Neuroendocrine control of reproduction in the male penaeid prawn,Parapenaeopsis hardwickii (Miers) (Crustacea,Decapoda, Penaeidae)

Effects of bilateral eyestalks ablation and injections of eyestalks, (Es) brain (Br) and thoracic ganglia (ThG) extract separately on the androgenic gland and testis development of Es-ablated (Experiment 1) and normal (Experiment 2) P. hardwickii, were investigated. The androgenic gland activity increased significantly in prawns having Es-ablated (Group II), and eyestalkless (Groups VI & VII) and normal (Groups D & E) prawns received Br and ThG extracts, separately, as compared to their respective controls (Groups I & A). Injection of unboiled Es extract in eyestalkless (Group V) and normal (Group C) prawns arrested the androgenic gland activity. Simultaneously, there was a significant (p<0.05) increase in the diameter of testicular follicles, testis weight, testis index and number of mature spermatocytes per follicle in the prawns of groups II, VI & VII of experiment 1 and of groups D & E of experiment 2 when compared to their respective controls. Injection of Es extract into the eyestalkless (Group V) and normal (Group C) prawns ceased testicular development. A significant (<0.05) decrease in testicular protein and midgut gland glycogen and lipid was found in groups II, VI & VII of experiment 1 and in groups D & E of experiment 2, but the glycogen and lipid content of the testis increased. These results indicate that the hormones released from the neuroendocrine centres regulate androgenic gland activity and spermatogenesis.     

Role of eyestalk hormone in the carbohydrate metabolism of a marine penaeid prawn,Parapenaeopsis hardwickii (MIERS) (Crustacea,Decapoda, Penaeidae)

Data furnished here concern with the role of eyestalk hormone in the regulation of carbohydrate metabolism in Parapenaeopsis hardwickii. Bilateral eyestalk ablation has brought about a significant (P < 0.01) fall and rise in the glycogen content in the midgut gland and abdominal muscle respectively. Although eyestalk ablation resulted in a significant (P < 0.01) depletion of fat in midgut gland, n0 significant (P > 0.05) change was observed in the abdominal muscle. Eyestalk extract administration in eyestalk-less prawns has significantly (P < 0.05) restored the glycogen and fat metabolites in the midgut gland. There was an obvious change in the glycogen content of the midgut gland and abdominal muscle of normal prawns when injected with eyestalk extracts from prawns in different molting stages. Eyestalk extract from intermolt prawns caused a significant (P < 0.05) decrease and increase in the glycogen quantity in the midgut gland and abdominal muscle respectively. Eyestalk extract from premolt and postmolt prawns has, although not significantly (P > 0.05), decreased and increased the utilization of glycogen respectively in the midgut gland. The physiological significance of these findings are discussed briefly.Paper forms part IV of the series

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Blood glucose in marine Penaeid Prawns. III. Variation in relation to ovarian growth in Parapenaeopsis Hardwickii (Miers) (Crustacea,Decapoda, Penaeidae)

In the present study on female Parapenaeopsis hardwickii information is presented concerning the variation in blood glucose concentration during the different stages (I to V) of ovarian growth. A direct proportionality was found between blood glucose level and ovary growth. There was an incessant hike in blood glucose level as ovary development proceeds from stage I to IV but a drastic downfall was noticed in stage V, i.e. in the spawned prawns. Physiological significance of these findings are discussed.This study was supported by I.C.A.R., New Delhi, India through a Project on Reproductive Endocrinology of Edible Prawns     

The role of biogenic amines in the control of blood glucose level in the decapod crustacean,Carcinus maenas L.

