PAG-EEG_2022-04-17

Anxiety and panic are both elicited by threat and co-occur clinically. But, at the neural level, anxiety appears to inhibit the generation of panic; and vice versa. Panic and anxiety are thought to engage more posterior/medial (m) and anterior (a) parts of the periaqueductal gray (PAG), respectively. Anxiety also engages the hippocampus and medial prefrontal cortex. Here we tested if mPAG but not aPAG stimulation would suppress prefrontal and hippocampal theta rhythm as do anxiolytic drugs. Twelve male rats with implanted electrodes were stimulated alternately (30 s interval) in the left PAG or right reticular formation (RPO - as a positive control) with recording in the left prelimbic cortex and left and right hippocampus. PAG stimulation was set to produce freezing and RPO to produce 7-8 Hz theta rhythm before tests lasting 10 minutes on each of 5 days. mPAG stimulation decreased, and aPAG increased, theta power at all sites during elicited freezing. mPAG, but not aPAG, stimulation decreased prefrontal theta frequency. Stimulation did not substantially change circuit dynamics (pairwise phase consistency and partial directed coherence). Together with previous reports, our data suggest that panic- and anxiety-control systems are mutually inhibitory, and neural separation of anxiety and panic extends down to the aPAG and mPAG, respectively. Our findings are consistent with recent proposals that fear and anxiety are controlled by parallel neural hierarchies extending from PAG to the prefrontal cortex.

The data are provided as Spike2 files. Trigger coding is: StimOnRPO = onset of 1s RPO train; StimOnPAG = onset of 8s PAG train; Inject (downward) = pump on; StimOff = offset of train; StimOn = onset of train; Stim = stimulation pulses. Channel coding is: P = prefrontal; HR = right hippocampus; HL = left hippocampus; digits are electrode numbers. Note that recording was against a common reference, but analysis was of electrode pairs (e.g. the difference of HR2 and HR5 for calculation of a nominal bipolar right hippocampal recording). Voltage values are after amplification x5,000. Sampling rate is 512Hz.