OCCURRENCE AND PROPERTIES OF CATECHOL-O-METHYL TRANSFERASE IN ADRENERGIC NEURONS

—A study has been made of the catechol-O-methyl transferase activity of some peripheral tissues after sympathetic denervation. A fall in catechol-O-methyl transferase activity was found in some organs, e.g. rat and rabbit vas deferens, cat nictitating membrane and rabbit submaxillary gland but not in mouse heart and spleen. It was found that suboptimal concentrations of S-adenosylmethionine did not reveal a significant difference between normal and denervated organs but at optimal concentrations a fall was seen in some organs. Catechol-O-methyl transferase activity was present in bovine splenic nerve and in adrenal medulla. It is suggested that the fall in enzyme activity after denervation indicates a neuronal cellular localization. A kinetic study of catechol-O-methyl transferase from normal and denervated rat vas deferens suggested that the neuronal and extraneuronal catechol-O-methyl transferase had different kinetic properties and an estimation of the kinetic constants of the neuronal enzyme was made.     

A rapid radioenzymatic assay for dopamine and N-acetyldopamine.

Dopamine (DA) was measured in various tissue extracts as [³H]methoxy-N-acetyldopamine after incubation with two partially purified enzymes, catechol-O-methyl transferase (EC 2.1.1.1) and N-acetyltransferase (EC 2.3.1.5), in the presence of [³H]adenosylmethionine and acetyl-CoA. This product can be separated quantitatively from labeled products of norepinephrine and epinephrine by solvent extraction. N-Acetyl-DA can be assayed by omitting the acetylating system from the incubation mixture. The procedure is rapid, convenient for processing large numbers of samples, and has a sensitivity of approximately 0.1 pmol. It has been used to measure DA in ganglia and in individual neurons from gastropod mollusks.     

The influence of functional alteration on monoamine oxidase and catechol-O-methyl transferase in the visual pathway of rats

—Rats were reared in complete darkness or under chronic stimulation with flashing light from birth to the age of 7 weeks. Light deprivation caused a significant increase in monoamine oxidase activity (measured with [¹⁴C]serotonin) of about 30 per cent in the structures of the visual pathway. Chronic stimulation with flashing light had no influence on the activity of monoamine oxidase in either visual or non-visual structures. The activity of catechol-O-methyl transferase in the brain areas of light-deprived rats was reduced, in light-stimulated rats it was slightly increased. In mother rats kept together with their litters in either complete darkness or flashing light for 5 weeks no change in monoamine oxidase activity was observed. The activity of catechol-O-methyl transferase in mother rats kept in darkness was significantly decreased in all brain regions studied; in light-stimulated animals the enzyme activity was not affected.     

NORADRENALINE METABOLIZING ENZYMES IN NORMAL AND SYMPATHETICALLY DENERVATED VAS DEFERENS

—A surgical technique for sympathetically denervating the vas deferens has been evaluated biochemically. A slight fall in soluble muscle protein content and no significant change in DNA content of the operated vas deferens were found. This indicates that the surgical procedure causes only a slight degree of tissue damage and may be useful for investigating the cellular localization and properties of noradrenaline metabolizing enzymes. In three species examined (rat, guinea pig and rabbit), monoamine oxidase activity of the vas deferens fell by approximately 50 per cent after denervation. The time course of the fall in monoamine oxidase activity of rat vas deferens was parallel to that of the disappearance of noradrenaline suggesting that this proportion of the total enzyme activity had a neuronal localization. The remaining enzyme activity is presumably located extraneuronally. Significant falls in catechol-O-methyl transferase activity were found in rat and rabbit vas deferens after denervation but not in guinea pig. The rabbit and rat vas deferens had respectively approximately 60 and 30 per cent of the catechol-O-methyl transferase activity associated with the sympathetic nerves. A complete loss of DOPA decarboxylase and tyrosine hydroxylase activities occurred in rat vas deferens after denervation, suggesting that these noradrenaline synthesizing enzymes have an entirely neuronal localization.     

