Histamine Immunoreactive Elements in the Central and Peripheral Nervous Systems of the Snail, Biomphalaria spp., Intermediate Host for Schistosoma mansoni

Abstract

Histamine appears to be an important transmitter throughout the Animal Kingdom. Gastropods, in particular, have been used in numerous studies establishing potential roles for this biogenic amine in the nervous system and showing its involvement in the generation of diverse behaviours. And yet, the distribution of histamine has only previously been described in a small number of molluscan species. The present study examined the localization of histamine-like immunoreactivity in the central and peripheral nervous systems of pulmonate snails of the genus Biomphalaria. This investigation demonstrates immunoreactive cells throughout the buccal, cerebral, pedal, left parietal and visceral ganglia, indicative of diverse regulatory functions in Biomphalaria. Immunoreactivity was also present in statocyst hair cells, supporting a role for histamine in graviception. In the periphery, dense innervation by immunoreactive fibers was observed in the anterior foot, perioral zone, and other regions of the body wall. This study thus shows that histamine is an abundant transmitter in these snails and its distribution suggest involvement in numerous neural circuits. In addition to providing novel subjects for comparative studies of histaminegic neurons in gastropods, Biomphalaria is also the major intermediate host for the digenetic trematode parasite, which causes human schistosomiasis. The study therefore provides a foundation for understanding potential roles for histamine in interactions between the snail hosts and their trematode parasites.

Exploring the role of biogenic amines in schistosome host–parasite interactions

“…SmGPR-1 was also found on the surface of the snail stage, sporocysts [6], but the significance of this observation was unclear because Biomphalaria snails were not known to produce histamine. However, new evidence by Croll and colleagues has shown for the first time that the snails have a well-developed histaminergic system [8]. An elegant, detailed analysis of histamine-containing cells in two different species of Biomphalaria found an extensive network of histaminergic neurons throughout the snail CNS and peripheral nervous system [8].…”

“…However, new evidence by Croll and colleagues has shown for the first time that the snails have a well-developed histaminergic system [8]. An elegant, detailed analysis of histamine-containing cells in two different species of Biomphalaria found an extensive network of histaminergic neurons throughout the snail CNS and peripheral nervous system [8]. The authors describe several possible neural sources for exogenous histamine in the snail, either in innervated tissues or free fluid spaces.…”

“…The authors describe several possible neural sources for exogenous histamine in the snail, either in innervated tissues or free fluid spaces. Given that schistosomes are known to stimulate histamine release in the definitive host (see [2]), the authors speculate that sporocysts may have a similar effect in the snail, potentially changing histamine-controlled behaviours such as feeding and locomotion [8].…”

“…A search of existing genomic and transcriptome data using computational tools has not found a clear homolog of histidine decarboxylase, the enzyme responsible for histamine biosynthesis. Given the new study by Croll and colleagues [8], we should now consider the possibility that histamine may be entirely of host origin and more research is needed to identify the transporters involved in this uptake, not only for sporocysts but also the mammalian stages. These are exciting new developments, which will undoubtedly stimulate further research into this important area of schistosome biology.…”

“…The other mechanism involves transport of host HA across the tegument and then uptake into parasite neurons via specific transporters. While most of the evidence supporting this model comes from mammalian stages of the parasite, a recent study from the Croll lab [8] suggests HA may also play an important role in the interaction with the snail intermediate host.…”