Showing papers on "Dentate gyrus published in 1975"

An autoradiographic study of the time of origin and the pattern of granule cell migration in the dentate gyrus of the rat

Abstract: The dentate gyrus of the rat contains about 600,000 granule cells. These small neurons are generated over a prolonged period from the 14th day of gestation until sime time after the second postnatal week. The majority of the cells pass through their last phase of DNA synthesis in the postnatal period, and during the peak period of cell generation, between the fifth and seventh days after birth, up to 50,000 granule cells are formed each day. Contrary to earlier reports, most of the cells pass through their last mitotic division either within the stratum granulosum itself, or within the hilar region of the developing gyrus. The precursor population of cells in the hilar region must therefore constitute a pool of true neuroblasts. The origin of this pool of cells has not been definitely established but it seems probable that its cells are derived from the neuroepithelium lining the lateral ventricle adjacent to the region from which the hippocampal pyramidal cells are generated. Examination of the final location of granule cells labeled at different stages reveals three distinct morphogenetic gradients in the gyrus. The cells in the dorsal blade tend to be formed earlier than those in the ventral blade; cells in the more caudal (or temporal) portions of the gyrus are generated earlier than those in more rostral (or septal) regions; and in all regions the more superficial neurons in the stratum granulosum are formed earlier than the deeper granule cells. The bearing of some of these findings on the development and organization of the connections of the dentate gyrus is discussed.

The Development of Hippocampal Function: Implications for Theory and for Therapy

Abstract: One thesis of this chapter is that the hippocampus may have two different but related modes of functioning. The simpler of the two, present in infancy and at times in adulthood, consists of a gross or nonspecific inhibition of emotional reactivity in general. The generation of nonspecific inhibition requires only that the hippocampal pyramidal cells be functionally developed and that they be driven by some synchronized input such as the θ-pacing system. The second functional mode is called “stimulus-specific inhibition” because it corresponds to a specific inhibition of an emotional reaction to a particular stimulus or set of stimuli. Stimulus-specific inhibition can be carried out only when the hippocampal pyramidal cells are “informed” of the stimulus via the temporoammonic tract and its major target, the dentate gyrus. The specific form of inhibition is at best only rudimentarily developed at birth and develops in synchrony with the maturation of the dentate gyrus. The development of stimulus-specific inhibition, it will be argued, is interfered with by early stressful i experience. The harmful effects of early stress on adult behavior appear to be counteracted by drugs which enhance cholinergic transmission.

Postnatal Development of the Hippocampal Dentate Gyrus Under Normal and Experimental Conditions

Abstract: Recent studies using [3H] thymidine autoradiography produced convincing evidence that in the development of a particular brain region the small, short-axoned cells come into existence after the larger long-axoned cells. Indeed, in an altricial rodent, the rat, the granular nerve cells of the olfactory bulb, hippocampus, cerebellum, and cochlear nucleus are formed exclusively or predominantly after birth (Altman and Das, 1965a). There are indications that these short-axoned neurons (microneurons) arise from late-forming secondary germinal matrices (like the subependymal layer of the forebrain ventricles and the external germinal layer of the cerebellar cortex), in contrast to the long-axoned neurons (macroneurons) which originate from the periventricular primary matrix, the neuroepithelium (Altman, 1969). We do not as yet have an adequate explanation of the delayed formation of microneurons but the importance of these elements in the maturation of brain functions is indicated by behavioral studies. For instance, interference with the postnatal acquisition of cerebellar granule cells by experimental means produces behavioral deficits comparable to those seen after decerebellation (Wallace and Altman, 1969a,b; Altman et al., 1971; Brunner and Altman, 1973).

The actions of volatile anaesthetics on synaptic transmission in the dentate gyrus.

Abstract: 1. The action of four volatile anaesthetics on the evoked synaptic potentials of in vitro preparations of the hippocampus were examined. 2. All four anaesthetics (ether, halothane, methoxyflurane and trichloroethylene) depressed the synaptic transmission between the perforant path and the granule cells at concentrations lower than those required to maintain anaesthesia in intact animals. 3. The population excitatory post-synaptic potential (e.p.s.p.) and massed discharge of the cortical cells (population spike) were depressed at concentrations of the anaesthetics lower than those required to depress the compound action potential of the perforant path nerve fibres. None of the anaesthetics studied increased the threshold depolarization required for granule cell discharge. Furthermore, frequency potentiation of the evoked cortical e.p.s.p.s was not impaired by any of the anaesthetics studied. 4. It is concluded that all four anaesthetics depress synaptic transmission in the dentate gyrus either by reducing the amount of transmitter released from each nerve terminal in response to an afferent volley, or by decreasing the sensitivity of the post-synaptic membrane to released transmitted or by both effects together.