AXONAL TRANSPORT OF CATECHOLAMINE SYNTHESIZING AND METABOLIZING ENZYMES

The rates of accumulation of the catecholamine synthesizing and metabolizing enzymes proximal to a ligation on the sciatic nerve of the rat were studied. Dopamine-β hydroxylase (EC 1.14.2.1) and tyrosine hydroxylase (EC 1.14.3a) accumulated at a similar rapid rate, and catechol-O-methyl-transferase (EC 2.1.1.6), choline acetyltransferase (EC 2.3.1.6) and monoamine oxidase (EC 1.4.3.4) accumulated at the same slow rate, whereas DOPA decarboxylase (EC 4.1.1.26) accumulated at an intermediate rate. Based on clearance of the rapidly accumulating enzymes, absolute flow rates were estimated to be: 106-167 mm/24 h for tyrosine hydroxylase; 138-185 mm/24 h for dopamine-β-hydroxylase; and 36-86 mm/24 h for DOPA decarboxylase. In contrast, the mean rate of transport of the slowly accumulating enzymes (monomine oxidase, catechol-O-methyltransferase and choline acetyltransferase) was approximately 3 mm/24 h. Colchicine and vinblastine completely blocked the axonal transport of both the rapidly and slowly transported enzymes. Studies of the subcellular distribution of each enzyme failed to confirm the suggestion that particulate enzymes are transported rapidly and soluble enzymes slowly. Our results suggest that the transport and inactivation of dopamine-β-hydroxylase, DOPA decarboxylase, and tyrosine hydroxylase are under different controls than monoamine oxidase and catechol-O-methyltransferase.     

THE ELEVATION OF CEREBRAL HISTAMINE-N-AND CATECHOL-O-METHYL TRANSFERASE ACTIVITIES BY l-METHIONINE-dl- SULFOXIMINE1

Abstract— The administration of the convulsant, l -methionine-dl-sulfoximine (MSO), increased histamine N-methyl transferase (E.C. 2.1.1.8) (HMT) activity in rat and mouse brain and, to a lesser extent, catechol-O-methyl transferase (E.C. 2.1.1.6) (COMT) activity in rat brain. The duration of this effect was shortened by co-administration of l -methionine. The increased HMT activity was seen in 5 or 7 rat brain regions tested. l -Methionine administration had no effect on the activity of either enzyme. Partially purified HMT preparations from rat or guinea-pig brain exhibited no alterations in activity after the in vitro addition of MSO or l -methionine over a wide range of histamine and S-adenosyl-l -methionine concentrations. Rat brain COMT was equally unaffected by MSO and l -methionine. The in vitro inhibition of HMT and COMT by S-adenosyl-l -homocysteine was the same whether tested on preparations derived from MSO-treated or control animals. The data are discussed with respect to the possible involvement of aberrant methylation processes in the MSO-induced seizure.     

CATECHOLAMINES IN FETAL AND NEWBORN RAT BRAIN

The levels of dopamine and norepinephrine were determined in the brains of fetal and newborn rats by means of a sensitive, radiometric-enzymatic assay. Catecholamines were converted to their 3-O-methylated derivatives in the presence of catechol-O-methyl transferase (EC 2.1.1.1) and [³ H-methyl]S-adenosylmethionine; and the [³H]-derivatives were isolated by selective extraction. The assay had a sensitivity for dopamine and norepinephrine of 100 picograms and was linear to at least 30 nanograms of catecholamines. Both amines were present at 15 days of gestation and increased 15-fold in content during the last week of gestation. The regional distribution of these neurotransmitters in the brain of the newborn rat correlated with the distribution of their biosynthetic enzymes. An investigation of the effects of reserpine, pheniprazine, α-methyl-para-tyrosine, diethyldithiocarbamate and l -DOPA on the levels of dopamine and norepinephrine in the brains of the 18-day gestational fetus indicated that the levels of these neurotransmitters are under controls similar to those known to occur in the brain of the adult rat.     

Catechol-O-methyl transferase and monoamine oxidase activities in brains of mice susceptible and resistant to audiogenic seizures

The activities of catechol-O-methyl transferase (COMT), monoamine oxidase (MAO), and a methanol forming enzyme were studied in whole brain homogenates and in livers obtained from DBA/2J, C57B1/6J, and F₁ hybrid mice. DBA/2J mice are extremely susceptible to audiogenic seizures, where as C57B1/6J mice are resistant to sound-induced convulsions. C57B1/6J mice were found to have significantly higher brain levels of COMT, while MAO activities were not different in animals of these genotypes. No methanol forming activity was detected in animals of either strain. No differences were found in hepatic activities of either COMT or MAO. Pyrogallol was shown to protect DBA/2J animals against audiogenic seizures.     

