A requirement for local protein synthesis in neurotrophin-induced hippocampal synaptic plasticity

Science

Volumn 273, Issue 5280, 1996, Pages 1402-1406

  Kang, Hyejin ^a   Schuman, Erin M ^a  

^a CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

BRAIN DERIVED NEUROTROPHIC FACTOR; NEUROTROPHIN 3;

ANIMAL TISSUE; ARTICLE; CONTROLLED STUDY; HIPPOCAMPUS; NERVE CELL PLASTICITY; NONHUMAN; PRIORITY JOURNAL; PROTEIN DETERMINATION; PROTEIN EXPRESSION; PROTEIN SYNTHESIS; RAT; SYNAPTIC TRANSMISSION;

EID: 0029794770     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.273.5280.1402     Document Type: Article

References (63)

1. S. Otani, C. J. Marshall, W. P. Tate, G. V. Goddard, W. C. Abraham, Neuroscience 28, 519 (1989); M. Krug, B. Loessner, T. Ott, Brain Res. Bull. 13, 39 (1984); P. G. Montarolo et al., Science 234, 1249 (1986); P. V, Nguyen, T. Abel, E. R. Kandel, ibid. 265, 1104 (1994).
2. S. Otani, C. J. Marshall, W. P. Tate, G. V. Goddard, W. C. Abraham, Neuroscience 28, 519 (1989); M. Krug, B. Loessner, T. Ott, Brain Res. Bull. 13, 39 (1984); P. G. Montarolo et al., Science 234, 1249 (1986); P. V, Nguyen, T. Abel, E. R. Kandel, ibid. 265, 1104 (1994).
3. S. Otani, C. J. Marshall, W. P. Tate, G. V. Goddard, W. C. Abraham, Neuroscience 28, 519 (1989); M. Krug, B. Loessner, T. Ott, Brain Res. Bull. 13, 39 (1984); P. G. Montarolo et al., Science 234, 1249 (1986); P. V, Nguyen, T. Abel, E. R. Kandel, ibid. 265, 1104 (1994).
4. S. Otani, C. J. Marshall, W. P. Tate, G. V. Goddard, W. C. Abraham, Neuroscience 28, 519 (1989); M. Krug, B. Loessner, T. Ott, Brain Res. Bull. 13, 39 (1984); P. G. Montarolo et al., Science 234, 1249 (1986); P. V, Nguyen, T. Abel, E. R. Kandel, ibid. 265, 1104 (1994).
5. P, K. Stanton and J. M, Sarvey, J. Neurosci. 4, 3080 (1984); P, Osten, L. Valsamis, A. Harris, T. C. Sacktor, ibid. 16, 2444 (1996).
6. P, K. Stanton and J. M, Sarvey, J. Neurosci. 4, 3080 (1984); P, Osten, L. Valsamis, A. Harris, T. C. Sacktor, ibid. 16, 2444 (1996).
7. H, P. Davis and L. R. Squire, Psychol. Bull. 96, 518 (1984); V. F. Castellucci, H. Blumenfeld, P. Goelet, E. R. Kandel, J. Neurobiol. 20, 1 (1989); T. Tully, T. Preat, S. C. Boynton, M. Del Vecchio, Cell 79, 35 (1994).
8. H, P. Davis and L. R. Squire, Psychol. Bull. 96, 518 (1984); V. F. Castellucci, H. Blumenfeld, P. Goelet, E. R. Kandel, J. Neurobiol. 20, 1 (1989); T. Tully, T. Preat, S. C. Boynton, M. Del Vecchio, Cell 79, 35 (1994).
9. H, P. Davis and L. R. Squire, Psychol. Bull. 96, 518 (1984); V. F. Castellucci, H. Blumenfeld, P. Goelet, E. R. Kandel, J. Neurobiol. 20, 1 (1989); T. Tully, T. Preat, S. C. Boynton, M. Del Vecchio, Cell 79, 35 (1994).
