| Popis: |
Despite the recent increase in research into the High Pressure Neurological Syndrome (HPNS), the mechanisms of action of pressure are still unclear. This research examines the effects of compression to 61 ATA with pure helium (pO2 1.0 atm.) on local cerebral glucose metabolism, and the behavioural characteristics of male CD-l mice, and compares these data with the equivalent values from mice compressed either with 10% /90% nitrogen/helium mixture (pO2 1.0 atm.) or pretreated with 2-amino-7-phosphonoheptanoic acid (2-APH), an excitatory amino acid antagonist, and compressed on helium (pO2 1.0 atm.). Both these latter two treatments have previously been demonstrated to postpone the onset of HPNS tremor. Compression of mice to 61 ATA with pure helium causes, initially, the onset of hyperactivity, which progresses to a fine intention tremor, and then a coarse postural tremor as compression is continued. The onset of HPNS tremor is accompanied by an increase in the activity of the 12.0 - 23.0 Hz waveband,with a mean peak frequency of 17.0 ± 1.5 Hz. Compression to 61 ATA with helium caused a significant increase in the uptake of [^14C]2-deoxyglucose, ([^14C]2-DG), in the majority of the regions examined, while lesser increases were seen in the remainder. Particular sensitivity to pressure was observed in the cerebellar cortex, pons, sensorimotor cortex, internal capsule, and selected visual and auditory nuclei. The nature of these increases is unclear, but it is proposed that it may reflect a change in the firing characteristics of central neurones with a tendency towards repetitive firing. Compression of mice with trimix (He/N_2O_2) or pretreatment with 2-APH inhibited this increase in metabolic activity, although the exact mechanism for this inhibition is unknown. It is proposed that changes in the activity of the olivo-cerebellar pathway are responsible for the onset of HPNS tremor. The observation that the regional distribution of [^14C]2-DG in the cerebellar cortex is not homogenous suggests that while these central alterations maybe associated with the onset of tremor the increasing severity may reflect changes in peripheral somatosensory inputs. |
