Circadian Regulation of Hippocampal Long-Term Potentiation

Abstract

The goal of this study is to investigate the possible circadian regulation of hippocampal excitability and long-term potentiation (LTP) measured by stimulating the Schaffer collaterals (SC) and recording the field excitatory postsynaptic potential (fEPSP) from the CA1 dendritic layer or the population spike (PS) from the soma in brain slices of C3H and C57 mice. These 2 strains of mice were of interest because the C3H mice secrete melatonin rhythmically while the C57 mice do not. The authors found that the magnitude of the enhancement of the PS was significantly greater in LTP recorded from night slices compared to day slices of both C3H and C57 mice. They also found significant diurnal variation in the decay of LTP measured with fEPSPs, with the decay slower during the night in both strains of mice. There was evidence for a diurnal rhythm in the input/output function of pyramidal neurons measured at the soma in C57 but not C3H mice. Furthermore, LTP in the PS, measured in slices prepared during the day but recorded during the night, had a profile remarkably similar to the night group. Finally, PS recordings were carried out in slices from C3H mice maintained in constant darkness prior to experimentation. Again, the authors found that the magnitude of the enhancement of the PS was significantly greater in LTP recorded from subjective night slices compared to subjective day slices. These results provide the 1st evidence that an endogenous circadian oscillator modulates synaptic plasticity in the hippocampus.

Contributions of impaired hippocampal plasticity and neurodegeneration to age-related deficits in hormonal pulsatility

“…Circadian-phase-dependent alterations in hippocampal LTP have also been demonstrated (Chaudhury et al, 2005;Harris and Teyler, 1983; but see Nishikawa et al, 1995). Nocturnal rodents sacrificed at the beginning of the dark phase showed greater LTP, relative to animals sacrificed at the beginning of the light phase (Chaudhury et al, 2005). The latter study also demonstrated that hippocampal slices from animals sacrificed during the light phase and maintained prior to induction of LTP during the dark phase also showed greater LTP.…”

“…The latter study also demonstrated that hippocampal slices from animals sacrificed during the light phase and maintained prior to induction of LTP during the dark phase also showed greater LTP. This opens the possibility that a cell-autonomous clock exists in the hippocampus as well as the hypothalamus (Chaudhury et al, 2005).…”

“…In the hypothalamus, isolated slices will show circadian-phasedependent changes in LTP, likely supported by an intrinsic cell-autonomous clock mechanism (Nishikawa et al, 1995). Circadian-phase-dependent alterations in hippocampal LTP have also been demonstrated (Chaudhury et al, 2005;Harris and Teyler, 1983; but see Nishikawa et al, 1995). Nocturnal rodents sacrificed at the beginning of the dark phase showed greater LTP, relative to animals sacrificed at the beginning of the light phase (Chaudhury et al, 2005).…”

Circadian modulation of interval timing in mice

“…These results are in agreement with previous work related to circadian modulation of other behavioral and physiological functions such as synaptic plasticity. For example, Chaudhury et al (2005) demonstrated in mice a diurnal rhythm in excitability and LTP in hippocampal brain slices, with an enhancement of the population spike magnitude in LTP recorded from subjective night slices compared to subjective day slices. Circadian rhythms are disrupted under constant light (LL) illumination.…”

Circadian waveform bifurcation, but not phase-shifting, leaves cued fear memory intact

“…Taken together, these results may reflect a "time-stamp" for circadian phase (and not environmental time) of retrieval, found previously in hamsters in a conditioned place preference protocol [18]. Circadian rhythms have also been observed in hippocampal long-term potentiation (LTP), a prominent cellular model of learning [19,20].…”