Diego Restrepo (Ph.D.)

The goal of my research is to understand, in health and disease, how brain circuits mediate responses to sensory input. We study how brain circuits in sensory processing areas, amygdala, hippocampus and cortex mediate behaviors such as associative learning. We use an interdisciplinary approach employing advanced molecular biology, animal genetics, bioinformatics, awake behaving recording with surgically implanted tetrodes, modification of circuit processing by optogenetics and generation of new devices and computational resources to understand brain signal processing. My research involves studies in animal model systems and humans. Importantly, my laboratory has substantial collaboration with engineers and physicists.

The following are highlights of accomplishments in the lab:

1. My early publications directly addressed what the role of Ca2+ is in the transduction pathway of olfactory sensory neurons (OSNs) of the main olfactory epithelium. Using functional fluorescence microscopic imaging my laboratory provided the first demonstration that odors elicit influx of Ca2+ into the OSNs mediated by opening of cAMP-gated (CNG) channels and recently showed that Ca2+ influx into the sensory cilia takes place in discrete microdomains. In addition, we showed that a subset of OSNs do not express the Ca2+-activated Cl- channels thought to depolarize cells after the CNG channel allows a ciliary influx of Ca2+. In this subset of cells the increase of intraciliary Ca2+ elicits opening of a ciliary Ca2+-gated transient receptor potential M5 (TRPM5) channel. Interestingly a substantial number of mitral cells innervating glomeruli targeted by TRPM5-bearing OSNs in the main olfactory bulb innervate the medial amygdala. This structure involved in sexual behavior was previously thought to receive innervation only from the accessory olfactory bulb that responds to pheromones and other semiochemicals. In addition, we showed that this subset of TRPM5-bearing main olfactory epithelium OSNs responds at low concentrations to semiochemicals such as MHC peptides and putative pheromones. This is relevant to human olfaction because humans do not have a vomeronasal organ, but do have a main olfactory epithelium.

    
2. My laboratory pioneered recording of odor Ca2+ responses in isolated human OSNs obtained by biopsy of the olfactory epithelium and used this technique and human neuronal cell culture to study olfactory transduction as well as olfactory function in the elderly, anosmics, olfactory neuroblastoma and depressed patients. We found that the human OSNs respond to odors more specifically than rodent OSNs. In addition we found that OSNs respond differently to odors in unmedicated depressed patients compared to controls. Finally, we showed that, while OSNs respond specifically to odors in adult human OSNs (<45 years old), OSNs from older individuals (>65 years old) respond to multiple odors suggesting that in the elderly these neurons are less selective, perhaps by expressing multiple olfactory receptors per cell leading to an “olfactory white” response that mediates the decrease in odor sensitivity in the elderly.

    

   a. Rawson NE, Gomez G, Cowart BJ, Kriete A, Pribitkin E, Restrepo D. Age-associated loss of selectivity in human olfactory sensory neurons. Neurobiol Aging. 2012;33:1913-9. Epub 2011/11/15. doi: 10.1016/j.neurobiolaging.2011.09.036. PubMed PMID: 22074806; PubMed Central PMCID: PMC3299952.

   b. Hahn CG, Gomez G, Restrepo D, Friedman E, Josiassen R, Pribitkin EA, et al. Aberrant intracellular calcium signaling in olfactory neurons from patients with bipolar disorder. Am J Psychiatry. 2005;162(3):616-8. Epub 2005/03/03. doi: 162/3/616 [pii] 10.1176/appi.ajp.162.3.616. PubMed PMID: 15741484.

   1. c.  Restrepo D, Okada Y, Teeter JH, Lowry LD, Cowart B, Brand JG. Human olfactory neurons respond to odor stimuli with an increase in cytoplasmic Ca2+. Biophys J. 1993;64(6):1961-6. Epub 1993/06/01. doi: S0006-3495(93)81565-0 [pii] 10.1016/S0006-3495(93)81565-0. PubMed PMID: 8369416; PubMed Central PMCID: PMC1262528.

      d. Rawson NE, Gomez G, Cowart B, Brand JG, Lowry LD, Pribitkin EA, et al. Selectivity and response characteristics of human olfactory neurons. J Neurophysiol. 1997;77(3):1606-13. Epub 1997/03/01. PubMed PMID: 9084623.

       
3. Ours was among the first laboratories performing recordings in the olfactory bulb, piriform cortex and other olfactory brain areas in awake behaving mice. We made the surprising finding that the spike rate of mitral cells responds to whether the odor is rewarded (odor value), not to the odor identity. Subsequently we have found that the gamma frequency spike-field coherence responds to an odor feature consistent with odor identity. Finally, we have used optogenetics to show that mice can differentiate between pulses of glomerular input that differ by 10 msec in duration. These studies demonstrate that the olfactory system functions in a very different manner in the awake behaving animal compared to the anesthetized animal or to the circuit in brain slice preparations. This implies that in order to understand function of this circuit in the awake behaving animal it is key to understand modulation and centrifugal feedback to the olfactory bulb.

