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Fernández-Montoya J, Martin YB, Negredo P, Avendaño C. Changes in the axon terminals of primary afferents from a single vibrissa in the rat trigeminal nuclei after active touch deprivation or exposure to an enriched environment. Brain Struct Funct 2017; 223:47-61. [PMID: 28702736 DOI: 10.1007/s00429-017-1472-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Accepted: 07/05/2017] [Indexed: 02/03/2023]
Abstract
Lasting modifications of sensory input induce structural and functional changes in the brain, but the involvement of primary sensory neurons in this plasticity has been practically ignored. Here, we examine qualitatively and quantitatively the central axonal terminations of a population of trigeminal ganglion neurons, whose peripheral axons innervate a single mystacial vibrissa. Vibrissa follicles are heavily innervated by myelinated and unmyelinated fibers that exit the follicle mainly through a single deep vibrissal nerve. We made intraneural injections of a mixture of cholera-toxin B (CTB) and isolectin B4, tracers for myelinated and unmyelinated fibers, respectively, in three groups of young adult rats: controls, animals subjected to chronic haptic touch deprivation by unilateral whisker trimming, and rats exposed for 2 months to environmental enrichment. The regional and laminar pattern of terminal arborizations in the trigeminal nuclei of the brain stem did not show gross changes after sensory input modification. However, there were significant and widespread increases in the number and size of CTB-labeled varicosities in the enriched condition, and a prominent expansion in both parameters in laminae III-IV of the caudal division of the spinal nucleus in the whisker trimming condition. No obvious changes were detected in IB4-labeled terminals in laminae I-II. These results show that a prolonged exposure to changes in sensory input without any neural damage is capable of inducing structural changes in terminals of primary afferents in mature animals, and highlight the importance of peripheral structures as the presumed earliest players in sensory experience-dependent plasticity.
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Affiliation(s)
- Julia Fernández-Montoya
- Department of Anatomy, Histology and Neuroscience, Medical School, Autonoma University of Madrid, c/Arzobispo Morcillo 2, 28029, Madrid, Spain
| | - Yasmina B Martin
- Departamento de Anatomía, Facultad de Ciencias de la Salud, Universidad Francisco de Vitoria, UFV, Edificio E, Ctra. M-115, Pozuelo-Majadahonda Km 1,800, Pozuelo de Alarcón, 28223, Madrid, Spain
| | - Pilar Negredo
- Department of Anatomy, Histology and Neuroscience, Medical School, Autonoma University of Madrid, c/Arzobispo Morcillo 2, 28029, Madrid, Spain
| | - Carlos Avendaño
- Department of Anatomy, Histology and Neuroscience, Medical School, Autonoma University of Madrid, c/Arzobispo Morcillo 2, 28029, Madrid, Spain.
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2
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Kaloti AS, Johnson EC, Bresee CS, Naufel SN, Perich MG, Jones DL, Hartmann MJZ. Representation of Stimulus Speed and Direction in Vibrissal-Sensitive Regions of the Trigeminal Nuclei: A Comparison of Single Unit and Population Responses. PLoS One 2016; 11:e0158399. [PMID: 27463524 PMCID: PMC4963183 DOI: 10.1371/journal.pone.0158399] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2016] [Accepted: 06/15/2016] [Indexed: 11/24/2022] Open
Abstract
The rat vibrissal (whisker) system is one of the oldest and most important models for the study of active tactile sensing and sensorimotor integration. It is well established that primary sensory neurons in the trigeminal ganglion respond to deflections of one and only one whisker, and that these neurons are strongly tuned for both the speed and direction of individual whisker deflections. During active whisking behavior, however, multiple whiskers will be deflected simultaneously. Very little is known about how neurons at central levels of the trigeminal pathway integrate direction and speed information across multiple whiskers. In the present work, we investigated speed and direction coding in the trigeminal brainstem nuclei, the first stage of neural processing that exhibits multi-whisker receptive fields. Specifically, we recorded both single-unit spikes and local field potentials from fifteen sites in spinal trigeminal nucleus interpolaris and oralis while systematically varying the speed and direction of coherent whisker deflections delivered across the whisker array. For 12/15 neurons, spike rate was higher when the whisker array was stimulated from caudal to rostral rather than rostral to caudal. In addition, 10/15 neurons exhibited higher firing rates for slower stimulus speeds. Interestingly, using a simple decoding strategy for the local field potentials and spike trains, classification of speed and direction was higher for field potentials than for single unit spike trains, suggesting that the field potential is a robust reflection of population activity. Taken together, these results point to the idea that population responses in these brainstem regions in the awake animal will be strongest during behaviors that stimulate a population of whiskers with a directionally coherent motion.
