Urotensin II in Invertebrates: From Structure to Function in Aplysia californica
(A) Diagram of the buccal ganglion neurons involved in generating feeding behavior, highlighting the sensory neuron cluster. The larger motoneurons are present as a cluster on the dorsal surface of the ganglion (the larger orange cells above), while the smaller sensory neurons are present in a cluster on the dorsal-medial aspect of the ganglion. The population of buccal sensory neurons is heterogeneous. They are grouped into at least three clusters with distinct sensory properties and transmitter contents. The radula mechanoafferent neurons (green) innervate the subradular tissue and contain SCP and enterin. The S1 sensory neuron cluster (purple) is present only on the caudal surface and is distinguished by a slightly larger size than the S2 sensory neuron cluster (brown). The S1 cluster contains primarily FMRFamide, while S2 contains primarily FRFamide. Here, we show that apUII is expressed in both the S1 and S2 clusters. Note that the commissure is twisted, so that on the left, the rostral surface of the buccal ganglion is shown, while the right side shows the caudal surface. Nerve abbreviations, Com: buccal commissure; CBC: cerebral-buccal connective; EN, esophageal nerve; N, buccal nerve; RN: radular nerve. (B) In-situ hybridization staining of the buccal and cerebral ganglion shows the distribution of apUII mRNA expressing neuron somata. The buccal sensory neurons express the mRNA for apUII. Abbreviations, rBG: rostral side of the buccal ganglion; cBG: caudal side of the buccal ganglion; dCG: dorsal side of the cerebral ganglion; vCG: ventral side of the cerebral ganglion. S1, S2, A-, F- and C-neuronal clusters are labeled.