Behavioral Ecotoxicology - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 257

primates. Numerous characteristics of individual neuron physiology are highly con-
served in both vertebrates and invertebrates. Synaptic transmission occurs in similar
manner in different taxa, whereas intraspecific variations are recorded depending
on the type of neuron, its localization in the nervous system, and the location of the
synapse on the sending and receiving neurons. Processes involved in synaptic trans-
mission, particularly the role of neurotransmitters such as acetylcholine, are potential
targets for pharmacological and toxicological impairments. In addition to modifying
AChE activity (Chapter 4), exposure to environmental neurotoxicants can also affect
brain levels of other neurotransmitters such as serotonin (5-HT), dopamine, or gamma-
aminobutyric acid.
In the freshwater fish Channa punctata , exposure to endosulfan induces a decrease in
5-HT and AChE activity with changes in surfacing behavior (Gopal et al. 1985). Dopamine
concentration was also affected but differently according to the level and duration of
endosulfan exposure. In the fish Pimephales promelas exposed to mercury (1.69 to 13.57 μg
L -1 as mercuric chloride HgCl 2 for 10 days), foraging and capture speed were disturbed
but neither differences in brain levels of norepinephrine, serotonin, and dopamine or its
metabolite l-DOPA were shown nor any inhibition of AChE activity (Grippo and Heath
2003). On the contrary, in the fish Mugil cephalus , exposure to mercury was linked to a
progressive loss of locomotion capability and serotonin level was decreasing (Thomas et
al. 1981). Grippo and Heath (2003) suggested that such discrepancies could be due to envi-
ronmentally realistic versus acute exposure procedures. However, in the estuarine fish
Fundulus heteroclitus collected from a contaminated area and showing high brain mercury
concentrations, a reduction of general activity was correlated to low brain concentrations
of serotonin (Weis et al. 2001). In the fish Pimephales promelas , exposure to lead induces vari-
ous behavioral disturbances associated with changes in neurotransmitter concentrations
(serotonin, norepinephrine and its metabolite, vanillylmandelic acid) (Weber et al. 1991,
1997). Similarly, in rainbow trout ( Oncorhynchus mykiss ) exposed to lead and cadmium,
physiological profiles were affected with a trend toward high activity of serotonin in dom-
inant individuals, but the social hierarchy established before exposure was not affected
(Sloman et al. 2005). These discrepancies could, again, have their origin in exposure condi-
tions (0.5 or 1.0 mg Pb L -1 for 4 weeks in the study of Weber et al. 1991; 0.046 or 0.325 mg Pb
L -1 for 48 h in the study of Sloman et al. 2005). In the coral reef fish Thalassoma bifasciatum ,
the link between serotonin and aggressive behavior has been shown after exposure to
fluoxetine (a drug used as inhibitor of serotonin resorption), which is still present in efflu-
ents after the treatment of wastewater (Perreault et al. 2003). In hybrid striped bass ( Morone
saxatilis × M. chrysops ), sublethal exposure to fluoxetine decreases the ability to capture
prey in association with decreases in brain serotonin activity (Gaworecki and Klaine 2008).
In the goldfish Carassius auratus , DDT induces interferences with behavior, either innate or
acquired, and neurotransmitters (high concentration of brain serotonin and depletion of
dopamine concentrations) (Weis and Weis 1974; McDonald 1979). In Fundulus grandis , PCBs
affect both locomotion and dopamine and norepinephrine concentrations (Fingerman and
Russell 1980).
Adkins-Regan and Weber (in Dell'Omo 2002) have listed molecules (neurotransmitters,
neuromodulators, neurohormones, and hormones) considered as involved in behaviors
important for an ecology's organisms as a consequence of their actions on the nervous sys-
tem. Among these regulators, many are neuropeptides, some of which are widely distrib-
uted such as vasopressin-oxytocin-like molecules (nonapeptides), GnRH (gonadotropin
releasing hormone, decapeptides), or P substance (family of tachykinins) that are present
in both vertebrates and invertebrates. Steroid hormones are also numerous and widely