Structural plasticity in the olfactory system of adult spiny lobsters: postembryonic development permits life-long growth, turnover, and regeneration

Caribbean spiny lobsters ( Panulirus argus ) rely on their sense of olfaction for many behaviours. Growth of their olfactory systems, and maintenance of olfactory function, is ensured by structural change that occurs continuously throughout life. In this paper, we review recent studies on postembryonic development in the olfactory system of P. argus and several other decapod species. Major structural change occurs in both the peripheral and central olfactory systems; it includes addition and loss of olfactory receptor neurons (ORNs), aesthetasc and other sensilla, and interneurons associated with the olfactory lobes of the brain. From these studies it is clear that continuous growth and turnover of olfactory tissue is a normal process in decapod crustaceans. In addition, we describe for the first time mechanisms that enable the peripheral olfactory system of spiny lobsters to regenerate after injury. We monitored the regeneration of olfactory tissue using in vivo incorporation of the cell proliferation marker 5- bromo-2'-deoxyuridine (BrdU). Our results show that regeneration after partial antennular amputation, which reduces the length of the antennule and thereby the number of ORNs, occurs as a result of upregulation of the normal mode of ORN addition and down-regulation of loss. In contrast, localized injury to aesthetasc sensilla, which causes the associated ORNs to degenerate but does not reduce antennular length, is followed by local regeneration of olfactory tissue.