Peripheral Influences on Connectivity in the Developing Rat Trigeminal System

  • Herbert P. Killackey
Part of the NATO Advanced Study Institutes Series book series (NSSA, volume 27)


The trigeminal system of the rat shows a high degree of discrete anatomical organization. I would like to take this opportunity to review the evidence for peripheral influences on the development of this discrete anatomical organization in both the normal animal and in ones which have suffered neonatal receptor damage. In fact, among other things, I would like to demonstrate that the loss of several whiskers can have as severe an effect on the structural organization of the brain as the loss of an eye. In this brief review I will not attempt to be all-inclusive. Rather, I will focus on the contribution that I and my several collaborators have made. The impetus for our studies of the trigeminal system was the report of Woolsey and Van Der Loos (1970) that in the portion of mouse somatosensory neocortex devoted to the vibrissae representation the cells of layer IV are arranged into discrete aggregates which they termed “barrels.” Further, the number and spatial distribution of the “barrels,” as well as physiological evidence (Woolsey, 1967; Welker, 1971), suggested that in both the rat and mouse there was a unique one-to-one relationship between a particular cytoarchitectonic unit, or “barrel,” and a mystacial vibrissae. Given this high degree of functional and structural organization in the neocortical layer where thalamocortical projections terminate, a natural question to ask was whether or not this discrete organization was also reflected in the afferent projections to this cortical layer. Utilizing anterograde degeneration techniques, I was able to determine that in the rat the terminations of the thalamocortical projections to the vibrissae representation portion of somatosensory cortex are indeed arranged into discrete clusters (Killackey, 1973). Further, the spatial distribution of these clusters replicated the distribution of sinus hair and vibrissae follicles on the muzzle of the rat (Killackey and Leshin, 1975). The discrete nature of these thalamocortical projections is relatively unique and contrasts with the continuous distribution of thalamocortical projections to the face region of cortex in such generalized mammalian species as the opossum and hedgehog (Killackey, 1973). Furthermore, thalamocortical projections are continuous in a rodent species which has developed visual specializations and inhabits an arboreal niche, the Eastern grey squirrel (Killackey, 1973). However, other terrestrial rodents in which the vibrissae are well developed, such as the gerbil, also exhibit discontinuous thalamocortical projections. The available evidence would suggest that this is a specialization of the somatosensory system which has chiefly evolved in small rodents (Woolsey, Welker and Schwartz, 1975). Perhaps the somatosensory system is able to provide the most reliable information about the external world to small rodents which are normally very close to the earth’s surface, spend time burrowing beneath the ground, and generally inhabit a niche where both visual and auditory information is limited. In this regard it should be noted that rats and other rodents have evolved Stereotypic patterns of whisker movements, termed “whisking,” which seem to play an extremely important role in their environmental exploration (Vincent, 1912; Welker, 1964).


