Permanent cessation of the activity of posterior lymph hearts in the voluntarily and forcibly submerged toad Bufo arenarum

We studied the effect of voluntary and forced submergence with a new techni que for chronically recording lymph heart activity in the toad Bufo arenaru m. Voluntary submergence induced an immediate cessation of the beats, which lasted as long as submergence was maintained. Forced submergence also prod uced beat arrest but the cessation occurred gradually. The lymph heart cess ation was coincident with the appearance of a state of immobility. The dura tion of the forced submergence was shown to be important for the occurrence of some behavioural peculiar phenomena and of lymph heart activity followi ng emergence. The section of the spinal cord immediately below the medulla oblongata suppresses the lymph heart cessation elicited by forced submergen ce. (C) 1999 Elsevier Science Inc. All rights reserved.