Conservative nature of oestradiol signalling pathways in the brain lobes of octopus vulgaris involved in reproduction, learning and motor coordination

Oestradiol plays crucial roles in the mammalian brain by modulating reproductive behaviour, neural plasticity and pain perception. The cephalopod Octopus vulgaris is considered, along with its relatives, to be the most behaviourally advanced invertebrate, although the neurophysiological basis of its behaviours, including pain perception, remain largely unknown. In the present study, using a combination of molecular and imaging techniques, we found that oestradiol up-regulated O. vulgaris gonadotrophin-releasing hormone (Oct-GnRH) and O. vulgaris oestrogen receptor (Oct-ER) mRNA levels in the olfactory lobes; in turn, Oct-ER mRNA was regulated by NMDA in lobes involved in learning and motor coordination. Fluorescence resonance energy transfer analysis revealed that oestradiol binds Oct-ER causing conformational modifications and nuclear translocation consistent with the classical genomic mechanism of the oestrogen receptor. Moreover, oestradiol triggered a calcium influx and cyclic AMP response element binding protein phosphorylation via membrane receptors, providing evidence for a rapid nongenomic action of oestradiol in O. vulgaris. In the present study, we demonstrate, for the first time, the physiological role of oestradiol in the brain lobes of O. vulgaris involved in reproduction, learning and motor coordination.

L-glutamate and its ionotropic receptors in the nervous system of cephalopods

In several species of cephalopod molluscs there is good evidence for the presence of L-glutamate in the central and peripheral nervous system and evidence for both classes of ionotropic receptor, AMPA/kainate and NMDA.The best evidence for glutamate being a transmitter in cephalopods comes from pharmacological, immunohistochemical and molecular investigations on the giant fibre system in the squid stellate ganglion. These studies confirm there are AMPA/kainate-like receptors on the third-order giant axon. In the (glial) Schwann cells associated with the giant axons both classes of glutamate receptor occur.Glutamate is an excitatory transmitter in the chromatophores and in certain somatic muscles and its action is mediated primarily via AMPA/kainate-like receptors, but at some chromatophores there are NMDA-like receptors.In the statocysts the afferent crista fibres are also glutamatergic, acting at non-NMDA receptors.In the brain (of Sepia) a neuronal NOS is activated by glutamate with subsequent production of nitric oxide and elevation of cGMP levels. This signal transduction pathway is blocked by D-AP-5, a specific antagonist of the NMDA receptor.Recently immunohistochemical analysis has demonstrated (in Sepia and Octopus) the presence of NMDAR2A /B - like receptors in motor centres, in the visual and olfactory systems and in the learning system. Physiological experiments have shown that glutamatergic transmission is involved in long term potentation (LTP) in the vertical lobe of Octopus, a brain area involved in learning. This effect seems to be mediated by non-NMDA receptors. Finally in the CNS of Sepia NMDA-mediated nitration of tyrosine residues of cytoskeletal protein such as alpha-tubulin, has been demonstrated.

Effects of estradiol and progesterone on the reproduction of the freshwater crayfish Cherax albidus

In this study we have investigated the role of 17beta-estradiol and progesterone in the reproduction of the crayfish Cherax albidus by using vitellogenin (VTG) as a biomarker. Early-vitellogenic (EV), full-vitellogenic (FV), and non-vitellogenic (NV) females of Cherax albidus were treated with 17beta-estradiol, progesterone, or both for 4 weeks. Levels of VTG mRNA in the hepatopancreas were detected by RT-PCR. The PCR product was sequenced and showed 97% homology with Cherax quadricarinatus VTG. 17beta-estradiol was more effective than progesterone and 17beta-estradiol plus progesterone in increasing the vitellogenin transcript in the hepatopancreas of EV and FV females. On the contrary, progesterone was more effective than 17beta-estradiol and 17beta-estradiol plus progesterone in increasing the vitellogenin concentration in the hemolymph of EV and FV females. Hepatopancreas histology and fatty acid composition of females injected with hormones showed major modifications. No effects were registered in NV females. In conclusion, 17beta-estradiol and progesterone influence VTG synthesis, although our data indicate that they act through different pathways and are not effective until the proper hormonal environment is established, as demonstrated by their inefficacy in NV females.

