Biology Faculty: John Schmidt

John Schmidt

Professor of Biological Sciences; Director of Center for Neuroscience Research
PhD, University of Michigan

Office BI121A
Telephone (518) 442-4309
Fax (518) 442-4767

Areas of Interest

  • Developmental Neurobiology
  • Development of Retinotopic Maps in Zebrafish
  • Activity-Driven Refinement of Retinotectal Synapses
  • Expression of Genes in Retinal Projections as GFP Fusion Proteins
  • Timelapse Imaging and Dynamic Analysis of Growth
  • Actin, Myosin and Growth Cone Motility
  • Myosin Light Chain Kinase, Rho kinase



Research in my laboratory centers on activity-driven refinement of retinotectal projection in zebrafish:
Visual activity, acting via NMDA receptors, refines developing retinotectal maps by shaping retinal arbors. Initially, retinal axons emit many transient side branches along the shaft (resembling a "bottlebrush"), but some branches are stabilized and branch further to give a mature arbor. When MK801 blocks NMDA receptors, dynamic rates of branch addition and deletion increase twofold, as if this prevents release of a stabilizing signal. Ca ++ entry through NMDARs is known to activate phospholipase A2 (cPLA2, a PSD protein) to release arachidonic acid (AA), a putative retrograde signal (Bliss & Collingridge, Nature 1993). AA released by a second enzyme (DAG lipase) mediates L1, NCAM, N-cadherin and FGF stimulation of axon growth via protein kinase C (PKC) activation and GAP-43 phosphorylation to stabilize F-actin (Meiri et al. J Neurosci.1998). We propose that postsynaptic cPLA2 releases AA as a retrograde signal to tap into this presynaptic growth control mechanism.

We previously reported that blocking either presynaptic PKC or DAG lipase causes increased branch turnover like MK801, but additionally causes arbors to remain immature due to interruption of the growth pathway. We have blocked AA release from cPLA2 by injecting into tectal ventricle either a selective pharmacological inhibitor (AACOCF3) or an antisense oligo to suppress expression. Both methods increased branch turnover without effect on arbor maturation (below), a result more similar to that of blocking NMDA receptors. Scrambled oligos had no effect. Injection of the antisense oligo into eye to suppress only presynaptic cPLA2 produced no effect, suggesting a role for postsynaptic cPLA2. After MK801 treatment, exogenous AA reversed the increase in dynamic rates (bar graph).

Axons exposed to antisense oligos
Graph of results

Finally, we are using the fluorogenic cPLA2 substrate PED6 (Mol. Probes) to show that trains of spikes (driven by strobe illumination) activate tectal cPLA2. The results implicate the cPLA2-AA-PKC-GAP43 pathway as a part of an F-actin based mechanism of synaptic stabilization.

research picture

Next, we used DNA constructs to express GAP-43 in retinal ganglion cells as GFP(green fluorescent protein) fusion proteins and assessing the effects on retinal arbor morphology (below). Injection into fertilized eggs results in scattered GFP expression in neurons, including ganglion cells in the eye (A), and their axons can be seen exiting in the optic nerve head and forming arbors in brain (arrows in B and C). GAP43-GFP fusion proteins can also be expressed in axons and observed in time-lapse at half hour intervals (D1 through 4).

Neurons expressing GFP

These arbors expressing excess GAP43 were abnormally large (see figure below). However, if the protein kinase C phosphorylation site was mutated from serine to alanine (which cannot be phosphorylated), then the arbors did not grow and remained immature. This demonstrated that it was not the level of the protein that mattered, but only the form that was in the phosphorylated state. In addition to growth, the phosphorylated GAP43 cause increased branching.

We are now investigating whether the polarity complex, which contains an atypical PKC, might also be involved in branch formation. The polarity complex, which is necessary for initial axon formation, includes Par3, Par6, cdc42 and atypical protein kinase C (aPKCz) and is recruited and assembled at the growing axon tip by PI3 Kinase (phosphatidyl-inositol-3-kinase). The complex forms a positive feedback loop downstream of PI3 Kinase and organizes both the microtubule and F-actin cytoskeletons.  The activity of the aPKCz is essential for polarity complex activation, and it can be activated by retrograde AA signaling. PI3Kinase, which both recruits and is the upstream activator of the polarity complex, was also tested for involvement in branch formation. The results showed that few branches could be formed when any of these were blocked or expression suppressed. These results suggest a portion of the pathways through which activity can affect the growth and branching of retinotectal arbors.


