J C Farmer’s research while affiliated with University of North Carolina at Chapel Hill and other places

Rats with complete spinal transections were compressed in helium-oxygen to 120 bars. Tremors and increased EMG activity in limbs rostral as well as caudal to the lesions were observed beginning at 30 bars. Spinal seizures occurred at 95 bars, similar to cortical seizure thresholds of intact rats. Denervated limbs remained flaccid throughout the dives. No rostro-caudal progression of symptoms was evident in normal animals, but fluctuation of symptoms with increasing pressure was frequently observed. These findings are consistent with the hypothesis that the effects of pressure on aggregates of neurons exceed those on isolated components.

To evaluate the interaction between high pressure nervous syndrome (HPNS) seizures and cerebellar integrity, seizure threshold pressure (Pc) of normal rats was compared with that of rats sustaining cerebellar ablation two weeks prior to exposure to 136 ATA in a helium-oxygen atmosphere. All rats exhibited severe HPNS symptoms which culminated in seizures. Pc was reduced in cerebellectomized animals, and the number of seizure episodes increased twofold, but the average duration of seizure episodes was unchanged. The spike-and-wave pattern in the electroencephalogram remained a prominent feature in both groups.

Electroencephalographic activity of the frontal cortex, cerebellar vermis, and superior vestibular nucleus was recorded in awake rats during the high pressure nervous syndrome (HPNS) by means of permanently implanted electrodes. Power-spectrum analysis revealed a decline in the faster frequencies and an increase in the slow frequences as the seizure end-point was approached. Effects of compression to 4500 fsw varied from severe tremor and myoclonic jerks to status epilepticus, with seizures occurring at an average depth of 3560 fsw. In all animals, multifocal-spiking activity progressed in severity with increasing depth. The predominant seizure pattern observed was a spike and slow-wave pattern reminiscent of absence seizures. Initial evidence of generalized seizure activity was equally divided between the cerebellum and cortex. It is concluded that the cerebellum participates in HPNS seizures. Possible evolution of the syndrome by loss of Purkinje cell inhibitory influence on subcortical sites that modulate cortical excitability is discussed.