    

   a. Li A, Gire DH, Restrepo D. Υ spike-field coherence in a population of olfactory bulb neurons differentiates between odors irrespective of associated outcome J Neurosci. 35(14):5808-22. doi: 10.1523/JNEUROSCI.4003-14.2015. PubMed PMID: 25855190, 2015.

   b. Li A, Gire DH, Bozza T, Restrepo D. Precise detection of direct glomerular input duration by the olfactory bulb. JNeurosci. 2014;34:16058-64. doi: 10.1523/JNEUROSCI.3382-14.2014.

   c. Gire DH, Whitesell JD, Doucette W, Restrepo D. Information for decision-making and stimulus identification is multiplexed in sensory cortex. Nat Neurosci. 2013;16:991-3. Epub 2013/06/25. doi: 10.1038/nn.3432. PubMed PMID: 23792942.

   d. Doucette W, Gire DH, Whitesell J, Carmean V, Lucero MT, Restrepo D. Associative Cortex Features in the First Olfactory Brain Relay Station. Neuron. 2011;69:1176-87. Epub 3/24/2011.

    
4. shape memory polymer-based electrodes that would slowly self-implant compliant conductors into the brain, and both decrease initial trauma resulting from implantation and enhance long-term biocompatibility for long-term neuronal measurement and stimulation in brain tissue.  In addition, in order to understand the constraints of inserting probes in brain tissue we performed a study of micrometer-scale penetration mechanics and material properties of mouse brain tissue in vivo. Finally in a collaboration with engineers and physicists we have developed a novel electrowetting fiber coupled microscope that will allow future imaging and optogenetic modulation of neuronal activity deep in brain tissue. These techniques are designed to provide novel tools for studying and modifying brain function.

   a. Sharp AA, Panchawagh HV, Ortega A, Artale R, Richardson-Burns S, Finch DS, et al. Toward a self-deploying shape memory polymer neuronal electrode. J Neural Eng. 2006;3(4):L23-30. Epub 2006/11/25. doi: S1741-2560(06)33474-X [pii] 10.1088/1741-2560/3/4/L02. PubMed PMID: 17124327.

   b. Lin W, Margolskee R, Donnert G, Hell SW, Restrepo D. Olfactory neurons expressing transient receptor potential channel M5 (TRPM5) are involved in sensing semiochemicals. Proc Natl Acad Sci U S A. 2007;104(7):2471-6. Epub 2007/02/03. doi: 0610201104 [pii] 10.1073/pnas.0610201104. PubMed PMID: 17267604; PubMed Central PMCID: PMC1892929.

   c. Meyer SA, Ozbay, B., Restrepo, D., Gibson, E.A. Super-resolution imaging of ciliary microdomains in isolated olfactory sensory neurons using a custom STED microscope. Proc SPIE. 2014;8950, Single Molecule Spectroscopy and Superresolution Imaging VII, 89500W (March 4, 2014). doi: doi:10.1117/12.2041784.

   d. Zane, R., Popovic, Z., Sharp, A. and Restrepo, D. 2009. Systems and methods for receiving and managing power in wireless devices. US Patent No. 7,956,572.

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1. a.   Lopez F, Delgado R, Lopez R, Bacigalupo J, Restrepo D. Transduction for Pheromones in the Main Olfactory Epithelium Is Mediated by the Ca2+-Activated Channel TRPM5. J Neurosci. 2014;34(9):3268-78. Epub 2014/02/28. doi: 10.1523/JNEUROSCI.4903-13.2014. PubMed PMID: 24573286; PubMed Central PMCID: PMC3935088.
2. b.   Gonzalez-Silva C, Vera J, Bono MR, Gonzalez-Billault C, Baxter B, Hansen A, et al. Ca2+-activated Cl- channels of the ClCa family express in the cilia of a subset of rat olfactory sensory neurons. PLoS One. 2013;8(7):e69295. Epub 2013/07/23. doi: 10.1371/journal.pone.0069295. PubMed PMID: 23874937; PubMed Central PMCID: PMC3706372.
3. c.   Restrepo D, Miyamoto T, Bryant BP, Teeter JH. Odor stimuli trigger influx of calcium into olfactory neurons of the channel catfish. Science. 1990;249(4973):1166-8. Epub 1990/09/07. PubMed PMID: 2168580.
4. d.   Thompson JA, Salcedo E, Restrepo D, Finger TE. Second-order input to the medial amygdala from olfactory sensory neurons expressing the transduction channel TRPM5. J Comp Neurol. 2012;520(8):1819-30. doi: 10.1002/cne.23015. PubMed PMID: 22120520; PubMed Central PMCID: PMC3716388.