1. Administration of biogenic amines into intact Carcinus maenas induces dose- and timedependent elevation of hemolymph glucose level.2. Removal of the neurosecretory centre containing the crustacean hyperglycemic hormone (CHH) by ablation of the eyestalks did not induce hypoglycemia.3. Injection of dopamine (DA) into eyestalkless crabs showed no hyperglycemic effect, while serotonin (5-HT), epinephrine (E), norepinephrine (NE), and octopamine (OA) elevated glucose levels.4. The dopaminergic effect was significantly reduced by administration of trifluoperazine (TFP).5. 5-HT and OA were found to be strong elevators of glucose levels, while the other biogenic amines had moderate effects only.6. The results indicate, that DA exerts its hyperglycemic effect by stimulating the release of CHH from the eyestalk neurosecretory centre. Elevation of hemolymph glucose level by 5-HT, OA, E, and NE, occurs independently of CHH.     

Hyperglycaemic effects of 5-hydroxytryptamine and dopamine in the freshwater prawn, Macrobrachium malcolmsonii

The effects of 5-hydroxytryptamine (5-HT; serotonin) and dopamine (DA) on tissue carbohydrate metabolism and haemolymph glucose levels in the freshwater prawn, Macrobrachium malcolmsonii, were investigated. Injection of 5-HT and DA produced hyperglycaemia in a dose-dependent and time-dependent manner, with DA being more effective than 5-HT. Interestingly, 5-HT and DA induced hyperglycaemia only in intact prawns but not in bilaterally eyestalk-ablated individuals. Total carbohydrate (TCHO) and glycogen levels decreased and phosphorylase activity increased in the hepatopancreas and muscle of intact prawns after being injected with 5-HT or DA. However, bilateral eyestalk ablation decreased haemolymph glucose and tissue phosphorylase activity and increased TCHO and glycogen levels of the hepatopancreas and muscle. Injection of 5-HT or DA did not cause significant changes in these variables in eyestalk-ablated prawns. It is hypothesized that 5-HT and DA induce hyperglycaemia in prawns by stimulating the release of crustacean hyperglycaemic hormone (CHH) from the X-organ sinus gland (XO-SG) complex located in the eyestalk.     

Effects of eyestalk ablation on moulting and growth of penaeid prawn Metapenaeus dobsoni (de Man)

Penaeid prawns M. dobsoni of two different size ranges were ablated both unilaterally (UEA) and bilaterally (BEA) and subjected to individual study. The UEA prawns consumed almost the same amount of food as the control prawns in the size group, 35-40mm, but consumed about 57.8% more food than the control prawns in the larger size group, 48-53mm. Growth was estimated as length and weight changes and significant variation was observed. The moult rate and dry moult weight showed marked differences. Average intermoult period increases with second ablation. Dry weight of moult in every succeeding moult was found to decrease irrespective of the level of ablation. Unilateral eyestalk ablation resulted in increase in dry weight whereas bilateral eyestalk ablation reduced the dry weight of moult and this decrease in the rate increased after each subsequent moult. In the larger size group, values of protein efficiency ratio (PER) were almost same as that of the lower size group. The UEA prawns exhibited highest conversion efficiency. The production rate of UEA prawns was 84% more than that of the control whereas BEA prawns indicated negative production. The same trend followed for net growth efficiency also. The results suggest that unilateral eyestalk ablation can be resorted to accelerate growth and conversion efficiency. Eyestalk ablation has been frequently resorted in matured forms for inducing maturation of gonads. For the first time attempts have been made to compare between the effects of removing one eyestalk versus two and changes taking place in juvenile forms especially in their physiology related to growth.     

