In Vivo Firing Pattern And Field Potential Rhythm Regulation Of Hippocampal PV Interneurons

The hippocampus is a very important brain region related to higher cognitive functions such as learning,memory and spatial navigation.It is mainly composed of excitatory pyramidal neurons and inhibitory interneurons.Pyramidal neurons are mainly involved in the encoding and storage of event information.While the hippocampal interneurons play an crucial role in the regulation of the complex neuronal network in the hippocampus in spite of the number less than pyramidal neurons.PV-positive interneurons are the most common type of neurons in hippocampus,and they are also a very important biochemical classification.At present,there have been a lot of work on the study of PV interneurons in morphology,molecular biology,electrophysiology of brain slices in vitro,electrophysiology of anesthesia in vivo and behavioral science,but there is still a lack of systematic observation and research on electrophysiology of natural state in vivo.We combined multi-channel in vivo recording technique with optogenetics to record PV interneurons in different behavioral states in dorsal hippocampal CA1(dCA1)of mice for a long time.In order to understand the role of PV interneurons in hippocampus and other brain regions,and to enhance the cognition of the regulation mechanism of brain local neural network,we focused on the in vivo firing pattern of PV interneurons and the relationship between their firing activity and local field potential.In order to construct the photogenetic PV-eNpHR3.0-EYFP mice required for the experiment,Adeno-associated virus(p AVV)was used to transfect and express inhibitory light channel protein(eNpHR3.0)on the PV interneurons of hippocampal CA1 of PV-Cre mice specifically.A total of 12 PV-positive interneurons were identified on five mice.The firing patterns of 12 PV-positive interneurons in different behavioral states were investigated,and it was found that almost all the changes in the firing activity of PV interneurons were regulated by behavioral states.Most of the PV Interneurons firing activities increased during AE and REM periods,while a few of the PV Interneurons increased during SWS.Some PV interneurons showed different peak potential interval distribution and autocorrelation characteristics.At the same time,it was found that nearly half of PV interneurons showed obvious phase-locked relationship with Ripple rhythm oscillation but not with Gamma and Theta.We further analyzed the effect of inhibiting hippocampal PV interneurons in different states of mice,and found that the hippocampal field electricity significantly changed when photoinhibition of PV interneurons.Specifically,the Theta and Gamma oscillations of hippocampal field electricity significantly increased during wakefulness.This phenomenon has not been reported in previous studies,and the specific mechanism needs to be further explored.At the same time,the influence of PV interneurons on Ripple events during the SWS period was investigated,and it was found that photoinhibition of PV interneurons could increase the incidence of Ripple oscillation but had little effect on the amplitude and duration of Ripple,which provided evidence support for us to think about the functional significance of PV interneurons on the occurrence of hippocampal Ripple.In conclusion,in vivo multi-channel electrode recording technique combined with optogenetics technique can effectively label and screen the PV interneurons of hippocampal CA1.The PV interneurons of hippocampus CA1 have a variety of different in vivo firing patterns.Photoinhibition of PV interneurons enhances Theta and Gamma oscillations and increases the incidence of Ripple oscillation events during SWS.These rarely discovered and reported experimental phenomena will provide in vivo experimental basis for further exploring the regulation mechanism of PV in hippocampal local neural network.