Graduate Thesis Or Dissertation

 

Neuronal and hormonal control of the vascular system of the marine mollusc, Aplysia californica Public Deposited

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  • The vascular system of Aplysia californica is a simple visceromotor system with three main arteries innervated by a small pool of identified neurons. I used this system to study the functions of neuropeptide transmitters and their actions on neural and muscle tissues. A central finding of this study is that a natural release of peptide transmitters from the bag cell neurons triggers a long-term (>lhr) increase in the contractile activity of two major arteries. This activity appears to be mediated hormonally since denervation of the arteries does not abolish the response. The contraction pattern is behaviorally significant since it is likely to increase blood flow to reproductive organs while diverting it away from digestive organs. Bag cell neurons also affect motoneurons (LBvc) innervating the arteries. Stimulated bag cell activity inhibited (<5 min) and subsequently excited (>20 min) LB, neurons but not sufficiently to cause vasoconstriction. Infusions of bag cell peptides, a-BCP and ELH, into the abdominal ganglion mimicked the inhibitory and excitatory responses of vasomotor neurons, respectively. SCPb, and FMRF also altered LB,, activities for prolonged periods. These peptides may modulate the excitability of the vasomotor neurons and thus alter the effectiveness of neural pathways regulating phasic contractions of the arteries. The direct (hormonal) effects of neuropeptide transmitters were tested on isolated artery segments. a-BCP caused sustained tonic contractions of the AA and prolonged phasic contractions of the GeA, whereas, SCPb and FMRF caused relaxation. In general the effects of peptides were more complex and longer lasting than those of conventional neurotransmitters (5HT, ACh). These experiments suggest that the vasculature is regulated at two levels: 1) at the central nervous system where peptide transmitters excite or inhibit motor neurons, thus altering the effectiveness of phasic neural commands, and 2) at the vascular muscle, where the same peptide transmitters may act hormonally to induce long term changes in artery contractions. In this way a small set of peptide transmitters with long lasting actions can produce a complex set of behavioral outputs.
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