Biomedical subjects

Pascale Rabbah

Publications and source records attributed to Pascale Rabbah.

4 recordsLinked to original sources

PubMed2007

Distinct synaptic dynamics of heterogeneous pacemaker neurons in an oscillatory network.

Many rhythmically active networks involve heterogeneous populations of pacemaker neurons with potentially distinct synaptic outputs that can be differentially targeted by extrinsic inputs or neuromodulators, thereby increasing possible network output patterns. To understand the roles of heterogeneous pacemaker neurons, we characterized differences in synaptic output from the anterior burster (AB) and pyloric dilator (PD) neurons in the lobster pyloric network. These intrinsically distinct neurons are strongly electrically coupled, coactive, and constitute the pyloric pacemaker ensemble. During pyloric oscillations, the pacemaker neurons produce compound inhibitory synaptic connections to the follower lateral pyloric (LP) and pyloric constrictor (PY) neurons, which fire out of phase with AB/PD and with different delay times. Using pharmacological blockers, we separated the synapses originating from the AB and PD neurons and investigated their temporal dynamics. These synapses exhibited distinct short-term dynamics, depending on the presynaptic neuron type, and had different relative contributions to the total synaptic output depending on waveform shape and cycle frequency. However, paired comparisons revealed that the amplitude or dynamics of synapses from either the AB or PD neuron did not depend on the postsynaptic neuron type, LP or PY. To address the functional implications of these findings, we examined the correlation between synaptic inputs from the pacemakers and the burst onset phase of the LP and PY neurons in the ongoing pyloric rhythm. These comparisons showed that the activity of the LP and PY neurons is influenced by the peak phase and amplitude of the synaptic inputs from the pacemaker neurons.

Animals↗

PubMed2005

Synaptic dynamics do not determine proper phase of activity in a central pattern generator.

Rhythmic motor activity often requires neuronal output to the muscles to arrive in a particular sequence. At the pattern-generator level, this requires distinct activity phases in different groups of constituent neurons. The phase differences between rhythmically active neurons in a network are thought to arise from the interplay between their intrinsic properties and the temporal dynamics of synapses among these neurons. In the rhythmically active pyloric network of the lobster Panulirus interruptus, synaptic connections from the pacemaker ensemble to the follower neurons [lateral pyloric (LP) and pyloric constrictor (PY)] are thought to be primarily responsible for the proper phase of activity (pacemaker-LP-PY) across all frequencies (0.5-2 Hz) of the pyloric rhythm. We test this hypothesis by characterizing the synapses from the pacemaker ensemble to the LP and PY neurons. Paired comparisons show that these two synapses are not significantly different in strength or in the extent of short-term depression. To examine the level to which intrinsic properties of the follower neurons determine their relative activity phase, we block all chemical synapses within the network and drive the LP and PY neurons rhythmically using artificial synaptic currents with identical strength and dynamics implemented with the dynamic-clamp technique. In response to these identical synaptic inputs, the LP and PY neurons maintain the proper relative phase of activity. These results strongly indicate that the relative phase of activity among these follower neurons within the pyloric network is not dictated by their synaptic inputs but is solely determined by their distinct intrinsic properties.

Animals↗

PubMed2005

Computational model of electrically coupled, intrinsically distinct pacemaker neurons.

Electrical coupling between neurons with similar properties is often studied. Nonetheless, the role of electrical coupling between neurons with widely different intrinsic properties also occurs, but is less well understood. Inspired by the pacemaker group of the crustacean pyloric network, we developed a multicompartment, conductance-based model of a small network of intrinsically distinct, electrically coupled neurons. In the pyloric network, a small intrinsically bursting neuron, through gap junctions, drives 2 larger, tonically spiking neurons to reliably burst in-phase with it. Each model neuron has 2 compartments, one responsible for spike generation and the other for producing a slow, large-amplitude oscillation. We illustrate how these compartments interact and determine the dynamics of the model neurons. Our model captures the dynamic oscillation range measured from the isolated and coupled biological neurons. At the network level, we explore the range of coupling strengths for which synchronous bursting oscillations are possible. The spatial segregation of ionic currents significantly enhances the ability of the 2 neurons to burst synchronously, and the oscillation range of the model pacemaker network depends not only on the strength of the electrical synapse but also on the identity of the neuron receiving inputs. We also compare the activity of the electrically coupled, distinct neurons with that of a network of coupled identical bursting neurons. For small to moderate coupling strengths, the network of identical elements, when receiving asymmetrical inputs, can have a smaller dynamic range of oscillation than that of its constituent neurons in isolation.

Animals↗

PubMed2005

Effect of electrical coupling on ionic current and synaptic potential measurements.

Recent studies have found electrical coupling to be more ubiquitous than previously thought, and coupling through gap junctions is known to play a crucial role in neuronal function and network output. In particular, current spread through gap junctions may affect the activation of voltage-dependent conductances as well as chemical synaptic release. Using voltage-clamp recordings of two strongly electrically coupled neurons of the lobster stomatogastric ganglion and conductance-based models of these neurons, we identified effects of electrical coupling on the measurement of leak and voltage-gated outward currents, as well as synaptic potentials. Experimental measurements showed that both leak and voltage-gated outward currents are recruited by gap junctions from neurons coupled to the clamped cell. Nevertheless, in spite of the strong coupling between these neurons, the errors made in estimating voltage-gated conductance parameters were relatively minor (<10%). Thus in many cases isolation of coupled neurons may not be required if a small degree of measurement error of the voltage-gated currents or the synaptic potentials is acceptable. Modeling results show, however, that such errors may be as high as 20% if the gap-junction position is near the recording site or as high as 90% when measuring smaller voltage-gated ionic currents. Paradoxically, improved space clamp increases the errors arising from electrical coupling because voltage control across gap junctions is poor for even the highest realistic coupling conductances. Furthermore, the common procedure of leak subtraction can add an extra error to the conductance measurement, the sign of which depends on the maximal conductance.

Analysis of Variance↗