COOPER'S RESEARCH

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(A) Neuromodulation of identified sensory and motor neurons.

(B) Quantal assessment of neurotransmission.

(C) Understanding the basic components involved in vesicular release at nerve terminals.

(D) Sterological methods for characterization of synaptic structures.

Recently, I have broadened my research goals to understand how animals can alter properties of neurotransmission by their behaviors which are expressed during development and in the adult stages when animals are subjected to various physiological and ecological stresses. This line of research encompasses genetic, physiological, behavioral and evolutionary aspects of the organisms under investigation (visual crayfish, blind cave crayfish, and Drosophila). An example of one aspect of this broad, life encompassing research interest is when 2 crayfish are placed together they will fight until one of the combatants withdraws. The success is based largely on physical size. The establishment of dominant and submissive individuals by behaviors have an effect on survival and reproduction of the species. A number of recent findings have implicated the levels of neuromodulators in the nervous system to be the sole factor in establishing a dominant or submissive status. The amine, serotonin in particular, has been implicated in the control of aggression in crustaceans and most vertebrate species, including humans. I plan to substantiate if serotonin really is a major player in establishing the behavioral status of crayfish by bioassays of the levels in the blood while animals are establishing their social status. Various factors such as the state of hunger, visual cues, parasitism and pheromones are currently being addressed in relation to social status among crayfish in my laboratory. We are also addressing learned verus innate behaviors among visual, visual impaired and cave adapted blind crayfish in establishing combats and posturing positions. This will bring us full circle to genetic variations over evolutionary time scales among species and the effects of neuromodulators on neural circuits which have evolved to carry out given behaviors.

Multiple research disciplines are being examined separately but they are all interrelated. With the successful outcome of published findings over the last 4 years from my laboratory, I believe this approach will continue to bare fruit.

Specific research topics are as follows:

(A) Neuromodulation of identified sensory and motor neurons.

The long-term objective of this project is to understand not only the detailed mechanisms of synaptic differentiation among neurons but also those mechanisms employed between neurons and muscle cells. The nerve cell is chemically integrated with other cells at morphologically-identified locations called synapses. The characteristics of the synapse are affected by its activity level which modulates long-term alterations in both synaptic structure and performance. Neuromodulators that are endogenously released either enhance or suppress synaptic efficacy, in turn affecting the behavioral state of an animal. Neuromodulators affect cellular process by various intracellular messenger cascades that are dependent on the type of neuromodulator and its associated receptor. Such changes are believed to play a role in learning and memory, as well as in the behavioral state of an animal.

The crustacean and Drosophila nervous systems lends themselves to easy experimentation and provide direct correlation of structure and function at identified, single cells, as well as at individual synapses. These model nervous systems not only provides for an assessment of the effects of neuromodulators on well characterized behaviors, but also allows correlation between identified synapses and certain behavioral components, thus permitting the identification of specific, cellular mechanisms underlying synaptic differentiation. With the use of recent pharmacological compounds and fluorescent dyes, mechanisms by which neuromodulators influence neurotransmitter release, either transiently or long-term, may now be addressed. An established and precise method of identifying and recording from a synaptic site allows for its subsequent serial reconstruction using electron microscopic techniques. Since the axons of the motor neurons are relatively large in crustacean
nervous systems, intracellular injections of compounds ease the dissection of intracellular signaling systems either in the absence or presence of neuromodulators. Additional effort in this area will provide a clearer understanding of the mechanisms employed by neuromodulators that result in a behavioral change in response to alterations in the nervous system. [See Latest Reseach]

(B) Quantal assessment of neurotransmission.

We continue to develop better methods in assessment of quantal methods utilized to assess synaptic transmission. These methods have been taken in to practice by the scientific community.

(C) Understanding the basic components involved in vesicular release at nerve terminals.

Other aspects of research efforts are continuing in collaboration with Dr. Sidney Whiteheart in the Dept. of Biochemistry at the UK Medical School. He is carrying the molecular based research efforts while I advance the physiological based experimentation. The initial investigations of a synaptically-relevant molecule, alpha-SNAP (He et al., 1999; MS Thesis from my lab) suggest that other molecules may be used similarly to address their functional significance in synaptic transmission. Molecules that dock synaptic vesicles are of special interest.

(D) Sterological methods for characterization of synaptic structures

We have continued projects that develop quantitative techniques for reconstructing the dimensions and spatial distribution of synaptic structures in the pre- and post-synaptic tissue from conventional transmission electron microscopy. To distinguish two aspects of the problem: (1) The reconstruction of size and shape of an object; and (2) The problem of resolving small changes of optical density associated with thin slices of these structures. The analysis should allow one to obtain information on the following synaptic structures: (1) vesicles; (2) presynaptic dense bodies associated with the active zone; and, (3) non-spherical objects such as synaptic areas. It is very important to understand, quantitatively, the scale of morphological features when trying to draw comparisons between specimens. This is especially relevant to our projects of ultrastructural differences in high-and low-output synapses and interconversion of phasic to tonic motor neurons.