10. A. M. Lohof, N. Ip, M.-M. Poo, Nature 363, 350 (1993); E. S. Levine, C. F. Dreyfus, I. B. Black, M. R. Plummer, Proc. Natl. Acad. Sci. U.S.A. 92, 8074 (1995); H. Kang and E. M. Schuman, Science 267, 1658 (1995). Recently, however, two groups [S. L. Patterson et al., Neuron 16, 1137 (1996); A. Figurov, L. D. Pozzo-Miller, P. Olafson, T. Wang, B. Lu, Nature 381, 706 (1996)] have shown that BDNF perfused at slow flow rates ( 10 to 25 ml/hour) in interface chambers did not independently enhance synaptic strength in hippocampal slices. Under these experimental conditions, Patterson et al. showed that incubation with BDNF for several hours was required before BDNF could be detected immunohistochemically in the depth of the slice. Our own studies (H. Kang, L. N. Jia, K. Y. Suh, L. Tang, E. M. Schuman, Learn. Mem., in press) confirmed these observations and indicated that BDNF introduced at a low perfusion rate (25 ml/hour) penetrates the tissue slowly and does not result in synaptic enhancement.
11. A. M. Lohof, N. Ip, M.-M. Poo, Nature 363, 350 (1993); E. S. Levine, C. F. Dreyfus, I. B. Black, M. R. Plummer, Proc. Natl. Acad. Sci. U.S.A. 92, 8074 (1995); H. Kang and E. M. Schuman, Science 267, 1658 (1995). Recently, however, two groups [S. L. Patterson et al., Neuron 16, 1137 (1996); A. Figurov, L. D. Pozzo-Miller, P. Olafson, T. Wang, B. Lu, Nature 381, 706 (1996)] have shown that BDNF perfused at slow flow rates ( 10 to 25 ml/hour) in interface chambers did not independently enhance synaptic strength in hippocampal slices. Under these experimental conditions, Patterson et al. showed that incubation with BDNF for several hours was required before BDNF could be detected immunohistochemically in the depth of the slice. Our own studies (H. Kang, L. N. Jia, K. Y. Suh, L. Tang, E. M. Schuman, Learn. Mem., in press) confirmed these observations and indicated that BDNF introduced at a low perfusion rate (25 ml/hour) penetrates the tissue slowly and does not result in synaptic enhancement.
12. A. M. Lohof, N. Ip, M.-M. Poo, Nature 363, 350 (1993); E. S. Levine, C. F. Dreyfus, I. B. Black, M. R. Plummer, Proc. Natl. Acad. Sci. U.S.A. 92, 8074 (1995); H. Kang and E. M. Schuman, Science 267, 1658 (1995). Recently, however, two groups [S. L. Patterson et al., Neuron 16, 1137 (1996); A. Figurov, L. D. Pozzo-Miller, P. Olafson, T. Wang, B. Lu, Nature 381, 706 (1996)] have shown that BDNF perfused at slow flow rates ( 10 to 25 ml/hour) in interface chambers did not independently enhance synaptic strength in hippocampal slices. Under these experimental conditions, Patterson et al. showed that incubation with BDNF for several hours was required before BDNF could be detected immunohistochemically in the depth of the slice. Our own studies (H. Kang, L. N. Jia, K. Y. Suh, L. Tang, E. M. Schuman, Learn. Mem., in press) confirmed these observations and indicated that BDNF introduced at a low perfusion rate (25 ml/hour) penetrates the tissue slowly and does not result in synaptic enhancement.
13. A. M. Lohof, N. Ip, M.-M. Poo, Nature 363, 350 (1993); E. S. Levine, C. F. Dreyfus, I. B. Black, M. R. Plummer, Proc. Natl. Acad. Sci. U.S.A. 92, 8074 (1995); H. Kang and E. M. Schuman, Science 267, 1658 (1995). Recently, however, two groups [S. L. Patterson et al., Neuron 16, 1137 (1996); A. Figurov, L. D. Pozzo-Miller, P. Olafson, T. Wang, B. Lu, Nature 381, 706 (1996)] have shown that BDNF perfused at slow flow rates ( 10 to 25 ml/hour) in interface chambers did not independently enhance synaptic strength in hippocampal slices. Under these experimental conditions, Patterson et al. showed that incubation with BDNF for several hours was required before BDNF could be detected immunohistochemically in the depth of the slice. Our own studies (H. Kang, L. N. Jia, K. Y. Suh, L. Tang, E. M. Schuman, Learn. Mem., in press) confirmed these observations and indicated that BDNF introduced at a low perfusion rate (25 ml/hour) penetrates the tissue slowly and does not result in synaptic enhancement.