Methionine-enkephalin induces hyperglycemia through eyestalk hormones in the estuarine crab Scylla serrata

The hypothesis is tested that methionine-enkephalin, a hormone produced in and released from eyestalk of crustaceans, produces hyperglycemia indirectly by stimulating the release of hyperglycemic hormone from the eyestalks. Injection of methionine-enkephalin leads to hyperglycemia and hyperglucosemia in the estuarine crab Scylla serrata in a dose-dependent manner. Decreases in total carbohydrate (TCHO) and glycogen levels of hepatopancreas and muscle with an increase in phosphorylase activity were also observed in intact crabs after methionine-enkephalin injection. Eyestalk ablation depressed hemolymph glucose (19%) and TCHO levels (22%), with an elevation of levels of TCHO and glycogen of hepatopancreas and muscle. Tissue phosphorylase activity decreased significantly during bilateral eyestalk ablation. Administration of methionine-enkephalin into eyestalkless crabs caused no significant alterations in these parameters when compared to eyestalk ablated crabs. These results support the hypothesis that methionine-enkephalin produces hyperglycemia in crustaceans by triggering release of hyperglycemic hormone from the eyestalks.     

Histochemical localization of acid and alkaline phosphatases and glucose-6-phosphatase of the hepatopancreas of the crab, Scylla serrata (Forskål)

Simultaneous histochemical localization of non-specific monophosphate esterases, acid and alkaline phosphatases, as well as a specific monophosphate esterase, glucose-6-phosphatase has been made on the hepatopancreas of the marine crab, Scylla serrata (Forskål). Maximum activity of the 3 enzymes was observed in the juvenile and mature absorptive cells. Lining cells of the main hepatopancreatic duct exhibited a moderate activity of the 3 enzymes whereas the embryonic and fibrillar cells and connective tissue of the gland showed negative reactions for the 3 enzymes. The secretory cells showed a positive reaction for these enzymes only at the brush border.Bilateral eyestalk removed evoked a rise in the activity of the 3 enzymes within 2–4 h. The same effect was observed after injection of eyestalk extract to both normal and eyestalkless animals followed by restoration to the normal level after 24 h.The present observations indicate that glucose-6-phosphatase and acid phosphatase may be under the direct influence of eyestalk hormone(s) while alkaline phosphatase activity appears to be related to changes in the substrate. The physiological significance of the various cell types and enzymes is discussed.     

Species-specific effects on hemolymph glucose control by serotonin, dopamine, and L-enkephalin and their inhibitors in Squilla mantis and Astacus leptodactylus (crustacea)

Hemolymph glucose level is controlled by crustacean Hyperglycemic Hormone (cHH) released from the eyestalk neuroendocrine centers under conditions of both physiological and environmental stress. Biogenic amines and enkephalin have been found to mediate the release of several neurohormones from crustacean neuroendocrine tissue. We investigated the effect of serotonin, dopamine, and Leucine-enkephalin in vivo--injected into the stomatopod Squilla mantis and the decapod Astacus leptodactylus--whether increasing or depressing glycemia. Serotonin had a marked effect in elevating glucose level compared with initial values in both species. 5-HT1-like receptors are more involved in mediating serotonin action as co-injected cyproheptadine was a more effective antagonist than ketanserin (5-HT2-like receptor inhibitor). Dopamine injection in intact animals produced a decrease below initial levels of hemolymph glucose. This effect was significantly antagonized by domperidone. No significant effect of both amines occurred in eyestalkless animals. L-enkephalin shows a differential effect: in S. mantis it induced hypoglycemia while in A. leptodactylus it caused an increase of glucose level. Co-injected antagonist naloxone affected the direction of the response. Serotonin appears to provide a major control on glucose mobilization, whereas dopamine and L-enkephalin act as modulators whose plasticity in use or action varies among species.     

Calcium–calmodulin dependent protein kinase I from Macrobrachium nipponense: cDNA cloning and involvement in molting

