Neuregulin 3 promotes excitatory synapse formation on hippocampal interneurons

Hippocampal GABAergic interneurons are crucial for cortical network function and have been implicated in psychiatric disorders. We show here that Neuregulin 3 (Nrg3), a relatively little investigated low‐affinity ligand, is a functionally dominant interaction partner of ErbB4 in parvalbumin‐positive (PV) interneurons. Nrg3 and ErbB4 are located pre‐ and postsynaptically, respectively, in excitatory synapses on PV interneurons in vivo. Additionally, we show that ablation of Nrg3 results in a similar phenotype as the one described for ErbB4 ablation, including reduced excitatory synapse numbers on PV interneurons, altered short‐term plasticity, and disinhibition of the hippocampal network. In culture, presynaptic Nrg3 increases excitatory synapse numbers on ErbB4⁺ interneurons and affects short‐term plasticity. Nrg3 mutant neurons are poor donors of presynaptic terminals in the presence of competing neurons that produce recombinant Nrg3, and this bias requires postsynaptic ErbB4 but not ErbB4 kinase activity. Furthermore, when presented by non‐neuronal cells, Nrg3 induces postsynaptic membrane specialization. Our data indicate that Nrg3 provides adhesive cues that facilitate excitatory neurons to synapse onto ErbB4⁺ interneurons.     

Morphology of the green livers in upstream migrants of Petromyzon marinus L.

A morphological comparison was made of the green livers of male and female lampreys (Petromyzon marinus L.) collected during the upstream (prespawning) migration. Light and electron microscope histochemistry for iron, and both thin sections and freeze-fracture replicas in the electron microscope, revealed some sexual dimorphism in these livers. Ferric iron is much more abundant in the liver of females and is present in the cytoplasmic matrix, in dense bodies, and in vacuoles of hepatocytes. The numerous vacuoles of females may be the deposition site of biliverdin and other bile components that would account for the darker green coloration of the liver compared to males. Hepatocytes in females are also characterized by prominent rough endoplasmic reticulum and Golgi apparatus that reflect the involvement of the cells in vitellogenesis. The presence of numerous lipid droplets in the hepatocytes of males indicates that the liver is an important storage site for fat. The lipid droplets are associated with electron-dense deposits of unknown nature. Large gap junctions typify the parenchymal cells of both male and female livers. Perisinusoidal and sinusoidal cells are similar to those in the nonparenchymal region in other vertebrate livers, namely, endothelial and Kupffer cells, lipocytes (Ito), and some granulated cells. The relationship of lipocytes to fibrous tissue and fibrogenesis is discussed.     

Ultrastructure of neurosecretory granule exocytosis by crayfish sinus gland induced with ionic manipulations

Neurosecretory granule exocytosis from axon terminals in the crayfish (Orconectes virilis) sinus gland can be effected by alterations in intracellular ionic concentrations through modification of the bathing medium or by electrical stimulation. This may result in increased numbers of exocytotic profiles involving one granule (single exocytosis) or several granules (compound exocytosis), which we interpret as evidence of stimulated neurosecretion. Our results suggest that increased free intracellular Ca⁺⁺ together with a decrease in intracellular K⁺ are prerequisite for and sufficient to elicit increased exocytosis from sinus gland terminals. Similar release, stimulated by horseradish peroxidase, indicates that local surface permeability changes are involved. A minor response to high-K⁺-Ringer, and secretion via compound exocytosis, are uncharacteristic of cells with a neural ancestry.     

Structural modulation of the surface and cytoplasm of oocytes during vitellogenesis in the lobster,Homarus americanus. An electron microscope-protein tracer study

The present investigation describes the ultrastructural changes which occur at the surface and in the cytoplasm of developing oocytes of the lobster, Homarus americanus, during vitellogenesis. The immature oocytes showed no surface specializations of the oolemma and no pinocytotic activity was observed. Horseradish peroxidase (HRP) tracer studies showed penetration of the tracer into the perivitelline space, but no uptake by the oocytes. The surfaces of oocytes examined during vitellogenesis, when yolk protein accumulation was maximal, exhibited numerous microvilli that projected into the perivitelline space, often appearing to be embedded in the follicular cell mass. In addition, the plasma membrane of vitellogenic oocytes contained many pinocytotic pits frequently situated at the bases of microvilli. The perivitelline space was engorged with electrondense material which appeared similar to that contained in pinocytotic structures of the oocytes. Vitellogenic oocytes incubated in HRP showed uptake of tracer reaction product by the coated pits and vesicles of the oolemma. Aggregation and subsequent fusion of these vesicles into large multivesicular bodies of ingested material were also observed in vitellogenic oocytes. Animals artificially induced to undergo vitellogenesis exhibited modulations of oocyte ultrastructure similar to those of normal vitellogenesis, notably, pinocytotic incorporation of extra-oocytic material and hypertrophy of oocyte surface microvilli. This study supports the hypothesis for a dual source of yolk protein in the American lobster.     

Crustecdysone-induced modulation of electrical coupling and gap junction structure in crayfish hepatopancreatocytes

Crustecdysone, the hormone responsible for onset and regulation of the molt cycle in Crustacea, causes an increase in ionic coupling of cells of the hepatopancreas concomitant with the events of the molt. Hepatopancreatic tissue incubated for up to 4 hr in modified Eagle Basal Medium containing crustecdysone, exhibited an approximate 29% decrease in intercellular resistance as compared with tissue incubated in control medium. This represents a 29% increase in ionic coupling between hepatopancreatocytes following treatment with crustecdysone. Examination of platinum replicas of freeze-fractured, crustecdysone-treated hepatocyte plasma membrane revealed that most of the gap junction plaques were round with tightly packed intramembrane particles; a condition indicative of highly coupled cells. Similar preparations of control plasmalemmae demonstrated many gap junction plaques which were round or irregular in shape with very loosely packed particles and were indicative of uncoupled junctions. Results of this study are identical to those from a previous investigation of the electrophysiology and freeze-fracture morphology of hepatopancreatocytes during the molt cycle (McVicar and Shivers, 1984), and are thus presumed to reflect a crustecdysone-controlled increase in cell communications in vivo.     

Immortalized mouse brain endothelial cells are ultrastructurally similar to endothelial cells and respond to astrocyte-conditioned medium

Summary Studies of brain microvessel endothelial cell physiology and blood-brain barrier properties are often hampered by the requirement of repeatedly producing and characterizing primary endothelial cell cultures. The use of viral oncogenes to produce several immortalized brain microvessel cell lines has been reported. The resulting cell lines express many properties of the blood-brain barrier phenotype but do not completely mimic primary endothelial cells in culture. As immortalized brain microvessel endothelial cell lines have not yet been produced from mice, we transformed mouse brain endothelial cells with the adenovirus E1A gene using a retroviral vector (DOL). Eight of 11 clones produced exhibited an endothelial-like cobblestone morphology and were characterized as endothelial with a panel of antibodies, lectins, and ultrastructural criteria. These cells are endothelial in origin and share ultrastructural features with primary cultures of endothelial cells. Examination of freeze fracture and transmission electron micrographs show adherens junctions exist between the transformed cells, and culture in astrocyte-conditioned medium induces the formation of gap junctions. This is one indication that responses to astrocyte-derived factors are retained by the transformed cell lines.