Brain monoamines and the high pressure neurological syndrome

Abstract

The effects of high pressure on the whole brain concentrations of 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), dopamine (DA), and noradrenaline (NA) were determined in the mouse. Application of high pressure (over 100atm) elevated the brain 5-HIAA concentrations but had little or no influence on the concentrations of 5-HT, DA, or NA. The pressure-induced increase in 5-HIAA was still present after the administration of the monoamine-depleting drugs, parachlorophenylalanine (PCPA), α-methyl- p-tyrosine (α-MPT), reserpine, and FLA-63. Reserpine (4 mg/kg) and FLA-63 (50mg/kg) lowered the pressure at which tremors, convulsions, and death occurred. In contrast, PCPA (3 doses of 300 mg/kg) and α-MPT (2 doses of 250 mg/kg) did not alter the threshold pressures for the behavioural end-points in the high pressure neurological syndrome. Thus, the depletions of 5-HT or of DA and NA alone do not seem to affect the response to pressure, and it may be that alterations in tremor and convulsion threshold pressures are dependent upon a balance of all the monoamine neurotransmitter systems. The involvement of monoamines in the high pressure neurological syndrome resembles to some extent their postulated roles in electroshock, pentylenetetrazol and auditory convulsions.