Focal stimulation of the thalamic reticular nucleus induces focal gamma waves in cortex.

Electrical stimulation of the thalamic reticular nucleus (TRN; 0.5-s trains of 500-Hz 0.5-ms pulses at 5-10 microA) evokes focal oscillations of cortical electrical potentials in the gamma frequency band ( approximately 35-55 Hz). These evoked oscillations are specific to either the somatosensory or auditory cortex and to subregions of the cortical receptotopic map, depending on what part of the TRN is stimulated. Focal stimulation of the internal capsule, however, evokes focal slow potentials, without gamma activity. Our results suggest that the TRN's role extends beyond that of general cortical arousal to include specific modality and submodality activation of the forebrain.

Fine structure of hippocampal dendrites in the dentate fascia of LS/SS-mice after chronic ethanol treatment.

1. The effect of ethanol and its withdrawal on the dendritic microtubules in the dentate fascia of male mice was studied in the ethanol-sensitive, long-sleep (LS) line and the ethanol-insensitive, short-sleep (SS) line. 2. Both mouse lines were treated with a liquid ethanol diet. Dendrites in the dentate molecular layer (DML) of the right hippocampus were examined. 3. They revealed marked changes in microtubule density as compared with the controls. While the microtubule density in LS mice was significantly reduced by 15% and 18% in the middle and distal third of the DML, respectively, in SS mice the reduction (by 12%) took place in the distal third only. During withdrawal a recovery of the microtubule density has been observed in both lines.

Changes in GABAergic and non-GABAergic synapses during chronic ethanol exposure and withdrawal in the dentate fascia of LS and SS mice.

Ethanol-sensitive LSIBG and ethanol-insensitive SSIBG mice were exposed to ethanol (23.5% ethanol-derived calories) for 4 months. Half of the animals was sacrificed at this time and the other half was withdrawn from the ethanol diet for 1 month. GABA immunoelectron microscopy was used to study the impact of the treatments on synaptic contacts in the dentate molecular layer. In the LS mice a significant loss of non-GABAergic axospinous synapses (26.7%; p < 0.05) was observed during ethanol exposure which was followed by a loss of GABAergic synapses on dendritic shafts (54.7%; p < 0.01) during withdrawal. In the SS mice there was a significant decrease in the non-GABAergic axospinous synapses (23.5%; p < 0.05) and a significant increase in axodendritic synapses (63.3%; p < 0.05) during ethanol exposure. The observed changes in the GABAergic and non-GABAergic innervation of the dentate fascia induced by ethanol were observed in the projection zone of the perforant path. They could adversely affect the hippocampal physiology with a consequent impairment of mnemonic functions.

Inhibitory contacts on dendritic spines of the dentate fascia.

GABA-containing axon terminals were observed in the distal two-thirds of the dentate molecular layer to contact spines and dendrites of the granule cells. These contacts have the morphological characteristics of inhibitory synapses: they contain pleomorphic vesicles and have symmetrical junctional specializations. Convergence of an asymmetrical, non-GABAergic and a symmetrical, GABAergic synapse on one spine was often observed.

Aging and the neurocytoskeleton.

It has been often demonstrated that during senescence some neurons undergo atrophic changes while others add new processes and terminals. Because microtubules form a substantial component of the dendritic and axonal cytoskeleton, we have studied the amount of tubulin and acetylated alpha-tubulin in three young (6 months) and three old (24 months) rats (Fischer 344). We have used sodium dodecyl sulfate (SDS) extracts of brain homogenates and Triton solubilized fractionated brain homogenates. With the first method we did not detect any age-related differences in total brain protein, total tubulin, or in relative amounts of acetylated alpha-tubulin. With the second method, we have observed a small systematic increase in relative amount of acetylated alpha-tubulin in the Ca2+/cold insoluble fraction. These results are similar to those reported in the literature, and they indicate a possible alteration in the cytoskeletal dynamics.

Distribution of acetylated alpha-tubulin in brain. In situ localization and biochemical characterization.

We studied the solubility properties of brain acetylated alpha-tubulin, as well as the localization of this tubulin in brain tissue. Endogenous unpolymerized tubulin and cytoskeletal tubulin were fractionated after brain Triton-solubilization. Using the immunoblotting technique, we found that acetylated alpha-tubulin was recovered in the cytoskeletal fraction, and that most (92%) of the acetylated microtubules of this fraction were depolymerized by cold/Ca2+ treatment. In another set of experiments, axonal and soma-dendritic preparations were found to have equivalent amounts of acetylated alpha-tubulin. By immunogold electron microscopy, we established that acetylated microtubules are widely distributed in dendrites of the central nervous system.

Effect of age on blood vessels and neurovascular appositions in the CA1 region of the rat hippocampus.

