OVERVIEW OF ADULT HIPPOCAMPAL NEUROGENESIS The dentate gyrus represents a unique system for the study of interactions between neuronal development and experience. While this hippocampal subfield has been extensively investigated in relationship to the ongoing process of adult neurogenesis, the mnemonic contributions of mature granule neurons have remained enigmatic. Much of the rationale for fo...

Considerable interest has recently focused on the weaver mutation, which causes inward rectifier channel alterations leading to profound impairment of neuronal differentiation and to severe motor dysfunction in mice (Hess, 1996). The principal targets of mutation are cerebellar granule cells, most of which fail to differentiate and degenerate in a premigratory position (Rakic and Sidman, 1973a,...

Beginning on the second postnatal day, either two (2X group), four (4X group) or six (6X group) daily or alternate daily exposures to lowlevel X-irradiation (150-200 r) were used to interfere with the acquisition of granule cells in the olfactory bulb, hippocampus, and cerebellum of the rat. At 60 days of age, the relationship between post-irradiation recovery and permanent granule cell loss wa...

Granule cells of the human hippocampal dentate gyrus were examined. In controls, granule cells displayed somatic spines and cell nuclei with small infoldings. In addition, the cytoplasm of human granule cells always displayed lipofuscin. Subsurface cisterns of endoplasmic reticulum were frequently observed in the human granule cells. Two types of axosomatic synapses were found; most frequently ...

ÐMigration of the granule cells is a major stage of cerebellar maturation. Granule cells express neurotrophins and their receptors; however, their role in cell migration has not been de®ned. In this study we investigated the effects of exogenous neurotrophins on the movement and neurite extension of granule cells from glial-free cerebellar cell reaggregates in vitro. Our results provide direct ...

The neurons generated at the germinal rhombic lip undergo long distance migration along divergent pathways to settle in widely dispersed locations within the hindbrain, giving rise to cerebellar granule cells and precerebellar nuclei. Neurotrophin-3 (NT-3) signaling has been shown to be required for proper migration and survival of cerebellar granule cells. The molecular bases that govern NT-3 ...

Synaptic reorganization of the dentate gyrus inner molecular layer (IML) is a pathophysiological process that may facilitate seizures in patients with temporal-lobe epilepsy. Two subtypes of IML neurons were originally described by Ramón y Cajal (1995), but have not been thoroughly studied. We used two-photon imaging, infrared-differential interference contrast microscopy and patch clamp record...

Although apoptotic cellular degeneration has been reported to be extremely rapid with the use of in vitro models, the time needed to clear apoptotic neurons in the in vivo brain is unknown. In this study we used a simple morphological approach to solve this problem. Four days after adrenalectomy (ADX), all of the operated rats morphologically displayed hippocampal granule cell apoptosis that wa...

In Pavlovian delay eyeblink conditioning, the cerebellum represents the passage-of-time (POT) between onsets of conditioned and unconditioned stimuli (CS and US, respectively). To study possible computational mechanisms of the POT representation we built a large-scale spiking network model of the cerebellum. Consistent with our previous rate-coding model, we found two conditions necessary for t...

On their long lateral dendrites, mitral cells of the olfactory bulb form dendrodendritic synapses with large populations of granule cell interneurons. The mitral-granule cell microcircuit operating through these reciprocal synapses has been implicated in inducing synchrony between mitral cells. However, the specific mechanisms of mitral cell synchrony operating through this microcircuit are lar...