A. Ter Maat

Acth-Like Immunoreactivity In 2 Electrotonically Coupled Giant-Neurons In The Pond Snail Lymnaea-Stagnalis

SummaryTwo giant neurons (diameter 130 μm) were identified immunocytochemically by means of the unlabeled antibody enzyme technique with anti ACTH 1–39 and 1–24 in the pond snail Lymnaea stagnalis. The cells are located in the visceral and the right parietal ganglion, respectively. They contain moderately electron dense elementary granules (diameter 150–160 nm). By means of the intracellular horseradish peroxidase injection technique it was shown that the cells send fibres into the neuropiles of various ganglia and into nerves. Synapses occur on the fine fibre branches in the neuropile. Synapse-like structures were found on the cell bodies and on the major fibres. The giant neurons are electrotonically coupled. With toluidine blue staining for small peptides it was demonstrated that in the central nervous system of the pond snail numerous peptidergic neurons occur in addition to those identified with the classical staining methods for neurosecretion.

Induction of egg-laying in the pond snail Lymnaea stagnalis by environmental stimulation of the release of ovulation hormone from the Caudo—Dorsal Cells

Ovipository activity decreases when specimens of the pond snail, Lymnaea stagnalis, are kept in closed jars that are not cleaned regularly. When the snails are transferred from dirty to clean water, egg-laying occurs within 3 h in over 90% of the animals. The number of eggs per egg mass laid after water change is directly related to the length of the period between the induced and the previous oviposition. The relationship is similar to that found when snails are injected with a very high dose (20-times threshold) of egg-laying hormone. The latency of oviposition, which depends on the dose of ovulation hormone, is not affected by the oviposition interval. The size of the egg capsule depends on the number of ripe eggs in the ovotestis and the packaging capacity of the female accessory sex organs. The role of a number of component factors of the water-change stimulus was studied. Elevated O2-content of the water, a clear jar and clean water all have a positive effect on egg-laying. Clean water is the most e...

Allohormones A class of Bioactive substances favoured by sexual selection.

Abstract. During close bodily contact, many species transfer substances that influence the behaviour or physiology of conspecifics. Such transfer is especially common during courtship and copulation. When this is the case the involved bioactive substances are favoured by sexual selection because their effects include increased egg production, inhibited remating, and changed sperm transport or storage in the partner. The direct mode of action of these substances is fundamentally different from that of pheromones and nuptial gifts. Therefore, the term allohormone is introduced here. An allohormone is defined as a substance that is transferred from one individual to another free-living member of the same species and that induces a direct behavioural or physiological response, bypassing external sensory organs. Although we emphasise the importance of allohormones in reproductive processes, allohormones may also have important functions outside of copulation.

Sex role alternation in the simultaneously hermaphroditic pond snail Lymnaea stagnalis is determined by the availability of seminal fluid

Encounters between potential mating partners are usually accompanied by sexual conflict. In the case of internally fertilizing simultaneous hermaphrodites that perform one sexual role at a time, this conflict arises over the sexual roles. If both animals prefer to mate in one role, and simultaneous reciprocal insemination is not possible, the conflict can be resolved by sex role swapping after the first insemination, potentially resulting in a form of sperm trading called conditional reciprocity. Although sequentially reciprocal insemination has been reported in several hermaphroditic species, we investigated whether conditional reciprocity is the only possible explanation for such mating patterns. We studied the pond snail Lymnaea stagnalis in which sexual isolation increases male sexual drive. Sex role alternation occurred only in pairs where both animals had been isolated and may be conditional. Previous studies in freshwater molluscs have interpreted the occurrence of role alternations per se as conditional reciprocity. However, based on our finding and a review of previous studies, we conclude that future experiments need to be designed very carefully to prove the existence of conditional reciprocity.

NPY in invertebrates: molecular answers to altered functions during evolution.

As in Lymnaea stagnalis NPY plays a key role in regulating energy flows but has no effect on food intake, two important questions arise: 1) How is the amount of food consumed related to energy storage? 2) Can we give a molecular explanation for this alteration in function of NPY during evolution? Recent data have shown that also in Lymnaea a leptin-like factor is produced by glycogen storing cells which inhibits food intake, a Lymnaea storage feedback factor (LySFF). So, food consumption seems in balance with the amount of energy stored in this animal. We suppose that NPY neurons in Lymnaea have receptors for LySFF so that their activity in regulating energy homeostasis reflects the amount of stored energy. By comparing the molecular structure of NPYs in invertebrates it became clear that only molluscan and arthropod NPY are synthesized from a prohormone similar to vertebrate NPYs and should be considered as real invertebrate homologs of NPY. Based on pharmacological data we suppose that the identified Lymnaea NPY receptor is a Y1 subtype. This might explain that LyNPY has no effect on food intake in Lymnaea as this function of NPY in mammals is regulated through the Y5 subtype receptor.