Rats aged 3, 9, 24 and 30 months were used in this study. Increased basal lamina thickening in capillaries, muscular large vessels and nonmuscular large vessels was shown with advancing age. There is also an age-related increase in the area of mitochondria in smooth muscle cells. These ultrastructural changes may underlie observed age-related functional changes in the vasculature. They may be a compensatory response of the vessel wall cells to a declining capacity to handle the continual and varying shear stress exerted by the blood. Ultrastructural differences between capillaries and the two types of large vessels are reported and discussed in terms of their functional significance. It was noted that there are more dendrites adjacent to capillaries than to large vessels, however, this was unaffected by increasing age. Since advancing age did not alter the number of neuronal processes adjacent to vessels, age-related compromises in vessel function may not be subjected to neuronal regulation.

Effect of age on blood vessels and neurovascular appositions in the rat dentate fascia.

Rats aged 3, 9, 24 and 30 months were used in this study. We show increased basal lamina thickening and increased mitochondrial presence in walls of capillaries and not in walls of large vessel populations with age. This suggests that age selectively affects capillary structure. Ultrastructural differences between capillaries and two types of large vessels are reported and discussed in terms of their probable functional significance. In particular it was noted that there are more axon terminals, axons and dendrites adjacent to capillaries than to large vessels and that this was unaffected by increasing age. It is not clear whether the proximity of neuronal processes to a vessel wall serves a function, however, the larger number adjacent to capillaries than to large vessels indicates a more significant role for them in capillary rather than in large vessel function. Since increasing age did not alter the number of neuronal processes adjacent to vessels, age-related compromises in vessel function may be unrelated to neuronal regulation. The age-related changes are discussed as possible vascular markers for the aging brain.

Nuclear pore complex frequency in CA1 pyramidal cells of the aging rat.

The frequency and the diameter of nuclear pore complexes, and the nuclear perimeter, were studied in CA1 pyramidal cells of the hippocampi from 3-, 9-, 24-, and 30-month-old rats (Fischer 344). No changes with age in any of these parameters were observed. This finding is discussed in terms of varied responses of different brain areas to the effects of aging.

Distribution of MAP2 in dendritic spines and its colocalization with actin. An immunogold electron-microscope study.

The distribution of MAP2 and actin in dendritic spines of the visual and cerebellar cortices, dentate fascia, and hippocampus was determined by using immunogold electron microscopy. By this approach, we have confirmed the presence of MAP2 in dendritic spines and identified substructures within the spine compartment showing MAP2 immunoreactivity. MAP2 immunolabeling was mainly associated associated with filaments which reacted with a monoclonal anti-actin antibody. Also, by immunogold double-labeling we colocalized MAP2 with actin on the endomembranes of the spine apparatus, smooth endoplasmic reticulum, and in the postsynaptic density. Labeling was nearly absent in axons and axonal terminals. These results indicate that MAP2 is an actin-associated protein in dendritic spines. Thus, MAP2 may organize actin filaments in the spine and endow the actin network of the spine with dynamic properties that are necessary for synaptic plasticity.

In situ localization of myosin and actin in dendritic spines with the immunogold technique.

The in situ detection of macromolecules by means of immunoelectron microscopy provides information about their ultrastructural localization in cellular compartments. With this technique, we have demonstrated that the contractile proteins actin and myosin are both localized in dendritic spines at densities exceeding those of other neuronal compartments. Myosin was associated with actin filaments, with spine plasma membrane, and with membranes of the spine apparatus. Given the dynamic properties of actin and myosin, these data suggest that these proteins may be involved in the mechanism of synaptic plasticity in general and in morphometric change resulting from intense synaptic activation in particular.

Astrocyte proliferation precedes a decrease in basket cells in the dentate fascia following chronic ethanol treatment in mice.

The effect of chronic ethanol administration on the density of basket cells in the dentate gyrus of mice selectively bred for their sensitivity to acute ethanol exposure (long-sleep, LS and short-sleep, SS) was assessed in two experiments. In addition, the effect of chronic ethanol on the density of dentate granule cells and astrocytes was examined. In the first experiment, mice received 3 weeks of a liquid ethanol diet with 35% of their calories derived from ethanol (EDC). In this experiment, LS mice did not demonstrate a change in the density of granule cells or in the density of basket cells. There was, however, a significant increase in the density of astrocytes as a result of this treatment for the LS mice. The SS mice were unaffected on all measures. In the second experiment, portions of which have been reported previously, mice received a diet with 23% EDC for 3 months. As a result of this exposure, LS mice showed a significant decrease in the density of basket cells, but there was no change in the density of granule cells or astrocytes. There was no difference between controls and experimental mice from the SS group on any of these parameters. These results suggest that at least in the dentate gyrus, chronic ethanol treatment selectively reduces the density of basket cells but only in mice that are more sensitive to the hypnotic effects of acute ethanol exposure. Furthermore, this effect seems to be preceded by an apparent increase in the density of astrocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of chronic ethanol consumption on the fine structure of the CA1 stratum oriens in short-sleep and long-sleep mice: short-term and long-term exposure.