Progesterone induces activation in Octopus vulgaris spermatozoa

The purpose of the present study was to determine whether Octopus vulgaris spermatozoa are activated by progesterone stimulation. Spermatozoa were collected from the spermatophores in the Needham's sac of the male (MS) and from the spermathecae of oviducal glands of the female (FS). We used transmission (TEM) and scanning (SEM) electron microscopy to study the morphology of untreated, Ca2+ ionophore A23187 and progesterone-treated MS spermatozoa, and untreated FS spermatozoa. We showed that ionophore and progesterone stimulation of MS spermatozoa induce breakdown of the membranes overlapping the acrosomal region, exposing the spiralized acrosome. These modifications resemble the acrosome reaction observed in other species. FS stored in the spermathecae did not show the membranes covering the acrosomal region present in the MS spermatozoa. When ionophore and progesterone treatments were performed in Ca2+-free artificial sea water, no changes were observed, suggesting the role of external calcium in modifying membrane morphology. Lectin studies showed a different fluorescence distribution and membrane arrangement of FS-untreated spermatozoa with respect to the MS, suggesting that spermatozoa transferred in the female genital tract after mating, are stored in a pre-activated state. The plasma membrane of the untreated MS and FS spermatozoa was labelled with Progesterone-BSA-FITC, indicating the presence of plasma membrane progesterone receptor. Taken together these data suggest that progesterone induces an acrosome- like reaction in MS spermatozoa similar to that induced by calcium elevation. In addition progesterone may play a role in the pre-activation of spermatozoa stored in the female tract, further supporting the hypothesized parallelism between cephalopods and vertebrates.

Sex steroid hormone fluctuations and morphological changes of the reproductive system of the female of Octopus vulgaris throughout the annual cycle

Sex steroids (17beta-estradiol and progesterone) and morphological variations of the reproductive system of the female of Octopus vulgaris from the Bay of Naples were followed over a period of 2 years. The increase in the ovary weight was independent of body weight as demonstrated by the gonado-somatic index (GSI). Both 17beta-estradiol and progesterone have been detected in the ovary of O. vulgaris, and their concentrations changed in correlation with the ovarian development. No 17beta-estradiol or progesterone was found in the hemolymph. 3beta-Hydroxysteroid dehydrogenase activity has been detected in the ovary, indicating that in the female of O. vulgaris the reproductive system is a source of sex steroid hormones. According to the morphological changes of the ovary, the ovarian cycle can be divided into the following phases: previtellogenesis; early vitellogenesis, full vitellogenesis and late vitellogenesis. The morphological changes of the oviducts and oviducal glands throughout the reproductive cycle were in accordance with their role in the transport and secretion of gelatinous coat covering the eggs, as well as in sperm storage and sperm reactivation during fertilization. J. Exp. Zool. 289:33-47, 2001.

Nitric oxide synthase (NOS) in the brain of the cephalopod Sepia officinalis

Nitric oxide synthase-like protein (NOS) is shown to be present in specific regions of the central nervous system (CNS) of the cephalopod mollusc Sepia officinalis (cuttlefish). NOS activity, which is Ca(2+)/calmodulin-dependent, was determined by measuring the conversion of L-[(14)C]arginine in L-[(14)C]citrulline. The partially purified NOS from brain and optic lobes exhibited on SDS-PAGE a band at 150 kDa that was immunolabelled by antibodies raised against the synthetic peptide corresponding to the amino acids 1,414-1,429 of the C-terminus of rat nNOS. This same antibody was then used for immunohistochemical staining of serial sections of the cuttlefish CNS to reveal localized specific staining of cell bodies and fibers in several lobes of the brain. Staining was found in many lower motor centers, including cells and fibers of the inferior and superior buccal lobes (feeding centers); in some higher motor centers (anterior basal and peduncle lobes); in learning centers (vertical, subvertical, and superior frontal lobes); and in the visual system [retina and deep retina (optic lobe)]. Immunopositivity was also found in the olfactory lobe and organ and in the sucker epithelium. These findings suggest that nitric oxide (NO) may be involved as a signaling molecule in feeding, motor, learning, visual, and olfactory systems in the cuttlefish brain. The presence of NOS in the cephalopod "cerebellum" and learning centers is discussed in the context of the vertebrate CNS.

