Abstract
The nervous system expresses neuromolecules that play a crucial role in regulating physiological processes. Neuromolecule synthesis can be regulated by oxygen-dependent enzymes. Bivalves are a convenient model for studying air exposure-induced hypoxia. Here, we studied the effects of hypoxia on the expression and dynamics of neurotransmitters, and on neurotransmitter enzyme distribution, in the central nervous system (CNS) of the scallop Azumapecten farreri. We analyzed the expression of the neurotransmitters FMRFamide and serotonin (5-HT) and the choline acetyltransferase (CHAT) and universal NO-synthase (uNOS) enzymes during air exposure-induced hypoxia. We found that, in early-stage hypoxia, total serotonin content decreased in some CNS regions but increased in others. CHAT-lir cell numbers increased in all ganglia after hypoxia; CHAT probably appears de novo in accessory ganglia. Short-term hypoxia caused increased uNOS-lir cell numbers, while long-term exposure led to a reduction in their number. Thus, hypoxia weakly influences the number of FMRFamide-lir neurons in the visceral ganglion and does not affect peptide expression in the pedal ganglion. Ultimately, we found that the localization and level of synthesis of neuromolecules, and the numbers of cells expressing these molecules, vary in the scallop CNS during hypoxia exposure. This indicates their possible involvement in hypoxia resistance mechanisms.
Highlights
Many invertebrates, such as marine bivalves, have adapted to reduced concentrations or a total lack of oxygen during their evolution [1,2,3]
We study the effects of air exposure-induced hypoxia on the activity of neurotransmitter synthesis enzymes, including choline acetyltransferase (CHAT) and universal nitric oxidesynthase, and the expression of 5-HT and FMRFamide in the central nervous system (CNS) of the scallop species A. farreri, in the case of disturbances to their escape behaviors
We discovered that the exposure of A. farreri to hypoxia causes changes in the expression of neurotransmitters (FMRFamide peptide and monoamine 5-HT) and enzymes (CHAT and universal nitric oxide (NO)-synthase (uNOS)) involved in ACh and NO synthesis in the ganglia of the CNS
Summary
Many invertebrates, such as marine bivalves, have adapted to reduced concentrations (hypoxia) or a total lack of oxygen (anoxia) during their evolution [1,2,3]. A characteristic protective behavioral response of scallops to stressful conditions (such as abnormal temperature, predation pressure, or low oxygen concentrations in seawater) is escape facilitated by contraction of the adductor muscle [10,11,12], which is crucial for survival. This type of behavior is known to be associated with discrete signaling systems. It can be hypothesized that a forced restriction of movements would induce significant changes in the metabolism of neurotransmitters and neurohormones
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