Nitric oxide mediates glutamate-evoked dopamine release in the medial preoptic area.

Dopamine (DA) release in the medial preoptic area (MPOA) of the hypothalamus is an important facilitator of male sexual behavior. The presence of a receptive female increases extracellular DA in the MPOA, which increases further during copulation. However, the neurochemical events that mediate the increase of DA in the MPOA are not fully understood. Here we report that glutamate, reverse-dialyzed into the MPOA, increased extracellular DA, which returned to baseline after the glutamate was removed. This increase was prevented by co-administration of the nitric oxide synthase inhibitor NG-nitro-l-arginine methyl ester (L-NAME), but not by the inactive isomer, Nw-nitro-d-arginine methyl ester (D-NAME). In contrast, extracellular concentrations of the major metabolites of DA were decreased by glutamate, suggesting that the DA transporter was inhibited. These decreases were also inhibited by L-NAME, but not D-NAME. These results indicate that glutamate enhances extracellular DA in the MPOA, at least in part, via nitric oxide activity. Therefore, glutamatergic stimulation of nitric oxide synthase may generate the female-induced increase in extracellular DA in the MPOA, which is important for the expression of male sexual behavior.

Apoptosis--a death-inducing mechanism tightly linked with morphogenesis in Hydractina echinata (Cnidaria, Hydrozoa).

Programmed cell death is not only known as a mechanism mediating tissue destruction, but also as an organismic tool for body shaping and regulation of morphological events during development. Here we report the tight and vital link of the most prominent form of programmed cell death, apoptosis, to one of the oldest, most basic, and most radical developmental processes, the metamorphosis of the marine hydrozoon Hydractinia echinata. Apoptosis, represented by DNA fragmentation, appears very early during metamorphosis, approximately 20 minutes post induction. It is then executed in a very distinct spatial and temporal pattern, including the removal or phagocytosis of a large number of larval cells prior to the appearance of stolons and tentacles. Our data indicate a developmental program striving to reduce all body parts that are no longer necessary, before reaching a distinct turning point, when the development of adult features is initiated. During these events, morphogenesis of basal and apical structures correlates with recycling of that particular larval region, indicated by the presence of apoptosis. Based on these data, the necessity of apoptosis for normal development of adult patterns is inferred and a fundamental association of apoptosis with developmental processes can be stated.

Immunohistochemical studies of GLWamides in Cnidaria.

GLWamides are a recently described, novel family of neuropeptides in Cnidaria. Antibodies specific for the GLWamide terminus have been raised and used to evaluate the occurrence and localisation of immunopositive material in various Cnidaria in order to determine whether GLWamides are present and to obtain a first impression of the possible regulatory role of these neuropeptides. GLWamide immunoreactivity has been found in all species tested and is not confined to distinct life stages but is present during most of the life cycle of the Cnidaria. Additionally, GLWamides are expressed by different nerve cells at different life stages. GLWamide-immunoreactive cells constitute a subset of the neural equipment. Overall our data suggest that GLWamides generally occur in the nervous system of Cnidaria and that these peptides are multifunctional. Putative functions other than the control of development include the regulation of nematocyst discharge, muscle contraction and the regulation of gastric function.

The role of GLWamides in metamorphosis of Hydractinia echinata.

The metamorphosis of many marine invertebrate larvae is induced by environmental signals. Upon reception of the cues, internal signals have to be set in motion to convey information to all cells of the larvae. For hydrozoan larvae it was hypothesised that ectodermal neurosensory cells at the anterior part are those cells receptive of the inducer. Recently, it was shown that novel peptides with a common GLWamide terminus are found in Cnidaria. These peptides are located in a specific subset of the anterior sensory cells. It was hypothesised that the neuropeptides represent an internal signal coordinating the metamorphic process. In the current study we present further evidence for this hypothesis. Induction of metamorphosis is very specific for the GLWamide terminus and amidation is essential. The potency to metamorphose is strongly correlated with the presence of GLWamide-immunoreactive cell bodies. Our data fit our hypothesis about a very important role of GLWamides in the initiation of the morphogenetic processes very well.