Remodeling of hippocampal synapses after hippocampus-dependent associative learning.

The aim of this study was to determine whether hippocampus-dependent associative learning involves changes in the number and/or structure of hippocampal synapses. A behavioral paradigm of trace eyeblink conditioning was used. Young adult rabbits were given daily 80 trial sessions to a criterion of 80% conditioned responses in a session.

Synapse restructuring associated with the maintenance phase of hippocampal long-term potentiation.

Synapses in the middle molecular layer of the rat dentate gyrus were analyzed by electron microscopy during the maintenance phase of long-term potentiation (LTP). LTP was induced by high-frequency stimulation of the medial perforant path carried out on each of 4 consecutive days. The dentate gyrus was examined electron microscopically 13 days following the fourth stimulation.

Structural synaptic plasticity associated with the induction of long-term potentiation is preserved in the dentate gyrus of aged rats.

Changes in synaptic numbers were examined in the hippocampal dentate gyrus of aged (28 months old) rats following the induction of long-term potentiation (LTP) by high-frequency stimulation of the medial perforant path carried out on each of 4 consecutive days. Potentiated animals were sacrificed 1 hour after the fourth stimulation. Stimulated but not potentiated and implanted but not stimulated rats of the same chronological age served as controls.

Age-related loss of axospinous synapses formed by two afferent systems in the rat dentate gyrus as revealed by the unbiased stereological dissector technique.

Previous attempts to elucidate whether a loss of hippocampal synapses occurs during aging provided conflicting results, possibly due to the unavailability, at the time, of unbiased methods for synapse quantitation. This study was designed to reexamine the issue by means of modern technical procedures that provide unbiased estimates of synaptic numbers. Groups of 14 young adult (5 months old) and 14 aged (28 months old) male Fischer-344 rats were compared.

[A comparative study of the quantitative distribution and ultrastructure of Langerhans cells in the epidermis of patients with chronic benign dermatoses and mycosis fungoides].

Using histoenzymatic assay for ATPase activity and electron microscopy, Langerhans' cells (LC) in biopsy specimens taken from skin lesions of 20 patients with chronic benign dermatoses (CBD) and of 28 patients suffering from mycosis fungoides (MF) were identified. In the early lesions of MF the reduction of the number of cell dendrites, disappearance of normal arrangement and the reduced absolute quantity of LC were observed on comparison with patients with CBD. Ultrastructurally, the destroyed forms of LC were predominantly observed in MF lesions, while in cases of CBD most of the LC were functionally active.