Gesa Merker

Reactivity pattern of vasopressin-containing neurons and its relation to the antipyretic reaction in the pregnant guinea pig

SummaryChanges in the content of vasopressin-immunoreactive material in neurons and their projections were examined in pregnant and nonpregnant guinea pigs as well as in mother and newborn animals. Before sacrifice all animals used in the present study were submitted to a pyrogen test, during which the pregnant animals displayed a reduced fever response to exogenous pyrogen. The unlabeled enzyme-immunoperoxidase method was used in the present study. Light microscopic examination showed that, in comparison to all other groups examined, the pregnant animals exhibited a reduced content of the vasopressin-immunoreactive substance in the supraoptic nucleus (SON), in the neuronal pathways extending between the paraventricular nucleus (PVN) and the SON, as well as in the axons projecting to the neural lobe of the pituitary. An increased amount of vasopressin-immunoreactive material was observed during pregnancy especially in the medial portion of the PVN, in axonal distensions in the external zone of the median eminence and in the extrahypothalamic projection sites of the PVN in the lateral septum and in the amygdala. In the pregnant animals neurovascular contacts of vasopressinergic perikarya and fibers were abundant in the PVN; in the lateral septum and in the amygdala vasopressinergic terminals appeared to contact neurons of other types. It is suggested from the present immunocytochemical results that activation of neurons in the medial portion of the PVN and the increased number of vasopressinergic terminals and preterminals in the lateral septum and in the amygdala might be functionally involved in fever suppression at the term of pregnancy.

Fever response in the guinea pig before and after parturition

The febrile response to an intramuscular injection of bacterial endotoxin (E. coli 4 microgram/kg) was tested in guinea pigs at the end of pregnancy in the time period extending from 8 days before until 3 days after parturition. In comparison to non-pregnant female controls both fever height and fever index were reduced in mother guinea pigs one week before parturition. This response was gradually reduced and reached its minimum on the last day before parturition. Immediately after parturition the fever response was still suppressed in mother animals as well as in newborns. Several hours after birth the fever response increased again in both groups of animals. The onset time and duration of fever were, however, shorter than in controls. The full fever responsivity was not reached until several days postpartum. Apparently the guinea pig develops an active antipyresis during the last phase of pregnancy. This resembles the suppression of fever in ewes at term of pregnancy where endogenous arginine-vasopressin has been proposed as an antipyretic agent. The vasopressinergic neuronal systems have therefore been localized by immunohistochemical methods in the brains of the guinea pigs whose responses to bacterial endotoxin were studied. These studies, which are described in detail in a following paper, support the involvement of vasopressin in natural antipyresis in the guinea pig.

Changes in body temperature and vasopressin content of brain neurons, in pregnant and non-pregnant guinea pigs, during fevers produced by Poly I : Poly C

The synthetic polyribonucleotide pyrogen Poly I : Poly C (800 μg · kg−1) was injected intramuscularly on alternate days into pregnant and non-pregnant female guinea pigs. Pregnant animals, close to term, had smaller fevers in response to the pyrogen than did non-pregnant animals. Repeated injections of the pyrogen caused sequentially smaller fevers for the first 3–4 injections, particularly in non-pregnant animals, and this appeared to be like the tolerance usually developed to repeated injections of endotoxin. Continued pyrogen injections then caused, in non-pregnant animals, fevers of increasing magnitude until the original fever levels were reached, whereas in pregnant guinea pigs the fever responses remained reduced until parturition. The development of tolerance was associated with an increase in immunoreactivity for arginine vasopressin (AVP) in some neurons in the medial part of the paraventricular nucleus, and in terminals in the lateral septum and amygdala similar to changes found in these areas at term of pregnancy. These observations raise the possibility that AVP in these regions may have a role in the development of tolerance to pyrogens, and further quantitative studies of the AVP content of, and release from, nerve terminals projecting to the limbic system seem warranted.

