Source of the tentacular hormone in terrestrial pulmonates

Neuroendocrine disruption: more than hormones are upset

Only a small proportion of the published research on endocrine-disrupting chemicals (EDC) directly examined effects on neuroendocrine processes. There is an expanding body of evidence that anthropogenic chemicals exert effects on neuroendocrine systems and that these changes might impact peripheral organ systems and physiological processes. Neuroendocrine disruption extends the concept of endocrine disruption to include the full breadth of integrative physiology (i.e., more than hormones are upset). Pollutants may also disrupt numerous other neurochemical pathways to affect an animal's capacity to reproduce, develop and grow, or deal with stress and other challenges. Several examples are presented in this review, from both vertebrates and invertebrates, illustrating that diverse environmental pollutants including pharmaceuticals, organochlorine pesticides, and industrial contaminants have the potential to disrupt neuroendocrine control mechanisms. While most investigations on EDC are carried out with vertebrate models, an attempt is also made to highlight the importance of research on invertebrate neuroendocrine disruption. The neurophysiology of many invertebrates is well described and many of their neurotransmitters are similar or identical to those in vertebrates; therefore, lessons learned from one group of organisms may help us understand potential adverse effects in others. This review argues for the adoption of systems biology and integrative physiology to address the effects of EDC. Effects of pulp and paper mill effluents on fish reproduction are a good example of where relatively narrow hypothesis testing strategies (e.g., whether or not pollutants are sex steroid mimics) have only partially solved a major problem in environmental biology. It is clear that a global, integrative physiological approach, including improved understanding of neuroendocrine control mechanisms, is warranted to fully understand the impacts of pulp and paper mill effluents. Neuroendocrine disruptors are defined as pollutants in the environment that are capable of acting as agonists/antagonists or modulators of the synthesis and/or metabolism of neuropeptides, neurotransmitters, or neurohormones, which subsequently alter diverse physiological, behavioral, or hormonal processes to affect an animal's capacity to reproduce, develop and grow, or deal with stress and other challenges. By adopting a definition of neuroendocrine disruption that encompasses both direct physiological targets and their indirect downstream effects, from the level of the individual to the ecosystem, a more comprehensive picture of the consequences of environmentally relevant EDC exposure may emerge.

[Apparent immunoreactivity of CRF in the tentacles of the mollusk Helix pomatia]

In the Gastropod Mollusc Helix pomatia (Pulmonata: Stylommatophora), an antiserum raised against ovine CRF 41 reveals a neuropeptide in some primary sensory neurons distributed beneath the epithelium of the higher tentacles (optic) and the lower tentacles. The collar cells and the lateral cells of both kinds of tentacles are innervated by some CRF immunoreactive fibers. Considering the given results, these processes probably originate in the central ganglia, but also in the tentacular sensory neurons. The neuropeptide revealed by our immunserum would be involved in the regulation of the exocrine secretion of the collar and lateral cells. It may also take part in the regulation of the endocrine secretion of collar cells in both sorts of tentacles.

Evidence for neurosecretory control of the optic gland in terrestrial pulmonates

The optic gland in terrestrial pulmonates secretes gonadotropic hormone. The present study investigates the fine structure of the optic gland to clarify the control of secretion. Animals used were the slug, Limax marginatus, and the snail, Euhadra peliomphala. The optic gland cell has a process and the cytoplasm is filled with large granules about 750-1300 nm in diameter with a thin cortex in L. marginatus and 800-1700 nm delimited by a thick peripheral layer in E. peliomphala. These gland cells are characterized by well-developed granular endoplasmic reticulum. Granule formation was seen in the region of the Golgi apparatus. During the breeding season, the medial neurosecretory cells of the brain are active in the production and release of secretory materials. Although no neurosecretory cell bodies occur in the tentacular ganglion, neurosecretory axons penetrate into the optic gland cells. Cobalt filling reveals that axons of the medial neurosecretory cells project to the tentacular ganglion, near the optic gland. These results suggest that the optic gland is controlled by a neurohormone originating from the medial neurosecretory cells of the brain.

[Action of the extract from the optic tentacles of juvenile and adult snails on the in vivo development of the albumin gland of Helix aspersa]

Injected optic tentacle homogenates in Helix aspersa were shown to cause a decrease in growth rate and albumen gland development. The effects of optic tentacles removed from young animals and from adult animals were compared. In young animals, injections of adult optic tentacle homogenate resulted in a reduction in both growth rate and albumen gland weight. In older adult animals injected with adult optic tentacle homogenate, growth and albumen gland development decreased, but not to the same extent as in young animals. In contrast, the inhibitory effect of the young tentacle homogenate was inverted. The possible source of a tentacular factor is discussed in relation to its possible origin in other investigated pulmonates, and also the mechanism of the homogenates heterochronic action.