  • Schmidt, JT, Apraku, E, Mariconda, L & Morillo, F (2014) Evidence for involvement of the polarity complex, PI3 Kinase and Protin Kinase C in retinotectal arbor branching. (In preparation)
  • Leu, BH, Koch, E & Schmidt, JT (2010) GAP43 phosphorylation is critical for growth and branching of retinotectal arbors in zebrafish. Developmental Neurobiology 70: 897-911.
  • Leu, B.H. & Schmidt, J.T. (2008) Arachidonic acid as a retrograde signal controlling growth and dynamics of retinotectal arbors. Developmental Neurobiology 68:18-30.
  • Ghiradella, H. & Schmidt, J.T. (2008) Lighting a cold lantern: Flash control in the firefly. In Encyclopedia of Entymology, J. Capinara (ed.) Springer-Verlag, Berlin.
  • Ghiradella, H. & Schmidt, J.T. (2004) Fireflies at one hundred plus: A new look at flash control. In J.S. Edwards (ed), Fireflies at Fifty, Integrative and Comparative Biology 44:203-212.
  • Schmidt, J.T. (2004) Activity-Driven Sharpening of the Retinotectal Projection: The search for Retrograde Synaptic Signaling Pathways. J. Neurobiology, Special Issue in Honor of Friedrich Bonhoeffer 59: 114-133.
  • Schmidt, J.T., Fleming, M.R. & Leu, B.H. (2004) Presynaptic Protein Kinase C Controls Maturation and Branch Dynamics of Developing Retinotectal Arbors: Possible role in activity-driven sharpening J. Neurobiology, 58: 328-340.
  • Schmidt, J.T., Morgan, P., Dowell, N. & Leu, B-H. (2002) Myosin Light Chain Phosphorylation and Growth Cone Motility. J. Neurobiology 52: 175-188.
  • Schmidt, J.T., Buzzard, M., Borress, R. & Dhillon, S. (2000). MK801 increases retinotectal arbor size in developing zebrafish without affecting kinetics of branch elimination and addition. Journal of Neurobiology 42, 303-314.
  • From the Archives (<2000):
  • Easter, S.S. & Schmidt, J.T. (1977). Reversed visuomotor behavior mediated by induced ipsilateral retinal projections in goldfish. Journal of Neurophysiology 40, 1245-1254.
  • Springer, A.D., Heacock, A.M., Schmidt, J.T. & Agranoff, B.W. (1977). Bilateral tectal innervation by regenerating optic nerve fibers in goldfish: a radioautographic, electrophysiological and behavioral study. Brain Research 128, 417-427.
  • Schmidt, J.T. (1978). Retinal fibers alter tectal positional markers during the expansion of the half retinal projection in goldfish. Journal of Comparative Neurology 177, 279-300.
  • Schmidt, J.T. & Easter, S.S. (1978). Independent biaxial reorganization of the retinotectal projection: a reassessment. Experimental Brain Research 31, 155-162.
  • Easter, S.S., Schmidt, J.T. & Leber, S.M. (1978). The paths and destinations of the induced ipsilateral retinal projection in goldfish. Journal of Embryology and Experimental Morphology 45, 145-159.
  • Schmidt, J.T. (1979). The laminar organization of optic fibers in the tectum of goldfish. Proceedings of the Royal Society of London [Biology] 205, 287-306.
  • Freeman, J.A., Schmidt, J.T. & Oswald, R.E. (1980). Effect of a-bungarotoxin on retinotectal synaptic transmission in the goldfish and the toad. Neuroscience 5, 929-942.
  • Oswald, R.E., Schmidt, J.T., Norden, J.J. & Freeman, J.A. (1980). Localization of a-bungarotoxin binding sites to the goldfish retinotectal projection. Brain Research 187, 113-127.
  • Schmidt, J.T. & Freeman, J.A. (1980). Electrophysiologic evidence that the retinotectal projection in the goldfish is nicotinic cholinergic. Brain Research 187, 129-142.
  • Schmidt, J.T., Edwards, D.L. & Stuermer, C.A.O. (1983). The re-establishment of synaptic transmission by regenerating optic axons in goldfish: Time course and effects of blocking activity by intraocular injection of tetrodotoxin. Brain Research 269, 15-27.
  • Schmidt, J.T. (1983). Regeneration of the retinotectal projection following compression onto a half tectum in goldfish. Journal of Embryology and Experimental Morphology 77, 39-51.
