acetyltransferase

observed

that

aluminium

exposure

increased

choline

activity in some brain regions of mice.

Aluminium

exposure

both

in vitro and

in vivo,

produced

significant

decrease in AChE activity at extended duration of exposure. Studies by

Gulya et al (12) and Patocka (26) have established the inhibitory effects

of aluminium exposure at longer duration. Yates et al (33) have reported

that intracisternal injection of aluminium

decreased

AChE

activity

in

rabbits.

Aluminium

at

higher

concentration

has

a

non-competitive

inhibitory effect on AChE (17). The activity of choline acetyltransferase

was decreased by aluminium in brain tissue homogenate (3). Therefore in

vitroand in vivoaluminium exposure produces

cholinergic enzymes.

biphasic

effect

on

the

to

Hypothesis on the mechanism of aluminium induced biphasic

effect on the cholinergic system

The

physiological

processes

of

organisms

have

inherent

capability

overcome stress. Toxic stress to physiological and biochemical processes

of the organism could lead to increased protein/enzyme synthesis (29).

Aluminium induced biphasic response may be due to the cell's biochemical

response to the toxic stress. It is suggested that increase in response

at lower dose of aluminium may be due to the physiological response to

the toxic exposure. Continuos exposure to aluminium can supersede

the

the

cells inherent ability to overcome stress leading

to

decrease

in

biochemical response. Nicholls et al (22,23) have reported the biphasic