or an NO donor inhibited IPSCs and partially occluded DSI in a CB1R-dependent manner. Furthermore, an NO scavenger applied extracellularly or postsynaptically also decreased DSI, whereas L-arginine, the precursor for NO, prolonged it. DSI of electrically evoked IPSCs was also blocked by an inhibitor of NOS in the presence, but not in the absence, of carbachol. In line with our electrophysiological data, double immunohistochemical staining revealed an NO-donor-induced cGMP accumulation in CB1R-positive axon terminals. Using electron microscopy, we demonstrated the postsynaptic localization of neuronal NOS at symmetrical synapses formed by CB1R-positive axon terminals on pyramidal cell bodies, whereas NO-sGC was found in the presynaptic terminals. These electrophysiological and anatomical results in the hippocampus suggest that NO is involved in depolarization-induced CB1R-mediated suppression of IPSCs as a retrograde signal molecule and that operation of this cascade is conditional on cholinergic receptor activation.Comparative StudyJournal ArticleResearch Support, N.I.H. ExtramuralResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

Quantum dot–based multiphoton fluorescent pipettes for targeted neuronal electrophysiology

Targeting visually-identified neurons for electrophysiological recording is a fundamental neuroscience technique; however, its potential is hampered by poor visualization of pipette tips in deep brain tissue. We describe a technique whereby quantum dots coat glass pipettes providing strong two-photon contrast at deeper penetration depths than current methods. We demonstrate utility in targeted patch-clamp recording experiments and single cell electroporation from identified rat and mouse neurons in vitro and in vivo