Somatosensory Cortex Thalamocortical Projection Developmental Neurobiology Thalamocortical Axon Vibrissa Follicle 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Akers, R. M., and H. P. Killackey (1978). Development of segmented corticothalamic projections to the ventrobasal complex of the rat. Soc. for Neurosci. Abstracts 4:547.Google Scholar
  2. Akers, R. M., and H. P. Killackey (1979). Segregation of cortical and trigeminal afferents to the ventrobasal complex of the neonatal rat. Brain Res. 161:527–532.PubMedCrossRefGoogle Scholar
  3. Angel, A., and K. A. Clarke (1975). An analysis of the representation of the forelimb in the ventrobasal thalamic complex of the albino rat. J. Physiol. (Lond.) 249:399–423.Google Scholar
  4. Belford, G. R. (1978). Development of peripherally related segmentation in the ventrobasal complex of the rat. Anat. Rec. 190:336.Google Scholar
  5. Belford, G. R., and H. P. Killackey (1978a). Normal and abnormal segmentation in the trigeminal complex of the young rat. Soc. for Neurosci. Abstracts 4:547.Google Scholar
  6. Belford, G. R., and H. P. Killackey (1978b). Anatomical correlates of the forelimb in the ventrobasal complex and the cuneate nucleus of the neonatal rat. Brain Res. 158:450–455.PubMedCrossRefGoogle Scholar
  7. Belford, G. R., and H. P. Killackey (1979). Vibrissae representation in subcortical trigeminal centers of the neonatal rat. J. Comp. Neur. 185:305–322.CrossRefGoogle Scholar
  8. Hand, P. J., J. H. Greenberg, R. R. Miselis, W. L. Weller, and M. Reivich (1978). A normal and altered cortical column: A quantitative and qualititative (14C)—2 deooxyglucose (2DG) mapping study. Soc. for Neurosci. Abstracts 4:553.Google Scholar
  9. Ivy, G., and H. P. Killackey (1978). Developmental changes in the distribution of the thalamocortical relay cells of the ventrobasal complex of the rat. Soc. for Neurosci. Abstracts 4:554.Google Scholar
  10. Killackey, H. P. (1973). Anatomical evidence for cortical subdivisions based on vertically discrete thalamic projections from the ventral posterior nucleus to cortical barrels in the rat. Brain Res. 51:326–331.PubMedCrossRefGoogle Scholar
  11. Killackey, H. P., and G. Belford (1976). Discrete afferent terminations in the trigeminal pathway of the neonatal rat. Anat. Rec. 184:446.Google Scholar
  12. Killackey, H. P., and G. R. Belford (1979). The formation of afferent patterns in the somatosensory complex of the neonatal rat. J. Comp. Neur. 183:285–304.PubMedCrossRefGoogle Scholar
  13. Killackey, H. P., G. Belford, R. Ryugo, and D. K. Ryugo (1976). Anomalous organization of thalamocortical projections consequent to vibrissae removal in the newborn rat and mouse. Brain Res. 104:309–315.PubMedCrossRefGoogle Scholar
  14. Killackey, H. P., G. O. Ivy, and T. J. Cunningham (1978). Anomalous organization of SMI somatotopic map consequent to vibrissae removal in the newborn rat. Brain Res. 155:136–140.PubMedCrossRefGoogle Scholar
  15. Killackey, H. P., and S. Leshin (1975). The organization of specific thalamocortical projections to the posteromedial barrel subfield of the rat somatic sensory cortex. Brain Res. 86:469–472.PubMedCrossRefGoogle Scholar
  16. Lorente de N′o, R. (1922). La corteza cerebral del raton. Trab. Lab. Invest. Biol. 20:41–78.Google Scholar
  17. Lorente de N′o, R. (1938). Cerebral cortex: Architecture, intracortical connections and motor projections. In: Physiology of the Nervous System, J. F. Fulton (ed.), Oxford University Press, New York, pp. 291–339.Google Scholar
  18. Nord, S. G. (1967). Somatotopic organization in the spinal trigeminal nucleus, the dorsal column nuclei and related structures in the rat. J. Comp. Neur. 130:343–355.PubMedCrossRefGoogle Scholar
  19. Ryugo, D. K., R. Ryugo, and H. P. Killackey (1975). Changes in pyramidal cell density consequent to vibrissae removal in the newborn rat. Brain Res. 96:82–87.PubMedCrossRefGoogle Scholar
  20. Shipley, M. T. (1974). Response characteristics of single units in the rat’s trigeminal nuclei to vibrissa displacements. J. Neurophysiol. 37:73–90.PubMedGoogle Scholar
  21. Smith, R. L. (1973). The ascending fiber projections from the principal sensory trigeminal nucleus in the rat. J. Comp. Neur. 148:423–441.PubMedCrossRefGoogle Scholar
  22. Torvik, A. (1956). Afferent connections to the sensory trigeminal nuclei, the nucleus of the solitary tract and adjacent structures. An experimental study in the rat. J. Comp. Neur. 106:51–132.PubMedCrossRefGoogle Scholar
  23. Valverde, F. (1971). Rate and extent of recovery from dark rearing in the visual cortex of the mouse. Brain Res. 33:1–11.PubMedCrossRefGoogle Scholar
  24. Van Der Loos, H. (1976). Barreloids in mouse somatosensory thalamus. Neurosci. Lett. 2:1–6.CrossRefGoogle Scholar
  25. Van Der Loos, H., and T. A. Woolsey (1973). Somatosensory cortex: Structural alterations following early injury to sense organs. Science 179:395–398.PubMedCrossRefGoogle Scholar
  26. Vincent, S. B. (1912). The function of the vibrissae in the behavior of the white rat. Behavior Monog. 1:7–85.Google Scholar
  27. Waite, P. M. E. (1973). Somatotopic organization of vibrissal responses in the ventrobasal complex of the rat thalamus. J. Physiol. 228:527–540.PubMedGoogle Scholar
  28. Waite, P. M. E., and P. K. Taylor (1978). Removal of whiskers in young rats causes functional changes in cerebral cortex. Nature 274:600–604.PubMedCrossRefGoogle Scholar
  29. Welker, C. (1971). Microelectrode delineation of fine grain somatotopic organization of SMI cerebral neocortex in albino rat. Brain Res. 26:259–275.PubMedGoogle Scholar
  30. Welker, C., and T. A. Woolsey (1974). Structure of layer IV in the somatosensory neocortex of the rat: Description and comparison with the mouse. J. Comp. Neur. 158:437–454.PubMedCrossRefGoogle Scholar
  31. Welker, W. I. (1964). Analysis of sniffing of the albino rat. Behavior 22:223–244.CrossRefGoogle Scholar
  32. Weller, W. L., and Johnson, J. I. (1975). Barrels in cerebral cortex altered by receptor disruption in newborn, but not in five-day-old mice (Cricetidae and Muridae). Brain Res. 83:504–508.PubMedCrossRefGoogle Scholar
  33. White, E. L. (1978). Identified neurons in mouse SMI cortex which are postsynaptic to thalamocortical axon terminals: A combined Golgi-electron microscopic and degeneration study. J. Comp. Neur. 181:627–662.PubMedCrossRefGoogle Scholar
  34. Woolsey, T. A. (1967). Somatosensory, auditory and visual cortical areas of the mouse. Johns Hopkins Medical Journal 121:91–112.PubMedGoogle Scholar
  35. Woolsey, T. A., and H. Van Der Loos (1970). The structural organization of layer IV in the somatosensory region (SI) of the mouse cerebral cortex. Brain Res. 17:205–242.PubMedCrossRefGoogle Scholar
  36. Woolsey, T. A., C. Welker, and R. Schwartz (1975). Comparative anatomical studies of the SMI face cortex with special reference to the occurrence of “barrels” in layer IV. J. Comp. Neur. 164:79–94.PubMedCrossRefGoogle Scholar

Copyright information

© Plenum Press, New York 1979

Authors and Affiliations

  • Herbert P. Killackey
    • 1
  1. 1.Department of PsychobiologyUniversity of California, IrvineIrvineUSA

Personalised recommendations