Simultaneous two-photon imaging of intracellular chloride concentration and pH in mouse pyramidal neurons in vivo provides valuable insights into the functioning of these neurons. The study focuses on understanding the role of chloride concentration and pH in the regulation of neuronal activity.

Simultaneous two-photon imaging of intracellular chloride concentration and pH in mouse pyramidal neurons in vivo provides valuable insights into the functioning of these neurons. The study focuses on understanding the role of chloride concentration and pH in the regulation of neuronal activity.

Neuronal activity in the hibernating brain is a fascinating area of research that requires further investigation to determine the effects of temperature on specific cell types and brain nuclei. While structural plasticity, such as synapse and spine degradation and protein synthesis, is not considered in this study, it has been extensively discussed in recent reviews.

One of the key findings is that the firing rates of spontaneous neuronal activity are systematically reduced with decreasing body temperature. Neurons eventually stop firing at body temperatures of 15-18°C and remain silent for a period of deep torpor, which can last between 10-28 hours. However, when the body temperature increases, the neurons start firing again. This temperature-dependent reduction in firing rate is accompanied by changes in the waveform of the action potential, with a decrease in amplitude and an increase in spike width.

Interestingly, peripheral nerves and primary central brain regions seem to be more resistant to hypothermia-induced changes in neuronal activity compared to higher central brain regions. This suggests that these neurons in the periphery still maintain their functionality even at low temperatures, as they respond to peripheral stimuli and auditory cues during hibernation.

The limbic system-midbrain circuitry, which includes interconnections between the limbic system, hypothalamus, and brainstem reticular formation, is believed to play a role in the neural control of entrance into and arousal from torpor. This hypothesis is supported by studies that show in vivo histamine infusion into the hippocampi of hibernating ground squirrels prolongs hibernation bouts. Additionally, there is increased expression of histamine H1 and H2 receptors in the hippocampi of hibernating ground squirrels compared to euthermic ones.

Further studies have shown that the spontaneous neuronal activity of neurons in the medial preoptic area (MPOA) also changes with decreasing temperature. The firing rate, spike amplitude, and spike width are reduced as the temperature decreases. However, approximately 42% of these neurons remain active even at temperatures below 10°C, with an average cutoff temperature of 4.9°C. In contrast, the suprachiasmatic nucleus (SCN) neurons require a slightly higher temperature of 16.6°C for activity to be observed.

It is important to note that the use of c-Fos as a marker for neuronal activity during hibernation may not be reliable. This is because transcription of genes and protein synthesis are significantly depressed in deep torpor, potentially affecting the expression levels of c-Fos. Alternative markers may need to be explored to accurately reflect neuronal activity during hibernation.

Additionally, glucose utilization in the hibernating brain is significantly reduced. In deep torpor, the glucose utilization rate is only 1-2% of that in active animals. This suggests that channels and pumps responsible for glucose uptake and utilization may not be functioning properly during hibernation.

In conclusion, the study on neuronal activity in the hibernating brain provides valuable insights into the effects of temperature on specific cell types and brain regions. It highlights the importance of the limbic system-midbrain circuitry, histamine as a potential neuromodulator, and the differential responses of peripheral and central neurons to hypothermia.

Three actionable advice based on these findings are:

1. Further research should focus on understanding the structural plasticity underlying functional changes during hibernation, such as synapse and spine degradation, and protein synthesis.
2. Investigate alternative markers for neuronal activity during hibernation that are not affected by the depression of transcription and protein synthesis.
3. Explore the mechanisms responsible for glucose utilization during hibernation to better understand how channels and pumps are affected by the low temperatures.

This research opens up new avenues for understanding the complex mechanisms underlying neuronal activity in the hibernating brain. It provides a foundation for future studies to delve deeper into the molecular and cellular processes involved in hibernation and may have implications for understanding other states of reduced neuronal activity, such as anesthesia and coma.