Steroid production in toads

In Bufo arenarum, androgen biosynthesis occurs through a complete 5-ene pathway, including 5-androstane-3β,17β-diol as the immediate precursor of testosterone. Besides, steroidogenesis changes during the breeding period, turning from androgens to C₂₁-steroids such as 5-pregnan-3,20-diol, 3-hydroxy-5-pregnan-20-one and 5-pregnan-3,20-dione. In B. arenarum, steroid hormones are not involved in hCG-induced spermiation, suggesting that the steroidogenic shift to C₂₁-steroids during the breeding be not related to spermiation. The activity of 17-hydroxylase-C_17–20 lyase (CypP450_c17) decreases during the reproductive season, suggesting that this enzyme would represent a key enzyme in the regulation of seasonal changes. However, the increase in the affinity for pregnenolone of 3β-hydroxysteroid dehydrogenase (3HSD)/isomerase could also be involved. Moreover, the reduction in CypP450_c17 leading to a reduction in C₁₉-steroids, among them dehydroepiandrosterone (DHE), would contribute to the conversion of pregnenolone into progesterone, avoiding the non-competitive inhibition exerted by DHE on this transformation. Additionally, CypP450_c17 possesses a higher affinity for pregnenolone than for progesterone, explaining the predominance of the 5-ene pathway for testosterone biosynthesis. Animals in reproductive condition showed a significant reduction in circulating androgens, enhancing the physiological relevance of all the in vitro results. The in vitro effects of mGnRH and hrFSH on testicular steroidogenesis revealed that both hormones inhibited CypP450_c17 activity. In summary, these results demonstrate that, in B. arenarum, the change in testicular steroidogenesis during the reproductive period could be partially due to an FSH and GnRH-induced decrease in CypP450_c17 activity.     

The neurohypophysis of the foetal monkey

Summary The neurohypophysis of foetal macaque monkeys has been studied by optical and electron microscopy. Abundant elementary neurosecretory granules are present in the infundibular process by the middle third of gestation. Most of these are of variable electron density, and surrounded by a membrane larger than the granule, so that they appear haloed. A few fibres contain membrane-bounded electron-dense granules which show no halo. Inclusions of synaptic vesicle size are rare. The infundibular stem contains a few fibres with typical inclusions smaller than 1000 Å in diameter; the latter resemble inclusions in fibres of the median eminence.Dedicated to Professor W. Bargmann on his 60th birthday.     

The neurohypophysis of the crested newt

Summary In the crested newt, the ultrastructural organization of the pars nervosa is analogous to that already known in non-mammal tetrapods. An orderly array of ependymal cells makes up the inner limiting layer while less abundant pituicytes are irregularly distributed within this organ. Light and dark pituicytes can be distinguished on the basis of the relative density of the cytoplasmic matrix and the distribution of the cell organelles.Both the ependymal cells and pituicytes are rich in dense bodies and possess extensive processes which ramify among the nerve fibers, often reaching the pericapillary space which they can line for long distances.The main components of the pars nervosa are nerve fibers and nerve terminals (type A), containing electron dense granules 1200–2000 Å in diameter together with clear vesicles averaging 250–400 Å. These fibers are likely to correspond to the aldehyde fuchsin positive neurosecretory fibers revealed by light microscopy. Differences in the granule size within the fibers and terminals lead to further recognition of two subgroups (A₁ and A₂).Other fibers and terminals (type B) containing clear vesicles and granular vesicles 600 to 1000 Å in diameter, possibly of aminergic type, are also encountered. These fibers are rare and can be seen only in the portion of the pars nervosa near the pars intermedia of the adenohypophysis.Lastly, fibers and terminals containing only clear vesicles ranging from 250 to 400 Å (type C) are occasionally found.Nerve endings are often formed by type A fibers on the perivascular space and on the perivascular processes of the ependymal cells and pituicytes. In agreement with recent findings available in the literature, the occurrence of synaptoid contacts between these terminals and both pituicytes and ependymal cells may confirm the active role of these cells in transport and release of neurosecretion.Work supported by a grant from the Consiglio Nazionale delle Ricerche.We are gratefully indebted to Dr. G. Gendusa and P. Balbi for technical assistance, dr. G. E. Andreoletti for statistical analysis.     

No emotional fever in toads

Four Bufo marinus toads and one Bombina bombina toad were placed individually along a temperature gradient where they could regulate their body temperature through behavioral means. When injected intraperitoneally with killed Pseudomonas aeruginosa bacteria, the toads sought heat and raised their body core temperature. Gentle handling by the experimenter, however, was not followed by heat-seeking behavior and rising core temperature. These findings confirm the existence of behavioral fever, but not emotional fever, in the species studied.     

