Suspension of mitotic activity in dentate gyrus of the hibernating ground squirrel.

Neurogenesis occurs in the adult mammalian hippocampus, a region of the brain important for learning and memory. Hibernation in Siberian ground squirrels provides a natural model to study mitosis as the rapid fall in body temperature in 24 h (from 35-36°C to +4-6°C) permits accumulation of mitotic cells at different stages of the cell cycle. Histological methods used to study adult neurogenesis are limited largely to fixed tissue, and the mitotic state elucidated depends on the specific phase of mitosis at the time of day.

Three-dimensional synaptic ultrastructure in the dentate gyrus and hippocampal area CA3 in the Ts65Dn mouse model of Down syndrome.

Down syndrome (DS) results from trisomy of human chromosome 21. Ts65Dn mice are an established model for DS and show several phenotypes similar to those in people with DS. However, there is little data on the structural plasticity of synapses in the trisynaptic pathway in the hippocampus.

Complexity of contacts between synaptic boutons and dendritic spines in adult rat hippocampus: three-dimensional reconstructions from serial ultrathin sections in vivo.

The morphological relationship between a synapse and dendritic spine is an important determinant of synaptic function, and has been studied extensively with the electron microscope. This has revealed that the universal idea of one synapse per spine is no longer tenable; dendritic spines may on occasions form synapses with two or more axonal boutons. To elucidate the detailed structure and relationship of spines and their synaptic contacts in the molecular layers of the dentate gyrus of the adult rat, a study using 3-dimensional (3D) reconstructions was made from serial ultrathin sections (up to 150 sections per series), of both pre- and postsynaptic segments of axons and dendrites.

Membrane lipids and morphology of brain cortex synaptosomes isolated from hibernating Yakutian ground squirrel.

Synaptosomes were isolated from Yakutian ground squirrel brain cortex of summer and winter hibernating animals in active and torpor states. Synaptosomal membrane cholesterol and phospholipids were determined. The seasonal changes of synaptosomal lipid composition were found.

The glutamate receptor 2 subunit controls post-synaptic density complexity and spine shape in the dentate gyrus.

In adult brain the majority of AMPA glutamate receptor (GluR) subunits contain GluR2. In knock-out (KO) mice the absence of GluR2 results in consequences for synaptic plasticity including cognitive impairments. Here the morphology of dendritic spines and their synaptic contacts was analysed via three-dimensional reconstruction of serial electron micrographs from dentate gyrus (DG) of adult wild type (WT) and GluR2 KO mice.

A cell adhesion molecule mimetic, FGL peptide, induces alterations in synapse and dendritic spine structure in the dentate gyrus of aged rats: a three-dimensional ultrastructural study.

The FGL peptide is a neural cell adhesion molecule (NCAM) mimetic comprising a 15-amino-acid-long sequence of the FG loop region of the second fibronectin type III module of NCAM. It corresponds to the binding site of NCAM for the fibroblast growth factor receptor 1. FGL improves cognitive function through enhancement of synaptic function.

Expression of long-term potentiation in aged rats involves perforated synapses but dendritic spine branching results from high-frequency stimulation alone.

Evidence for morphological substrates of long-term changes in synaptic efficacy is controversial, partly because it is difficult to employ an unambiguous control. We have used a high-frequency stimulation protocol in vivo to induce long-term potentiation (LTP) in the hippocampal dentate gyrus of aged (22-month-old) rats and have found a clear distinction between animals that sustain LTP and those that fail to sustain it. The "failure group" was used as a specific/"like-with-like" control for morphological changes associated with the expression of LTP per se.

Rapid reversal of stress induced loss of synapses in CA3 of rat hippocampus following water maze training.

The impact was examined of exposing rats to two life experiences of a very different nature (stress and learning) on synaptic structures in hippocampal area CA3. Rats were subjected to either (i) chronic restraint stress for 21 days, and/or (ii) spatial training in a Morris water maze. At the behavioural level, restraint stress induced an impairment of acquisition of the spatial response.