and

effect of aluminium on protein synthesis in

rabbit

brain.

Miller

Levine (21) have reported the biphasic effect of aluminium on the AChE

activity

on

cultured

neuroblastoma

cells

and

Blume

et

al

(2)

have

demonstrated stimulation of AChE activity when cells reach a stationary

growth

phase.

Thus

the

increase

in

AChE

activity

at

lower

aluminium

concentration may be the response of the cells to overcome toxic stress.

Glial cells also contribute to the AChE activity in the brain tissue. A

marked

proliferation

of

glial

cells

contrasted

with

severe

neuronal

losses in rabbits injected with aluminium powder into cerebrospinal fluid

(11). Glial cells in co-culture with embryonic human brain

astroglial

cells for 12 days in vitro can increase the AChE activity two fold (27).

Increase in AChE activity at low dose of aluminium can also be due to

proliferation of glial cells to overcome the toxic stress.

AChE has structural polymorphism and two distinct forms of AChE have been

recognized. AChE is either asymmetric or globular. Globular form includes

monomeric,

dimeric

and

tetrameric

aggregates

which

may

exist

either

soluble or membrane bound (31). The membrane bound AChE may be sensitive

to the physical state of the surrounding lipid environment. Mazzanti et

al (18) have suggested that changes in AChE activity could be mediated by

the

physical

state

of

the

membrane.

As

aluminium

increases

lipid

peroxidation level in rat brain (24) and can affect membrane fluidity

(25),

it

is

suggested

that

changes

in

membrane

fluidity

produced

by

aluminium induced lipid peroxidation could lead to release of membrane

bound AChE. With increased aluminium concentration, the increased lipid