Radiation-induced interference with postnatal hippocampal cytogenesis in rats and its long-term effects on the acquisition of neurons and glia

Abstract: The long term consequences of graduated interference with the acquisition of hippocampal neurons and glia during early infancy were examined with quantitative histology and 3H-thymidine autoradiography. The head region containing the hippocampus was irradiated from day two on with either two (2X), four (4X), six (6X) or eight (8X) doses of 150–200r X-rays. The animals were killed at 30, 60, 90 and 120 days of age. The morphology of the hippocampus was normal in all irradiated groups with the characteristic interlocking folds of the pyramidal and granular layers. While the number of pyramidal cells of Ammon's horn was unaffected, the number of granule cells of the dentate gyrus was progressively and permanently reduced from control levels by the different dosage schedules (2X, 59% reduction; 4X, 77%; 6X, 83%; 8X, 84%). Incidental observations in control animals indicated a 20% increase in granule cells between 30 and 120 days of age in agreement with earlier observations of granule cell labelling after 3H-thymidine injections in adult rats. The time of origin of the approximately 15–16% of the granule cells surviving irradiation in the 8X group was determined by injecting either pregnant females (gestation days 19–20) or pups (days 0 and 1) with two successive doses of 3H-thymidine; the animals were irradiated from day two on with eight X-ray doses. The granule cells surviving in the postnatally injected group were all unlabelled and comparable in number to the unlabelled cells in control animals that were given five successive postnatal injections of 3H-thymidine. This established that the radioresistant complement of granule cells is formed prenatally. In the prenatally injected group, over half the surviving cells were labelled; it was assumed that those not labelled were formed before gestation day 19. In contrast to the permanent reduction in the number of granule cells, there was some reestablishment of the number of cells in the dentate molecular layer and the Ammonic stratum oriens; in the fimbria, recovery in cell number was complete by 60 days. In a supplementary autoradiographic experiment, cell proliferation in the granular layer and in the fimbria was determined at 60 days of age after a single postnatal injection of 3H-thymidine on either day 15 or day 20 in the control, 2X, 4X and 6X groups. The number of labelled cells in the irradiated groups was always well below control levels in the granular layer, but it was either above or at the same level as controls in the fimbria. Tentative interpretations were offered for the differential long-term effects of variable X-ray schedules on the neuronal and glial populations of the hippocampus.

A neurophysiological analysis of commissural projections to dentate gyrus of the rat.

Abstract: The electrophysiological properties of the commissural projections to the dentate gyrus of the rat were investigated using extracellular field-potential and unit-recording techniques. The following...

Fractionation of Hippocampal Function in Learning

Abstract: In 1967, Douglas was constrained to comment that “Within the past 5 years more studies of the effects of hippocampal lesions on behavior have been published than in all previous years combined. Despite this proliferation of specific knowledge no comparable advance has been made in the general understanding of hippocampal function” (Douglas, 1967, p. 416). The output of research in this area has continued unabated over these past years, but has there been any increase in understanding?

Neurobiology of LCM virus infection in rodents

Abstract: In addition to the previously reported data on the retinal and cerebellar immunopathology following infection of neonatal rats with LCM virus, we have found that there are long-term effects on behavioural and neurological development. Rats were inoculated intracerebrally with the E-350 strain at different ages during the first 3 weeks after birth. Behavioural tests were initiated when the animals were either 3 months or 1 year of age. The behavioural consequences appear to be a long-term alteration in emotional reactivity such that the infected animals are less responsive than controls as assessed by these measures. No alterations were detected in animals infected after the first postnatal week. Complementing these data are the findings of a collaterally progressive lesion of the hippocampal dentate gyrus as well as a loss in total cell number in the forebrain (as assessed by DNA, RNA, and protein determinations) amounting to about 20% of the brain mass. These behavioural, histological, and biochemical data indicate that there are forebrain structures, most probably within the limbic system, that are susceptible at critical phases of development to the pathological consequences of infection with LCM virus.

[Incorporation of 3H-thymidine into glial cells of the parietal region and cells of the subependymal zone of two-week and adult mice under normal conditions and following brain injury].

Abstract: Potencies of brain cells to DNA synthesis and proliferation were studied in two weeks old and adult mice in the norm and after the brain mechanical injury. No labeled large and middle neurons were found in the brain of intact and operated animals both under the pulse 3H-thymidine incorporation and saturation of mice with 3H-thymidine during 36 hrs. The same types of brains cells were labeled both in intact and operated two weeks old and adult mice: glial cells, cells of the subependymal zone, cells of the dentate gyrus inner margin, and sometimes, cells having characteristics of microneurons. The number of glial cells in the temporal cortex of intact mice diminished with the age. Under the brain trauma, the proliferative reaction of glia was expressed in a similiar way both in two weeks old and adult mice. The index of labeled cells in the subependymal zone is the same in these two age groups. With the age the cellular mass of subependymal zone decreases, rather than proliferative tendencies of supependymal zone. The brain traumatization resulted in the increase of labeled subependymal cell only under the direct injury of subependymal zone.

Local proliferation of cells of the granular layer of the dentate gyrus of the mouse hippocampus during postnatal ontogenesis and following brain injury

Abstract: The local cellular proliferation takes place in the inner part of the dentate gyrus granular layer, the subgranular zone, of mice. The proliferating cells of the subgranular zone are one of two sources of postnatal neurogenesis of the granular layer (another source-cells of the subependymal zone). The subgranular zone becomes markedly thinner with the age but even in adult mice the cellular proliferation occurs in it. Under the brain trauma, the proliferation of the subgranular zone cells is activated. Besides cell division in the subgranular zone, there is insignificant proliferation in the differentiated part of the granular layer. Special studies are, however, necessary to identify dividing cells in the differentiated part of the granular layer.