Teaching Neuroimmunology to Undergraduate Students: Resource for Full Course or Modular Implementation.

This paper describes a course I designed to teach neuroimmunology to undergraduate students. In this course I incorporated many active learning strategies to help make it a student-centered class, where they developed communication skills, while reading and analyzing primary literature articles. As the field of neuroimmunology is relatively new, most textbooks in the field approached the subject from the perspective of neurology and autoimmune diseases. Therefore, I used reading, analysis, and student-led presentation of primary papers in the classroom to not only develop critical thinking and application of the scientific method, but also oral communication skills. Other activities such as writing New York Times-style articles and literature review papers were employed to develop written communications skills. The goal of this article is to provide a reference tool for instructors trained in neuroscience to deploy an entire course on neuroimmunology or select a module or a single paper to incorporate into their existing course to offer students a taste for neuroimmunology.

Endogenous antibodies promote rapid myelin clearance and effective axon regeneration after nerve injury.

Degenerating myelin inhibits axon regeneration and is rapidly cleared after peripheral (PNS) but not central nervous system (CNS) injury. To better understand mechanisms underlying rapid PNS myelin clearance, we tested the potential role of the humoral immune system. Here, we show that endogenous antibodies are required for rapid and robust PNS myelin clearance and axon regeneration. B-cell knockout JHD mice display a significant delay in macrophage influx, myelin clearance, and axon regeneration. Rapid clearance of myelin debris is restored in mutant JHD mice by passive transfer of antibodies from naïve WT mice or by an anti-PNS myelin antibody, but not by delivery of nonneural antibodies. We demonstrate that degenerating nerve tissue is targeted by preexisting endogenous antibodies that control myelin clearance by promoting macrophage entrance and phagocytic activity. These results demonstrate a role for immunoglobulin (Ig) in clearing damaged self during healing and suggest that the immune-privileged status of the CNS may contribute to failure of CNS myelin clearance and axon regeneration after injury.

Target-specific regulation of synaptic amplitudes in the neocortex.

In layers 2/3 in the rat visual cortex, glutamatergic synapses, between pyramidal neurons and GABAergic interneurons, show target-specific depression or facilitation. To study the mechanisms regulating these short-term synaptic modifications, we recorded from synaptically connected pyramidal neurons (presynaptic) and multipolar or bitufted interneurons (postsynaptic). Evoked AMPA receptor (AMPAR)- or NMDA receptor (NMDAR)-mediated EPSCs were pharmacologically isolated at these pyramidal-to-interneuron synapses while altering release probability (P(r)) by changing the extracellular Ca2+ concentration ([Ca2+]o). At the pyramidal-to-multipolar synapse, which shows paired-pulse depression, elevation of [Ca2+]o from physiological concentrations (2 mm) to 3 mm increased the amplitude of the initial AMPAR-mediated EPSC and enhanced paired-pulse depression. In contrast, the initial NMDAR-mediated EPSC did not change in amplitude with raised P(r) nor was paired-pulse depression altered. This lack of an increase of NMDAR-mediated currents is not a result of Ca2+-dependent effects on the NMDAR. Rather, at the pyramidal-to-multipolar synapse, raised P(r) increases the transient glutamate concentration at individual release sites, possibly reflecting multivesicular release. In contrast, at the pyramidal-to-bitufted synapse, which shows facilitation, AMPAR- and NMDAR-meditated EPSCs showed parallel increases in response to raised P(r). Thus, our results reveal differential recruitment of AMPA and NMDARs at depressing and facilitating synapses in layers 2/3 of the cortex and suggest that the mechanisms regulating dynamic aspects of synaptic transmission are target specific.

DRPEER: a motif in the extracellular vestibule conferring high Ca2+ flux rates in NMDA receptor channels.

The high flux rate of Ca2+ through NMDA receptor (NMDAR) channels is critical for their biological function and may depend on a Ca2+ binding site in the extracellular vestibule. We screened substitutions of hydrophilic residues exposed in the vestibule and identified a cluster of charged residues and a proline, the DRPEER motif, positioned C terminal to M3, that is unique to the NR1 subunit. Charge neutralization or conversion of residues in DRPEER altered fractional Ca2+ currents in a manner consistent with its forming a binding site for Ca2+. Similarly, in a mutant channel in which all of the negative charges are neutralized (ARPAAR), the block by extracellular Ca2+ of single-channel current amplitudes is attenuated. In these same channels, the block by extracellular Mg2+ is unaffected. DRPEER is located extracellularly, and its contribution to Ca2+ influx is distinct from that of the narrow constriction. We conclude that key residues in DRPEER, acting as an external binding site for Ca2+, along with a conserved asparagine in the M3 segment proper, contribute to the high fractional Ca2+ currents in these channels under physiological conditions. Therefore, these domains represent critical molecular determinants of NMDAR function in synaptic physiology.

Voltage and concentration dependence of Ca(2+) permeability in recombinant glutamate receptor subtypes.

The channels associated with glutamate receptor (GluR) subtypes, namely N-methyl-D-aspartate receptors (NMDARs), and Ca(2+)-permeable alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors (AMPARs) and kainate receptors (KARs), are to varying degrees permeable to Ca(2+). To compare the mechanism of Ca(2+) influx, we measured Ca(2+) permeability relative to that of Na(+) (P(Ca)/P(Na)) using fractional Ca(2+) currents (P(f)) and reversal potential measurements over a wide voltage and Ca(2+) concentration range in recombinant NMDAR NR1-NR2A, AMPAR GluR-A(Q) and KAR GluR-6(Q) channels. For NR1-NR2A channels, P(Ca)/P(Na) derived from P(f) measurements was voltage independent but showed a weak concentration dependence. A stronger concentration dependence was found when P(Ca)/P(Na) was derived from changes in reversal potentials on going from a Na(+) reference solution to a solution with Ca(2+) as the only permeant ion ('biionic' condition). In contrast, P(Ca)/P(Na) was concentration independent when derived from changes in reversal potentials on going from a Na(+) reference solution to the same solution with added Ca(2+) ('high monovalent' condition). For GluR-A(Q) channels, P(Ca)/P(Na) derived from all three approaches was concentration independent, and for the reversal potential-based approaches were of comparable magnitude. Their most distinctive property was that P(Ca)/P(Na) derived from P(f) measurements was strongly voltage dependent. For GluR-6(Q) channels, P(Ca)/P(Na) derived from P(f) measurements was weakly voltage dependent. On the other hand, P(Ca)/P(Na) derived from all three approaches was the most strongly concentration dependent of any GluR subtype and, except for low Ca(2+) concentrations, the values were of comparable magnitude. Thus, the three Ca(2+)-permeable GluR subtypes showed unique patterns of Ca(2+) permeability, indicating that distinct biophysical and molecular events underlie Ca(2+) influx in each subtype.