Neurosecretory Control Research Articles

Effect of copper exposure on histamine concentrations in the marbled crayfish (Procambarus fallax forma virginalis)

Crustaceans can store excess copper in the hepatopancreas, an organ playing a role in digestive activity as well as in neurosecretory control. Here, we studied the effect of copper exposure on the level of histamine, an indicator of food spoilage in edible crustaceans. Histamine is also a neuromodulator in the intestinal nervous system of crustaceans, and a human allergen. Marbled crayfish (Procambarus fallax forma virginalis) were exposed to average measured values of 0.031 mg Cu/l and 0.38 mg Cu/l, respectively, for 14 days and then transferred to copper-free water for another 14 days. Concentrations of copper and histamine in the hepatopancreas and muscle were evaluated at different time points. Histamine levels were significantly higher in hepatopancreas and muscle tissues at the highest exposure level, but only after transfer of the animals to copper-free water. The increased histamine concentration following copper exposure may be explained by a (delayed) stress response, and by up-regulated histidine synthesis induced by copper, followed by decarboxylation to histamine.

Conserved Sensory-Neurosecretory Cell Types in Annelid and Fish Forebrain: Insights into Hypothalamus Evolution

Neurosecretory control centers form part of the forebrain in many animal phyla, including vertebrates, insects, and annelids. The evolutionary origin of these centers is largely unknown. To identify conserved, and thus phylogenetically ancient, components of neurosecretory brain centers, we characterize and compare neurons that express the prohormone vasotocin (vasopressin/oxytocin)-neurophysin in the developing forebrain of the annelid Platynereis dumerilii and of the zebrafish. These neurons express the same tissue-restricted microRNA, miR-7, and conserved, cell-type-specific combinations of transcription factors (nk2.1, rx, and otp) that specify their identity, as evidenced by the specific requirement of zebrafish rx3 for vasotocin-neurophysin expression. MiR-7 also labels another shared population of neurons containing RFamides. Since the vasotocinergic and RFamidergic neurons appear to be directly sensory in annelid and fish, we propose that cell types with dual sensory-neurosecretory properties were the starting point for the evolution of neurosecretory brain centers in Bilateria.

Involvement of genes required for synaptic function in aging control in C. elegans

To identify new genes required for neurosecretory control of aging in C. elegans. In view of the importance of nervous system in aging regulation, we performed the screen for genes involved in the aging regulation from genetic loci encoding synaptic proteins by lifespan assay and accumulation of lipofuscin autofluorescence. We further investigated the dauer formation phenotypes of their corresponding mutants and whether they were possibly up-regulated by the insulin-like signaling pathway. The genetic loci of unc-10, syd-2, hlb-1, dlk-1, mkk-4, scd-2, snb-1, ric-4, nrx-1, unc-13, sbt-1 and unc-64 might be involved in the aging control. In addition, functions of unc-10, syd-2, hlb-1, dlk-1, mkk-4, scd-2, snb-1, ric-4 and nrx-1 in regulating aging may be opposite to those of unc-13, sbt-1 and unc-64. The intestinal autofluorescence assay further indicated that the identified long-lived and short-lived mutants were actually due to the suppressed or accelerated aging. Among the identified genes, syd-2, hlb-1, mkk-4, scd-2, snb-1, ric-4 and unc-64 were also involved in the control of dauer formation. Moreover, daf-2 mutation positively regulated the expression of syd-2 and hlb-1, and negatively regulated the expression of mkk-4, nrx-1, ric-4, sbt-1, rpm-1, unc-10, dlk-1 and unc-13. The daf-16 mutation positively regulated the expression of syd-2 and hlb-1, and negatively regulated the expression of mkk-4, nrx-1, sbt-1, rpm-1, unc-10, dlk-1 and unc-13. These data suggest the possibly important status of the synaptic transmission to the animal's life-span control machinery, as well as the dauer formation control.