The effect of foetal decapitation on the antenatal development of the enzymes monoamine oxidase and catechol O-methyl transferase in rabbit foetuses

The development of the enzymes monoamine oxidase and catechol O-methyl transferase in rabbit foetuses was studied. The adrenocortical system of the rabbit foetuses was inactivated by hypophysectomy on the 18th day of foetal age. The hypophysectomy of the foetuses by decapitation in utero resulted in marked increases in the activities of the enzymes monoamine oxidase and catechol O-methyl transferase in most of the body organs determined 12 days after the operation. A single administration of adrenocorticotropic hormone or hydrocortisone to the decapitated foetuses reduced the activities of both the enzymes studied in most of the body organs. The results suggest that glucocorticoids present in the circulation of foetal animals act as inhibitory factor for enzymes of catecholamine degradation. The inactivation of glucocorticoidogenesis by removal of the hypophysis takes away this rate-limiting control and highly significant increases in the activities of the enyzmes monoamine oxidase and catechol O-methyl transferase occur.     

Choline acetyltransferase in individual neurons of Aplysia californica

The activities of choline acetyltransferase in the various ganglia of the nervous system of Aplysia californica and in some of the individually identifiable neurons in these ganglia were measured. At least four of the neurons were characterized by an apparent absence of the enzyme. The neurons containing measurable amounts of the enzyme had reproducible levels from animal to animal. Individual neurons from the same animal were generally characterized by different levels of activity whether expressed on a cell or a protein basis. However, those pairs of neurons previously classified as ‘homologous’ because of their similar appearance, location and/or electrophysiological function, also contained the same total amounts of enzyme activity.     

Ammonia-lyase and O-methyl transferase activities related to lignification in wheat leaves infected with botrytis

The deposition of lignin around wounds in wheat leaves infected with the non-pathogenic fungus Botrytis cinerea, was preceded by increases in ammonia-lyase and O-methyl transferase activities. The increases were localised in the lignifying tissues. Phenylalanine ammonia-lyase and tyrosine ammonia-lyase increased concurrently and were inseparable by gel filtration or DEAE cellulose chromatography, the two activities probably being the function of a single protein. Infection-specific isoenzymes for either of the ammonia-lyase activities were absent. Increases in caffeic acid O-methyl transferase and 5-hydroxyferulic acid O-methyl transferase activities closely followed those of the ammonia- lyases. It is unlikely that the increased proportion of syringyl groups found in infection-induced lignin is controlled by O-methyl transferase activity. A modified method for the estimation of O-methyl transferase activity in crude wheat extracts is described.     

Adaptive changes induced by high altitude in the development of brain monoamine enzymes

Exposure to high altitude (HA) affects neurotransmitter levels in the adult brain and induces a number of neurologic and behavioral disturbances. The present work was undertaken to investigate the effects of chronic exposure to a moderate hypoxic environment (natural altitude of 3800 m, 12.8% O₂ in inspired air) on the development from birth until adulthood of brain monoamine enzymes in rats. The activity of synthesizing (tyrosine and tryptophan hydroxylase) and catabolizing (catechol-O-methyl transferase and monoamine oxidase) enzymes was studied in discrete brain areas (cerebral cortex, cerebellum, mesodiencephalon, hypothalamus, corpus striatum, and pons medulla) and was shown to be selectively affected by HA, depending on the age of the animal and the brain region. In general, enzyme activity was less susceptible to HA during the first week after birth than at later ages, some brain areas such as the hypothalamus showing significant alterations in some enzymes throughout development, and in all enzymes at adulthood. Furthermore, in all brain areas and at all ages, tyrosine and tryptophan hydroxylase were more affected by HA than the catabolizing enzymes, and their activity was increased in some areas (e.g., cerebral cortex and cerebellum) but decreased in other areas (e.g., hypothalamus, mesodiencephalon, corpus striatum). These enzymatic changes and the corresponding alterations in precursor amino acids, particularly tryptophan, seem to be due more to the direct effect of hypoxia on oxygen-dependent enzymes, than to the stress. It appears that an hypoxic environment may provoke both early and long-term alterations in catecholamine and serotonin metabolism, thus neurotransmitter imbalances may explain some of the alterations in neurologic and endocrine development characteristic of the hypoxic animal.Part of this report was presented at the Sixth International Meeting of the International Society of Neurochemistry, Copenhagen, 1977.     