Thermosensitivity of preoptic neurones in a hibernator (golden hamster) and a non-hibernator (guinea pig)

SummaryThermosensitivity of preoptic units was studied at hypothalamic temperatures (Thy) ranging from 8–43°C in golden hamsters in a non-hibernating state as well as in guinea pigs. In golden hamsters 2 types of thermoresponsive preoptic neurones were found: 1. Neurones sensitive toThy ranging from 10–42°C with an exponential characteristic and very high spontaneous firing rates (29–59 imp/s) atThy 36–37°C. 2. Neurones with a bell-shaped temperature-firing rate characteristic, a negative temperature coefficient atThy 40–30°C, a maximal activity atThy 20–30°C and a positive temperature coefficient (+0.8 to +4 imp/s·°C) even atThy close to 10°C. In guinea pigs thermoresponsive preoptic units became inactive or insensitive to thermal stimulation as soon asThy fell below 30°C. These results suggest that in hibernators central nervous structures involved in temperature regulation are adapted to maintain their function over the wide range of core temperatures which occur during the different phases of hibernation.

Do corticosteroids control heat production in hibernators

SummaryPresent experiments indicate that in hedgehogs two different control mechanisms of non-shivering thermogenesis (NST) exist.1.During arousal from hibernation catecholamines control heat production in the interscapular brown adipose tissue.2.In a non-hibernating state, cold-induced NST is controlled by a desoxycorticosterone-like acting compound. The effector system of this second mode of NST is obviously not the interscapular brown fat pad but a layer of brown adipose tissue which covers the whole back of the hedgehog.

Ultrastrukturveränderungen motorischer Vorderhornzellen des Kaninchens unter abgestufter Ischämie

SummarySpinal ventral horn motoneurons from the lumbar region in the rabbit were examined in the electron microscope during different states of temporary ischemia. Ischemia caused variable effects upon the motoneuron cytoplasmic structures. Alterations were particularly evident in mitochondria and endoplasmic reticulum; a swelling and water uptake by these organelles were observed already after a 5-minute blockade of blood supply. After prolonged ischemia, reproducible structural changes and membrane alterations were especially evident in mitochondria; within a cell, the swollen mitochondria occurred next to less damaged mitochondria. Centrally located ventral horn cells were affected more than peripherally located cells. The structural alterations of the mitochondria and the endoplasmic reticulum are interpreted to be caused by a disturbance of cellular energy and water metabolism.ZusammenfassungDie motorischen Vorderhornzellen im Rückenmark des Kaninchens wurden im Lumbaibereich nach abgestufter temporärer Ischämie elektronenmikroskopisch untersucht. Die cytoplasmatischen Strukturen und Organellen dieser Zellen werden unterschiedlich stark durch die Zirkulationsunterbrechung beeinflußt; besonders eindrucksvoll sind die Veränderungen der Mitochondrien und des endoplasmatischen Retikulums. Vor allem zeigen die Mitochondrien mit zunehmender Ischämiedauer ganz charakteristische, reproduzierbare Strukturveränderungen. Sowohl an den Mitochondrien als auch am endoplasmatischen Retikulum sind bereits nach einer Blockade der Blutzufuhr von 5 min deutliche Folgen der Ischämie zu erkennen (Schwellung, Wasseraufnahme). Zentral gelegene Vorderhornzellen sind durchgehend stärker von der Zirkulationsunterbrechung betroffen als peripher gelegene Zellen. Innerhalb einer Zelle finden sich nach längerer Ischämiedauer nebeneinander Gruppen stark geschwollener und weniger geschädigter Mitochondrien. Die durch Ischämie an den Mitochondrien und am endoplasmatischen Retikulum hervorgerufenen Schwellungen und Membranveränderungen sind als Folge einer Störung des Energie- und Wasserhaushaltes der Zelle aufzufassen.

[On the ultrastructure of the "brain" and the sense organs of Protodrillus rubrophyaryngaeus Jaegersten (Archiannelida). With special consideration of the neurosecretory cells].

