Chemico-Biological Interactions 119 – 120 (1999) 371 – 378
Effects of organophosphates on cholinesterase
activity and neurite regeneration in Aplysia
M. Srivatsan *
Department of Physiology, Uniersity of Kentucky College of Medicine, 800, Rose Street, Lexington,
KY 40536 -0084, USA
Abstract
In Aplysia, a marine mollusc, acetylcholinesterase (AChE) is present in cholinergic and
non-cholinergic neurons and in hemolymph. Aplysia hemolymph has a very high level of
AChE which promotes neurite growth in primary cultures of dopaminergic neurons via a
non-catalytic mechanism. In contrast, AChE is known to facilitate neurite growth in
cholinoceptive neurons by hydrolyzing ACh which inhibits neurite growth. In order to test
whether AChE’s site-specific neurotrophic action varies with the neuronal phenotype, we
investigated the effects of active-site inhibited hemolymph AChE on neurite growth of
cholinergic neurons of Aplysia in primary culture. Organophosphates being long-acting
active site inhibitors of AChE were chosen for this study. The effects of active site inhibited
hemolymph AChE was tested on large cholinergic neurons, R2 (abdominal ganglion) and
LPL1 (left pleural ganglion) as well as small cholinergic neurons (buccal ganglion) of
Aplysia, maintained in culture. Partially purified hemolymph AChE was inhibited by either
10 M of echothiophate or 5 M of paraoxon. Neurons were maintained in (1) L15 (defined
medium) alone; (2) L15 +echothiophate; (3) L-15 +paraoxon; (4) L-15 +hemolymph
AChE; (5) L15 +hemolymph AChE +echothiophate; and (6) L-15 +hemolymph AChE +
paraoxon. Addition of uninhibited hemolymph AChE significantly increased neurite growth
of cultured neurons compared to L15 alone. In the presence of echothiophate-inhibited or
praoxon-inhibited AChE, neurite growth was significantly reduced when compared to
L15 +uninhibited AChE. While the presence of echothiophate by itself did not reduce
survival or neurite growth when compared to L-15 alone, the presence of paraoxon by itself
markedly reduced survival and neurite growth of cultured neurons. The results show that
AChE’s catalytic action contributes to enhance neurite growth in cholinergic neurons and the
effects of paraoxon appears to differ from that of echothiophate on cholinergic neurons of
Aplysia. © 1999 Elsevier Science Ireland Ltd. All rights reserved.
* Tel.: +1-606-2579124; fax: +1-606-3231070.
E-mail address: msriv1@pop.uky.edu (M. Srivatsan)
0009-2797/99/$ - see front matter © 1999 Elsevier Science Ireland Ltd. All rights reserved.
PII:S0009-2797(99)00048-4