Hypophysiotrophic thyrotropin releasing hormone (TRH) synthesizing neurons. Ultrastructure, adrenergic innervation and putative transmitter action

The neuropeptide thyrotropin releasing hormone (TRH) is capable of influencing both neuronal mechanisms in the brain and the activity of the pituitary-thyroid endocrine axis. By the use of immunocytochemical techniques, first the ultrastructural features of TRH-immunoreactive (IR) perikarya and neuronal processes were studied, and then the relationship between TRH-IR neuronal elements and dopamine-beta-hydroxylase (DBH) or phenylethanolamine-N-methyltransferase (PNMT)-IR catecholaminergic axons was analyzed in the parvocellular subnuclei of the hypothalamic paraventricular nucleus (PVN). In control animals, only TRH-IR axons were detected and some of them seemed to follow the contour of immunonegative neurons. Colchicine treatment resulted in the appearance of TRH-IR material in parvocellular neurons of the PVN. At the ultrastructural level, immunolabel was associated with rough endoplasmic reticulum, free ribosomes and neurosecretory granules. Non-labelled axons formed synaptic specializations with both dendrites and perikarya of the TRH-synthesizing neurons. TRH-IR axons located in the parvocellular units of the PVN exhibited numerous intensely labelled dense-core and fewer small electron lucent vesicles. These axons were frequently observed to terminate on parvocellular neurons, forming both bouton- and en passant-type connections. The simultaneous light microscopic localization of DBH or PNMT-IR axons and TRH-synthesizing neurons demonstrated that catecholaminergic fibers established contacts with the dendrites and cell bodies of TRH-IR neurons. Ultrastructural analysis revealed the formation of asymmetric axo-somatic and axo-dendritic synaptic specializations between PNMT-immunopositive, adrenergic axons and TRH-IR neurons in the periventricular and medial parvocellular subnuclei of the PVN. These morphological data indicate that the hypophysiotrophic, thyrotropin releasing hormone synthesizing neurons of the PVN are directly influenced by the central epinephrine system and that TRH may act as a neurotransmitter or neuromodulator upon other paraventricular neurons.     

A simple integrative electrophysiological model of bursting GnRH neurons

In this paper a modular model of the GnRH neuron is presented. For the aim of simplicity, the currents corresponding to fast time scales and action potential generation are described by an impulsive system, while the slower currents and calcium dynamics are described by usual ordinary differential equations (ODEs). The model is able to reproduce the depolarizing afterpotentials, afterhyperpolarization, periodic bursting behavior and the corresponding calcium transients observed in the case of GnRH neurons.     

The origin and ultrastructural characteristics of corticotropin-releasing factor (CRF)-immunoreactive nerve fibers in the posterior pituitary of the rat

Summary A fine network of corticotropin-releasing factor (CRF)-immunopositive fibers was found in the posterior lobe of the pituitary of the rat. The intermediate and distal lobes were free of CRF-immunoreactivity. Varicose, terminal-like axons were frequently observed around capillary vessels. Surgical isolation of the paraventricular nuclei resulted in a complete disappearance of CRF-immunoreactive fibers from the posterior lobe. CRF-immunopositive fibers show the general characteristics of peptidergic axons. These ultrastructural observations support the idea that CRF is secreted into capillary vessels.     

Effect of cooling rate,cryoprotectant and holding time at different transfer temperatures on the survival of cryopreserved cell suspension culture (Puccinellia distans (L.) Parl.)

Reflexed saltmarsh-grass suspension cultures produced by seed callus were frozen to the liquid nitrogen temperature. Cooling rates, cryoprotectants and holding times were taken as a function of transfer temperatures. The highest survival of cells (45%) was found at a freezing rate of 1°C min^-1, without cryoprotectant treatments. The cryoprotectants (proline, dimethyl sulphoxide, glycerol), used at different concentrations and transfer temperatures, increased the survival rate. The maximum value was 78% at 12.5% (w/v) of proline with –30°C transfer temperature. Considerable improvement of viability (from 0% to 95%) among the 12.5 and 15.0% (v/v) dimethyl sulphoxide cryopreserved cells was achieved by holding them at – 20°C for 10–30 min before plunging into the liquid nitrogen. A 20 min holding time at 15.0% (v/v) glycerol level and – 30°C transfer temperature significantly enhanced the viability of the explants from 42% to 92%. Plants were successfully regenerated from cells cryopreserved with proline (w/v) and dimethyl sulfoxide (v/v) levels of 12.5 and 15.0%, respectively.     