„Gehirn,“ Auge und Statozysten vonProtodrilus rubropharyngaeus Jaegersten (Archiannelida) wurden licht- und elektronenmikroskopisch untersucht. Das Gehirn vonProtodrilus besteht aus Nervenzellen und der Neuroglia. Nachgewiesen wurden sowohl faserhaltige als auch protoplasmatische (filamentfreie) Gliazellen. Der zentrale Neuropilkern wird von den feinsten Auslaufern der Nerven- und Gliazellen gebildet. Die Sinnesorgane vonProtodrilus werden mit den entsprechenden Bildungen bei Polychaetenlarven und Turbellarien verglichen. Das Gehirn vonProtodrilus enthalt zahlreiche neurosekretorische Elemente. Die grosen, mit Paraldehydfuchsin elektiv farbbaren Perikaryen dieser Zellen finden sich vornehmlich in einer bestimmten Anordnung in der Nahe der Palpen, des Nuchalorgans und des dorsalen Coeloms. Im elektronenmikroskopischen Bild gelang es, funf verschiedene Typen von Elementargranula und Blaschen nachzuweisen. Nur ein Teil dieser Substanzen ist mit konventionellen Neurosekretmethoden farbbar. Vielfach enthalten neurosekretorische Perikaryen und Axone mehr als einen (einheitlichen) Typ der Elementargranula. Die Klassifizierung der neurosekretorischen Zelltypen auf einer chemischen und biologischen Basis ist beiProtodrilus noch ungeklart.SummaryThe brain, eye, and statocysts ofProtodrilus rubropharyngaeusJaegersten (Archiannelida) were examined with the light and electron microscope. The brain ofProtodrilus is composed of neurons and neuroglia. Fibrous and protoplasmic neuroglia cells were observed. The central neuropile is formed by the finest processes of the nervous and glial elements. The sensory organs ofProtodrilus can be compared with similar structures in larvae of polychaetes and in turbellaria. The brain ofProtodrilus shows a remarkable accumulation of neurosecretory elements. By means of the light microscopy (paraldehydefuchsin method) large selectively stainable perikarya were found in a particular arrangement near the palps, the nuchal organ and the dorsal coelomic cavity. In the electron micrographs it is possible to demonstrate five different types of elementary granules and vesicles. Only a part of these materials can be stained by conventional methods. A great number of perikarya and unmyelinated neurosecretory nerve fibers display more than one uniform type of elementary granules. InProtodrilus the problem of different neurosecretory cell types and their chemical and biological properties is still open to discussion.Zusammenfassung„Gehirn,“ Auge und Statozysten vonProtodrilus rubropharyngaeusJaegersten (Archiannelida) wurden licht- und elektronenmikroskopisch untersucht. Das Gehirn vonProtodrilus besteht aus Nervenzellen und der Neuroglia. Nachgewiesen wurden sowohl faserhaltige als auch protoplasmatische (filamentfreie) Gliazellen. Der zentrale Neuropilkern wird von den feinsten Ausläufern der Nerven- und Gliazellen gebildet. Die Sinnesorgane vonProtodrilus werden mit den entsprechenden Bildungen bei Polychaetenlarven und Turbellarien verglichen. Das Gehirn vonProtodrilus enthält zahlreiche neurosekretorische Elemente. Die großen, mit Paraldehydfuchsin elektiv färbbaren Perikaryen dieser Zellen finden sich vornehmlich in einer bestimmten Anordnung in der Nähe der Palpen, des Nuchalorgans und des dorsalen Coeloms. Im elektronenmikroskopischen Bild gelang es, fünf verschiedene Typen von Elementargranula und Bläschen nachzuweisen. Nur ein Teil dieser Substanzen ist mit konventionellen Neurosekretmethoden färbbar. Vielfach enthalten neurosekretorische Perikaryen und Axone mehr als einen (einheitlichen) Typ der Elementargranula. Die Klassifizierung der neurosekretorischen Zelltypen auf einer chemischen und biologischen Basis ist beiProtodrilus noch ungeklärt.