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Affiliation(s)
- Aniket S. Kaloti
- Interdepartmental Neuroscience Program, Northwestern University, Evanston, IL, United States of America
| | - Erik C. Johnson
- Department of Electrical and Computer Engineering, University of Illinois, Urbana, IL, United States of America
- Coordinated Science Laboratory, University of Illinois, Urbana, IL, United States of America
- Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, IL, United States of America
| | - Chris S. Bresee
- Interdepartmental Neuroscience Program, Northwestern University, Evanston, IL, United States of America
| | - Stephanie N. Naufel
- Department of Biomedical Engineering, Northwestern University, Evanston, IL, United States of America
| | - Matthew G. Perich
- Department of Biomedical Engineering, Northwestern University, Evanston, IL, United States of America
| | - Douglas L. Jones
- Department of Electrical and Computer Engineering, University of Illinois, Urbana, IL, United States of America
- Coordinated Science Laboratory, University of Illinois, Urbana, IL, United States of America
- Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, IL, United States of America
- Advanced Digital Sciences Center, Illinois at Singapore Pte., Singapore, Singapore
| | - Mitra J. Z. Hartmann
- Department of Biomedical Engineering, Northwestern University, Evanston, IL, United States of America
- Department of Mechanical Engineering, Northwestern University, Evanston, IL, United States of America
- * E-mail:
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Lottem E, Gugig E, Azouz R. Parallel coding schemes of whisker velocity in the rat's somatosensory system. J Neurophysiol 2014; 113:1784-99. [PMID: 25552637 DOI: 10.1152/jn.00485.2014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The function of rodents' whisker somatosensory system is to transform tactile cues, in the form of vibrissa vibrations, into neuronal responses. It is well established that rodents can detect numerous tactile stimuli and tell them apart. However, the transformation of tactile stimuli obtained through whisker movements to neuronal responses is not well-understood. Here we examine the role of whisker velocity in tactile information transmission and its coding mechanisms. We show that in anaesthetized rats, whisker velocity is related to the radial distance of the object contacted and its own velocity. Whisker velocity is accurately and reliably coded in first-order neurons in parallel, by both the relative time interval between velocity-independent first spike latency of rapidly adapting neurons and velocity-dependent first spike latency of slowly adapting neurons. At the same time, whisker velocity is also coded, although less robustly, by the firing rates of slowly adapting neurons. Comparing first- and second-order neurons, we find similar decoding efficiencies for whisker velocity using either temporal or rate-based methods. Both coding schemes are sufficiently robust and hardly affected by neuronal noise. Our results suggest that whisker kinematic variables are coded by two parallel coding schemes and are disseminated in a similar way through various brain stem nuclei to multiple brain areas.