Tripartite Neuroendocrine Activation of the Human Growth Hormone (GH) Axis in Women by Continuous 24-Hour GH-Releasing Peptide Infusion: Pulsatile, Entropic, and Nyctohemeral Mechanisms1

Despite the discovery of potent GH-releasing peptides (GHRPs) more than 15 yr ago and the recent cloning of human, rat, and pig GHRP receptors in the hypothalamus and pituitary gland, the neuroregulatory mechanisms of action of GHRP agonists on the human hypothalamo-somatotroph unit are not well delineated. To gain such clinical insights, we evaluated the ultradian (pulsatile), entropic (pattern orderliness), and nyctohemeral GH secretory responses during continuous 24-h i.v. infusion of saline vs. the most potent clinically available hexapeptide, GHRP-2 (1 microg/kg x h) in estrogen-unreplaced (mean serum estradiol, 12 +/- 2.4 pg/mL) postmenopausal women (n = 7) in a paired, randomized design. Blood was sampled every 10 min for 24 h during infusions and was assayed by ultrasensitive GH chemiluminescence assay. Pulsatile GH secretion was quantitated by deconvolution analysis, orderliness of GH release patterns by the approximate entropy statistic, and 24-h GH rhythmicity by cosinor analysis. Statistical analysis revealed that GHRP-2 elicited a 7.7-fold increase in (24-h) mean serum (+/-SEM) GH concentrations, viz. from 0.32 +/- 0.042 (saline) to 2.4 +/- 0.34 microg/L (GHRP-2; P = 0.0006). This occurred via markedly stimulated pulsatile GH release, namely a 7.1-fold augmentation of GH secretory burst mass: 0.87 +/- 0.18 (control) vs. 6.3 +/- 1.3 microg/L (GHRP-2; P = 0.0038). Enhanced GH pulse mass reflected a commensurate 10-fold (P = 0.023) rise in GH secretory burst amplitude [maximal GH secretory rate (micrograms per L/min) attained within a secretory pulse] with no prolongation in event duration. GH burst frequency, interpulse interval, and calculated GH half-life were all invariant of GHRP-2 treatment. Concurrently, as detected in the ultrasensitive GH assay, GHRP-2 augmented deconvolution-estimated interpulse (basal) GH secretion by 4.5-fold (P = 0.025). The approximate entropy of 24-h serum GH concentration profiles rose significantly during GHRP-2 infusion; i.e. from 0.592 +/- 0.073 (saline) to 0.824 +/- 0.074 (GHRP-2; P = 0.0011), signifying more irregular or disorderly GH release patterns during secretagogue stimulation. Cosinor analysis of 24-h GH rhythms disclosed a significantly earlier (daytime) acrophase at 2138 h (+/- 140 min) during GHRP-2 stimulation vs. 0457 h (+/-42 min) during saline infusion (P = 0.013). Concomitantly, the cosinor amplitude rose 6-fold (P = 0.018), and the mesor (cosine mean) rose 5-fold (P = 0.003). Fasting (0800 h) plasma insulin-like growth factor (IGF-I) concentrations rose by -11 +/- 12 microg/L during saline infusion and by 102 +/- 18 microg/L during GHRP-2 infusion (P = 0.0036). GHRP-2 infusion did not modify (24-h pooled) serum LH, FSH, or TSH concentrations and minimally increased serum (pooled) daily PRL (6.8 +/- 0.83 vs. 12 +/- 1.2 microg/L; P < 0.05) and cortisol (5.3 +/- 0.59 to 7.0 +/- 0.74; P < 0.05) concentrations. In summary, 24-h constant iv GHRP-2 infusion in the gonadoprival female neurophysiologically activates the GH-IGF-I axis by potentiating GH secretory burst mass and amplitude by 7- to 10-fold and augmenting the basal (nonpulsatile) GH secretion by 4.5-fold. GHRP-2 action is highly selective, as it does not alter GH secretory burst frequency, interpulse interval, event duration, or GH half-life. GHRP-2 effectively elevates IGF-I concentrations, unleashes greater disorderliness of GH release patterns, and heightens the 24-h rhythmicity of GH secretion. These tripartite features of GHRP-2's action in estrogen-withdrawn (postmenopausal) women also characterize normal human puberty and/or sex steroid regulation of the GH-IGF-I axis. However, how or whether GHRP-2 interacts further with sex hormone modulation of GH neurosecretory control in older women and men is not yet known.