14. A. M. Lohof, N. Ip, M.-M. Poo, Nature 363, 350 (1993); E. S. Levine, C. F. Dreyfus, I. B. Black, M. R. Plummer, Proc. Natl. Acad. Sci. U.S.A. 92, 8074 (1995); H. Kang and E. M. Schuman, Science 267, 1658 (1995). Recently, however, two groups [S. L. Patterson et al., Neuron 16, 1137 (1996); A. Figurov, L. D. Pozzo-Miller, P. Olafson, T. Wang, B. Lu, Nature 381, 706 (1996)] have shown that BDNF perfused at slow flow rates ( 10 to 25 ml/hour) in interface chambers did not independently enhance synaptic strength in hippocampal slices. Under these experimental conditions, Patterson et al. showed that incubation with BDNF for several hours was required before BDNF could be detected immunohistochemically in the depth of the slice. Our own studies (H. Kang, L. N. Jia, K. Y. Suh, L. Tang, E. M. Schuman, Learn. Mem., in press) confirmed these observations and indicated that BDNF introduced at a low perfusion rate (25 ml/hour) penetrates the tissue slowly and does not result in synaptic enhancement.
15. A. M. Lohof, N. Ip, M.-M. Poo, Nature 363, 350 (1993); E. S. Levine, C. F. Dreyfus, I. B. Black, M. R. Plummer, Proc. Natl. Acad. Sci. U.S.A. 92, 8074 (1995); H. Kang and E. M. Schuman, Science 267, 1658 (1995). Recently, however, two groups [S. L. Patterson et al., Neuron 16, 1137 (1996); A. Figurov, L. D. Pozzo-Miller, P. Olafson, T. Wang, B. Lu, Nature 381, 706 (1996)] have shown that BDNF perfused at slow flow rates ( 10 to 25 ml/hour) in interface chambers did not independently enhance synaptic strength in hippocampal slices. Under these experimental conditions, Patterson et al. showed that incubation with BDNF for several hours was required before BDNF could be detected immunohistochemically in the depth of the slice. Our own studies (H. Kang, L. N. Jia, K. Y. Suh, L. Tang, E. M. Schuman, Learn. Mem., in press) confirmed these observations and indicated that BDNF introduced at a low perfusion rate (25 ml/hour) penetrates the tissue slowly and does not result in synaptic enhancement.
16. 2. The initial slope (1 to 2 ms) of field excitatory postsynaptic potentials (EPSPs) evoked by stimulation of the Schaffer collateral- commissural afferents (once every 15 s) was measured in the stratum radiatum at a depth of 100 to 150 μm below the slice surface. The application and storage of the neurotrophic factors were as previously described (4). Anisomycin and cycloheximide were maintained as 40 mM stock solutions in ethanol at 4°C. The final concentration (0.1%) of ethanol to which the slices were exposed had no detectable effect on synaptic transmission. All experiments with protein synthesis inhibitors were paired with a same-day control experiment in which BDNF or NT-3 potentiated synaptic transmission. Inhibitors were applied at least 30 min before the addition of neurotrophin. BDNF and NT-3 potentiated synaptic strength at least 30% in 84.4 and 83.7% of control experiments, respectively. The percent of baseline measurements indicated in the text were obtained 170 to 180 min after the application of neurotrophin, unless otherwise noted. Ensemble average plots represent group means of each EPSP slope, for all experiments, aligned with respect to the time of neurotrophin application. Statistical significance was assessed by paired f tests or one-way analysis of variance; a P value of < 0.05 was considered statistically significant.
17. 3H]leucine into trichloroacetic acid-precipitable material. When compared to controls, anisomycin and cycloheximide inhibited protein synthesis by 71.9 ± 5.2 and 71.2 ± 6.0%, respectively (n = 4 for each inhibitor).
18. S. Feig and P. Lipton [J, Neurosci. 13, 1010 (1993)] estimated that the minimal time required for somatically synthesized protein to reach the dendritic region is 5 to 10 min at physiological temperature. This transport time would be substantially increased at room temperature.
19. O. Steward and W. B. Levy, J. Neurosci. 2, 284 (1982); K. M. Harris and J. Spacek, Soc. Neurosci. Abstr. 21, 594 (1995).
20. O. Steward and W. B. Levy, J. Neurosci. 2, 284 (1982); K. M. Harris and J. Spacek, Soc. Neurosci. Abstr. 21, 594 (1995).
21. Pyramidal neurons were disconnected from the stratum radiatum with a small microdissection knife visualized under a dissecting microscope. Sham lesions were introduced as a single vertical cut through both the upper and lower blades of the dentate gyrus. The microlesions were performed 1 hour after preparation of the hippocampal slices, Lesioned slices were allowed to recover for at least 2 hours before electrophysiological recording. Only those lesioned slices that required stimuli of < 220 μA to produce a field EPSP slope of 0.1 mV/ms were used. The average stimulus size in control and lesion experiments was 90.1 and 123.1 μA, respectively. Complete dissociation of the cell bodies from the neuropil was confirmed by cresyl violet staining. Sections were visualized with a Zeiss Axioplan microscope (2.5X objective).