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Affiliation(s)
- Eran Lottem
- Department of Physiology and Cell Biology, Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Erez Gugig
- Department of Physiology and Cell Biology, Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Rony Azouz
- Department of Physiology and Cell Biology, Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel
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4
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Jacquin MF, Arends JJA, Renehan WE, Waite PME, Shortland PJ. Whisker-related circuitry in the trigeminal nucleus principalis: Topographic precision. Somatosens Mot Res 2014; 32:8-20. [PMID: 25019347 DOI: 10.3109/08990220.2014.937414] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Single whiskers are topographically represented in the trigeminal (V) nucleus principalis (PrV) by a set of cylindrical aggregates of primary afferent terminals and somata (barrelettes). This isomorphic pattern is transmitted to the thalamus and barrel cortex. However, it is not known if terminals in PrV from neighboring whiskers interdigitate so as to violate rules of spatial parcellation predicted by barrelette borders; nor is it known the extent to which higher order inputs are topographic. The existence of inter-whisker arbor overlap or diffuse higher order inputs would demand additional theoretical principles to account for single whisker dominance in PrV cell responses. In adult rats, first, primary afferent pairs responding to the same or neighboring whiskers and injected with Neurobiotin or horseradish peroxidase were rendered brown or black to color-code their terminal boutons. When collaterals from both fibers appeared in the same topographic plane through PrV, the percentage of the summed area of the two arbor envelopes that overlapped was computed. For same-whisker pairs, overlap was 5 ± 6% (mean ± SD). For within-row neighbors, overlap was 2 ± 5%. For between-row neighbors, overlap was 1 ± 4%. Second, the areas of whisker primary afferent arbors and their corresponding barrelettes in the PrV were compared. In the transverse plane, arbor envelopes significantly exceeded the areas of cytochrome oxidase-stained barrelettes; arbors often extended into neighboring barrelettes. Third, bulk tracing of the projections from the spinal V subnucleus interpolaris (SpVi) to the PrV revealed strict topography such that they connect same-whisker barrelettes in the SpVi and PrV. Thus, whisker primary afferents do not exclusively project to their corresponding PrV barrelette, whereas higher order SpVi inputs to the PrV are precisely topographic.
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Affiliation(s)
- Mark F Jacquin
- Department of Neurology, Washington University School of Medicine , St Louis, MO , USA
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Xiang C, Arends JJA, Jacquin MF. Whisker-related circuitry in the trigeminal nucleus principalis: ultrastructure. Somatosens Mot Res 2014; 31:141-51. [PMID: 24738912 DOI: 10.3109/08990220.2014.905469] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Trigeminal (V) nucleus principalis (PrV) is the requisite brainstem nucleus in the whisker-to-barrel cortex model system that is widely used to reveal mechanisms of map formation and information processing. Yet, little is known of the actual PrV circuitry. In the ventral "barrelette" portion of the adult mouse PrV, relationships between V primary afferent terminals, thalamic-projecting PrV neurons, and gamma-aminobutyric acid (GABA)-ergic terminals were analyzed in the electron microscope. Primary afferents, thalamic-projecting cells, and GABAergic terminals were labeled, respectively, by Neurobiotin injections in the V ganglion, horseradish peroxidase injections in the thalamus, and postembedding immunogold histochemistry. Primary afferent terminals (Neurobiotin- and glutamate-immunoreactive) display asymmetric and multiple synapses predominantly upon the distal dendrites and spines of PrV cells that project to the thalamus. Primary afferents also synapse upon GABAergic terminals. GABAergic terminals display symmetric synapses onto primary afferent terminals, the somata and dendrites (distal, mostly) of thalamic-projecting neurons, and GABAergic dendrites. Thus, primary afferent inputs through the PrV are subject to pre- and postsynaptic GABAergic influences. As such, circuitry exists in PrV "barrelettes" for primary afferents to directly activate thalamic-projecting and inhibitory local circuit cells. The latter are synaptically associated with themselves, the primary afferents, and with the thalamic-projecting neurons. Thus, whisker-related primary afferent inputs through PrV projection neurons are pre- and postsynaptically modulated by local circuits.