THE CHARACTERIZATION OF HISTIDINE DECARBOXYLASE AND ITS DISTRIBUTION IN NERVES, GANGLIA AND IN SINGLE NEURONAL CELL BODIES FROM THE CNS OF APLYSIA CALIFORNICA

Histamine (HA) is present in substantial quantities in all ganglia of Aplysia californica. Within the cerebral ganglia this amine is known to be concentrated in at least two identified neurons designated C-2 neurons. In this study a combination of chemical and enzymatic analyses was employed to provide evidence for the existence of a biochemical pathway for HA synthesis in ganglia and individual neurons of this marine mollusk. Examination of extracts of individual neurons dissected from ganglia organ-cultured in the presence of [³H]histidine showed that every neuron accumulated labelled histidine, but only the HA-containing C-2 neurons synthesized and stored labelled HA suggesting that the formation of HA in Aplysia could be catalyzed by the enzyme histidine decarboxylase (HDC). HDC activity was studied with a new microradiometric assay. Many of the properties of the molluscan HDC studied were found to correspond to the vertebrate enzyme. Enzyme activity was inhibited by α-hydrazino-histidine but unaffected by concentrations of α-methyldopa or by 5-(3,4-dihydroxycinnamoyl) salicylic acid which produced nearly complete inhibition of aromatic amino acid decarboxylase activity. HDC was measurable in nervous but not other Aplysia tissues assayed. All 5 major ganglia contained HDC activity which spanned a 15-fold range between the least and most active ganglia. Only 4 of the 13 nerve trunks assayed yielded measurable enzymic activity; these active nerves were associated with the cerebral ganglia which has the highest HDC activity of all measured ganglia. Of the numerous individual neurons assayed for HDC, only the C-2 cells showed measurable enzyme activity, about 25 pmol/cell/h or 70 μmol/g protein/h. Since the activity of HDC in the HA-containing neurons was at least three orders of magnitude larger than all other neurons assayed in the cerebral and other ganglia, these data appear to provide a direct metabolic basis for the selective presence of HA in these cells, and they indicate that the cellular presence of HDC provides a useful biochemical marker for the location of HA-rich neurons in Aplysia.     

Enzymes of the γ-glutamyl,cycle in ‘aging’ WI-38 fibroblasts and in HeLa S3 cells

γ-Glutamyltransferase ((5-glutamyl)-peptide:amino-acid 5-glutamyltransferase, EC 2.3.2.2) activity of WI-38 fibroblasts decreased only slightly in relation to a constant amount of cell-associated protein as the cells were carried in culture serially from middle to late passage numbers leading toward senescence, e.g., from population doubling level 27 through 41. Also, when the enzyme activity was expressed on the basis of a unit number of cells or unit amount of DNA, little change occurred over that range of PDLs. As the culture approached ‘phase-out’, the transferase activity rose sharply regardless of how the activity was expressed. The possibility is considered that the large increase in activity could be a reflection of a significant increase in size of cells and therefore changes in the membranes where the transferase is located.The occurrence of other enzymes of the ‘gg-glutamyl cycle’ in WI-38 and HeLa S₃ cells also was demonstrated. These included γ-glutamylcyclotransferase ((γ-l-glutamyl)-l-amino-acid γ-glutamyltransferase (cyclizing), EC 2.3.2.4) and 5-oxoprolinase, whose actitivies showed no large increase comparable to that of the γ-glutamyltransferase, as the culture approached ‘phase-out’.     

Platelet-Mediated Metabolism of the Common Dietary Flavonoid,Quercetin

Background

Flavonoid metabolites remain in blood for periods of time potentially long enough to allow interactions with cellular components of this tissue. It is well-established that flavonoids are metabolised within the intestine and liver into methylated, sulphated and glucuronidated counterparts, which inhibit platelet function.

Methodology/Principal Findings

We demonstrate evidence suggesting platelets which contain metabolic enzymes, as an alternative location for flavonoid metabolism. Quercetin and a plasma metabolite of this compound, 4′-O-methyl quercetin (tamarixetin) were shown to gain access to the cytosolic compartment of platelets, using confocal microscopy. High performance liquid chromatography (HPLC) and mass spectrometry (MS) showed that quercetin was transformed into a compound with a mass identical to tamarixetin, suggesting that the flavonoid was methylated by catechol-O-methyl transferase (COMT) within platelets.

Conclusions/Significance

Platelets potentially mediate a third phase of flavonoid metabolism, which may impact on the regulation of the function of these cells by metabolites of these dietary compounds.     