22. U. Frey, M. Krug, R, Brodemann, K. Reymann, H. Matthies, Neurosci. Lett. 97, 135 (1989).
23. J. C. Lauterborn, T. M. D. Tran, P. J. Isackson, C. M. Gall, NeuroReport 5, 273; D. Amaral, personal communication.
24. J. C. Lauterborn, T. M. D. Tran, P. J. Isackson, C. M. Gall, NeuroReport 5, 273; D. Amaral, personal communication.
25. The isolation of either CA3 or CA1 cell bodies also allowed assessment of the relative importance of somatic gene transcription and translation in the pre- and postsynaptic neurons, respectively. In the CA3 isolation experiments, the synaptic enhancement induced by either BDNF or NT-3 did not differ in magnitude or duration from that observed in the sham-lesioned slices (Fig. 2, C and D). However, in the CA1 isolation experiments, the late phase of the neurotrophin-induced potentiation was significantly reduced relative to that apparent in controls (P < 0.05), although the duration was unchanged (Fig. 3, C and D). On the basis of these observations, postsynaptic somatic transcription or translation, or both, appear to be required at times greater than 1 hour after neurotrophin application.
26. C. A. Altar et al., & Eur. J. Neurosci. 6, 1389 (1994); S. Marty et al., J, Neurosci. 16, 675 (1996),
27. C. A. Altar et al., & Eur. J. Neurosci. 6, 1389 (1994); S. Marty et al., J, Neurosci. 16, 675 (1996),
28. A receptor antagonist bicuculline [mean percent of baseline at 80 to 90 min: BDNF plus bicuculline, 192.5 ± 13.7 (n = 6), P < 0.001 ; NT-3 plus bicuculline, 188.2 ± 16.0 (n = 6), P < 0.001). However, another group [H. G. Kim, T. Wang, P. Olafsson, B. Lu, Proc. Natl. Acad. Sci, U.S.A 91, 12341 (1994)] has shown that NT-3 can modulate GABAergic transmission in cultured cortical neurons.
29. TRKB immunostaining has been observed in glia in the fimbria [X. F. Zhou, L F. Parada, D. Soppet, R. A. Rush. Brain Res. 622, 189 (1993)], but appears to be absent from glia in the CA3-CA1 synaptic neuropil (X. F. Zhou and R. A. Rush, personal communication).
30. TRKB immunostaining has been observed in glia in the fimbria [X. F. Zhou, L F. Parada, D. Soppet, R. A. Rush. Brain Res. 622, 189 (1993)], but appears to be absent from glia in the CA3-CA1 synaptic neuropil (X. F. Zhou and R. A. Rush, personal communication).
31. F. Lamballe, R. J. Smeyne, M. Barbacid, J. Neurosci. 14, 14 (1994); N. Y. Ip, Y, Li, G. D. Yancopoulos, R. M. Lindsay, ibid 13, 3394 (1993); J. P. Merlio. P. Ernfors, M. Jaber, H. Persson, Neuroscience 51, 513 (1992).
32. F. Lamballe, R. J. Smeyne, M. Barbacid, J. Neurosci. 14, 14 (1994); N. Y. Ip, Y, Li, G. D. Yancopoulos, R. M. Lindsay, ibid 13, 3394 (1993); J. P. Merlio. P. Ernfors, M. Jaber, H. Persson, Neuroscience 51, 513 (1992).
33. F. Lamballe, R. J. Smeyne, M. Barbacid, J. Neurosci. 14, 14 (1994); N. Y. Ip, Y, Li, G. D. Yancopoulos, R. M. Lindsay, ibid 13, 3394 (1993); J. P. Merlio. P. Ernfors, M. Jaber, H. Persson, Neuroscience 51, 513 (1992).
34. R. Vassar et al., Cell 79, 981 (1994); K. J. Ressler, S. L, Sullivan, L B, Buck, ibid., p. 1245; E. Mohr, S. Fehr, D. Richter, EMBO J. 10, 786 (1991); A. E. Gioio et al., J. Neurochem. 63, 13 (1994); L. Davis. P, Dou, M. DeWit, S. B. Kater, J. Neurosci. 12, 4867 (1992); R. Kleiman.G. Banker, O. Steward, ibid. 14, 1130 (1994).
