Contribution of single-unit spike waveform changes to temperature-induced alterations in hippocampal population spikes

Abstract

Brain temperature changes accompany exploratory behavior and profoundly affect field potential amplitudes recorded in hippocampus. The waveform alterations in fascia dentata include a reduction in population spike area, which might be explained by fewer granule cells firing in response to a given stimulus or by an alteration in the size or shape of the individual action potentials. This study was designed to assess these alternate possibilities. In experiment 1, changes in the shape and firing rates of single cells recorded in the fascia dentata of awake rats were compared with changes in the population spike before and after a bout of activity. Single-unit amplitudes were significantly reduced following exploration, and there was a small (< 3%) change in unit spike-width. These changes, however, were insufficient to account, in a linear fashion, for the entire decline in the population spike. In experiment 2, radiant heat was used to manipulate brain temperature in anesthetized rats. As in the first experiment, the magnitude of change in the extracellular units was much smaller than the change in population spike amplitude. The spontaneous firing rates of the cells were also modified by brain temperature changes. In experiment 3, the polysynaptic, contralateral commissural response (which covaries with changes in the ipsilateral population spike at a fixed temperature) was measured as a function of either exploratory behavior or radiant heat. The relationship between the ipsilateral population spike and corresponding polysynaptic commissural response was altered following exploration and passive warming in a manner consistent with a reduction in net granule cell output, reduced transmission efficacy through the polysynaptic circuit, or a combination of these. Taken together these data suggest that at least two factors contribute to temperature-dependent changes in the perforant path-evoked population spikes recorded in the fascia dentata: changes in the size of individual action potentials and alterations in discharge of action potentials in response to a given stimulus.

Synaptic transmission in the neocortex during reversible cooling

“…Furthermore, since reliable inactivation of the local networks can be achieved only at temperatures that severely affect basal synaptic transmission, cooling is hardly an adequate method for studying the input to the cooled region. 15 Our results also help to identify cellular processes which underlie changes in the amplitude of evoked field potentials, accompanying minor changes of the brain temperature in vivo, 2,13,34 and provide direct evidence for the mechanisms that were suggested to account for the field potential changes. 2,34,37,40 Our data demonstrate that lowering the temperature by a few degrees led to depolarization of the cells and a corresponding increase of their excitability, to an increase of the EPSP duration, and to an increase in both the amplitude and the width of action potentials in the neocortical cells.…”

Neurocognitive and Somatic Components of Temperature Increases during g-Tummo Meditation: Legend and Reality

“…Future studies of experts in g-tummo meditation who are capable of elevating and maintaining elevated CBT may offer promising research insights and approaches to investigating mechanisms of CBT regulation. Because many variables underlying neuronal functioning (e.g., transport via ion-selective channels, amplitude and duration of single-unit spikes) are temperature-dependent [42], [43], possibility of self-regulation of CBT may have a direct effect on self-regulating and maximizing neurocognitive activity. If future studies show that it is possible to self regulate CBT, by mastering vase breathing in conjunction with guided mental imagery without extensive meditation experience, it will open a wide range of possible medical and behavior interventions, such as adapting to and functioning in hostile (cold) environments, improving resistance to infections, boosting cognitive performance by speeding response time, and reducing performance problems associated with decreased body temperature as reported in human factor studies of shift work and continuous night operations [44], [45].…”

Field potential recordings in dentate gyrus of anesthetized rats: Stability of baseline

“…Several papers have now documented the effects of alterations in brain temperature on field potential recordings in the hippocampus. Increases in EPSP slope and declines in PS amplitude accompany a rise in body temperature, whereas increases in PS amplitude with delays in onset latency and a slowing of the rising phase of the EPSP are observed when body temperature is lowered (Moser et al, 1993;Andersen and Moser, 1995;Erickson et al, 1996). Although general anesthetics including pentobarbital and urethane produce hypothermia (Lomax et al, 1964;Lomax, 1966;Janocko and Mycek, 1986), core and brain temperature were maintained at a constant normothermic level in the present study.…”