Regulation of hemolymph osmolytes and gill Na +/K +-ATPase activities during acclimation to saline media in the freshwater shrimp Macrobrachium olfersii (Wiegmann, 1836) (Decapoda, Palaemonidae)

To evaluate the mechanisms of long-term osmotic adaptation to saline media, total hemolymph osmolytes, hemolymph sodium and chloride concentrations, and gill Na +/K +-ATPase activities were measured in the freshwater shrimp Macrobrachium olfersii (Wiegman) after acclimation for 10 or 20 days to media of <0.5, 21 and 28‰ salinity. Total hemolymph osmolytes are maintained strongly hyperosmotic to the external medium in low and moderate salinities, becoming slightly hyperosmotic at high salinity. In contrast, however, hemolymph [Na +] and [Cl −] are distinctly hyporegulated at the higher salinities. This difference in response pattern to acclimation apparently results from the presence of free amino acids in the hemolymph as a consequence of the synthesis of intracellular organic osmolytes. The resulting hyperosmotic regulation both avoids water loss from the animal in saline media and provides an osmotic gradient, allowing the uptake of water from the medium for excretion of the salt load. Gill Na +/K +-ATPase activities decrease by ≈35% after acclimation to saline media, suggesting that the rates of the cellular mechanisms responsible for salt uptake in freshwater become reduced, avoiding excessive salt loading. A Na +-ATPase activity is salinity independent. These data are examined with regard to the intrinsic coupling between the physiological alterations taking place in hemolymph osmolytes during acclimation to saline media and the concomitant ultrastructural rearrangements in the salt transporting tissues of the gills, and their possible neurosecretory control mechanisms.

Evidence for neurosecretory control of the optic gland in terrestrial pulmonates

The optic gland in terrestrial pulmonates secretes gonadotropic hormone. The present study investigates the fine structure of the optic gland to clarify the control of secretion. Animals used were the slug, Limax marginatus, and the snail, Euhadra peliomphala. The optic gland cell has a process and the cytoplasm is filled with large granules about 750–1300 nm in diameter with a thin corfex in L. marginatus and 800–1700 nm delimited by a thick peripheral layer in E. peliomphala. These gland cells are characterized by well-developed granular endoplasmic reticulum. Granule formation was seen in the region of the Golgi apparatus. During the breeding season, the medial neurosecretory cells of the brain are active in the production and release of secretory materials. Although no neurosecretory cell bodies occur in the tentacular ganglion, neurosecretory axons penetrate into the optic gland cells. Cobalt filling reveals that axons of the medial neurosecretory cells project to the tentacular ganglion, near the optic gland. These results suggest that the optic gland is controlled by a neurohormone originating from the medial neurosecretory cells of the brain.

6 Growth hormone neurosecretory dysfunction

The basis for understanding clinical disorders in the neuroregulation of GH secretion is derived from the complexity of the CNS-hypothalamic-pituitary axis. Studies in animals and humans demonstrate an anatomic, physiological and pharmacological evidence for neurosecretory control over GH secretion including neurohormones (GRH, somatostatin), neurotransmitters (dopaminergic, adrenergic, cholinergic, serotonergic, histaminergic, GABAergic), and neuropeptides (gut hormones, opioids, CRH, TRH, etc). The observation of a defect in the neuroregulatory control of GH secretion in CNS-irradiated humans and animals led to the hypothesis of a disorder in neurosecretion, GHND, as a cause for short stature. We speculate that in this heterogeneous group of children a disruption in the neurotransmitter-neurohormonal functional pathway could modify secretion ultimately expressed as poor growth velocity and short stature.