35. R. Vassar et al., Cell 79, 981 (1994); K. J. Ressler, S. L, Sullivan, L B, Buck, ibid., p. 1245; E. Mohr, S. Fehr, D. Richter, EMBO J. 10, 786 (1991); A. E. Gioio et al., J. Neurochem. 63, 13 (1994); L. Davis. P, Dou, M. DeWit, S. B. Kater, J. Neurosci. 12, 4867 (1992); R. Kleiman.G. Banker, O. Steward, ibid. 14, 1130 (1994).
36. R. Vassar et al., Cell 79, 981 (1994); K. J. Ressler, S. L, Sullivan, L B, Buck, ibid., p. 1245; E. Mohr, S. Fehr, D. Richter, EMBO J. 10, 786 (1991); A. E. Gioio et al., J. Neurochem. 63, 13 (1994); L. Davis. P, Dou, M. DeWit, S. B. Kater, J. Neurosci. 12, 4867 (1992); R. Kleiman.G. Banker, O. Steward, ibid. 14, 1130 (1994).
37. R. Vassar et al., Cell 79, 981 (1994); K. J. Ressler, S. L, Sullivan, L B, Buck, ibid., p. 1245; E. Mohr, S. Fehr, D. Richter, EMBO J. 10, 786 (1991); A. E. Gioio et al., J. Neurochem. 63, 13 (1994); L. Davis. P, Dou, M. DeWit, S. B. Kater, J. Neurosci. 12, 4867 (1992); R. Kleiman.G. Banker, O. Steward, ibid. 14, 1130 (1994).
38. R. Vassar et al., Cell 79, 981 (1994); K. J. Ressler, S. L, Sullivan, L B, Buck, ibid., p. 1245; E. Mohr, S. Fehr, D. Richter, EMBO J. 10, 786 (1991); A. E. Gioio et al., J. Neurochem. 63, 13 (1994); L. Davis. P, Dou, M. DeWit, S. B. Kater, J. Neurosci. 12, 4867 (1992); R. Kleiman.G. Banker, O. Steward, ibid. 14, 1130 (1994).
39. R. Vassar et al., Cell 79, 981 (1994); K. J. Ressler, S. L, Sullivan, L B, Buck, ibid., p. 1245; E. Mohr, S. Fehr, D. Richter, EMBO J. 10, 786 (1991); A. E. Gioio et al., J. Neurochem. 63, 13 (1994); L. Davis. P, Dou, M. DeWit, S. B. Kater, J. Neurosci. 12, 4867 (1992); R. Kleiman.G. Banker, O. Steward, ibid. 14, 1130 (1994).
40. E. R. Torre and O. Steward, J. Neurosci. 12, 762, (1992).
41. R. Kleiman, G. Banker, O. Steward, Neuron 5, 821 (1990); C. Garner, R. Tucker, A. Matus, Nature 336, 674 (1988); K. E. Burgin et al., J. Neurosci. 10, 1788 (1990); K. Miyashiro, M, Dichter, J. Eberwine, Proc. Natl. Acad Sci. U.S.A. 91, 10800 (1994).
42. R. Kleiman, G. Banker, O. Steward, Neuron 5, 821 (1990); C. Garner, R. Tucker, A. Matus, Nature 336, 674 (1988); K. E. Burgin et al., J. Neurosci. 10, 1788 (1990); K. Miyashiro, M, Dichter, J. Eberwine, Proc. Natl. Acad Sci. U.S.A. 91, 10800 (1994).
43. R. Kleiman, G. Banker, O. Steward, Neuron 5, 821 (1990); C. Garner, R. Tucker, A. Matus, Nature 336, 674 (1988); K. E. Burgin et al., J. Neurosci. 10, 1788 (1990); K. Miyashiro, M, Dichter, J. Eberwine, Proc. Natl. Acad Sci. U.S.A. 91, 10800 (1994).
44. R. Kleiman, G. Banker, O. Steward, Neuron 5, 821 (1990); C. Garner, R. Tucker, A. Matus, Nature 336, 674 (1988); K. E. Burgin et al., J. Neurosci. 10, 1788 (1990); K. Miyashiro, M, Dichter, J. Eberwine, Proc. Natl. Acad Sci. U.S.A. 91, 10800 (1994).
45. A. Rao and O Steward, J. Neurosci, 11, 2881 (1991).
46. H. M. Johntston and B. J. Morris, Mol. Brain Res. 31, 141 (1995); J, Neurochem. 63, 379 (1994); Neurosci. Left. 177, 5 (1994).