  • Schmidt, J.T. & Edwards, D.L. (1983). Activity sharpens the map during the regeneration of the retinotectal projection in goldfish. Brain Research 269, 29-39.
  • Boss, V.C. & Schmidt, J.T. (1984). Activity and the formation of ocular dominance patches in dually innervated tectum of goldfish. Journal of Neuroscience 4, 2891-2905.
  • Schmidt, J.T. (1985). Apparent movement of optic terminals out of a local postsynaptically blocked region in goldfish tectum. Journal of Neurophysiology 53, 237-251.
  • Schmidt, J.T. & Tieman, S.B. (1985). Eye-specific segregation of optic afferents in mammals, fish, and frogs: the role of activity. Cellular and Molecular Neurobiology 5, 5-34.
  • Schmidt, J.T. (1985). Factors involved in retinotopic map formation: Complementary roles for membrane recognition and activity-dependent synaptic stabilization. In Molecular Basis of Neural Development, ed. Edelman, G.M., Gall, W.E., & Cowan, W.M., Neurosciences Research Foundation.
  • Schmidt, J.T. & Eisele, L.E. (1985). Stroboscopic illumination and dark rearing block the sharpening of the regenerated retinotectal map in goldfish. Neuroscience 14, 535-546.
  • Schmidt, J.T. (1985). Formation of retinotopic connections: Selective stablization by an activity-dependent mechanism. Cellular and Molecular Neurobiology 5, 65-83.
  • Schmidt, J.T. (1985). Activity-dependent synaptic stabilization in development and learning: how similar the mechanisms? Cellular and Molecular Neurobiology 5, 1-3.
  • Schmidt, J.T. (1985). Selective stabilization of retinotectal synapses by an activity- dependent mechanism. Federation Proceedings 44, 2767-2772.
  • Schmidt, J.T., Eisele, L.E., Turcotte, J.C. & Tieman, D.G. (1986). Selective stabilization of retinotectal synapses by activity dependent mechanism. In Adaptive Processes in Visual and Oculomotor Systems, ed. Keller, E.L. & Zee, D.S., 63-70. New York: Pergamon Press.
  • Tieman, D.G., Murphey, R.K., Schmidt, J.T. & Tieman, S.B. (1986). A computer-assisted video technique for preparing high resolution pictures and stereograms from thick specimens. Journal of Neuroscience Methods 17, 231-245.
  • Benowitz, L.I. & Schmidt, J.T. (1987). Activity-dependent sharpening of the regenerating retinotectal projection in goldfish: relationship to the expression of growth- associated proteins. Brain Research 417, 118-126.
  • Eisele, L.E. & Schmidt, J.T. (1988). Activity sharpens the regenerating retinotectal projection in goldfish: sensitive period for strobe illumination and lack of effect on synaptogenesis and on ganglion cell receptive field properties. Journal of Neurobiology 19, 395-411.
  • Schmidt, J.T. & Shashoua, V.E. (1988). Antibodies to ependymin block the sharpening of the regenerating retinotectal projection in goldfish. Brain Research 446, 269-284.
  • Schmidt, J.T., Turcotte, J.C., Buzzard, M. & Tieman, D.G. (1988). Morphology of regenerated optic arbors in goldfish tectum. Journal of Comparative Neurology 269, 565-591.
  • Schmidt, J.T. & Tieman, S.B. (1989). Activity, growth cones and the selectivity of visual connections. Comments on Developmental Neurobiology 1, 11-28.
  • Schmidt, J.T. (1990). Long-term potentiation and activity-dependent retinotopic sharpening in the regenerating retinotectal projection of goldfish: Common sensitive period and sensitivity to NMDA blockers. Journal of Neuroscience 10, 233-246.
  • Schmidt, J.T. & Buzzard, M. (1990). Activity-driven sharpening of the regenerating retinotectal projection: Effects of blocking or synchronizing activity on the morphology of individual regenerating arbors. Journal of Neurobiology 21, 900-917.
  • Reich, J.B., Burmeister, D.W., Schmidt, J.T. & Grafstein, B. (1990). Effect of conditioning lesions on regeneration of goldfish optic axons: time course of the cell body reaction to axotomy. Brain Research 515, 256-260.