A simplified radiometric assay for plasma norepinephrine and epinephrine

An assay for plasma norepinephrine and epinephrine levels has been developed by the modification of published procedures. The plasma norepinephrine and epinephrine assay, when compared to currently available methods, provides a substantial decrease in the assay time while providing a 10-fold increase in sensitivity which allows the analysis to be performed on 0.75 ml or less of plasma. Norepinephrine and epinephrine are converted to their O-methylated analogs in the presence of catechol-O-methyl transferase and S-adenosylmethionine-methyl-³H. Following purification of the labelled normetanephrine and metanephrine by solvent extraction and thinlayer chormatography, the amines are oxidized to vanillin, purified by solvent extraction and counted. The specificity, linearity and precision of the assay are discussed.     

Possible roles of esterase, glutathione S-transferase, and superoxide dismutase activities in understanding aphid–cereal interactions

Activities of the detoxification enzymes esterase, glutathione S‐transferase, and of superoxide dismutase in aphids and aphid‐infested cereal leaves were assayed using polyacrylamide gel electrophoresis and a spectrophotometer to elucidate the enzymatic mechanisms of aphid resistance in cereal plants. A chlorosis‐eliciting Russian wheat aphid, Diuraphis noxia (Mordvilko), and non‐chlorosis‐eliciting bird cherry‐oat aphid, Rhopalosiphum padi (L.), and four cereals were used in this study. The four cereal genotypes were ‘Arapahoe’ (susceptible) and ‘Halt’ (resistant) wheat (Triticum aestivum L.), ‘Morex’ (susceptible) barley (Hordeum vulgare L.), and ‘Border’ (resistant) oat (Avena sativa L.). Esterase isozymes differed between the two aphid species, although glutathione S‐transferase and superoxide dismutase did not. Esterase, glutathione S‐transferase, and superoxide dismutase activities in either aphid species were not affected by the level of resistance of a cereal to D. noxia. The assays of cereal leaf samples showed that D. noxia feeding elicited an increase in esterase activity in all four cereal genotypes, although R. padi feeding did not. The increase of esterase activity in cereals, however, was not correlated to aphid resistance in the cereals. The time‐series assays of aphid‐infested cereal leaves showed that D. noxia‐infested Morex barley had a significant increase in esterase activity on all sampling dates (3, 6, and 9 days) in comparison with either uninfested or R. padi‐infested barley. No difference in glutathione S‐transferase activity was detected among either aphid infestations or sampling dates. The electrophoretic assays, however, revealed that aphid feeding elicited a significant increase in superoxide dismutase activity, which served as the control of glutathione S‐transferase activity assays. The increase in esterase and superoxide dismutase activities suggested that D. noxia feeding imposes not only toxic, but also oxidative stresses on the cereals. The ramification of using these enzyme activity data to understand the etiology of D. noxia‐elicited chlorosis is discussed.     

Peroxidase and Poly-Phenol Oxidase in Brassica juncea Plants Infected with Macrophomina phaseolina (Tassai) Goid. and their Implication in Disease Resistance

Studies on the peroxidase and poly-phenol oxidase activity in relatively resistant and susceptible strains of Brassica juncea at sequential intervals after inoculation with different isolates of Macrophomina phaseolina revealed that, fungus infected tissues had relatively higher activities of these oxidative enzymes in comparison to healthy plants, and tissues inoculated with ‘Weakly Virulent’ isolates always exhibited higher activity in comparison to ‘Moderately’, ‘Highly’ and ‘MostHighly Virulent’ isolates. At the early stages of the infection on 6th day, resistant plants showed higher activities in comparison to their susceptible counterparts. Very low activity of these enzymes could be recorded in healthy plants. Findings of this, study indicate the possible involvement of these oxidative enzymes in the resistance of this disease.     

Catecholamine-Derived Tetrahydroisoquinolines: O-Methylation Patterns and Regional Brain Distribution Following Intraventricular Administration in Rats

