Kamal Sharma - US grants

DESCRIPTION (provided by applicant): Spinal cord receives information that originates in the peripheral nerve endings and in the supraspinal motor centers. This information is integrated and used for generating a proper motor response. How does spinal cord achieve this complex integration task? The specificity of motor functions is encoded in different motor neuron subtypes that innervate distinct muscle targets. Sandwiched between the incoming information and the motor output are a multitude of premotor interneurons. How these neurons process information is not understood. Most interneurons in the spinal cord and elsewhere in the vertebrate CNS have eluded analysis because of the lack of specific markers to identify them. In transgenic mice cre-recombinase based indelible markers provide an unparalleled opportunity to study these neurons in the embryonic and adult spinal cord. Developmental studies have identified transcription factors that are expressed in subsets of interneurons, for example Lhx3. Promoters of these genes are ideal candidates for targeting cre-recombinase to select interneuron subtypes. A cre-reporter can then introduce an indelible mark in these interneurons and facilitate their identification throughout development and in the adult spinal cord. Marked and lineally related interneurons provide an opportunity to test the role of transcription factors and cell-cell interactions in cell-fate specification during development and maturation during the postnatal life. The proposed experiments will use this strategy to mark the progeny of the Lhx3+ lineage, determine the role of four transcription factors and notch-mediated cell-cell communication in cell-fate specification. Further, synaptic partners of the marked neurons and their neurotransmitter properties will be determined. The information generated from these studies will further our understanding of the spinal motor circuits and the role of interneurons in the control of motor functions in health and disease.

DESCRIPTION (provided by applicant): Two neural circuits that we propose to study control appetitive Pavlovian learning and sleep. Abnormalities in these neural circuits are linked to drug addiction and sleep disorders, two major human health problems with severe negative consequences to human productivity. We focus on a class of neurons that originate from one of the five known progenitor domains in the ventral neural tube. These neurons are called the V2a neurons and are generated throughout the hindbrain and spinal cord. Following genetic ablation of V2a neurons, mice show significant deficit in appetitive Pavlovian learning and sleep. Which V2a neurons are recruited to neural circuits that regulate appetitive Pavlovian learning and sleep? Do V2a neurons project to and connect with known elements of the neural circuitry underlying appetitive Pavlovian learning and sleep? Finding answers to these questions is significant at three levels. (1) It would lead to important new insights for understanding the evolution and adaptability of the nervous system and how microcircuits are assembled. (2) It would for the first time demonstrate that inputs from pontine nuclei are needed for appetitive Pavlovian learning and that V2a neurons and their connections to the mesolimbic system might play a critical role in drug addiction. (3) It will provide neural basis of sleep induced muscle atonia and sleep disorders caused by its malfunction. To answer the aforementioned questions we have devised a genetic strategy to target pontine V2a neurons that originate from rhombomere 1 (r1-V2a neurons). We propose to use a mouse genetics approach to test three hypotheses. (1) The r1-V2a lineage generates neurons that populate functionally diverse pontine tegmental nuclei. (2) The r1-V2a neurons regulate appetitive Pavlovian learning via direct projections to the RMTg. (3) The r1-V2a neurons regulate sleep architecture via direct projections to interneurons in the ventral spinal cord. Successful completion of these studies will demonstrate that embryonic V2a neurons originating from r1 are recruited to distinct neural circuits that regulate appetitive Pavlovian learning and sleep. PUBLIC HEALTH RELEVANCE: Dedicated neural circuits control each motor task performed by humans and animals. How do these neural circuits develop? Is there an underlying principle that guides the evolution and development of neural circuits? Important insights into these questions can be gained by understanding the relationship between neuronal cell fate decisions in the embryo and neuronal function in the adult. Successful completion of our studies would demonstrate that pontine r1-V2a neurons contribute to neural circuits that control appetitive Pavlovian learning and sleep. Our studies would show for the first time that one function of pontine r1-V2a to RMTg connections is appetitive Pavlovian learning. Mouse models that we have generated will be invaluable tools for understanding the physiological basis of appetitive learning and addiction to drugs of abuse. Our studies would also show that descending projections from pontine r1-V2a to the ventral spinal interneurons play a critical role in neural control of sleep and a potential target for drug discover to ameliorate sleep disorder.