SUMMARY Itch is the least well understood of all the somatic senses, and the neural circuits that underlie this sensation are poorly defined. Here we show that the atonal-related transcription factor Bhlhb5 is transiently expressed in the dorsal horn of the developing spinal cord and appears to play a role in the formation and regulation of pruritic (itch) circuits. Mice lacking Bhlhb5 develop self-inflicted skin lesions and show significantly enhanced scratching responses to pruritic agents. Through genetic fate-mapping and conditional ablation we provide evidence that the pruritic phenotype in Bhlhb5 mutants may be due to selective loss of a subset of inhibitory interneurons in the dorsal horn. Our findings suggest that Bhlhb5 is required for the survival of a specific population of inhibitory interneurons that regulate pruritis and provide evidence that the loss of inhibitory synaptic input results in abnormal itch.

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Here we studied the role of signaling through ErbB-family receptors in interactions between unmyelinated axons and non-myelinating Schwann cells in adult nerves. We generated transgenic mice that postnatally express a dominant-negative ErbB receptor in non-myelinating but not in myelinating Schwann cells. These mutant mice present a progressive peripheral neuropathy characterized by extensive Schwann cell proliferation and death, loss of unmyelinated axons and marked heat and cold pain insensitivity. At later stages, C-fiber sensory neurons die by apoptosis, a process that may result from reduced GDNF (glial cell line-derived neurotrophic factor) expression in the sciatic nerve. Neuregulin 1 (NRG1)-ErbB signaling mediates, therefore, reciprocal interactions between non-myelinating Schwann cells and unmyelinated sensory neuron axons that are critical for Schwann cell and C-fiber sensory neuron survival. This study provides new insights into ErbB signaling in adult Schwann cells, the contribution of non-myelinating Schwann cells in maintaining trophic support of sensory neurons, and the possible role of disrupted ErbB signaling in peripheral sensory neuropathies.

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