Volume regulation in an intertidal oligochaete, Clitellio arenarius (Müller). I. Short‐term effects and the influence of the supra‐ and subesophageal ganglia

AbstractTerrestrial oligochaetes demonstrate significant volume and osmoregulatory abilities that are under neurosecretory control. In the marine Oligochaete, little is known of volume or osmoregulatory capacities. However, histological evidence has linked cerebral neurosecretion and osmoregulation. The present study investigates water, ion, and volume regulation in an intertidal oligochaete and the effects of ablation of primary neurosecretory centers (supra‐and subesophageal ganglia) on these parameters. Control, sham‐operated, and ablated Clitellio arenarius were acutely transferred to diluted seawaters. Osmolality and Na, K, Cl (mEq/liter) concentrations were determined in total tissue water and in extracellular fluids. Extracellular volume was determined (using micropuncture techniques) as the fraction of the total tissue water in which 14C‐polyethylene glycol was distributed. With transfer to diluted seawater, all worms demonstrated hyperosmotic conformity. Tissue osmolality decreased in all animals at the same rate indicating no effect of ablation on integumental water permeability. Two phases of volume regulation were observed. In phase 1 (0–6 hours) osmolality decreased while water content (gm H2O/gm solute free dry weight = s.f.d.w.) increased both intra‐ and extracellularly. During this period, some volume regulation was accomplished in the control groups, particularly during the first 5 minutes, by the excretion of extracellular Na and Cl (μmoles/gm s.f.d.w.) which limited water gain. Ablated worms, reflecting less extracellular solute loss, gained more water than control groups. In phase 2 (6–18 hours) osmolality was constant, and all groups demonstrated a slow intra‐ (IC) and extracellular (EC) regulatory volume decrease. The solutes that accompanied volume loss were Na (EC), Cl (IC), and unmeasured solutes (IC). Reduction in intracellular solute content was the most significant loss occurring during this period with little difference among the groups tested. We hypothesize the primary effect of ablation is on extra‐ rather than intracellular volume regulation.

Small Motor Axons in Orthopteran Insects: A Reinvestigation of the Innervation of the Femoral Retractor Unguis Muscle in a Stick Insect and two Species of Locust

ABSTRACT The motor innervation of the femoral retractor unguis muscle in a stick insect and two species of locust was investigated morphologically and electrophysiologically. In all three insects a somewhat variable number of axons with diameters less than 2 μm, some even less than 0·5 μm, accompany much larger ones in the motor nerve supplying the muscle. In the stick insect Carausius probably more than six motoneurones, including at least one inhibitory, control the muscle. In the two species of locust two populations of muscle fibres, ‘red’, and ‘white’, can be distinguished according to their respectively high and low levels of succinate dehydrogenase and their different patterns of innervation. The ‘red’ muscle fibres in Schistocerca have, in addition to one or two ‘fast’ excitors, two inhibitors, and in Locusta ‘red’ fibres receive a further one or sometimes two ‘slow’ excitors, giving a more complex innervation pattern of the ‘red’ compared to the ‘white’ fibres. An additional neurosecretory control by at least one neurone is indicated by the presence of characteristic nerve endings throughout the muscle. Of the two ‘fast’ motor axons in both locusts, one innervates the ‘red’ and the other the ‘white’ muscle fibres but both axons, to a lesser extent, also synapse with muscle fibres of the other type. The synaptic responses they evoke here are, however, only of small or intermediate amplitude. The existence of ‘slow’ excitatory innervation in Locusta ‘red’ fibres shows that functional synaptic contacts from one motoneurone can be restricted to a small region of a muscle fibre whilst those from other motoneurones are present along almost the entire length of the same fibre. Some of the difficulties in comparing morphologically demonstrated numbers of axon profiles with electrophysiologically derived numbers of motoneurones are discussed.

Fluid secretion by the midgut caeca of the crab, Cancer magister

1. 1. The composition and rate of production of fluid by the anterior and posterior midgut caeca (AMC and PMC, respectively) of the crab, Cancer magister, were studied in vivo and in vitro. Under both conditions these structures produced a small volume of fluid (2.2–3.4 μl/hr) which was, with the exception of sulfate ion, nearly isoionic with the serum. 2. 2. Caecal fluid had relatively low levels of amylolytic and, less frequently, proteolytic activities. 3. 3. The in vivo rate of fluid production was not increased by feeding or by osmotic stress. 4. 4. Ligation of the AMC did not impair secretion of a peritrophic membrane around the fecal strand formed after feeding. 5. 5. It is concluded that the midgut caeca do not have a significant function in osmoregulation or formation of the peritrophic membrane and that they probably have, at best, a minor role in the digestive processes of C. magister. Further, it is suggested that the rate and direction of fluid transport by the midgut caeca may be under neurosecretory control.

