Alterations in the levels and distribution of octopamine in the central nervous system and ovary of the Pacific white shrimp, Litopenaeus vannamei, and its possible role in ovarian development

Abstract

Octopamine (OA) is a major neurotransmitter that has not been studied in the Pacific white shrimp, Litopenaeus vannamei. Therefore, we investigated changes in OA levels, its distribution in regions of the central nervous system (CNS) and ovary during the ovarian maturation cycle, as well as its possible role in regulating ovarian maturation. OA exhibited the highest concentration in the brain and thoracic ganglia at ovarian stage II, and then declined to the lowest concentration at ovarian stages III and IV. In the cerebral ganglia, OA-immunoreactivity (OA-ir) was present in neurons of clusters 6, 17, the anterior and posterior medial protocerebral, olfactory, antenna II, and tegumentary neuropils. In the circumesophageal, subesophageal, thoracic ganglia and abdominal ganglia, OA-ir was detected in several neuropils, neurons and fibers. The high level of intensity in OA immunostaining was observed in early developmental stage of oocyte by comparison with low level of OA-ir in late stages of oocyte development. Functionally, OA-injected female shrimps at doses of 2.5×10(-7) and 2.5×10(-6)mol/shrimp, showed significantly decreased gonado-somatic indices, oocyte diameters, and hemolymph vitellogenin levels, compared with control groups. This study showed changes of OA in the CNS and ovary reaching the highest level in early ovarian stages and declining in late stages, and it decreased hemolymph vitellogenin levels, suggesting significant involvement of OA in female reproduction in this species.

Keywords: Central nervous system; Litopenaeus vannamei; Octopamine; Ovarian development; Vitellogenin.