  • Wolpaw, J.R. & Schmidt, J.T. (1991). Preface. Annals of the New York Academy of Sciences 627, ix-xi
  • Schmidt, J.T. (1991). Long-term potentiation and activity driven retinotopic sharpening in the regenerating retinotectal projection of goldfish. Annals of the New York Academy of Sciences 627, 10-25.
  • Schmidt, J.T., Schmidt, R., Lin, W., Jian, X. & Stuermer, C.A.O. (1991). Ependymin as a substrate for outgrowth of axons from cultured explants of goldfish retina. Journal of Neurobiology 22, 40-54.
  • Schmidt, J.T. (1991). Effects of blocking or synchronizing activity on the morphology of individual regenerating arbors in the goldfish retinotectal projection. Annals of the New York Academy of Sciences 627, 385-389.
  • Wolpaw, J.R., Schmidt, J.T. & Vaughan, T.M. (1991) Activity Driven CNS changes in learning and develoment. Edited conference proceedings, Annals of the New York Academy of Sciences, vol. 627, 1-399.
  • King, W.M. & Schmidt, J.T. (1991). A cholinergic circuit intrinsic to optic tectum modulates retinotectal transmission via presynaptic nicotinic receptors. Annals of the New York Academy of Sciences 627, 363-367.
  • King, W.M. & Schmidt, J.T. (1991). The long latency component of retinotectal transmission: Enhancement by stimulation of nucleus isthmi or tectobulbar tract and block by nicotinic cholinergic antagonists. Neuroscience 40, 701-712.
  • King, W.M. & Schmidt, J.T. (1993). Nucleus isthmi in goldfish: In vitro recordings and fiber connections revealed by HRP injections. Visual Neuroscience 10, 419-437.
  • Schmidt, J.T. & Buzzard, M. (1993). Activity-driven sharpening of the retinotectal projection in goldfish: Development under stroboscopic illumination prevents sharpening. Journal of Neurobiology 24, 384-399.
  • Schmidt, J.T. (1994). C-kinase manipulations disrupt activity-driven retinotopic sharpening in regenerating goldfish retinotectal projection. Journal of Neurobiology 25, 555-570.
  • Jian, X., Hidaka, H. & Schmidt, J.T. (1994). Kinase requirement for retinal growth cone motility. Journal of Neurobiology 25, 1310-1328.
  • Jian, X., Hidaka, H. & Schmidt, J.T. (1994). Kinase requirement for retinal growth cone motility. Journal of Neurobiology 25, 1310-1328.
  • Schmidt, J. & Coen, T. (1995). Changes in retinal arbors in compressed projections to half tecta in goldfish. Journal of Neurobiology 28, 409-418.
  • Schmidt, J.T. (1995). The modulatory cholinergic system in goldfish tectum may be necessary for retinotopic sharpening. Visual Neuroscience 12, 1093-1103.
  • Schmidt, J.T. & Lemere, C.A. (1996). Rapid activity-dependent sprouting of optic fibers into a local area denervated by application of beta-bungarotoxin in goldfish tectum. Journal of Neurobiology 29, 75-90.
  • Jian, X., Szaro, B.G. & Schmidt, J.T. (1996). Myosin light chain kinase: Expression in neurons and upregulation during axon regeneration. Journal of Neurobiology 31, 379-391.
  • Schmidt, J.T. (1998). Up-regulation of protein kinase C in regenerating optic nerve fibers of goldfish: Immunohistochemistry and kinase activity assay. Journal of Neurobiology 36, 315-324.
  • Schmidt, J.T. & Schachner, M. (1998). Role for cell adhesion and glycosyl (HNK-1 and oligomannoside) recognition in the sharpening of the regenerating retinotectal projection in goldfish. Journal of Neurobiology 37, 659-671.
  • Zhang, C.Y. & Schmidt, J.T. (1998). Adenosine A2 receptors mediate retinotectal presynaptic inhibition: Uncoupling by C-kinase and role in LTP during regeneration. Journal of Neurophysiology 79, 501-510.
  • Zhang, C.Y. & Schmidt, J.T. (1999). Adenosine A1 and class II metabotropic glutamate receptors mediate shared presynaptic inhibition of retinotectal transmission. Journal of Neurophysiology 82, 2947-2955.