Neural and Neurosecretory Control of the Decapod Crustacean Auxiliary Heart

An auxiliary heart is found in many decapod crustaceans at the anterior end of the dorsal median artery. A brief description of the anatomy is given here, followed by an exploration of the reflex and neurosecretory control. The relationship between the activity of the main heart and auxiliary heart and the integration of the auxiliary heart with other blood pressure regulating systems of the body are discussed.

Control of protease secretion in the intestine of fifth instar larvae of Rhodnius prolixus

Groups of four Rhodnius prolixus larvae in the 5th-instar received no food or were given once only through a special feeder, similar weights of food solutions. These were either protein solutions (whole human blood, its plasma or erythrocytes, egg albumin, bovine serum albumin, haemoglobin) or non-protein solutions (saline, casein hydrolysate, dextran, maltose). Following feeding, the protein content and caseinolytic activity of the larval midgut homogenates, determined between the 3rd and 14th days, were practically the same in starved larvae and in larvae receiving non-protein solutions. In the protein-fed larvae the protein content and the specific protease activity increased. These findings exclude neurosecretory control and indicate that ingested protein stimulate the proteolytic activity of R. prolixus midgut.

Some physiological and pharmacological characteristics of the stimulus induced release of norepinephrine from the rabbit superior cervical ganglion

The cervical sympathetic nerve stimulated release of norepinephrine (NE) from the rabbit superior cervical ganglion (SCG) was characterized. The quantity of NE released per impulse declined with increasing stimulation frequency over the range of 3/sec to 15/sec. Nerve stimulated NE release was potentiated by 1 micromolar desmethylimipramine and 25 micromolar phenoxylbenzamine and inhibited by 1 micromolar bretylium, 25 micromolar methoxamine and 1 micromolar prostaglandin E1. These results suggest that nerve stimulated NE release in the rabbit SCG occurs from sympathetic fibers which are subject to the same neurosecretory control mechanisms as sympathetic fibers elsewhere in the autonomic nervous system.

Gill-tissue respiration in the crab Eriocheir sinensis.

Respiration and hydration of excised gill tissue were studied in Eriocheir sinensis adapted to fresh water and seawater, and in eyestalkless (ESR) crabs adapted to fresh water. Anterior red gills are morphologically and functionally different from posterior white gills. Red gills in fresh water have a greater fluid content than white gills. Red and white gills in seawater are similar. Freshwater-adapted white gills have the highest respiratory rate; seawater-adapted red gills have the lowest rate. Wet weight/dry weight comparisons between eyestalkless and normal crabs, of either red or white gills, show some differences. Fluid content of normal white gills is higher, and of normal red gills is Lower, when compared with comparable gills from ESR crabs. Respiration rates of both types of gills from eyestalkless crabs are higher when compared with gills from control crabs. Electron microscope studies support conclusions based on the respiration and hydration measurements. Cells of red gills in fresh water have characteristics of inactive cells, whereas those cells of white gills are metabolically active and are concluded to be responsible for salt regulation. The roles of the two gills are discussed relative to volume regulation, salt balance, changes in gill permeability, and neurosecretory control.