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Affiliation(s)
- Chuanxi Xiang
- Department of Neurology, Washington University School of Medicine , St Louis, MO , USA
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Mosconi T, Arends JJ, Jacquin MF. Null mutations of NT-3 and Bax affect trigeminal ganglion cell number but not brainstem barrelette pattern formation. Somatosens Mot Res 2013; 30:114-9. [PMID: 23614607 DOI: 10.3109/08990220.2013.775118] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Trigeminal ganglion (TG) neurons innervate the grid-like array of whisker follicles on the face of the mouse. Central TG axons project to the trigeminal (V) brainstem nuclear complex, including the nucleus principalis (PrV) and the spinal subnucleus interpolaris (SpVi), where they innervate barrelettes that are organized in a pattern that recapitulates the whisker pattern on the face. Neurotrophin-3 (NT-3) supports a population of TG cells that supply slowly adapting mechanoreceptors in the whisker pad. We examined mice at embryonic day 17 (E17) and on the day of birth (P0) with null mutations of NT-3, Bax, a proapoptotic gene associated with naturally occurring cell death, and Bax/NT-3 double knockout (KO) mutants to determine if: (1) the number of TG cells would be reduced; (2) eliminating the Bax gene would rescue the NT-3-dependent neurons; and (3) the central projections of the rescued axons in the Bax/NT-3 double KO mice would fail to develop the barrelette patterns in the PrV and SpVi subnuclei. In mice at E17, NT-3(-/-) mutants had 65% fewer TG neurons than found in age-matched wild-type (WT) mice, and at P0, the number was reduced by 55% (p < 0.001 for both). Bax null mutant mice at E17 had 132% of the WT number of TG cells (p < 0.001), although the numbers returned to WT levels by P0. Bax/NT-3 double KO mice at E17 had TG cell numbers equal to those seen in WT, but the double KO failed to retain WT TG neuron numbers in P0 mice (39% fewer cells; p < 0.001). In all cases of reduced experimental neuron numbers, and in the E17 Bax(-/-) mice with supernumerary cells, the barrelette patterns in the PrV and SpVi were normal. Only a slight qualitative reduction in overall barrelette field area and clarity of barrelettes were seen. These results suggest that NT-3 is not necessary for barrelette pattern formation in the brainstem.
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Affiliation(s)
- Tony Mosconi
- Department of Physical Therapy, Western University of Health Sciences, Pomona, CA, USA
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Kleinfeld D, Deschênes M. Neuronal basis for object location in the vibrissa scanning sensorimotor system. Neuron 2011; 72:455-68. [PMID: 22078505 DOI: 10.1016/j.neuron.2011.10.009] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/13/2011] [Indexed: 01/10/2023]
Abstract
An essential issue in perception is how the location of an object is estimated from tactile signals in the context of self-generated changes in sensor configuration. Here, we review the pathways and dynamics of neuronal signals that encode touch in the rodent vibrissa sensorimotor system. Rodents rhythmically scan an array of long, facial hairs across a region of interest. Behavioral evidence shows that these animals maintain knowledge of the azimuthal position of their vibrissae. Electrophysiological measurements have identified a reafferent signal of the azimuth that is coded in normalized coordinates, broadcast throughout primary sensory cortex and provides strong modulation of signals of vibrissa contact. Efferent signals in motor cortex report the range of the scan. Collectively, these signals allow the rodent to form a percept of object location.
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Affiliation(s)
- David Kleinfeld
- Department of Physics and Section of Neurobiology, University of California, San Diego, La Jolla, CA 92093, USA.
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8
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Xiang C, Zhang KH, Yin J, Arends JJA, Erzurumlu RS, Jacquin MF, Chen ZF. The transcription factor, Lmx1b, is necessary for the development of the principal trigeminal nucleus-based lemniscal pathway. Mol Cell Neurosci 2010; 44:394-403. [PMID: 20621716 DOI: 10.1016/j.mcn.2010.05.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2009] [Revised: 04/21/2010] [Accepted: 05/13/2010] [Indexed: 11/29/2022] Open
Abstract
Little is known of transcriptional mechanisms underlying the development of the trigeminal (V) principal sensory nucleus (PrV), the brainstem nucleus responsible for the development of the whisker-to-barrel cortex pathway. Lmx1b, a LIM homeodomain transcription factor, is expressed in embryonic PrV. In Lmx1b knockout ((-)(/)(-)) mice, V primary afferent projections to PrV are normal, albeit reduced in number, whereas the PrV-thalamic lemniscal pathway is sparse and develops late. Excess cell death occurs in the embryonic Lmx1b(-)(/)(-) PrV, but not in Lmx1b/Bax double null mutants. Expression of Drg11, a downstream transcription factor essential for PrV development and pattern formation, is abolished in PrV, but not in the V ganglion. Consequently, whisker patterns fail to develop in PrV by birth. Rescued PrV cells in Lmx1b/Bax double (-)(/)(-)s failed to rescue whisker-related PrV pattern formation. Thus, Lmx1b and Drg11 may act in the same genetic signaling pathway that is essential for PrV pattern formation.
