Resetting of 'synaptic tags' is time- and activity-dependent in rat hippocampal CA1 in vitro.

We have recently proposed that the maintenance of hippocampal long-term potentiation (LTP) and depression depends on at least two required processes: induction of LTP must set (1) process-specific 'synaptic tags' which capture (2) process-unspecific plasticity-related proteins (PRPs), synthesized via a heterosynaptic interaction [Neurobiol Learn Mem 82 (2004) 12]. The 'tag' as well as the PRPs are characterized by a relatively short half-life of several minutes up to a few hours before they degrade most likely by processes such as dephosphorylation. The question now arose whether the 'tags' can also be reset in an activity-dependent manner, thus preventing the processing of PRPs with the result of transient short-lasting plasticity. Here we have investigated this topic during early-LTP and found that low-frequency stimulation shortly after early-LTP-induction (5 min) resets the 'tag' or the 'tag complex' of macromolecules preventing any lasting forms of LTP and thus, preventing the formation of a memory trace.

Podophyllum hexandrum prevents radiation-induced neuronal damage in postnatal rats exposed in utero.

Podophyllum hexandrum has been shown to mitigate radiation injuries and especially the haemopoietic syndrome in adult mice. To monitor the radiation-induced changes in the nervous system, the neurons of postnatal young mice and their modification by P. hexandrum, were studied histologically for differences in the apical and basal dendritic branching and intersections in the CA1 neurons of the hippocampal region of rats which were delivered a 2 Gy gamma dose while in utero (day 17 of gestation). Irradiation significantly reduced the dendritic branching and intersections but pre-irradiation administration of the extract of P. hexandrum (i.p. 200 mg/kg/b.w., 2 h) reduced the damage in postnatal young mice. These studies indicate that P. hexandrum provides protection to neurons against radiation-induced damage and the mechanism of neuronal damage and its repair need to be investigated further.

Effects of Podophyllum hexandrum on radiation induced delay of postnatal appearance of reflexes and physiological markers in rats irradiated in utero.

Effect of 2.0 Gy gamma-dose delivered to rats in utero on 17th day of gestation was studied to monitor the radiation induced retardation of neurophysiological development in postnatal young ones. Rhizome of Podophyllum hexandrum which has been well documented for mitigating radiation injuries in adult mice was attempted for modifying radiation damage. Rats were observed from postnatal day 1 to 25 for the age of the appearance of physiological markers (pinna detachment, inscisor's eruption, eye opening) and acquisition of reflexes (surface righting, visual placing, reflex suspension, negative geotaxis). In irradiated groups there was a significant weight reduction in mother rats and offsprings throughout the experimental period. There was radiation-induced delay in the appearance of pinna detachment but not in eye opening and inscisor's eruption. Appearance of the reflexes were also delayed due to irradiation. Preirradiation administration of the extract of Podophyllum hexandrum (i.p., 200 mg/kg/b.w.) mitigated radiation induced postnatal physiological alterations. These studies have implications in protection against damage (in utero) due to planned radiation exposure.