Light and electron microscopic studies on the neurosecretory control of diapause incidence in Pieris rapae crucivora

The incidence of diapause was shown to be determined humorally during the larval-pupal ecdysis by means of brain extirpation experiments. On the basis of this observation, light and electron microscopic changes in the neurosecretory type II cells in the pars intercerebralis-corpus cardiacum system during pharate pupal and early pupal stages were examined in insects reared under long day-length (non-diapause individuals) and in insects reared under short day-length (diapause individuals). In the diapause individuals, neurosecretory granules in NS-II cells increased during the pupal instar and large aggregates of granules packed the cytoplasm. Thereafter, inclusion bodies showing cytoplasmic breakdown of the granules appeared. In the non-diapause individuals, on the contrary, electron micrographs suggesting the release of neurosecretory material from axon terminals were obtained just after the pupal ecdysis. There were very few granules, with many Golgi bodies and much rough ER 8 to 12 hr after the ecdysis. It is concluded that adult development is determined by the release of neurosecretory material from the axon terminals of NS-II cells at the larval-pupal ecdysis. If release does not occur, the pupae enter diapause. It is also thought that differences in day-length during the larval stages influence the activities of NS-II cells before pupation.

Neurosecretory control of ecdysone release during puparium formation of flies

Larvae of Sarcophaga argyrostoma fail to pupariate while kept wet, but do so upon transfer to dry conditions after about 28 hr. This period is lengthened to 42 hr after injection of tetrodotoxin, and shortened to 12 hr after injection of ecdysone, independently of whether they are kept wet or dry. It is 12 hr in larvae injected with ecydsone plus tetrodotoxin (which inhibits the puparial contraction) or ecdysone plus α-MDH (which inhibits subsequent tanning). It is rather the lack of inhibitory stimulation arising from a wet surrounding which allows the CNS to activate the ring gland (RG), than a positive stimulation caused by dry conditions. Hind parts of larvae, previously kept wet, were implanted with the CNS-RG complex, or CNS or RG alone, taken from wet-treated larvae kept dry for various periods. Implantation with the CNS-RG complex from donors of any age induced a high percentage of pupariation, but it occurred sooner, the older the donors. When implanted with RG alone, the age of the donors was decisive; almost no effect at the time of transfer to the dry, and an increasing effect thereafter. When the donors were prepupae at various periods after puparium formation the effect decreased with increasing age, but was identical when CNS-RG or RG alone were implanted. CNS alone from donors of any age before or after pupariation had no effect. Before pupariation the ring gland becomes increasingly more active while the reverse holds after pupariation. The nervous connection between CNS and RG is important rather as a duct for the neurosecretory material, than for its electrical charge-carrying properties.

Interpretation of crayfish hepatopancreatic function based on fine structural analysis of epithelial cell lines and muscle network.

The ultrastructure of R-, F-, and B-cells and of the myoepithelial network in crayfish hepatopancreas tubules was studied as a basis for the functional interpretation of hepatopancreatic digestive activity: 1. R-cells absorb luminal nutrients, mainly via contact digestion and molecular transport, and they store and metabolize glycogen and lipids. To this extent, R-cells combine the functions of vertebrate intestinal absorptive and hepatic parenchymal cells. 2. F-cells synthesize digestive enzymes and sequester them in a supranuclear vacuole which enlarges by pinocytic intake of luminal nutrients and fluids. 3. F-cell to B-cell transformation results from continued engorgement of the F-cell's supranuclear vacuole until only the nuclear region and a pinocytically activeapical complex remain identifiable. 4. B-cell secretion involves pinching off of the apical complex followed by extrusion of the enzyme-rich vacuolar contents. 5. The tubule's myoepithelial network consists of circular fibers, each containing a single myofibril, which branch to form longitudinal fibers. Sarcomeres are long (10–12 μ) and each thick myofilament is surrounded by 11–13 thin ones. This arrangement permits coordinated, tonic contractions of tubule segments which transport nutrients “in” and enzymes “out”. 6. Neurosecretory control of tubular function is suggested by the presence of vesicle-containing, extratubular cell processes which contact the circular muscle fibers.