N-Methyl-D-aspartate receptor stimulation activates tyrosinase and promotes melanin synthesis in the ink gland of the cuttlefish Sepia officinalis through the nitric Oxide/cGMP signal transduction pathway. A novel possible role for glutamate as physiologic activator of melanogenesis

The tyrosinase-catalyzed conversion of l-tyrosine to melanin represents the most distinctive biochemical pathway in the ink gland of the cuttlefish Sepia officinalis; however, the molecular mechanisms underlying its activation have remained so far largely uncharted. In this paper we demonstrate for the first time that l-glutamate can stimulate tyrosinase activity and promote melanin synthesis in Sepia ink gland via the N-methyl-d-aspartate (NMDA) receptor/NO/cGMP signal transduction pathway. Incubation of intact ink glands with either l-glutamate or NMDA resulted in an up to 18-fold increase of tyrosinase activity and a more than 6-fold elevation of cGMP levels. Comparable stimulation of tyrosinase was induced by an NO donor and by 8-bromo-cGMP. An NMDA receptor antagonist, NO synthase (NOS) inhibitors, and a guanylate cyclase blocker suppressed NMDA-induced effects. Immunohistochemical evidence indicated that enhanced cGMP production was localized largely in the mature part of the ink gland. Increased de novo synthesis of melanin was demonstrated in NMDA- and NO-stimulated ink glands by a combined microanalytical approach based on spectrophotometric determination of pigment levels and high performance liquid chromatography quantitation of pyrrole-2,3, 5-tricarboxylic acid, a specific melanin marker, in melanosome-containing fractions. These results fill a longstanding gap in the understanding of the complex biochemical mechanisms underlying activation of melanogenesis in the mature ink gland cells of S. officinalis and disclose a novel physiologic role of the excitatory neurotransmitter glutamate mediated by the NMDA receptor/NO/cGMP signaling pathway.

A calcium/calmodulin-dependent nitric oxide synthase, NMDAR2/3 receptor subunits, and glutamate in the CNS of the cuttlefish Sepia officinalis: localization in specific neural pathways controlling the inking system

Chemical, biochemical, and immunohistochemical evidence is reported demonstrating the presence in the brain of the cuttlefish Sepia officinalis of a Ca2+-dependent nitric oxide synthase, NMDAR2/3 receptor subunits, and glutamate, occurring in neurons and fibers functionally related to the inking system. Nitric oxide synthase activity was concentrated for the most part in the cytosolic fraction and was masked by other citrulline-forming enzyme(s). The labile nitric oxide synthase could be partially purified by ammonium sulfate precipitation of tissue extracts, followed by affinity chromatography on 2',5'-ADP-agarose and calmodulin-agarose. The resulting activity, immunolabeled at 150 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis by antibodies to rat neuronal nitric oxide synthase, depended on NADPH and tetrahydro-L-biopterin, and was inhibited by N(G)-nitro-L-arginine. NMDAR2/3 subunit-immunoreactive proteins migrating at 170 kDa could also be detected in brain extracts, along with glutamate (whole brain: 0.32 +/- 0.03 micromol of glutamate/mg of protein; optic lobes: 0.22 +/- 0.04; vertical complex: 0.65 +/- 0.06; basal lobes: 0.58 +/- 0.04; brachial lobe: 0.77 +/- 0.06; pedal lobe: 1.04 +/- 0.08; palliovisceral lobe: 0.86 +/- 0.05). Incubation of intact brains with 1.5 mM glutamate or NMDA or the nitric oxide donor 2-(N,N-diethylamino)diazenolate-2-oxide caused a fivefold rise in the levels of cyclic GMP, indicating operation of the glutamate-nitric oxide-cyclic GMP signaling pathway. Immunohistochemical mapping of Sepia CNS showed specific localization of nitric oxide synthase-like and NMDAR2/3-like immunoreactivities in the lateroventral palliovisceral lobe, the visceral lobe, and the pallial and visceral nerves, as well as in the sphincters and wall of the ink sac.

Localization of L-glutamate and glutamate-like receptors at the squid giant synapse

HPLC analysis of the amino acid contents of the second- and third-order giant fibres at the giant synapse in the stellate ganglion of the squid Loligo vulgaris shows that there are significantly higher amounts of L-glutamate and L-aspartate in the second-order (presynaptic) fibre than in the third-order (postsynaptic) fibre. Immunocytochemical staining of sections of the ganglion with an antibody raised against L-glutamate produces specific positive staining in the synaptic region of the second-order fibre. In contrast, staining with antibodies raised against glutamate-receptors (mammalian GluR1 with GluR2/3) produces positive staining in the third-order fibre at the postsynaptic region. These data provide further evidence for the hypothesis that L-glutamate is an excitatory transmitter at the giant synapse.

