| This thesis characterizes a system of peripheral neurons containing members of the crustacean hyperglycemic hormone (CHH) family of stress-related neuropeptides, and describes the complex modulation of activity in these neurons by monoamine systems in the American lobster, Homarus americanus. CHH peptides have been implicated in the regulation of blood glucose, molting, and gill ion transport, and are released when lobsters are subjected to thermal, osmotic, or hypoxic stress. Intracellular tracer injection revealed that CHH-containing neurons are extrasomatically coupled, and was used to characterize morphological subtypes projecting to the pericardial organs, the ventral nerve cord, bidirectionally, and locally. Intracellular recording was used to explore spontaneous, thermosensitive, and osmosensitive activity of the CHH-containing neurons in the detached second thoracic nerve root. These neurons, and neurons in the X-organ of the sinus gland were found to express aquaporin-like immunoreactivity. The second thoracic nerve roots are also the sites of neurohemal projections of the serotonin (5HT)/proctolin and octopamine systems, which have been implicated in the modulation of aggressive behavior. Immunohistochemistry and confocal microscopy were used to observe the relative configuration of 5HT-immunoreactive nerve endings to CHH-immunoreactive somata in the second thoracic nerve root. Intracellular recording and bath-application pharmacology were used to study changes in CHH-containing neuron activity in response to a range of physiologically plausible concentrations of 5HT and octopamine. Though both monoamines inhibit spontaneous activity in these neurons at high concentrations, an excitatory effect is elicited by low concentrations of octopamine. These neurons also desensitize to serotonin, suggesting that they adapt to ambient levels of serotonin released by the spontaneously active 5HT neurosecretory cells. The latter cell type contains the pentapeptide proctolin in its terminals. Proctolin, applied in conjunction with 5HT, may modulate the 5HT inhibitory effect. The complex effects of 5HT, proctolin, and octopamine on the activity of CHH-containing neurons demonstrate that neurosecretory cells can be tuned to different levels of activity and history of activity in other neuromodulatory systems. Thus, the CHH-like stress neuropeptide system in the peripheral nervous system of Homarus Americanus is an anatomically tractable system for further study of complex aspects of. |