Suppression of egg-laying during starvation in the snailLymnaea stagnalis by inhibition of the ovulation hormone producing Caudo-Dorsal cells

Starvation inhibits egg-laying in the snail, Lymnaea stagnalis. In starved animals the neurosecretory Caudo-Dorsal Cells (CDC), which produce the egg-laying hormone, are hyperpolarized as compared to the CDC of controls. However, they are more responsive to repetitive intracellular stimulation, which induces the hormone releasing discharge. Hyperpolarization is not found in the non-neurosecretory Cerebral Giant Cells, which indicates that the effect is specific for the CDC. It is also a characteristic effect of starvation as compared to another treatment (dirty water) inhibiting egg-laying.

Masculinity and receptivity in the hermaphrodite pond snail, lymnaea-stagnalis

Abstract Copulation activity in the hermaphrodite pond snail Lymnaea stagnalis increases with increasing periods of isolation and the latencies of the successive behaviours involved in copulation decrease with longer isolation periods. In pairs of snails in which the partners undergo different periods of isolation, the longest-isolated animal becomes the male. This warrants the conclusion that masculinity increases with increasing isolation periods. Snails acting as male copulants become females in the second copulation, one day later, and former females do not show preference for the male or the female role. Based on these findings, we propose a model for the sexual state of L. stagnalis which implies that snails are continuously receptive, but the level of masculinity varies between zero and a certain value depending on the time elapsed since previous copulation as a male.

Dual inhibitory action of FMRFamide on neurosecretory cells controlling egg laying behavior in the pond snail

We describe here the electrophysiological characterization of a dual inhibitory action of FMRFamide (FMRFa, Phe-Met-Arg-Phe-NH2) on the caudodorsal cells (CDCs) of the pond snail Lymnaea stagnalis: (i) a transient hyperpolarizing response (H-response) and (ii) a suppression of the excitability of the cells, which lasted as long as the peptide was present. Both effects of FMRFa occurred in silent, excitable cells as well as discharging cells. The effects were reversible and dose-dependent in the range of 10(-9) to 10(-5) M. The H-response was not blocked by any of the antagonists to classical neurotransmitters that were tested. The reversal potential of the H-response was dependent on the [K+]o, which suggests that K+ is the major charge carrier in this response. 4-Aminopyridine (4-AP) blocked the H-response but did not affect the suppression of the excitability by FMRFa. This indicates that the effects of the peptide on these cells are independent. Experiments on the mechanism of the inhibition of the excitability indicated that FMRFa blocks the cAMP-dependent activation of the pacemaking mechanism of the CDCs. In experiments with isolated cells it was demonstrated that the actions of FMRFa are mediated directly through receptors on CDCs (H-response: ED50 = 10(-8) M). Finally, anti-FMRFa-positive varicosities and axons close to the somata, the axons and the neurohaemal endings of the CDCs were demonstrated immunocytochemically. The duality of the action of FMRFa on the neural activity of CDCs indicates its role of high priority in the regulation of egg laying behavior.

Effects of frequent mating on sex allocation in the simultaneously hermaphroditic great pond snail (Lymnaea stagnalis)

Simultaneous hermaphrodites have the opportunity to control the allocation of resources to the male and female function depending on the circumstances. Such flexibility also provides the possibility to influence sex allocation in the mating partner. To investigate this idea, we measured egg production (female investment) and sperm production as well as prostate gland size (both are part of male investment) under different mating regimes in the great pond snail Lymnaea stagnalis. We find no evidence for the prediction from sex allocation theory that sperm production increases with mating frequency. However, we do find that animals with more mating opporunities develop smaller prostate glands, in which seminal fluid is produced. Moreover, repeated mating increases egg production, thus shifting allocation towards the female function, and probably decreases growth. So, our data hint at a three-way trade-off between part of the male function (prostate gland), female function, and growth. Interestingly, sex allocation seems to be shifted in the opposite direction from the one predicted by theory. We discuss how this feminization is suggestive of a direct manipulation by the sperm donor, probably to stimulate immediate sperm use.

Melatonin affects the temporal organization of the song of the zebra finch.

In birds and mammals, including humans, melatonin‐binding sites are abundant in brain areas that have no known clock function. Although the role of such binding sites is still unclear, it is assumed that these sites link neural functions to circadian or circannual demands of neuroendocrine homeostasis and reproduction. To investigate a possible direct role of melatonin in motor control, we studied the song and neural song system of the zebra finch. Neurons of two sensory‐motor areas of the descending song control circuit that are crucial for the organization of the song pattern, the HVC and RA, express the melatonin‐1B receptor (Mel1B), while the hypoglossal motor neurons of the song circuit express melatonin‐1C receptors (Mel1C). Application of melatonin to brain slices decreases the firing‐rate of RA‐neurons. Systemic administration of a Mel1B antagonist at the beginning of the night shortens the song and motif length and affects the song syllable lengths produced the next day. The temporal pattern of the song, however, does not undergo daily changes. Thus, melatonin is likely to affect a non‐circadian motor pattern by local modulation of song control neurons and in consequence alters a sexual signal, the song of the zebra finch.