Neurotransmitters

It is well established that altered neurotransmitter levels have long been associated with stress in many mammals. The purpose of this study was to determine if changes in the brain tissue concentration and/or turnover rates of the monoamine neurotransmitters could be used as an early indicator of physiological stress for fish in different aquatic ecosystems. Gray snapper, Lutjanus griseus, were collected from two sites, a pristine (control) and a polluted (experimental) site, classification based upon the hydrocarbon content of their sediment. The brains were quickly removed and dissected into three regions: frontal lobes, hypothalamus, and brain stem which were later analyzed for using high performance liquid chromatography. A decrease in brain tissue norepinephrine and dopamine concentration in the frontal lobes and hypothalamus was observed in individuals collected from the polluted site. No significant difference in either norepinephrine or dopamine concentration was present in the brain stem. Despite a decrease in dopamine levels, there was no significant change in dopamine turnover. There was a significant decrease in serotonin concentration in the hypothalamus at the polluted site. There was an increase in serotonergic activity in the hypothalamus and brain stem at the polluted site. A significant decrease in the weight of the hypothalamus in fish from the polluted site was also observed. These results suggest that a change in brain monoamines can be used as a early indicators of chronic environmental stress.

The amphibian retina is commonly used as a model system for studying function and mechanism of the visual system in electrophysiology, since the neural structure and synaptic mechanism of the amphibian retina are similar to higher vertebrate retinas. I determined the specific subtypes of receptors and channels that are involved in chemical and electrical synapses in the amphibian retina. My study indicates that glycine receptor subunits of GlyRº1, 3 and 4 and glutamate receptor subunit of GluR4 are present in bipolar and amacrine dendrites and axons to conduct chemical synapses in the retinal circuit. I also found that the gap junction channel, pannexin 1a (panx1a), is present in cone-dominated On-bipolar cells and rod-dominated amacrine processes possibly to connect rod-and cone-pathway in the inner retina. In addition, panx1a may form hemi-channels that pass ATP and Ca2+ signals. The findings of my study fill the gap of our knowledge about the subtypes of neurotransmitter receptors and gap junction channels conducting visual information in particular cell types and synaptic areas.