Hippocampal Mossy Fiber System Research Articles

Localization of enkephalin-like immunoreactivity to identified axonal and neuronal populations of the rat hippocampus.

The distribution of enkephalin-like immunoreactivity in the hippocampal formation of the rat was analyzed. Two specific projection systems are described. The first emerges from the hilus of the dentate gyrus and appears to terminate with notably large boutons on the proximal apical and, to a lesser extent, basal dendrites of hippocampal regio inferior pyramidal cells. This projection corresponds in source, position, and character to the hippocampal mossy fiber system. The second axonal population enters the temporal hippocampal formation from the medial wall of the subicular complex and follows the hippocampal fissure to occupy stratum lacunosum-moleculare of the hippocampus proper and the distal third of the dentate gyrus molecular layer; this pattern corresponds to the distribution of afferent input from the lateral entorhinal cortex and/or perirhinal area. Lesions of the hilus or retrohippocampal area caused a selective depletion of immunoreactivity in the mossy fiber fields and molecular layers of the dentate gyrus, respectively. Enkephalin-like immunoreactivity was found within the somata of three types of hippocampal neurons: 1) granule cells of the dentate gyrus, 2) occasional pyramidal shaped cells of field CA1 stratum pyramidale, and 3) varied scattered interneurons. Of this last group, two types of interneurons were consistently seen. The first occupy the border between stratum radiatum and stratum lacunosum-moleculare and extend processes at right angles to the long axis of the pyramidal cell dentrites, whereas the second lie within stratum radiatum of field CA1 and extend processes in alignment with the long axis of the pyramidal cell dendrites. Cells containing enkephalin-like immunoreactivity were also observed in the subiculum and retrohippocampal region, most notably including layers II and III of the lateral entorhinal cortex-perirhinal area--the probable source of extrinsic immunoreactive input to the hippocampal formation. Intraventricular colchicine treatment intensified the immunoreactive staining of some hippocampal neurons but did not reveal any cell types not seen to be labeled in untreated rats.

Enkephalin and zinc in the hippocampal mossy fiber system

Enkephalin and zinc in the hippocampal mossy fiber system

Lesion-induced rerouting of hippocompal mossy fibers in developing but not in adult rats.

AbstractThe organization of the hippocampal mossy fiber system which projects from the granule cells of fascia dentata to the pyramidal cells of the hippocampal regio inferior (CA3) was studied after chronic lesions had been applied to CA3 in neonatal (0–3 day old), 5 and 21 day old, and adult rats. The distribution of terminals was monitored by the histochemical Timm sulphide silver method, and the fibers were demonstrated by the original Nauta silver method.Complete transections of CA3 in neonatal rats induced a layer of aberrant, infrapyramidal mossy fiber terminals in CA3 up to 1,300 μm septal to the transection followed by a corresponding expansion of the suprapyramidal mossy fiber layer for at least 720 μm. At increasing distance above the lesion, the induced changes moved laterally in CA3, affecting more distal parts of the mossy fibers. Corresponding to the layer of aberrant infrapyramidal terminals were aberrant bundles of mossy fibers, with an abnormally ascending septal course. No aberrant mossy fibers or terminals were induced temporal to the complete transections.Partial CA3 lesions in neonates induced changes corresponding to those observed after complete transections septal to the lesions. In addition, a layer of aberrant infrapyramidal mossy fiber terminals was induced in CA3 as far as 900 μm temporal to the partial lesions, accompained by an expansion of the suprapyramidal layer. The infrapyramidal terminals were related to aberrant bundles of fibers which followed an abnormally steep, temporal course, from which they in turn leveled off to join the suprapyramidal bundles.Compared to neonatal lesions, hippocampal transections performed on day 5 induced a slightly less dense layer of aberrant infrapyramidal mossy fiber terminals in CA3, and although a transection on day 21 still induced aberrant infrapyramidal terminals, these were far less abundant than after lesions at day 5. Transections in adult rats induced no such changes at all, and additional denervation of CA3 by simultaneous removal of the commisural projection from the contralateral hippocampus did not have any effect.The lesion‐induced, but age‐dependent redistribution of mossy fibers to CA3 is discussed in terms of reactive reinnervation following partial deafferentation, and compensatory sprouting and rerouting due to pruning‐like effects of the lesions. A rerouting of developing, not fully matured mossy fibers is found to be most likely: Deprived of normal target areas, the fibers have been forced to grow in abnormal directions, ending up hyperinnervating adjacent, accessible levels through the formation of aberrant infrapyramidal terminals and expansion of the suprapyramidal zone.

Organization of the mossy fiber system of the rat studied in extended hippocampi. I. Terminal area related to number of granule and pyramidal cells.

AbstractA quantitative and qualitative study of the septotemporal organization of the hippocampal mossy fiber system has been carried out in the rat. Transverse sections of isolated and extended hippocampi were stained according to Nisel's or Timm's method. At 12 equidistant levels covering the entire length of the hippocampus the following parameters were measured: the length of the granule cell layer and the mossy fiber layer, the area of the fields containing mossy fiber boutons, the number of granule cells, and the number of pyramidal cells in the hilus and in the regio inferior.Septally the pyramidal layer of the regio inferior is broad and the cells within the layer are relatively widely spaced. Here the mossy fiber boutons intrude deep into the layer. At more temporal levels the cells are tightly packed, the cell‐layer is narrower, and the boutons predominantly terminate suprapyramidally.The length of the granular layer is greatest septally, while the length of the mossy fiber layer is greatest temporally. The area of the hilus, occupied by the mossy fiber boutons, is large at most of the temporal levels and small at the septal levels, whereas in CA3 the reverse is true. The greatest number of granule cells was found at the more septal levels. Conversely, the majority of the pyramidal cells in the hilus and in the regio inferior is situated temporally. The ratio of granule cells to pyramidal cells (hilus and regio inferior together) declines linearly from approximately ten at septal levels to approximately one at temporal levels. Because the mossy fibers are distributed fairly transverse to the long axis of the hippocampus, the variation in the ratio of granule cells to pyramidal cells reflects a corresponding variation in the number of innervating to innervated cells within the mossy fiber system.

Effects of catecholaminergic drugs upon memory storage processes in mice

These experiments examined the effects of drugs that interfere with catecholamine metabolism upon retention performance by Ha/ICR mice in an inhibitory avoidance task. When administered shortly before training, most of the drugs impaired subsequent retention performance. However, of the drugs studied, only diethyldithiocarbamate (DDC) produced retention deficits when administered posttraining. A series of experiments examined in detail the effects of DDC upon (1) retention performance of inhibitory avoidance learning, (2) whole brain norepinephrine and dopamine levels, (3) brain seizure activity recorded from cortical electrodes, and (4) Timm's staining in the hippocampal mossy fiber system. DDC influenced all measures, and the degree of effect varied directly with dose. But, the amnestic effect of DDC did not depend in any simple manner upon reduction of brain catecholamine levels or upon induction of brain seizure activity.