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Larry Morin


Department of Psychiatry and Behavioral Science

Ph.D. Rutgers Univ.

Phone: (631) 444-1613




The rest/activity cycle of mammals is generated by a master clock in the hypothalamic suprachiasmatic nucleus (SCN). This clock provides circadian (approximately 24 hr) timing information to the brain and body. The SCN is the target of 3 major regulatory pathways. It receives direct sensory input from the retina via the retinohypothalamic tract (RHT), a specialized visual pathway, and indirect photic and nonphotic information arriving through the geniculohypothalamic tract (GHT) that originates in the thalamic intergeniculate leaflet (IGL). The IGL itself is directly retinorecipient and is extensively connected to other midbrain visual nuclei. Information is relayed from the IGL to the SCN through neurotensin-, neuropeptide Y-, enkephalin- or GABA-containing neurons. The third major SCN-afferent projection is the raphe serotonergic system. Serotonin modulates the responsiveness of SCN neurons to light. The SCN, under the influence of these and other input pathways, serves to synchronize behavioral and physiological rhythms with the environmental photoperiod. Each of the above brain nuclei has numerous other efferent and afferent connections. The goals of this laboratory are to (A) describe the neuroanatomical sources of input to the circadian rhythm system; (B) discern the functions of those inputs; and (C) understand the efferent pathways by which the circadian clock might regulate the timing of behavior and physiology. The lab has also extended the definition of the circadian rhythm system to include one or more nuclei of the subcortical visual midbrain. We are also studying the structure and function of the vestibular system with respect to circadian rhythm regulation. Of particular interest at the moment is the role of melanopsin-containing retinal ganglion cells with respect to the regulation of circadian rhythms and subcortical visual function. The laboratory recently identified melanopsin-containing retinal ganglion cells innervating the SCN, IGL, pretectum and superior colliculus, and is pursuing the functions of these connections. The laboratory exploits the circadian locomotor rhythm as its primary index of rhythm function. We will continue to apply a wide variety of tract tracing methods, including viral transsynaptic labeling procedures, and advanced light and confocal laser microscopy techniques to identify cell types and connections. The long term goal of this project is to establish comprehensive understanding of the methods and anatomical routes by which various classes of environmental stimuli can modulate phase and period of the circadian clock.

  • Publications
  • Laboratory Personnel
    • Vidal, L. and Morin, L.P. (2007) Absence of normal photic integration in the circadian visual system: Response to millisecond light flashes. J.Neurosci. 27, 3375-3382. (PDF)
    • Morin, L.P. (2007) SCN organization reconsidered. J. Biol. Rhythms, 22, 3-13. (PDF)
    • Muscat, L. and Morin, L.P. (2006) Intergeniculate leaflet: contributions to photic and non-photic responsiveness of the hamster circadian system. Neuroscience, 140, 305-320. (PDF)
    • Morin, L.P. and Allen, C.N. (2006) The circadian visual system, 2005. Brain Res. Rev. 51, 1-60. (PDF)
    • Morin, L.P., Shivers, K.-T., Blanchard, J.H. and Muscat, L. (2006) Complex Organization of Mouse and Rat Suprachiasmatic Nucleus. Neuroscience 137, 1285-1297. (PDF)
    • Horowitz, S.S., Blanchard, J.H. and Morin, L.P. (2005) Medial vestibular connections with the hypocretin (orexin) system. J. Comp. Neurol., 487, 127-146. (PDF)
    • Morin, L.P. and Blanchard, J.H. (2005) Descending projections of the intergeniculate leaflet: relationship to the sleep/arousal and visuomotor systems. J. Comp. Neurol., 487, 204-216. (PDF)
    • Muscat, L., Tischler, R. and Morin, L.P. (2005) Functional analysis of the role of the median raphe as a regulator of hamster circadian system sensitivity to light. Brain Res. 1044, 59-66. (PDF)
    • Vidal, L. and Morin, L.P. (2005) Hypothalamic and zona incerta neurons expressing hypocretin, but not melanin concentrating hormone, project to the hamster intergeniculate leaflet. Neuroscience, 134, 1081-1090. (PDF)
    • Muscat, L. and Morin, L.P. (2005) Binocular contributions to the sensitivity and integrative capacity of the circadian rhythm system to light. J. Biol. Rhythms, 20, 513-525 (PDF)
    • Horowitz, S.S., Blanchard, J.H. and Morin, L.P. (2004) Intergeniculate leaflet and ventral lateral geniculate nucleus afferent connections: an anatomical substrate for functional input from the vestibulo-visuomotor system. J. Comp. Neurol., 474, 227-245. (PDF)
  • Jane Blanchard - Senior Research Associate
  • Luis Vidal - Postdoctoral Associate