Functional morphology of the digestive tract epithelium in Phoronis vancouverensis (Pixell): An ultrastructural and histochemical study

AbstractThe ultrastructure of the gut regions of the marine filter‐feeder Phoronis vancouverensis was correlated with enzyme activity as revealed histochemically. The oesophagus, proventriculus, and stomach epithlia showed intense esterase and acid and alkaline phosphatase activity. The staining reaction was confined primarily to small globules in the apical cytoplasm of the epithlial cells. Electron micrographs of the same regions showed a high incidence of zymogenlike granules, with a corresponding abundance of ribosomes and of rough endoplasmic reticulum. Also, the proventricular and to a lesser extent the stomach epithelia were found to contain a large number of lipid bodies. This was confirmed with positive Sudan IV staining for fats.The intestinal region of the gut was found devoid of esterase and phosphatase activity. The epithelial surface in this region was found elaborated into microvilli. The entire gut is ci iated. A new paired‐cilium apparatus is described in this phylum.From these findings Phoronis vancouverensis is concluded to be suitably adapted to its continuous filter‐feeding existence, with the anterior gut epithelia synthesizing hydrolytic enzymes for release into the lumina of the proventriculus and stomach. Subsequently, in the hindgut the products of initial extra‐cellular digestion are absorbed via the microvilli and treated intracellularly within the intestinal epithelium. The proventriculus is further thought to function in lipid absorption and storage. The presence of chromaffin‐like granules observed in some proventricular and intestinal epithelial cells suggests that digestion in this phylum may in part be under neurosecretory control.

Biological Rhythms in Terrestrial Arthropods

biological rhythms is very wide. The cycle s can range from some millis econds to some years. The rapid osci lla­ tions are especially characteristic of physiological rhythms which ensure the synchronization of all the internal process es in an organism. Such rhythms may be exemplifi ed by the rhythmic events in the enzym e-substrate system or by the pulsations of the heart muscle. Oscillations with daily or longer periods rank as a rule among ecolog ical rhythms which provid e for adapt a­ tion of plants and animals to fluctuations of enviro nmental factors. Internal oscillators are assumed to control such rhythms ; they are synch ronized by external timing elements (Zeitgeber = time-giv ers) which can be also termed as synch ronizers or entraining agents. Photope riod is especially im­ portant as this agent. The possession of int ernal oscillators enable s orga­ nisms to prepare in good ti me for the chang es of ecological conditions dur­ ing each day (daily rhyt hms), month (l unar rhythm s), or year (s eas onal rhyth ms). Adaptive implication and, cor res pondi ngly, mode of display ing the three type s of rhythms varies considerably. That's why, until recently, circadian and seasona l rhythms in arthropods have been investigated quite indepen­ dently. Daily rhythms were studied as biolo gical oscillations related to time measuring. As to inve stigations into seasonal cyclic phenomena , most atte n­ tion was paid to syst ems of neurosecr etory control of development and dia­ pause as well as to ecological aspects of the problem. The two points of view have been flected in reviews by Hark er (90) and de Wilde (207 ), published in previous volumes of Annual Review of Entomology. The material accumulated shows that some general princ iple s are th e basis of all the ecological rhythms. It dis plays especially clearly the synchro­ nization of the biological processes with rhythmic factors of the environ­ ment. The adaptations to lunar and seasonal periodicity evolve by way of 1 The follow in g abbrev iati ons are used in the text: PhPR (ph otop eriodic rea cti on); T of a free-running rhyth m); LL (constant ligh t); DD (constant darkness) ; LD (light-dark cycles which can be further specified as

Dual neurosecretory innervation of the adenohypophysis of Hippocampus, the sea-horse.

THE postulate that a dual control of endocrine function by two kinds of neurosecretory fibre may be a fundamental feature of neuroendocrine systems1 has received much support in recent years2–4. It has been suggested that type A fibres, containing peptide hormones, and type B fibres, containing monoamines, may regulate intrinsic endocrine cells of the pituitary. Direct synaptoid contacts (that is, contacts which morphologically resemble synapses elsewhere in the central nervous system) have been demonstrated in an elasmobranch fish, but so far only in the pars intermedia2. In a teleost fish, the eel, type A and type B fibres invade all lobes of the pituitary4. In this fish the fibre terminals are separated from the intrinsic cells of the pars distalis by vascular channels, and so a morphological proof that pars distalis function in teleosts is under dual neurosecretory control was still incomplete. This problem has now been investigated in Hippocampus. This species was chosen because it has been shown by Da Lage5, using light microscopy, that neurosecretory fibres are closely associated with pars distalis cells.