The effect of chronic ethanol administration on the fine structure of the hippocampal CA1 stratum oriens was examined in two lines of mice selectively bred for their differential sensitivity to acute ethanol exposure (long-sleep, LS and short-sleep, SS mice). Two experiments were performed. In the first experiment, mice received a liquid diet for 3 weeks with the final amount of ethanol being 35% ethanol-derived calories. In the second experiment, mice received 23.5% ethanol-derived calories for 3 months. Quantitative electron microscopy of the dendritic spines and synaptic appositions in the stratum oriens of CA1 revealed an interaction between diet and line of mice, but only in the 3-month exposure condition. This difference was due to a significant decrease in the density of spines and synaptic appositions in the LS mice receiving ethanol. Additionally, baseline differences between lines indicate that the lines are differing in the density of spine synapses in the absence of ethanol treatment. The possible interaction between acute sensitivity to ethanol and differences in fine structure are examined.

Changes in the nuclear pore complexes of the dentate granule cells in aged rats.

In 3-, 9-, 24-, and 30-month-old male rats (Fischer 344), the nuclear perimeter and the density and diameter of nuclear pore complexes in the granule cells of the dentate fascia were studied. Whereas the nuclear perimeter and the diameter of nuclear pore complexes did not change as a function of age, there was a significant loss of them at 24 months (20%), compared with the third month. This change suggests that the nucleocytoplasmic communication may be impaired with age which would adversely affect protein synthesis, and could explain the loss of the postsynaptic sites of the dentate fascia of aged rats.

Effect of chronic ethanol consumption on the fine structure of the dentate gyrus in long-sleep and short-sleep mice.

The effect of short- and long-term chronic ethanol consumption on the fine structure of the dentate gyrus was examined in two lines of mice selected for their differential sensitivity to acute ethanol administration. Quantitative electron microscopic analysis of dendritic spines, axon terminals, and synaptic appositions revealed significant differences between the long-sleep and short-sleep mice. In control preparations, long-sleep mice were found to have larger spine areas and perimeters, larger axon terminals, and longer synaptic appositions than short-sleep mice. In addition, the shape of dendritic spines in the long-sleep mice was significantly more complex than those of short-sleep mice. Ethanol tended to increase this complexity in long-sleep mice only. Ethanol had only a limited effect on the other anatomical measures. The results provide evidence for ultrastructural differences between the nervous systems of these lines of mice which may have a role in their differential sensitivity to acute ethanol administration.

Changes in the frequency of basket cells in the dentate fascia following chronic ethanol administration in mice.

The frequency of basket cells in the granule cell layer of the dentate fascia of Short Sleep (SS) and Long Sleep (LS) mice was determined following 3 months of ethanol exposure. These mice were bred for their differential susceptibility to the narcotic effects of acute doses of ethanol. The ethanol-insensitive SS mice were unaffected by the treatment while the ethanol-sensitive LS mice that received ethanol showed a significant decrease in basket cell frequency over their control group counterparts. These basket cells are thought to control the tonic level of activity of the granule cells. Thus, a decrease in basket cell frequency might lead to higher granule cell activity following chronic ethanol exposure. This effect could counteract the assumed stronger depressant effect of ethanol in the relatively ethanol-sensitive LS mice.

Calcium distribution in dendritic spines of the dentate fascia varies with age.

Calcium distribution in dendritic spines of the dentate fascia was studied as a function of age with the oxalate-pyroantimonate precipitation technique. In postnatal ages P3, P9, P24 and P30 spines were analyzed as to the presence of the spine apparatus (SA) and as to the presence of Ca2+ deposits within the SA and within the spine cytoplasm. The percentage of spines with SA-containing precipitates declined significantly between P3 and P24. Conversely, the percentage of spines with precipitates in the spine cytoplasm was significantly increased by P24. In the absence of an SA loss, this result suggests an age-related decrease in the Ca2+-sequestering capacity by the SA. These parameters were improved by P30 so that they approximated the values of P3. Such a seeming amelioration could be attributed to the fact that the mortality rate in rats sharply increases by P24, so that animals surviving this age represent a selected population in which a compensatory growth of spines has occurred and has secured functionally valid connections.

Actin filament organization within dendrites and dendritic spines during development.

The myosin S-1 subfragment was used to label actin filaments in the developing rat brain. The results show actin filaments present throughout the dendritic region with highest concentrations within growth cones and regions of spine development. Between 6 and 25 days postnatal, spines became more complex and actin filaments within them increased in number and formed a complex network. The observed organization of actin supports the hypothesis that actin has a role in the protrusion of spines from the dendrite during development.