Time-dependent reversal of primed burst-induced long-term potentiation (LTP) was investigated in the CA1 region of rat hippocampus following theta pulse stimulation (TPS) of Schaffer collaterals. The effect of TPS (5Hz, 900 pulses) on primed burst potentiatin was evaluated through the analysis of the slope of population excitatory post-synaptic potentials (pEPSPs) and amplitude of population spikes (PSs). TPS had no lasting effect on baseline synaptic responses, while produced a lasting depression of previously potentiated responses when delivered 3 mm after LTP induction. TPS produced progressively lower depotentiation at longer delays, until it had no effect 20 min after LTP induction. These results suggest that the hippocarnpal theta rhythm promotes the induction of LTP as well as its subsequent reversal. Reversal of LTP may function to refine memories and prevent saturation of the storage capacity of the neural network.

The effect of theta pulse stimulation (TPS) on pentylenetetrazol (PTZ)-induced long-term potentiation of population spikes (PS) was studied in the hippocampal CA1 in vitro. A transient PTZ application produced a long-lasting enhancement of PS amplitude. A 3-min episode of TPS delivered at a higher intensity produced complete reversal of the PTZ potentiation when delivered during the last minutes of PTZ application. Prior application of high-intensity TPS also decreased the amount of PTZ potentiation, whereas it had no long-lasting effect on baseline synaptic responses. High-intensity TPS induced reversal was blocked by adenosine A1 receptor antagonist and, furthermore, was reduced by protein phosphatase 1 inhibitor. The results suggest that mechanism of PTZ-induced LTP reversal involves activation of adenosine receptors and protein phosphatases.

Introduction: Effects of theta pulse stimulation (TPS) on CA1 synaptic transmission in pentylenetetrazol (PTZ) kindled rats were studied. Materials and Methods: ‏‏‏‏‏‏‏‏‏‏‏‏‏PTZ (45 mg/kg) was injected every 48 hours to NMRI male rats. Hippocampal slices were prepared from control, partially and fully kindled rats. Theta pulse was delivered to Schaffer collaterals and recording was made from strata radiatum and pyramidale of CA1 region of hippocampal slices. Results: PTZ kindling resulted in an enduring increase in fEPSP slope, but not OPS amplitude, in CA1 region of hippocampus. TPS decreased the amplitude of population spikes (PS) of partially and fully kindled rats which were significant in the latter as compared to controls. Discussion: It is concluded that repeated administration of PTZ can change susceptibility of CA1 synapses to TPS.

Purpose: Cognitive dysfunction is common in individuals with depression and these cognitive deficits may be associated with a risk of suicide. Therefore, the identification of the cognitive functions of depressed patients and the introduction of effective interventions on these factors are highly important. This study aimed to compare the effectiveness of repetitive Transcranial Magnetic Stimulation (rTMS) and Theta Burst Stimulation (TBS) to improve selective attention, working memory, and response time of depressed individuals with and without a history of suicide. Materials and Methods: This applied quasi-experimental study was conducted based on a pretest-posttest design. The population included 40 depressed patients referring to the clinics of Mashhad, Iran, in 2020. The samples were divided into four groups, namely individuals with a history of suicide subjected to treatment with rTMS, without a history of suicide receiving treatment with rTMS, with a history of suicide undergoing treatment with TBS, and without a history of suicide administered with TBS (n = 10 each). The data were collected using the Stroop Color and Word Test, Corsi block test, and reaction time tests and statistically analyzed using multivariate analysis of covariance. Results: The results confirmed the effectiveness of the intervention on the congruent reaction time, incongruent reaction time, working memory, simple reaction time, and selective reaction time in all four study groups (P < 0. 05). The results of multivariate analysis of covariance showed that the group had a significant effect on the variables of congruent reaction time, simple reaction time, and selective reaction time (P < 0. 05),however, it had no significant effect on the variables of incongruent reaction time and working memory (P > 0. 05). Conclusion: Compared to the rTMS method, the TBS had a greater effect on the variables of congruent reaction time, simple reaction time, and selective reaction time.