47. H. M. Johntston and B. J. Morris, Mol. Brain Res. 31, 141 (1995); J, Neurochem. 63, 379 (1994); Neurosci. Left. 177, 5 (1994).
48. H. M. Johntston and B. J. Morris, Mol. Brain Res. 31, 141 (1995); J, Neurochem. 63, 379 (1994); Neurosci. Left. 177, 5 (1994).
49. Anisomycin had no effect on basal synaptic transmission [mean percent of baseline: 105.7 ± 10.9 (n = 6), NS], the fiber volley amplitude [mean percent of baseline 170 to 180 min after anisomycin, 98.5 ± 5.7 (n = 6\, NS], or posttetanic potentiation after 100-Hz stimulation [mean percent of baseline 1 min after tetanus: 251.9 ± 13.9 before and 254.2 ± 5.8, after anisomycin (n = 4), NS].
50. A. Welcher, H. Kang, E. M. Schuman, unpublished observations.
51. A small extent of neurotrophin-stimulated synaptic enhancement persisted in the presence of anisomycin. Because our in vitro assays indicate that anisomycin inhibited protein synthesis by 72% (6), we cannot determine whether the residual enhancement was truly independent of protein synthesis or simply reflected the incomplete inhibition of protein synthesis by anisomycin.
52. H. N, Marsh et al., J. Neurosci. 13, 4281 (1993).
53. B. Berninger, D. E. Garcia, N Inagaki, C. Hahnel, D. Lindholm, NeuroReport 4, 1303 (1993).
54. L. A. Greene and D. R. Kaplan, Curr. Biol. 5, 579 (1995); R. A. Segal and M. E. Greenberg, Annu Rev. Neurosci. 19, 463 (199B).
55. L. A. Greene and D. R. Kaplan, Curr. Biol. 5, 579 (1995); R. A. Segal and M. E. Greenberg, Annu Rev. Neurosci. 19, 463 (199B).
56. J. N. Jovanovic et al., Proc. Natl. Acad. Sci, U.S.A. 93, 3679 (1996).
57. A. Bloch and H, Thoenen, Eur. J. Neurosci. 7, 1220 (1995).
58. R, J. Cabelli, A. Hohn, C. J. Shatz, Science 267, 1662 (1995); D. R. Riddle, D. C. Lo, L C. Katz, Nature 378, 189 (1995); S. Cohen-Cory and S. E. Fraser, ibid., p. 192; H. Funakoshi et al., Science 268, 1495 (1995); K. Rashid, Proc. Natl. Acad Sci. U.S.A. 92, 9495 (1995).
59. R, J. Cabelli, A. Hohn, C. J. Shatz, Science 267, 1662 (1995); D. R. Riddle, D. C. Lo, L C. Katz, Nature 378, 189 (1995); S. Cohen-Cory and S. E. Fraser, ibid., p. 192; H. Funakoshi et al., Science 268, 1495 (1995); K. Rashid, Proc. Natl. Acad Sci. U.S.A. 92, 9495 (1995).
60. R, J. Cabelli, A. Hohn, C. J. Shatz, Science 267, 1662 (1995); D. R. Riddle, D. C. Lo, L C. Katz, Nature 378, 189 (1995); S. Cohen-Cory and S. E. Fraser, ibid., p. 192; H. Funakoshi et al., Science 268, 1495 (1995); K. Rashid, Proc. Natl. Acad Sci. U.S.A. 92, 9495 (1995).
61. R, J. Cabelli, A. Hohn, C. J. Shatz, Science 267, 1662 (1995); D. R. Riddle, D. C. Lo, L C. Katz, Nature 378, 189 (1995); S. Cohen-Cory and S. E. Fraser, ibid., p. 192; H. Funakoshi et al., Science 268, 1495 (1995); K. Rashid, Proc. Natl. Acad Sci. U.S.A. 92, 9495 (1995).
62. R, J. Cabelli, A. Hohn, C. J. Shatz, Science 267, 1662 (1995); D. R. Riddle, D. C. Lo, L C. Katz, Nature 378, 189 (1995); S. Cohen-Cory and S. E. Fraser, ibid., p. 192; H. Funakoshi et al., Science 268, 1495 (1995); K. Rashid, Proc. Natl. Acad Sci. U.S.A. 92, 9495 (1995).
63. We thank J. Miller and Amgen for supplying BDNF and NT-3, and Caltech faculty and the Schuman lab for helpful discussions and comments. Supported by funds from the Sloan Foundation, John Merck Fund, and Pew Charitable Trusts to E.M.S.