الفهرس 
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Abstract
During the last few decades snails have served successfully as model organisms for numerous studies molecular, cellular, behavioral neurobiology, and neurotoxicology. The central nervous system (CNS) of snails contains giant neurons which are relatively easily accessible for different techniques thus permitting the combination of physiological, biochemical, morphological and molecular studies making snail’s CNS ideal model systems for the study of
fundamental mechanisms of nervous system. Therefore, the snail Biomphalaria
alexandrina, the intermediate host for the human parasitic disease Schistosoma
mansoni, can be used as a model organism to assess heavy metals risk factors for
severe neurotoxicity and neurodegenerative disorders and to investigate the
protective role and antioxidant activity of some plant extracts against heavy metals
neurotoxicity.
To verify the purpose of the present sbdy, the CNS of B. alexandrina was
described using immunocytochemical and histochemical techniques and some
important neurotransmitters were localized in the snail’s CNS and peripheral
tissues. Biological and biochemical responses were measured in snails after
exposure to two heavy metals, namely manganese (as manganese chloride) and
cadmium (as cadmium chloride). The general behavioral aspects of snails such as
feeding and locomotion were recorded in exposed snails and their values were
compared to those of controls. Also, the deteriorations in monoamines
neurotransmitters (dopamine, serotonin, homovanillic acid, and norepinephrine) in
the snails’ tissues were measured before and after exposure to the metals using
HPLC-UV. Similarly, antioxidants molecules such as catalase and reduced
glutathione in addition to lipid peroxidation were estimated in exposed and control
snails.
Finally, to abate the adverse effects induced by heavy metals in B.
alexandrina, the medicinal plants, Rosmarinus oficinalis (rosemary) and Ocmium
basilicum (basil) were chosen and the antioxidant capacities of their water extracts
were compared using biochemical techniques. The powerful plant extract (RWE)
was implemented in the modulation experiments and the same biological and
biochemical parameters were measured in snails exposed to combined treatment
with metals and the plant extract against those exposed to metals alone.
The results of the present study can be summarized in the following main
points:
Neuroantomical description of B. alexandrina using precise micro-dissection
revealed that, similar to other pulmonate snails, Biomphalaria CNS consists of
four symmetric ganglia; the buccal, cerebral, pedal, and pleural ganglia, a pair of
asymmetrical ganglia; the parietal ganglia, and one unpaired visceral ganglion.
Immunocytochemical, using antibodies against tyrosine hydroxylase, histamine,
and nitric oxide synthase, and histochemical techniques indicated that
catecholamines, histamine, and nitric oxide are widely distributed in the nervous
system with immunolabeled neurons abundant in the CNS and peripheral tissues
and intensely labeled fibers in the ganglionic neuropils, central tracts and
peripheral nerves B. alexandrina snails.
Acute and chronic exposure of B. alexandrina to manganese (Mn) and cadmium
(Cd) induced several adverse effects on different behavioral and biological
aspects of exposed snails as follow:
a. LC5() after acute exposure (96 hr) to a series of Mn and Cd concentrations,
were 156.57 and 0.38 mgll, respectively. Under exposure to the same
concentrations for 20 days, the survival curve of snails was gradually decreased in a dose-dependent manner. The highest survival rates were
obtained with 50 and 0.05 mgll concentrations of Mn and Cd, respectively.
b. Acute and chronic exposures of B. alexandrina to Mn and Cd caused a
reduction in the spontaneous locomotion and feeding activity of exposed
snails compared to control ones.
c. HPLC analyses of control B. alexandrina indicated the presence of
monoamines neurotransmitters, dopamine (DA), serotonin (5-HT),
homovanillic acid (HVA), and norepinephrine (NE) in the CNS and
peripheral tissues of the snails. These substances were found to be sensitive
to heavy metal exposure. Exposure to Mn and Cd caused decreased
concentrations of these monoamines in the tissues of B. alexandrina. Both
acute and chronic exposures induced significant reduction in DA, HVA, and
5-HT in the CNS and peripheral tissues of snails. In contrast, the exposure
led to a significant increase in norepinephrine concentration in B.
alexandrina tissues.
d. Exposure of B. alexandrina to heavy metals resulted in oxidative stress and
lipid peroxidation. Both of Mn and Cd decreased catalase (CAT), reduced
glutathione (GSH) levels in the CNS and peripheral tissues of exposed snails
compared to control unexposed ones. A significant increase in the lipid
peroxidation was observed in the CNS and peripheral tissues of Mn-and Cdexposed
snails compared to control snails.
The assay of antioxidant capacity of Rosmarinus officinalis and Ocmium
basilicum water extracts, using different biochemical techniques indicated
that, R. officinalis water extract (RWE) had higher antioxidant potential than
0. basilicum extract (425.72S.2 1 and l87.1*22.78 mg AAEIg extract,
respectively).