Neuropeptidergic control of the optic gland of Octopus vulgaris: FMRF-amide and GnRH immunoreactivity

In cephalopods, the endocrine optic glands on the optic tract control the maturation of the gonads. The glands are innervated by the optic gland nerve, which originates in the central nervous system. To explore the involvement of neuropeptides in the nervous control of the optic gland of Octopus vulgaris, the presence and distribution of Phe-Met-Arg-Phe-NH2 (FMRF-amide)-like and gonadotropin releasing homone (GnRH)-like peptides were examined in the central nervous system and optic gland by immunohistochemistry. For GnRH immunodetection, antibodies against four different forms of GnRH were used: cGnRH-I, cGnRH-II, sGnRH, and mGnRH. The optic gland nerve provides direct and indirect signals coming from the centres of integration of chemical, visual, and olfactive stimuli to modulate the glandular activity. In these centres, the subpedunculate area, the olfactory and optic lobes, and FMRF-amide-like and GnRH-like immunoreactivities were detected. The subpedunculate area seems to be the source of the FMRF-amide-like peptide, whereas the posterior olfactory lobule is the source of the GnRH-like peptide. The immunoreactive fibres for both neuropeptides leave their sources and directly enter the optic gland nerve. FMRF-amide- and GnRH-immunoreactive nerve endings are seen on the glandular cells. The evidence of a possible neuropeptidergic control of optic gland activity reinforces the analogies and the functional parallels in the octopus, insect, crustacean, and vertebrate hormonal systems.

Progesterone receptor in the reproductive system of the female of Octopus vulgaris: characterization and immunolocalization

In this study for the first time we have characterized a progesterone receptor in the reproductive system of the female of Octopus vulgaris. Scatchard analysis revealed that one binding component with high affinity and low capacity for the ligand was present only in the nuclear extract. Competition experiments showed that the progesterone receptor was strictly specific for progesterone. DNA-cellulose binding and DEAE-Sephacel both confirmed the presence of one 3H-progesterone binding component which eluted at a salt concentration of 0.14 +/- 0.05 M NaCl and 0.15 +/- 0.05 M NaCl respectively. By using monoclonal antibodies against chicken progesterone receptor (subunits A and B), we have localized on Western Blot one band of about 70 kDa. Immunoreactivity for progesterone binding molecules has been localized in the nuclei of the follicle cells of the ovary, of the proximal portion of the oviduct and of the outer region of the nidimental gland. These data, taken together, provide evidence that in Octopus vulgaris the progesterone receptor has biochemical and immunohistochemical characteristics resembling those of progesterone receptor in vertebrates.

A calcium-dependent nitric oxide synthase and NMDA R1 glutamate receptor in the ink gland of Sepia officinalis: a hint to a regulatory role of nitric oxide in melanogenesis?

Histochemical, immunohistochemical, and biochemical evidence is reported showing that the ink gland of the cuttlefish Sepia officinalis contains a calcium-dependent isoform of nitric oxide synthase as well as an NMDA R1 receptor subunit localized for the most part in the immature inner cells of the epithelial layer of the gland. These results may be taken to implicate a hitherto unrecognized regulatory role of the glutamate-nitric oxide pathway in the maturation and metabolic activity of melanin-producing cells in the cephalopod defense system.

Occurrence of sex steroid hormones and their binding proteins in Octopus vulgaris lam

The present study reports the presence of progesterone, testosterone and 17 beta-estradiol and their corresponding binding proteins in the reproductive system of Octopus vulgaris Lam (phylum Mollusca, subphylum Cephalopoda). These sex hormones occur in testis, vas deferens, seminal vesicle, prostate and Needham's sac. The hemolymph also contains a small, but significant, amount of these hormones and their carrier proteins. Among various tissues of the reproductive system, the seminal vesicle possesses the highest concentration of progesterone (4.8 ng/g tissue). The testis is the organ which contains the highest amount of testosterone (5.2 ng/g) whereas the prostate is the organ which contains the highest amount of 17 beta-estradiol (0.92 ng/g). The presence of these hormones has been ascertained by a radioimmunoassay method, an immunoenzymatic method and by a chemical (HPLC) method. Seatchard studies indicated that vas deferens and seminal vesicle contain specific sex steroid binding molecules at affinity levels comparable to those of vertebrate steroid receptors (0.5-5.0 pmol/g protein). In addition to the presence of the hormones, the delta 5,3 beta hydroxysteroid dehydrogenase, the key enzyme of steroidogenesis, also is found in testis. From a phylogenetic point of view, these findings are very interesting because they indicate a common origin of a sex hormonal system between Mollusca Cephalopoda and Vertebrates.

