Biomedical subjects

C Gentry

Publications and source records attributed to C Gentry.

22 records · Page 2Linked to original sources

PubMed1980

Loss and reacquisition of hippocampal synapses after selective destruction of CA3-CA4 afferents with kainic acid.

Intraventricular injections of kainic acid were used to destroy the hippocampal CA3-CA4 cells bilaterally in rats, thus denervating the inner third of the molecular layer of the fascia dentata and stratum radiatum of area CA1. Electron microscopic studies showed that this lesion reduced the synaptic density of the CA1 stratum radiatum by an average of 86%. The synaptic density of the inner third of the dorsal dentate molecular layer declined by two-thirds and the corresponding zone of the ventral dentate molecular layer by about half. Within 6-8 weeks the synaptic density of these laminae had been restored to the control value or nearly so. In the CA1 stratum radiatum about 72% of the synaptic contacts destroyed by the lesion were replaced, the inner third of the ventral dentate molecular layer recovered 75% of its lost synapses and the inner third of the dorsal dentate molecular layer apparently recovered virtually all of them. The newly formed synapses did not differ noticeably from those normally present. A kainic acid lesion reduced the synaptic density of the outer two-thirds of the dentate molecular layer by 30% within 3-5 days, despite a virtual absence of presynaptic degeneration in that zone. This result implies a substantial disconnection of perforant path synapses. It did not appear to depend on the extent of denervation of the inner zone. The loss of perforant path synapses was completely reversible. We suggest that the dentate granule cells shed a portion of their synapses in response to a substantial loss of neurons to which they project and regained them when their axons had formed new synaptic connections.

Afferent Pathways↗

PubMed1977

Synaptic replacement in the dentate gyrus after unilateral entorhinal lesion: electron microscopic analysis of the extent of replacement of synapses by the remaining entorhinal cortex.

In response to a unilateral entorhinal lesion the input from the contralateral entorhinal cortex to the dentate gyrus appears to increase. We have studied this crossed projection by electron microscopy in normal animals and in animals one year or more after a unilateral entorhinal lesion. In normal animals few degenerating boutons are found after a contralateral entorhinal lesion. However, when the contralateral lesion was made one year after an ipsilateral entorhinal lesion, degenerating boutons were readily identified. The boutons were relatively few in number, but formed an abnormally large number of synaptic contacts. These results support the previous conclusion that fibres from the contralateral entorhinal cortex form additional synapses when their ipsilateral homologues are removed. However, these new cortical synapses probably account for only a small portion of those formed in response to the lesion. Thus an anatomically homologous input does not, in this case, selectively capture most of the newly available synaptic sites.

Animals↗

PubMed1976

Distribution and mobility of lectin receptors on synaptic membranes of identified neurons in the central nervous system.

The distribution and mobility of concanavalin A (Con A) and Ricinus communis agglutinin (RCA) receptors (binding sites) on the external surfaces of Purkinje, hippocampal pyramidal, and granule cells and their attached boutons were studied using ferritin-lectin conjugates. Dendritic fields of these cells were isolated by microdissection and gently homogenized. Cell fragments and pre- and postsynaptic membranes were labeled with the ferritin-lectin conjugates at a variety of temperatures, and the distribution of lectin receptors was determined by electron microscopy. Both classes of these lectin receptors were concentrated at nearly all open and partially open postsynaptic junctional membranes of asymmetric-type synapses on all three neuron types. Con A receptors were most concentrated at the junctional membrane region, indicating that the mature neuron has a specialized nonrandom organization of carbohydrates on its outer surface. Lectin receptors located on postsynaptic junctional membranes appeared to be restricted in their mobility compared to similar classes of receptors on extrajunctional membrane regions. Labeling with ferritin-RCA and -Con A at 37 degrees C produced clustering of lectin receptors on nonjunctional surfaces; however, Con A and RCA receptors retained their nonrandom topographic distribution on the postsynaptic junctional surface. The restricted mobility of lectin receptors was an inherent property of the postsynaptic membrane since the presynaptic membrane was absent. It is proposed that structures in the postsynaptic density may be transmembrane-linked to postsynaptic receptors and thereby determine topographic distribution and limit diffusion of specialized synaptic molecules. Speicalized receptor displays may play an important role in the formation and maintenance of specific synaptic contacts.

Animals↗

PubMedDate not supplied

Uptake of lipids by developing oocytes of the hawkmoth Manduca sexta. The possible role of lipoprotein lipase.

A plasma membrane preparation of Manduca sexta ovarian follicles was shown to contain lipoprotein lipase activity that hydrolyzes the diacylglycerol moiety of the hemolymph lipoprotein, lipophorin. Kinetic analysis demonstrated that low density lipophorin (LDLp) is a better substrate for the identified lipase activity than high density lipophorin (HDLp). The activity has a pH optimum of 9-9.5 and is partially inhibited by NaCl concentrations higher than 0.5 M. Diisopropylfluorophosphate (DFP) inhibits the membrane bound lipoprotein lipase activity completely and irreversibly. Incubation of follicle plasma membranes with [3H]-DFP radiolabels a 100-kDa membrane protein that may represent the lipoprotein lipase. The present results suggest that lipoprotein lipase activity may play an important role in the uptake of lipids by M. sexta oocytes.

Animals↗