Abstract: The metabolism of 6,7-dihydroxy (catecholic) -1,2,3,4-tetrahydroisoquinoIines (TIQs) is of interest because the heterocyclic substances may form in mammals normally or during certain diseases via condensations of catecholamines (CAs) with aldehydes or α-keto acids. With a specific capillary gas chromatography procedure and confirmatory liquid chromatographic assays, we have determined the structural isomers and relative amounts of mono-O-methylated (phenolic) TIQ metabolites in several rat brain regions 40 min following the acute intracerebroventricular injection of four structurally related catecholic TIQs. In sharp contrast with the established selective m-O-methylation of dopamine (DA) by catechol-O-methyltransferase in brain, the two simple TIQs derived from DA produced predominantly or even exclusively the metabolic isomer arising from methylation of the original p-hydroxyl group (7-O-methylation). In three catecholaminergic brain regions examined, the 7-O-methyl isomer was the only detectable phenolic metabolite of (±) salsolinol-1-carboxylic acid (a condensation product of DA and pyruvic acid) and, as first noted by Bail et al. (1980), constituted 95% of the two possible isomeric mono-O-methyl metabolites of (±) salsolinol (TIQ derivative of DA and acetaldehyde). Though less, the 7-O-methyl isomers still were a significant proportion (40–55%) of the two mono-O-methylated metabolites of (±) 4-hydroxy-desmethylsalsolinol (a TIQ derived from norepinephrine and formaldehyde), or of the DOPA/acetaldehyde-derived TIQ, (cis) salsolinol-3-carboxylic acid. In the time frame of the study, all four administered TIQs showed higher levels in hypothalamus than in striatum or hippocampus, with the two carboxylated alkaloids displaying the greatest differences. However, for a given TIQ, the proportion present as mono-O-methyl metabolite(s) and the O-methyl isomer distribution did not differ across the three brain regions, indicating that O-methylation involved a single homogenous enzyme that was not saturated in vivo at the concentrations attained by the heterocyclic catechols. The most notable findings, that of exclusive methylation on the original p-hydroxyl group of a physiologically relevant CA derivative, and an O-methylation pattern that appeared dependent on the substituents on the heterocyclic ring, are explained on the basis of an important hydrophobic binding site in catechol-O-methyltransferase in vivo.     

A SURVEY OF NEUROENDOCRINE PHENOMENA IN NON-ARTHROPOD INVERTEBRATES

• 1 Neurosecretory phenomena are apparently ubiquitous among Metazoa.
• 2 In Hydra, neurosecretory products are probably involved in the control of growth and reproduction.
• 3 Secretory elements in the central nervous system of turbellarians probably promote fission, regeneration and reproduction.
• 4 The cerebral ganglia of nemertines are the source of a hormone which exercises an inhibitory influence on maturation of the gonads and the development of somatic sexual characteristics. A principle secreted by the ganglia and/or the associated cerebral organs controls weight regulation. A sex hormone controls sexual differentiation.
• 5 Secretory neurons may influence the production of exsheathing fluid and ecdysis in nematodes.
• 6 In nereid polychaetes, a single hormone which originates from the cerebral neuroendocrine system apparently promotes segment proliferation and inhibits maturation. However, in certain other polychaetes, contrasting endocrine mechanisms seem to operate.
• 7 In lumbricid oligochaetes, a hormone secreted by the cerebral ganglion (and possibly by other nervous centres also) promotes gonadal activity and the differentiation of somatic sexual characters. In some species the ganglion exerts an inhibitory influence on the associated processes of ‘diapause’ and posterior regeneration. The cerebral and suboesophageal ganglia are implicated in the control of osmoregulation. Cerebral neurosecretory cells in limicolous oligochaetes may influence regenerative growth and osmoregulation.
• 8 The cerebral ganglia of leeches secrete a gonadotrophic hormone.
• 9 In gastropod molluscs, hormones secreted by the cerebral ganglia, glandular ‘dorsal bodies’ and/or optic tentacles are responsible for the control of the development of the reproductive tract, and the activity of the gonads. Contrasting mechanisms are thought to operate in the different gastropod groups and there is conflicting evidence particularly with respect to the endocrine functions of the optic tentacles and the gonads. The ‘bag cells’ of the abdominal ganglion of ApZysiu secrete a hormone which induces egg-laying. Cells in the pleural and parietal ganglia probably control osmoregulation in Lymnaea.
• 10 The optic glands of cephalopods secrete a gonadotrophic hormone, but sex hormones are apparently absent. The functional significance of the neurovenous tissues (presumptive neurosecretory complexes of unusual character) is obscure in most cases.
• 11 The radial nerves of starfish are the source of a hormone which induces the production of I-methyl adenine by the follicle cells of the gonad. This second principle stimulates oocyte maturation and the shedding of male and female gametes.
• 12 The relevance of such information to the development of certain biological concepts and to various aspects of comparative physiology is briefly discussed.