Involvement of D-aspartic acid in the synthesis of testosterone in rat testes

D-Aspartic acid (D-Asp) is an endogenous amino acid which occurs in many marine and terrestrial animals. In fetal and young rats, this amino acid occurs prevalently in nervous tissue, whereas at sexual maturity it occurs in endocrine glands and above all in pituitary and testes. Here, we have studied if a relationship exists between the presence of D-Asp and the hormonal activity. The following results were obtained: 1) Both D-Asp and testosterone are synthesized in rat testes in two periods of the animal's life: before birth, about the 17th day after fertilization and, after birth, at sexual maturity. 2) Immunocytochemical studies have demonstrated that this enantiomer is localized in Leydig and Sertoli cells. 3) In vivo experiments, consisting of i.p. injection of D-Asp to adult male rats, demonstrated that this amino acid accumulates in pituitary and testis (after 5 h, the accumulation was of 12 and 4-fold over basal values, respectively); simultaneously, luteinizing hormone, testosterone and progesterone significantly increased in the blood (1.6-fold, p < 0.05; 3.0-fold, p < 0.01 and 2.9-fold, p < 0.01, respectively). 4) Finally, in vitro experiments, consisting of the incubation of D-Asp with isolated testes also demonstrated that this amino acid induces the synthesis of testosterone. These results suggest that free D-Asp is involved in the steroidogenesis.

D-aspartate in the male and female reproductive system of Octopus vulgaris lam

Free D-aspartate (D-Asp) has been previously found in the nervous system of Octopus vulgaris (Mollusca: Cepalopoda) and has recently also been found in many endocrine tissues of the rat. The present study examined whether this enantiomer also occurs in the reproductive system and the brain of the octopus. In this mollusk, D-aspartate was present in both the male and the female reproductive systems. In males, it was found at high concentrations in the prostate, vas deferens, Needham's sac, and testis. In females, a high concentration was found in the oviduct, accessory nidamental gland, and ovary. The concentration varied between 0.4 and 2.9 mumol/g wet tissue, which corresponds to a percentage of D-Asp/total D+L-Asp between 7 and 33%. No appreciable quantities of D-Asp were found in the digestive, excretory, circulatory, and muscular systems, indicating that in the octopus this enantiomer may play a role in both the nervous and the reproductive systems.

Glutathione suppresses spontaneous activity in the frog spinal cord

Spontaneous electrical activity in the isolated hemisected frog spinal cord increased in the presence of the SH reductant dithiothreitol (DTT) was reversibly suppressed by the oxidant 5-5'-dithio-bis-(2 nitrobenzoic acid) (DTNB) and was irreversibly suppressed by the sulphydryl modifying agents N-ethyl-maleimide (NEM) and monobromotrimethylammonio bimane. Glutathione (GSH), an important natural low molecular weight thiol, reversibly suppressed spontaneous activity. Cords pretreated with glutathione and successively exposed to NEM or bimane maintained their normal electrical activity. This indicates that GSH had interacted with the exposed sulphydryls and prevented their reaction with NEM or bimane. Incubation with bimane resulted in fluorescence-labelled neurones in the dorsal and ventral horns, whereas samples pretreated with NEM or with GSH were not labelled. Neurones appeared again fluorescent in cords preincubated with GSH and sequentially exposed to NEM or bimane. Both electrophysiological and histochemical methods indicate that exposed membrane sulphydryls are involved in the genesis and/or modulation of spontaneous electrical potentials.

Fluorescence-histochemical and ultrastructural research on the monoaminergic neurosecretory cells of the earthworm Octolasium complanatum (Annelida: Oligochaeta)

A study of the yellow fluorescent neurons (M-NSC) of the subesophageal ganglion of the earthworm Octolasium complanatum has been made by using alternate semithin and thin sections in a correlate fluorescence and electron microscopy technique and it results that elementary neurosecretory granules are present where the yellow fluorescent substance is. These granules are similar in size and morphology to the granules of monoamine type. The intimate contact of the capillaries with the granular cytoplasmic area of the M-NSC provides evidence of a probable release of the secretion from the cell body. These results support the hypothesis of the endocrine role of the M-NSC.