Calcium–calmodulin dependent protein kinase I is a component of a calmodulin-dependent protein kinase cascade and involved in many physiological processes. The full-length cDNA of calcium–calmodulin dependent protein kinase I (MnCaMKI) was cloned from the freshwater prawn Macrobrachium nipponense and its expression pattern during the molt cycle and after eyestalk ablation is described. The full-length cDNA of MnCaMKI is 3262 bp in length and has an open reading frame (ORF) of 1038 bp, encoding a 345 amino acid protein. The expression of MnCaMKI in three examined tissues was upregulated in the premolt stage of the molt cycle. Its expression was induced after eyestalk ablation (ESA): the highest expression level was reached 1 day after ESA in hepatopancreas, and 3 days after ESA in muscle. By dsRNA-mediated RNA interference assay, expression of MnCaMKI and ecydone receptor gene (MnEcR) was significantly decreased in prawns treated by injection of dsMnCaMKI, while expression of these two genes was also significantly decreased in prawns treated by injection of dsMnEcR, demonstrating a close correlation between the expression of these two genes. These results suggest that CaMKI in M. nipponense is involved in molting.     

Effects of eyestalk ablation on growth and food conversion efficiency of the freshwater prawn Macrobrachium lanchesteri (de Man)

Bilateral eyestalk ablation in the freshwater prawn Macrobrachium lanchesteri results in high mortality, while unilateral eyestalk ablated prawns exhibited a high survival rate. There was marked increase in the growth of bilateral eyestalk-ablated prawns (47.70 mg/prawn) as compared to those that were unilaterally ablated (19.19 mg/prawn).     

Bihormonal control of oogenesis in the freshwater prawn, Macrobrachium kistnensis

The hormonal control of oogenesis has been investigated in the freshwater prawn, Macrobrachium kistnensis. Experiments using bilateral eyestalk ablation and injection of eyestalk extract supported the presence of a gonad inhibiting factor in the eyestalk of female prawns. Injections of brain and thoracic ganglion extract in normal female prawns and in those subjected to bilateral eyestalk ablation revealed the presence of a gonad stimulating factor in the central nervous tissue.     

Neuroendocrine Correlates of Circadian Rhythmicity in Crustaceans

The secretion of neurohormones from the crustacean X-organ –sinus gland system is controlled by environmental influences,light being the most conspicuous. Two sets of photoreceptorsappear to mediate the influence of light on neurosecretion basedon intracellular recordings from X-organ neurons and estimationsof hormone release. Extra-retinal photoreceptors can initiateneurohormonal release from the eyestalk. Neurosecretory activity is also influenced by putative neurotransmitters.GABA is found in high concentrations in the medulla temninalisof the eyestalk and is released by stimulation, in a calcium-dependentmanner. Diurnal variations occur in the amounts of eyestalk neurohormones,either those present in the eyestalk or released by electricalstimulation of the isolated sinus gland. Rhythm phases varyfrom one hormone to another. Neurohormones secreted in the eyestalkare also found in other regions of the central nervous system.Rhythms of neurosecretion are present both in the secretionin the isolated eyestalk and in eyestalkless animals, thus indicatingthat rhythmicity is a distributed property of the neurosecretorysystem.     

Electrical stimulation of human lower extremities enhances energy consumption, carbohydrate oxidation, and whole body glucose uptake.

Our laboratory has recently demonstrated that low-frequency electrical stimulation (ES) of quadriceps muscles alone significantly enhanced glucose disposal rate (GDR) during euglycemic clamp (Hamada T, Sasaki H, Hayashi T, Moritani T, and Nakao K. J Appl Physiol 94: 2107-2112, 2003). The present study is further follow-up to examine the acute metabolic effects of ES to lower extremities compared with voluntary cycle exercise (VE) at identical intensity. In eight male subjects lying in the supine position, both lower leg (tibialis anterior and triceps surae) and thigh (quadriceps and hamstrings) muscles were sequentially stimulated to cocontract in an isometric manner at 20 Hz with a 1-s on-off duty cycle for 20 min. Despite small elevation of oxygen uptake by 7.3 +/- 0.3 ml x kg(-1) x min(-1) during ES, the blood lactate concentration was significantly increased by 3.2 +/- 0.3 mmol/l in initial period (5 min) after the onset of the ES (P < 0.01), whereas VE showed no such changes at identical oxygen uptake (7.5 +/- 0.3 ml x kg(-1) x min(-1)). ES also induced enhanced whole body carbohydrate oxidation as shown by the significantly higher respiratory gas exchange ratio than with VE (P < 0.01). These data indicated increased anaerobic glycolysis by ES. Furthermore, whole body glucose uptake determined by GDR during euglycemic clamp demonstrated a significant increase during and after the cessation of ES for at least 90 min (P < 0.01). This post-ES effect was significantly greater than that of the post-VE period (P < 0.01). These results suggest that ES can substantially enhance energy consumption, carbohydrate oxidation, and whole body glucose uptake at low intensity of exercise. Percutaneous ES may become a therapeutic utility to enhance glucose metabolism in humans.     

