Alan Gelperin - US grants

We are analyzing the neuronal basis of a rapid-onset, long-duration associative learning mechanism in the terrestrial slug, Limax maximus. The learning mechanism is part of the neural control system for feeding. We use behavioral experiments to define the major plastic capabilities of the neural control system for feeding. Neurophysiological and neurochemical experiments aim to define the critical synaptic loci of plastic changes and the causative biophysical and biochemical events which underly them. The proposed behavioral experiments will further characterize the associative learning ability of the isolated cerebral ganglia by testing for long term memory retention times of several days and the higher order conditioning phenomena (second order conditioning, compound conditioning and blocking) shown by the intact animal. Neurophysiological experiments will focus on changes in previously characterized dopaminergic and serotonergic neurons with learning and search for command neurons in the feeding network as potential loci for plastic changes. Neurochemical experiments will extend our observation that dietary choline augments memory retention by testing for the effects of dietary tyrosine and tryptophan on brain levels of dopamine and serotonin and on learning and memory retention. The design of successful therapeutic measures for learning and memory disorders such as senile dementia and Alzheimer's disease would be aided greatly by definition of the basic synaptic changes which underlie normal learning and memory storage. The proposed experiments will contribute to that definition.

DESCRIPTION (Adapted from the Investigator's Abstract) The long-term objective of this proposal is to understand the cellular and biochemical basis of long-term memory storage, using the storage of odor memories in the olfactory system of a terrestrial mollusk as a model system. We will test a specific cellular and biophysical model for how the major central site of odor information processing in the terrestrial slug Limax maximus forms odor memories as spatially segregated bands of neurons. The odor memory storage site, the procerebral (PC) lobe, is analogous to the mammalian olfactory bulb. The hypothesis to be tested is that olfactory memories are identified by odor learning-dependent uptake of a highly fluorescent dye, Lucifer yellow, by groups of neurons in the PC lobe. Learning-dependent dye uptake identifies the neurons involved in storing the odor memory for detailed biophysical and biochemical analysis. The specific aims of the proposed work will test several predictions of the hypothesis that the learning-dependent dye labeling identifies neurons storing an odor memory. The following specific experimental questions will be addressed; 1. If the slug is denied access to the dye-labeled neurons in the PC lobe after odor training, does it act naive in a behavioral test of odor memory function? 2. Does the spacing between two dye-labeled bands produced by learning about two odors predict the ability to discriminate between the two learned odors? 3. Are the dye labeled neurons present after odor training selectively activated by stimulation with the trained odor? 4.Do drugs which disrupt normal dynamics of neuronal activity in the PC lobe also degrade odor learning and odor discrimination? The computational model which leads to the specific experimental tests listed in the specific aims will be expanded to incorporate more specific details of the cellular biophysics and neuron connectivity in the PC lobe. We also will study the cellular mechanism of learning-dependent dye uptake to develop this memory localization tool for use in mammalian brain. The conserved nature of biochemical memory mechanisms and system design principles in olfactory systems makes it very likely that mechanisms for odor memory storage in the molluscan nervous system will have direct relevance to the mammalian nervous system. The results of this work will contribute to efforts to develop pharmacological interventions for clinical syndromes in which loss of memory function is a major component, such as mental retardation and Alzheimers disease.

A grant has been awarded to Dr. Nancy E. Rawson at the Monell Chemical Senses Center to purchase a confocal microscope with associated hardware and software. The Monell Center is a nonprofit research institute focused on acquiring a fuller understanding of the chemical senses. Recent studies have revealed that cell-cell interactions play an important role in modulating the output of a variety of sensory receptor cells. The confocal microscope permits us to directly observe intracellular processes and interactions between different cell types in preparations that more closely reflect those of the intact organism. In addition, chemosensory cells undergo regeneration throughout the life of the animal. In order to better understand this capability, studies of growing cells are carried out using methods to identify the different stages in the cells' lifespan and evaluate the effect of drugs or other treatments on the growth process.
The confocal microscope will be used in projects aimed at addressing a variety of questions ranging from understanding how individual receptor cells detect and respond to chemical stimuli; how experience influences the ways that organisms respond to chemosensory stimuli; how odor qualities are encoded in neural activity patterns in the brain; how stem cells divide and differentiate into mature sensory receptor cells; and how these sensory systems recover from damage. These projects utilize standard histology, lectin and immuno-histochemistry, in situ hybridization of fixed tissue specimens, and biophysical methods to study live tissue. These techniques provide a variety of kinds of data, ranging from protein and mRNA localization in peripheral and central components of the taste, olfactory and trigeminal systems to dynamic extra- and intracellular signalling in tissue slices, cultures and cell ensembles. The system will also be included as one educational component in our Minority Student Research Apprenticeship Training Program, which has provided summer research experiences for over 300 high school and college undergraduates since its inception.
The ability to examine cells in ensembles, such as whole taste buds, or thick tissue sections will dramatically improve our ability to understand how the sensory systems of taste, smell and chemical irritation function in the intact organism. The confocal microscope will also enhance our ability to provide state-of-the-art training experiences for students participating in our high school, college, graduate and post-doctoral training programs.