ULTRASTRUCTURE OF THE STOMATOGASTRIC GANGLION NEUROPIL OF THE CRAB, CANCER-BOREALIS

The stomatogastric ganglion (STG) of the crab, Cancer borealis, contai ns the neural networks responsible for rhythmic pattern generation of the foregut. Neuron counts indicate that the STG of C. borealis has 25 -26 neurons, 4-5 fewer than that found in lobsters. We describe the ul trastructural features of the ganglion by focusing on those that may b e involved in storage, release, or range of action of peptide modulato rs, including a lacunar system and multiple types of intercellular jun ctions. In the neuropil, we identify five synaptic profile classes tha t contain the invertebrate presynaptic apparatus (dense bars, small cl ear vesicles), two of which also contain dense core (modulator-contain ing) vesicles. These latter two are comprised of multiple immunocytoch emical classes that are not easily distinguished by structural criteri a. In addition, we find neurohemal-like profiles that contain primaril y dense core vesicles. Our finding that multiple profile types in the STG possess modulator-containing vesicles coincides with immunocytoche mical results better than do previous ultrastructural studies that rep ort only one such profile type. We show that a single modulatory input , stomatogastric nerve axon 1, makes only classical synapses and not n eurohemal-like profiles, although some modulators are found in both th ese profile types. These data provide the groundwork for understanding the architecture of modulatory input-target interactions and suggest ways that the specificity of modulatory effects within a complex neuro pil may be attained. (C) 1996 Wiley-Liss, Inc.