AJP - Regulatory, Integrative and Comparative Physiology, Vol 260, Issue 4 777-R784, Copyright © 1991 by American Physiological Society
Lack of osmoregulation in Aplysia brasiliana: correlation with response of neuron R15 to osphradial stimulation
E. Scemes, L. C. Salomao, J. C. McNamara and A. C. Cassola
Departamento de Fisiologia Geral, Universidade de Sao Paulo, Brazil.
The exposure of Aplysia brasiliana to dilute seawater (90 and 80%) caused
an increase of the relative weight, which returned to the original values
after a few hours. Both osmotic and chloride concentrations of the
hemolymph decreased on exposure to 80 and 90% dilute seawater, and after
3-h exposure there were no differences between the hemolymph and external
media osmotic and chloride concentrations. In contrast to the clear
regulatory capabilities reported for A. californica, A. brasiliana cannot
maintain the osmolality of its body fluid in dilute media. In A.
californica, osphradial receptors and neuron R15 are apparently involved in
this regulatory mechanism. Perfusion of osphradium of A. brasiliana with
dilute seawater (95-80%) did not affect electrical activity of the bursting
neuron R15; perfusion with 70 and 60% seawater caused a transient increase
in the duration of the quiescent period. In contrast to the model
established for A. californica, in A. brasiliana no relationship was found
between exposure of the osphradium to dilute media and electrical activity
in neuron R15, which is in accordance with the lack of an osmoregulatory
mechanism in this species. Such differences may reflect inherent
differences in salinity tolerance between the two species.
