Transsynaptic transport of wheat germ agglutinin expressed in a subset of type II taste cells of transgenic mice.
BACKGROUND
Anatomical tracing of neural circuits originating from specific subsets of taste receptor cells may shed light on interactions between taste cells within the taste bud and taste cell-to nerve interactions. It is unclear for example, if activation of type II cells leads to direct activation of the gustatory nerves, or whether the information is relayed through type III cells. To determine how WGA produced in T1r3-expressing taste cells is transported into gustatory neurons, transgenic mice expressing WGA-IRES-GFP driven by the T1r3 promoter were generated.


RESULTS
Immunohistochemistry showed co-expression of WGA, GFP and endogenous T1r3 in the taste bud cells of transgenic mice: the only taste cells immunoreactive for WGA were the T1r3-expressing cells. The WGA antibody also stained intragemmal nerves. WGA, but not GFP immunoreactivity was found in the geniculate and petrosal ganglia of transgenic mice, indicating that WGA was transported across synapses. WGA immunoreactivity was also found in the trigeminal ganglion, suggesting that T1r3-expressing cells make synapses with trigeminal neurons. In the medulla, WGA was detected in the nucleus of the solitary tract but also in the nucleus ambiguus, the vestibular nucleus, the trigeminal nucleus and in the gigantocellular reticular nucleus. WGA was not detected in the parabrachial nucleus, or the gustatory cortex.


CONCLUSIONS
These results show the usefulness of genetically encoded WGA as a tracer for the first and second order neurons that innervate a subset of taste cells, but not for higher order neurons, and demonstrate that the main route of output from type II taste cells is the gustatory neuron, not the type III cells.
Damak
Sami
S
Department of Physiology and Biophysics, Mount Sinai School of Medicine, 1425 Madison Avenue, Box 1677, New York, New York, 10029, USA. sami.damak@rdls.nestle.com
Mosinger
Bedrich
B
Margolskee
Robert F
RF
D000818:Animals; D005830:Geniculate Ganglion / Q000166:cytology / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007150:Immunohistochemistry; D008526:Medulla Oblongata / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D009434:Neural Pathways / Q000378:metabolism / Q000502:physiology; D011401:Promoter Regions, Genetic / Q000235:genetics; D021381:Protein Transport; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism*; D017552:Solitary Nucleus / Q000166:cytology / Q000378:metabolism; D013569:Synapses / Q000378:metabolism* / Q000502:physiology; D013650:Taste Buds / Q000166:cytology / Q000378:metabolism*; D012668:Trigeminal Ganglion / Q000166:cytology / Q000378:metabolism; D014909:Wheat Germ Agglutinins / Q000235:genetics / Q000378:metabolism*; D000098706:Taste Receptors, Type 2
D043562:Receptors, G-Protein-Coupled; D014909:Wheat Germ Agglutinins; C431926:taste receptors, type 1; D000098706:Taste Receptors, Type 2; D049452:Green Fluorescent Proteins