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This Article Full Text Full Text (PDF) All Versions of this Article: 102/1/399    most recent 91317.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Pratt, K. G. Articles by Aizenman, C. D. PubMed PubMed Citation Articles by Pratt, K. G. Articles by Aizenman, C. D.

Multisensory Integration in Mesencephalic Trigeminal Neurons in Xenopus Tadpoles

Department of Neuroscience, Brown University, Providence, Rhode Island

Submitted 15 December 2008; accepted in final form 19 April 2009

Mesencephalic trigeminal (M-V) neurons are primary somatosensory neurons with somata located within the CNS, instead of in peripheral sensory ganglia. In amphibians, these unipolar cells are found within the optic tectum and have a single axon that runs along the mandibular branch of the trigeminal nerve. The axon has collaterals in the brain stem and is believed to make synaptic contact with neurons in the trigeminal motor nucleus, forming part of a sensorimotor loop. The number of M-V neurons is known to increase until metamorphosis and then decrease, suggesting that at least some M-V neurons may play a transient role during tadpole development. It is not known whether their location in the optic tectum allows them to process both visual and somatosensory information. Here we compare the anatomical and electrophysiological properties of M-V neurons in the Xenopus tadpole to principal tectal neurons. We find that, unlike principal tectal cells, M-V neurons can sustain repetitive spiking when depolarized and express a significant H-type current. M-V neurons could also be driven synaptically by visual input both in vitro and in vivo, but visual responses were smaller and longer-lasting than those seen in principal tectal neurons. We also found that the axon of M-V neurons appears to directly innervate a tentacle found in the corner of the mouth of premetamorphic tadpoles. Electrical stimulation of this transient sensory organ results in antidromic spiking in M-V neurons in the tectum. Thus M-V neurons may play an integrative multisensory role during tadpole development.