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1

Time-dependent effets of swim stress on early-LTP in the hippocampal CA1 in freely moving rats

100%
Yeritsyan N., Frey J.
Acta Neurobiologiae Experimentalis
|
2009
|
tom 69
|
nr 3
Stress has been well-documented to affect hippocampal long-term potentiation (LTP), which is widely believed to underlie learning and memory at the cellular level. However, only few reports addressed the issue regarding the timing of presenting a stress episode in relation to LTP induction. Previously we could show that in the dentate gyrus a protein synthesis-independent early-LTP can be reinforced by swim stress into a protein synthesis-dependent late-LTP when the stress episode was applied within a time window of about 30 min around tetanization (Korz and Frey 2003). Considering the important role that the hippocampal CA1 plays in the processing of spatial and temporal information, we were now interested in studying the infl uence of swim stress on functional plasticity events in the CA1 region. Field potentials were recorded in freely moving rats subjected to a brief episode of swim 15 min before or after early-LTP induction in the CA1 by stimulating the contralateral CA3. Our results revealed that a swim episode alone exerted a transient depressing effect on baseline values of recorded fi eld potentials. Swim stress presented shortly after the induction of early-LTP resulted in its depotentiation. Furthermore, if the same stress protocol preceded early-LTP induction, it prevented the potentiation and induced a long-lasting depression of fi eld potentials. These data suggest that swim stress differentially alters synaptic plasticity in the CA1 when compared with the dentate gyrus.
2

Dopaminergic D1/D5-receptor blokade within the nucleus accumbens and its effect on hipocampal long-term potentation in the dentate gyrus of freely mooving animals

100%
Tabassum H., Frey J.
Acta Neurobiologiae Experimentalis
|
2009
|
tom 69
|
nr 3
Hippocampal long-term potentiation (LTP) is considered to be a cellular model of learning and memory. It has been shown that stimulation of modulatory brain regions can infl uence hippocampal LTP. Quite little is known of the role played by the nucleus accumbens (NAc) on hippocampal LTP. The NAc is the central component of the basal ganglia positioned to integrate signals arising from corticolimbic areas and to translate them into motor behavior. Electrical stimulation of the NAc core and shell region has been shown to modulate LTP in the dentate gyrus. We were now interested to study if the dopaminergic system within the NAc affects LTP in the dentate gyrus in freely moving animals. Thus, we have applied a specifi c dopaminergic D1/D5-receptor blocker, SCH23390, into the NAc and studied its possible effect on control potentials as well as on LTP in the dentate gyrus in freely moving rats. Interstingly, treated animals show a depression in baseline responses recorded in the dentate gyrus, just by D1/D5-blockade within the NAc. Furthermore, these animals were characterized by a reduced LTP after weak tetanic stimulation of the perforant path when compared with controls. As there is no direct dopaminergic connection between NAc and dentate gyrus, the effects must involve indirect mechanisms, such as glutamatergic and/or GABAergic pathways.
3

Long-term potentiation in hippocampal basal dendrites: role of diffrent modulatory systems

81%
Ramachandran B., Parvez S., Frey J.
Acta Neurobiologiae Experimentalis
|
2009
|
tom 69
|
nr 3
Long-term potentiation (LTP) and long-term depression (LTD) are considered to be cellular models suitable for studying the synaptic changes that likely occur during learning and memory. LTP has distinct phases, a transient protein synthesis-independent stage (early-LTP) followed under distinct circumstances by a late, longlasting and protein synthesis-dependent stage (late-LTP). In hippocampal CA1 neurons, LTP in either the apical or basal dendrites differ in their molecular requirement during induction as well as the setting of the tag, for example CaM kinase II mediates the setting of the tag in stratum radiatum but in basal dendrites (stratum oriens) the setting of the tag is mediated by either protein kinase A or protein kinase M zeta (Sajikumar et al. 2007). It has been reported that the late-LTP in the CA1 stratum radiatum requires the synergistic activation of different neurotransmitters during its induction (Frey 1997, Frey and Morris 1998). From this background we now investigated whether the LTP in stratum oriens requires similar or other synergistic interactions of different modulatory systems when compared with the stratum radiatum. Our preliminary studies using different selective antagonists of distinct modulatory transmitters systems revealed that late-LTP in basal dendrites is different with respect to its requirements for its induction when compared with late-LTP in apical CA1-dendrites.
4

Different regions of the apical branch of CAI dendrites express specific forms of LTD in hippocampal slices in vitro

81%
Parvez S., Ramachandran B., Frey J.
Acta Neurobiologiae Experimentalis
|
2009
|
tom 69
|
nr 3
Long-term potentiation (LTP) and long-term depression (LTD) of excitatory synaptic transmission are widespread phenomena expressed at many excitatory synapses in the mammalian brain. Because of its long duration, input specifi city and associative properties, LTP and LTD have been used as cellular models for memory. We wanted to investigate whether different locations on the apical dendritic branch could infl uence the induction of LTD and its related properties. Late-LTD could be induced in the apical CA1 dendrites by strong low-frequency stimulation (SLFS) pattern if the synapses were located distally, whereas, proximally located synapses were not able to maintain late-LTD. However, SLFS in both locations was able to trigger the synthesis of plasticity-related proteins, which could be evidenced by cross tagging experiments. In addition, we have investigated if hippocampal CA1-LTP prevents/occludes the establishment of LTD in the same synaptic input at specifi c time points after LTP-induction. We show induction of LTP occludes longer-lasting but not short-term LTD about 1 h after LTP-induction. However, after 4 h, i.e. after transformation of early- into late-LTP, also later forms of LTD can again be induced in the same synaptic input. Our results demonstrate that hippocampal neurons do not lose their capacity for the induction of longer forms of LTP or LTD after the establishment of late-LTP in the apical dendrites of hippocampal CA1- neurons.
5

Reinforcement of en early-LTP in the hipocampall CAI by stimulation of the ventral tegmental area in freely moving rats

81%
Scherf T., Frey J., Frey S.
Acta Neurobiologiae Experimentalis
|
2009
|
tom 69
|
nr 3
It has been shown that the prolonged maintenance of hippocampal long-term potentiation (LTP) requires heterosynaptic events during its induction. The ventral tegmental area (VTA), a modulatory input to the CA1 region is a heterogeneous group of dopaminergic cells and a major component of the mesolimbic dopamine system. We used a method which allowed us to simultaneously record both, the fi eld-EPSP and the population spike (POP) in the hippocampal CA1 in freely moving rats by stimulation of the contralateral CA3. We could show that an early-LTP in the CA1 region can be reinforced into a longer-lasting form by high-frequency stimulation of the VTA 15 min after its induction. This reinforcement of an early-LTP in CA1 was dependent on dopaminergic receptor activation and was also dependent on protein synthesis. We have now extended our studies and could show that high-frequency stimulation of the VTA alone, i.e. without LTP-induction in CA1, caused a delayed-onset potentiation for the recorded fi eld-EPSP and POP in the CA1 region in response to test stimulation of the contralateral CA3. This delayedonset potentiation was dependent on the synergistic activation of both the glutamatergic and the dopaminergic receptor activation, because paused glutamatergic test stimulation abolished this potentiation.
6
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Nowe niebezpieczeństwo dla kultur sosnowych [dot. zbioru pączków szczytowych sosny]

40%
Frey J.
Sylwan
|
1897
|
tom 15
|
nr 04
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