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Affiliation(s)
- Chuanxi Xiang
- Departments of Anesthesiology, Psychiatry, and Developmental Biology, Washington University School of Medicine, St. Louis, MO 63110, USA
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Bellavance MA, Demers M, Deschênes M. Feedforward inhibition determines the angular tuning of vibrissal responses in the principal trigeminal nucleus. J Neurosci 2010; 30:1057-63. [PMID: 20089914 PMCID: PMC6633092 DOI: 10.1523/jneurosci.4805-09.2010] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2009] [Revised: 11/04/2009] [Accepted: 12/05/2009] [Indexed: 11/21/2022] Open
Abstract
Trigeminal neurons that relay vibrissal messages to the thalamus receive input from first-order afferents that are tuned to different directions of whisker motion. This raises the question of how directional tuning is maintained in central relay stations of the whisker system. In the present study we performed a detailed analysis of the angular tuning properties of cells in the principal trigeminal nucleus of the rat. We found that stimulus direction systematically influences response latency, so that the degree of directional tuning and the preferred deflection angle computed with first-spike latency yielded results nearly similar to those obtained with spike counts. Furthermore, we found that inhibition sharpens directional selectivity, and that pharmacological blockade of inhibition markedly decreases the angular tuning of cellular responses. These results indicate that the angular tuning of cells in the first relay station of the vibrissal system is determined by fast feedforward inhibition, which shapes excitatory inputs at the very beginning of synaptic integration.
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Affiliation(s)
| | - Maxime Demers
- Centre de Recherche Université Laval Robert-Giffard, Québec City, Québec G1J 2R3, Canada
| | - Martin Deschênes
- Centre de Recherche Université Laval Robert-Giffard, Québec City, Québec G1J 2R3, Canada
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In DRG11 knock-out mice, trigeminal cell death is extensive and does not account for failed brainstem patterning. J Neurosci 2008; 28:3577-85. [PMID: 18385316 DOI: 10.1523/jneurosci.4203-07.2008] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
A previous study (Ding et al., 2003) showed that the homeodomain transcription factor DRG11 is necessary for pattern formation in the trigeminal nucleus principalis (PrV), the requisite brainstem nucleus for development of the whisker-to-barrel cortex pathway. However, it is not known how DRG11 contributes to pattern formation. Anatomical studies were performed in DRG11 knock-out (-/-) and DRG11/Bax double -/- mice to test the hypotheses that DRG11 is required for neuronal survival in the V pathway and that PrV cell death is sufficient to explain pattern alterations. At birth, DRG11(-/-) mice had equivalent cell loss in the V ganglion, PrV, and spinal V subnucleus interpolaris (SpVi). Because whisker-related patterns were normal in the SpVi, cell death would not appear to explain failed pattern formation in the mutant PrV. Electron microscopy revealed exuberant apoptosis and necrosis as the mechanisms of PrV cell death occurring in the late prenatal and newborn DRG11(-/-), when such cell death was up to six times more prevalent than normal. DRG11 heterozygote and Bax(-/-) mice were crossed in an attempt to dissociate PrV patterning anomalies from exuberant apoptosis in DRG11(-/-) mice. Both DRG11(-/-) and DRG11/Bax double -/- mutants lacked whisker-related patterning in their PrV, despite Bax(-/-)-induced rescue of V ganglion and PrV cells. Thus, apoptotic cell death is not a sufficient cause of failed pattern formation in the PrV of the DRG11(-/-). A signaling pathway involving DRG11 may, therefore, be the elusive PrV pattern maker.