Role of adenosine in the hypoxia-induced hypothermia of toads

The concept that hypoxia elicits a drop in body temperature (T(b)) in a wide variety of animals is not new, but the mechanisms remain unclear. We tested the hypothesis that adenosine mediates hypoxia-induced hypothermia in toads. Measurements of selected T(b) were performed using a thermal gradient. Animals were injected (into the lymph sac or intracerebroventricularly) with aminophylline (an adenosine receptor antagonist) followed by an 11-h period of hypoxia (7% O(2)) or normoxia exposure. Control animals received saline injections. Hypoxia elicited a drop in T(b) from 24.8 +/- 0.3 to 19. 5 +/- 1.1 degrees C (P < 0.05). Systemically applied aminophylline (25 mg/kg) did not change T(b) during normoxia, indicating that adenosine does not alter normal thermoregulatory function. However, aminophylline (25 mg/kg) significantly blunted hypoxia-induced hypothermia (P < 0.05). To assess the role of central thermoregulatory mechanisms, a smaller dose of aminophylline (0.25 mg/kg), which did not alter hypoxia-induced hypothermia systemically, was injected into the fourth cerebral ventricle. Intracerebroventricular injection of aminophylline (0.25 mg/kg) caused no significant change in T(b) under normoxia, but it abolished hypoxia-induced hypothermia. The present data indicate that adenosine is a central and possibly peripheral mediator of hypoxia-induced hypothermia.     

Multifaceted purinergic regulation of stimulus-secretion coupling in the neurohypophysis

The neurohypophysis is an original model of the CNS secretory system releasing vasopressin (AVP) and oxytocin (OXT), two neuropeptides hormones synthesized by the magnocellular neurons of the hypothalamus. Specific patterns of action potentials originating from cellular bodies of magnocellular neurons control the release of AVP and OT, but intra-neurohypophysis regulations do modulate the neuropeptides release. There is now good evidence for the effects of extracellular purines in the control of neurohypophysial secretion. This paper brings together evidence for the multiple, intricate actions of purines in the extracellular space of the neurohypophysis. It covers four main points. First, the activity-dependent release of endogenous ATP in the neurohypophysis. Second, the action of ATP on both neuronal and non-neuronal compartments of the neural lobe. Third, the termination of ATP positive feedback by ecto-nucleotidases. And finally the possible involvement of adenosine in the regulation of neurohypophysial secretion and glial plasticity. The data suggest that ATP and adenosine are physiological modulators of the release of neurohypophysial peptides by acting directly on nerve terminals and indirectly on neurohypophysial astrocytes. Since purinergic receptors are widespread in nervous and endocrine systems, the neurohypophysis appears as an useful model for studying the role of purines in the regulation of stimulus-secretion coupling and neuron-glia interactions. The feedback mechanisms found in the neurohypophysis could be ubiquitous, occurring throughout the central nervous system and in other secretory systems.     

Glycogen in Methanothrix

An intracellular glycogen was purified and characterized from the acetoclastic bacteria Methanothrix str. FE, its average chain length was about 13 glucose residues. Acetyl-CoA was shown to be synthesized by the action of acetate thiokinase; in addition pyruvate synthase, phosphoenolpyruvate synthetase and enzymes of gluconeogenesis were detected in cell extracts. For glycogen synthase activity, both adenosine diphosphate glucose and uridine diphosphate glucose were used as glycosyl donors, apparent K _m were, respectively, 8 M for ADPGlc and 625 M for UDPGLe, at the opposite the V _m were the same for both precursors. This was in accordance with competition experiments and strongly suggested that only one glucosyl transferase was involved and that ADPGlc was the physiological glycosyl donor in Methanothrix str. FE. In addition branching enzyme activity (1-4-glucan-6-glucosyl transferase) was detected in cell extracts.Abbreviations ADPGlc adenosine diphosphate glucose - UDPGlc uridine diphosphate glucose     

Development of the capillary system in the neurohypophysis of the rat

Summary The development of the vascular system in the neurohypophysis of the rat shows three periods of structural differentiation. The first period lasts until the 17th fetal day. During this period the superficial and the border plexuses are formed, and rapid vascularization of the neural lobe anlage takes place. The end of this period is marked by the formation of the perivascular space. The second period lasts from the 18th fetal day until the 10th day after birth. Its initial phase is characterized by the appearance of the first endothelial pores. During this period the formation of the internal capillaries proceeds, together with the maturation of the previously formed vascular elements. The third period lasts from the 10th postnatal day until the end of the first month after birth. At the end of this period the vascular net of the neural lobe has attained its fully developed state. The results of this study, together with data from previous investigations, lead to the conclusion that at the 18th fetal day the neural lobe displays signs of functional activity, and that the maturation of the vascular network in the neural lobe occurs more rapidly than the maturation of its other structural components.Research fellow of the Alexander von Humboldt Foundation.Dedicated to Prof. Dr. V. Becker, Department of Pathology, University of Erlangen, on the occasion of his 60th birthday