University of Texas at El Paso
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Research Interests

Neuromodulation is a fundamental physiological phenomenon underlying behavioral plasticity. Using a comprehensive research program that employs cellular, molecular, genetic, chemical, pharmacological and behavioral approaches, our goal is to explore the cellular and biochemical nature of neuromodulatory processes that are crucial for learning and memory, and behavioral adaptations to drugs of abuse. Neuromodulators such as dopamine, serotonin and norepinephrine exert pleiotropic effects in all animals. For example, dopamine plays a role in emotion, cognition and motor system in humans. These modulators function by binding to cell surface receptors to trigger intracellular biochemical changes. These changes, in turn, modify cellular output to generate behavioral responses. The beauty of the biological system is that there are multiple receptors for each modulator, and they are present in distinct brain areas, presumably to execute discrete physiological processes. One of the tantalizing key questions is: does one receptor carry out one or multiple functions? If it does multiple jobs, how does it control specificity? To tackle these issues, we are focusing on two modulators, dopamine and octopamine (functionally similar to norepinephrine of mammals) by employing Drosophila melanogaster as an animal model. Drosophila is being recognized as an important model organism, largely due to its well-characterized genetics, relatively short life cycle (approximately 2 weeks) and, most importantly, rather simple yet sophisticated nervous system that mediates highly versatile behaviors. Moreover, its genomic code has been completely deciphered, thus enabling expedited genetic manipulation.

Figure 1. Schematic presentation of the Drosophila brain structures; blue, mushroom bodies (MB); red, fan shaped bodies; green, ellipsoid bodies; pink, noduli; yellow, protocerebral bridge. CC, central complex that includes aforementioned four structures., AL, antennal lobes; SE, subesophageal ganglia; OL, optic lobes. The image is adapted and modified from Rein et al. 2002, www.flybrain.org


 

Multiple lines of evidence pinpoint the mushroom bodies (MB; Figure 1) of the Drosophila brain as a principal neural substrate for high-order brain functions such as associative learning and memory. Flies with malformed, missing, or functionally disrupted MB have defective olfactory learning, contextual generalization, and conditioned courtship.? Most remarkably, genes critical for learning and memory -dunce, rutabaga, DCO, leonardoVolado (alpha-integrin)- are predominantly enriched in the MB, strongly suggesting that the MB utilizes cAMP-, protein kinase C-, and/or the MAP kinase-mediated signal transduction cascades for modulation of synaptic plasticity underlying associative learning.


Figure 2. Expression pattern of dDA1 (D1-like dopamine receptor) in the Drosophila brain. A. Immunostaining of a whole mount CNS displaying dDA1-enriched mushroom body lobes (red) that are colocalized with the mushroom body- tagging GFP. B. Schematic presentation of the brain structures with enriched dDA1 proteins; blue, mushroom bodies; red, fan shaped bodies; green, ellipsoid bodies; pink, noduli. C-G. Immunostaining of frontal head sections displaying dDA1-enriched mushroom body lobes (g, a, b lobes and heel) and pedunduli (p), ellipsoid bodies(EB),? fan shaped bodies (FB) and noduli (NO).

Figure 3.  Dopaminergic neurons in adult Drosophila brain. anti-TH immunostaining


Figure 4.  dDA1 (D1-like dopamine receptor, red) expression with Dopaminergic neurons (Tyrosine hydroxylase GAL4/UAS- GFP, Green) in adult Drosophila brain. anti-dDA1 immunostaining on TH-GFP


These pathways are presumably triggered by binding of neuromodulators to their receptors on the MB neurons to activate the rut, adenylyl cyclase and phospholipase C. To explore the nature of the molecules that drive these processes in the MB leading to associative learning and memory, we identified three receptors that are highly enriched in the MB and they include dDA1 (D1-like dopamine receptor; Figure 2), DAMB (D5-like dopamine receptor; Figure 3) and OAMB (octopamine receptor; Figure 4). Quite remarkably these receptors stimulate increases in cAMP and intracellular calcium, key mediators of learning/memory signal transduction pathways, thus placing dDA1, DAMB and OAMB as primary candidates initiating the biochemical cascades for associative learning and memory. and Volado (alpha-integrin)- are predominantly enriched in the MB, strongly suggesting that the MB utilizes cAMP-, protein kinase C-, and/or the MAP kinase-mediated signal transduction cascades for modulation of synaptic plasticity underlying associative learning. These pathways are presumably triggered by binding of neuromodulators to their receptors on the MB neurons to activate the rut, adenylyl cyclase and phospholipase C. To explore the nature of the molecules that drive these processes in the MB leading to associative learning and memory, we identified three receptors that are highly enriched in the MB and they include dDA1 (D1-like dopamine receptor; Figure 2), DAMB  and OAMB. Quite remarkably these receptors stimulate increases in cAMP and intracellular calcium, key mediators of learning/memory signal transduction pathways, thus placing dDA1, DAMB and OAMB as primary candidates initiating the biochemical cascades for associative learning and memory.


Figure 5. Fly Tracker. Ca nton S male flies exposed to volatized cocaine are shown in the video clip (left panel). Traces of individual male flies exposed to alcohol vapor are shown in the right panels.


To assess related behavioral abnormalities of individual receptors, we have generated various genetic variants defective in each receptor and have implemented several behavioral paradigms including aversive and appetitive olfactory conditioning, conditioned courtship and a computer program-assisted locomotor tracking system named Fly Tracker (Figure 5). The goals are to measure associative learning, and subsequent short- or long-term memory formation and maintenance, sexual (courting, mating, and reproductive), and drug-induced behaviors. The drugs of interest are cocaine and alcohol, primarily because of broad implications for dopamine and adrenergic systems in mediating their effects. In addition, behavioral changes resulting from repetitive drug exposures likely recruit neuronal modifications underlying learning and memory. Therefore, our comparative studies of receptor mutants using various behavioral paradigms should help elucidate selectivity and diversity of dopaminergic and octopaminergic neuromodulatory functions relevant to associative learning/memory and drug sensitivity/addiction and provide a baseline to further investigate their underlying cellular mechanisms. Ultimately, these studies may shed light on effective prevention of and intervention in human disorders such as learning disorders, schizophrenia, drug addiction and alcoholism.