New technique in optical resolutions

The present paper illustrates the development of an advanced technique in optical resolution. Both of the amphetamine enantiomers can be obtained by a two-step distillation in nearly quantitative yield without any loss of the resolving agent. It is proved that the second-order interactions (H-bond) are sufficient for separation of enantiomers by distillation. © 1994 Wiley-Liss, Inc.     

Studies on epimerization-free methods for the preparation of aminosuccinyl peptides

Summary We have found that guanidine acetate catalyses the transformation of a -benzyl-aspartyl peptide (Boc-Asp-(OBzl)-Leu-Trp-OMe) to an aminosuccinyl peptide (Boc-Asu-Leu-Trp-OMe). The reaction was accompanied by partial epimerization. However, not even a small amount of epimerization could be detected when the aminosuccinyl peptide was synthesised from Boc-Asp-Leu-Trp-OMe with the addition of DIC, HOPfp and guanidine acetate (as a catalyst). This reaction seems to be suitable for the epimerization-free solid phase synthesis of aminosuccinyl peptides, e.g. Asu⁶-Lamprey-III-GnRH (Glp-His-Trp-Ser-His-Asu-Trp-Lys-Pro-Gly-NH₂).     

Immune challenge mediates vocal communication in a passerine bird: an experiment

Secondary sexual characters may have evolved in part to signalresistance to parasites. Avian song has been hypothesized tobe involved in this process, but the role of parasites in modulatingacoustic communication systems in birds remains largely unknown,owing to lack of experiments. We studied the relationship betweenparasitism, testosterone, song performance, and mating successin male collared flycatchers (Ficedula albicollis) by experimentallychallenging their immune system with a novel antigen. We predictedthat a challenge of the immune system would reduce song performance,and that this reduction would be conditional on the size ofa visual sexual signal, the forehead patch that was previouslyfound to reflect resistance. An antagonistic linkage betweentestosterone and immune function would predict that a challengeof the immune system should suppress testosterone level. Animmunological treatment by sheep red blood cells (SRBCs) triggereda decrease in body mass, testosterone level, and song rate,but other song traits were not significantly affected by theantigen challenge. Initial testosterone level was associatedwith forehead patch size and all song traits except song rate.SRBC injection caused stronger reduction in song rate amongmales with smaller forehead patches, and the change in songrate was also predictable by song features such as strophe complexityand length. We show that song rate and other song characteristicsmay be important cues in male-male competition and female choice.These results suggest that parasite-mediated sexual selectionhas contributed in shaping a complex acoustic communicationsystem in the collared flycatcher, and that testosterone mayplay an important role in this process. Parasitism may drivea multiple signaling mechanism involving acoustic and visualtraits with different signal function.     

Between‐male variation in sperm size,velocity and longevity in sand martins Riparia riparia

Sperm mobility is known to be an important determinant of a male's sperm competitive ability. Although more debated, sperm length and its relation to sperm swimming ability has also been proposed to determine a male's fertilisation potential. Furthermore, both mobility and length may covary with a male's phenotype, either positively (the phenotype‐linked fertility hypothesis) or negatively if, for instance, low‐quality males have less access to females but invest more in sperm production. Using dummy females, we collected sperm samples from wild sand martins Riparia raparia males. We investigated the relationship between sperm length and sperm swimming speed as measured by sperm straight line velocity (VSL), and determined whether sperm traits are correlated with male body size and condition. We found that total sperm length is repeatable within‐ejaculate and shows substantial inter‐male variation. Sperm length was associated with sperm velocity: males with short sperm have sperm that swim initially faster but die sooner, whereas males with longer sperm have sperm that swim more slowly but for a longer time. Smaller males produced sperm with higher overall velocity. This correlation between male size and sperm behaviour may reflect alternative fertilisation strategies where small males having less mating opportunities invest more in sperm competitive ability. The existence of such alternative strategies would participate in maintaining variation in sperm length and velocity in this species.