Chapter 52: The role of OVLT in fever and antipyresis

Publisher Summary This chapter describes the special role of the organum vasculosum laminae terminalis (OVLT) in both fever generation and suppression. The febrile increase in body temperature that may be beneficial because it accelerates and facilitates the activation of the immune defence is controlled by endogenous antipyretic systems. The basic mechanisms responsible for both the increase of body temperature and its suppression are only partly understood. The lymphokines produced and released from activated macrophages, monocytes and other mononuclear cells during microbial infection, tissue injury or immunological reactions are believed to act on hypothalamic neurons to alter the set point for temperature regulation. For their ability to increase body temperature, some of the lymphokines are called endogenous pyrogens. Among these interleukin-1 (IL-1) is thought to be the most potent mediator of fever. The peripheral interleukin can probably not penetrate into the brain. It is rather probable that it binds to specific receptors on astroglial processes in the perivascular space of the OVLT. This signal induces the production and release of prostaglandin E2 from the astroglial processes within the brain.

Licht- und elektronenmikroskopische Studien über die Fasergliastruktur der Epiphysen-Subcommissuralregion der Primaten

SummaryIn Cebus, Ateles, Macaca, and Pan, the fibrous neuroglia of the posterior commissure, the subcommissural complex and the adjoining recessus (Rec. mesocoelicus, Rec. pinealis) show definite organizational and structural features. In the posterior commissure, fiber bundles course radially and fiber end-feet terminate in the Pia mater. Neuroglia in the subependymal fiber layer of the Recessus pinealis and fibrous astroglia in the Epiphysis cerebri have characteristically short fiber bundles. In the subependymal glial layer of the subcommissural complex, fibrous astroglia forms a dense felt-like network around ependymal channels (Ateles). The dense network of neuroglial fibers surrounding the secretorily-active parts of the subcommissural complex suggests that metabolic exchange through the inner fibrous neuroglial layer is not hindered. Electron microscopy indicates that the processes of the fibrous astrocytes as well as of the corresponding perivascular formations of fibrous neuroglia are not entirely filled with glial filaments.ZusammenfassungBei Cebus, Ateles, Macaca und Pan wird die Gliaarchitektonik der Commissura posterior, des Subcommisuralkomplexes und der angrenzenden Rec. mesocoelicus und Rec. pinealis beschrieben. In allen diesen Abschnitten sind sowohl im Verlauf als auch in der Anordnung der Faserglia Gesetzmäßigkeiten zu erkennen. In der Commissura posterior finden sich gebündelte Radiärfasern, deren Endfüße die Pia mater durchsetzen. Kurze Faserbündel sind für die subependymale Gliafaserdeckschicht des Recessus pinealis und für die Fasergliatextur des Epiphysenparenchyms charakteristisch. In der subependymalen Gliaschicht des Subcommissuralorgans herrscht ein feines, füzartiges Gliafaserwerk vor, das um die in die Tiefe dringenden Ependymkanälchen (Ateles) eine besonders dichte Formation ausbildet. Die Tatsache, daß sekretorisch aktive Partien des Subcommissuralorgans von einem auffallend dichten Gliafasergeflecht eingehüllt werden, spricht gegen eine Behinderung des Stoffaustausches durch die innere Gliafaserdeckschicht. Elektronenmikroskopische Befunde zeigen, daß sowohl in diesen Ausläufern der Faserastrocyten als auch in den entsprechenden perivasculären Fasergliaformationen ein Fortsatzprofil nie vollständig von Gliafilamenten ausgefüllt wird.

Thermoadaptive influence on reactivity pattern of vasopressinergic neurons in the guinea pig

In cold-adapted guinea pigs, increased amounts of arginine-vasopressin (AVP) immunoreactive material could be visualized in neurons of the supraoptic and paraventricular nucleus, in fibers projecting to the neurohypophysis and in fiber terminals in the ventral lateral septum and in the amygdala. In warm-adapted animals the reactivity to AVP antiserum was poor in all neuronal structures examined. High AVP-immunoreactivity was accompanied by a reduced febrile response to bacterial pyrogen in cold-adapted guinea pigs.