Neuregulins are highly expressed in the CNS, especially in cholinergic neurons. We have examined the effect of neuregulin on nicotinic acetylcholine receptors (nAChRs) in neurons dissociated from the rat hippocampus. Rapid application of acetylcholine (ACh) induced a rapidly rising and decaying inward current in some of the neurons, which was completely blocked by methyllycaconitine, a specific antagonist of the ␣7 subunit of the nAChR. When the cells were treated with 5 nM neuregulin (NRG1-␤1) for 2-4 d, a twofold increase in amplitude of the peak ACh-induced current was observed, and there was a comparable increase in 125 I-␣-bungarotoxin binding. The fast ACh-induced peak current was prominent in large neurons that also contained GABA immunoreactivity. These presumptive GABAergic neurons constituted ϳ10% of neurons present in 7-to 9-d-old cultures. In addition to the large inward peak current, ACh also evoked transmitter release from presynaptic nerve terminals. Pharmacologic experiments indicated that the shower of PSCs was mediated by glutamate, with a small minority caused by the action of GABA. Chronic exposure to NRG1-␤1 increased the amplitude of ACh-evoked PSCs but not the minimum "quantal" PSC. NRG1-␤1 also increased the percentage of neurons that exhibited ACh-evoked PSCs.

Synapse formation at the neuromuscular junction (NMJ) requires an alternatively spliced variant of agrin (Z ؉ agrin) that is produced only by neurons. Here, we show that Nova1 and Nova2, neuronspecific splicing factors identified as targets in autoimmune motor disease, are essential regulators of Z ؉ agrin. Nova1/Nova2 double knockout mice are paralyzed and fail to cluster AChRs at the NMJ, and breeding them with transgenic mice constitutively expressing Z ؉ agrin in motor neurons rescued AChR clustering. Surprisingly, however, these rescued mice remained paralyzed, while electrophysiologic studies demonstrated that the motor axon and synapse were functional-spontaneous and evoked recordings revealed synaptic transmission and muscle contraction. These results point to a proximal defect in motor neuron firing in the absence of Nova and reveal a previously unsuspected role for RNA regulation in the physiologic activation of motor neurons.alternative splicing ͉ physiology ͉ neuromuscular junction ͉ neuron activity

Present data support the conclusion that protons serve as an important neurotransmitter to convey excitatory stimuli from inner ear type I vestibular hair cells to postsynaptic calyx nerve terminals. Time-resolved pH imaging revealed stimulus-evoked extrusion of protons from hair cells and a subsequent buildup

Thirteen newly isolated monoclonal antibodies (MAbs) were used to study relationships between reovirus outer capsid proteins fr3, ,ulc, and X2 (core spike) and the cell attachment protein fr1. We focused on al-associated properties of serotype specificity and hemagglutination (HA). Competition between MAbs revealed two surface epitopes on I,lc that were highly conserved between reovirus serotype 1 Lang (T1L) and serotype 3 Dearing (T3D). There were several differences between TlL and T3D c3 epitope maps. Studies using TlL x T3D reassortants showed that primary sequence differences between TlL and T3D ff3 proteins accounted for differences in a3 epitope maps. Four of 12 non-ffl MAbs showed a serotype-associated pattern of binding to 25 reovirus field isolates. Thus, for reovirus field isolates, different ff1 proteins are associated with preferred epitopes on other outer capsid proteins. Further evidence for a close structural and functional interrelationship between ff3/Ilc and ff1 included (i) inhibition by f3 and ,ulc MAbs of frl-mediated HA, (ii) enhancement of ffl-mediated HA by proteolytic cleavage of ff3 and ,ulc, and (iii) genetic studies demonstrating that ffl controlled the capacity of f3 MAbs to inhibit HA. These data suggest that (i) epitopes on fr3 and ,ulc lie in close proximity to ff1 and that MAbs to these epitopes can modulate ffl-mediated functions, (ii) these spatial relationships have functional significance, since removal of ff3 and/or cleavage of ,ulc to 8 can enhance ff1 function, (iii) in nature, the ff1 protein places selective constraints on the epitope structure of the other capsid proteins, and (iv) viral susceptibility to antibody action can be determined by genes other than that encoding an antibody's epitope.