Expressed sequence tags from eyestalk of kuruma prawn, Marsupenaeus japonicus

We analyzed the expressed sequence tags (ESTs) obtained from a cDNA library of the eyestalk of the kuruma prawn, Marsupenaeus japonicus, to examine gene expression profile with special focus on female reproduction. The assembly of 1988 ESTs created 136 contigs from 738 ESTs; however 1250 ESTs remained singletons. Significant similarities (blast score > or = 50 bits) to the DNA sequences in the databank were found for only 16.7% of the 1386 sequences (136 contigs plus 1250 singletons), suggesting that the eyestalk library contains many unknown genes. Ribosomal RNA and mitochondrial respiration enzymes with significant similarities were found abundantly in the ESTs, whereas genes related to maturation or endocrine systems were scarce. Three ESTs were assumed to encode novel eyestalk hormones with marked similarities to pigment-dispersing hormone, molt-inhibiting hormone and crustacean hyperglycemic hormone. Sequences encoding a product highly homologous to farnesoic acid O-methyltransferase, an enzyme that produces methyl farnesoate, were also found.     

Hyperglycemic responses to cold shock in the freshwater giant prawn, Macrobrachium rosenbergii

Crustacean hyperglycemic hormone (CHH), a neurohormone synthesized and released from the x-organ sinus gland complex, is primarily involved in carbohydrate metabolism; biogenic amines and peptidergic neuroregulators are known to modulate the release of CHH. Marked elevations of hemolymph glucose titers, which peaked within 2 h, were observed in both intact and bilaterally eyestalk-ablated prawns, Macrobrachium rosenbergii, when they were transferred directly from their optimal temperature of 28 °C to lower temperatures close to their lethal limit. Hyperglycemia can therefore be considered a characteristic response in this species under cold shock. Involvement of biogenic amines in the hyperglycemic response was also demonstrated. Hyperglycemic effects of epinephrine, dopamine and serotonin were mediated through CHH at the eyestalk level, but the response under cold shock was not exclusively mediated through CHH. It is suggested that factor(s) other than CHH are involved in the hyperglycemic response, possibly norepinephrine or/and octopamine. Accepted: 24 October 1998     

The rise in inosine monophosphate and l-lactate concentrations in muscle of live penaeid prawns (Penaeus japonicus,Penaeus monodon) stressed by storage out of water

• 1.1. This work aimed to establish why some species of prawns survived longer than others during simulated commercial shipment.
• 2.2. Metabolism of kuruma prawns, Penaeus japonicus, and black tiger prawns, P. monodon, stored for up to 24 hr in dry sawdust was studied by measuring concentrations of l-lactate, adenylate nucleotides and inosine monophosphate (IMP) in abdominal muscle.
• 3.3. When P. japonicus was stored in sawdust at 12°C the adenylate energy charge (AEC) did not fall and no lactate or IMP accumulated after 24 hr. However, the AEC fell in P. monodon stored at a temperature of 12°C and in P. japonicus stored at higher temperatures. When AEC fell below 0.5–0.6 there was an increase in muscle lactate and IMP concentration.
• 4.4. The results show that high concentrations of lactate and IMP in muscle tissue, at a given temperature, can be used to demonstrate that a prawn has been out of water for too long.