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Avendaño C, Machín R, Bermejo PE, Lagares A. Neuron numbers in the sensory trigeminal nuclei of the rat: A GABA- and glycine-immunocytochemical and stereological analysis. J Comp Neurol 2006; 493:538-53. [PMID: 16304625 DOI: 10.1002/cne.20778] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The volume, total neuron number, and number of GABA- and glycine-expressing neurons in the sensory trigeminal nuclei of the adult rat were estimated by stereological methods. The mean volume is 1.38+/-0.13 mm3 (mean+/-SD) for the principal nucleus (Vp), 1.59+/-0.06 for the n. oralis (Vo), 2.63+/-0.34 for the n. interpolaris (Vip), and 3.73+/-0.11 for the n. caudalis (Vc). The total neuron numbers are 31,900+/-2,200 (Vp), 21,100+/-3,300 (Vo), 61,600+/-8,300 (Vip), and 159,100+/-25,300 (Vc). Immunoreactive (-ir) neurons were classified as strongly stained or weakly stained, depending on qualitative criteria, cross-checked by a densitometric analysis. GABA-ir cells are most abundant in Vc, in an increasing rostrocaudal gradient within the nucleus. Lower densities are found in Vip and Vp. The mean total number of strongly labeled GABA-ir neurons ranges between 1,800 in Vp to 7,800 in Vip and 22,900 in Vc, and varies notably between subjects. Glycine-ir neurons are more numerous and display more homogeneous densities in all nuclei. Strongly labeled Gly-ir cells predominate in all nuclei, their total number ranging between 9,400 in Vp to 24,300 in Vip and 34,200 in Vc. A substantial fraction of immunolabeled neurons in all nuclei coexpress GABA and glycine. In general, all neurons strongly immunoreactive for GABA are small, while weakly GABA-ir cells which coexpress Gly are larger. In Vc, one-third of all neurons are immunoreactive: 16.6% of them are single-labeled for GABA and 31.6% are single-labeled for glycine. The remaining 51.8% express GABA and glycine in different combinations, with those showing strong double labeling accounting for 22.6%.
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Affiliation(s)
- Carlos Avendaño
- Department of Anatomy, Histology and Neuroscience, Medical School, Autonoma University of Madrid, 28029 Madrid, Spain.
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Formation of whisker-related principal sensory nucleus-based lemniscal pathway requires a paired homeodomain transcription factor, Drg11. J Neurosci 2003. [PMID: 12917357 DOI: 10.1523/jneurosci.23-19-07246.2003] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Little is known about the molecular mechanisms underlying the formation of the principal sensory nucleus (PrV) of the trigeminal nerve, a major relay station for somatotopic pattern formation in the trigeminal system. Here, we show that mice lacking Drg11, a homeodomain transcription factor, exhibit defects within the PrV, which include an aberrant distribution of Drg11-/- cells, altered expression of a molecular marker, unusual projections of primary afferents from trigeminal ganglion cells, and, subsequently, increased cell death. In addition, surviving PrV cells exhibit delayed and more spatially restricted ascending projections to the ventral posterior medial nucleus of the thalamus (VPm). These early embryonic abnormalities in the PrV lead to the failure to develop whisker-related patterns in the PrV, VPm, and somatosensory cortex. By contrast, somatotopic patterns exist in the spinal trigeminal subnuclei interpolaris (SpVi) and subnuclei caudalis (SpVc) and the dorsal column nucleus-based lemniscal and cortical pathway. Thus, the deficits in the trigeminal system of Drg11-/- mice are specific to the PrV. Our results demonstrate that Drg11 is essential for proper cellular differentiation and, subsequently, for the formation of the whisker-related lemniscal and cortical structures.
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Minnery BS, Simons DJ. Response properties of whisker-associated trigeminothalamic neurons in rat nucleus principalis. J Neurophysiol 2003; 89:40-56. [PMID: 12522158 DOI: 10.1152/jn.00272.2002] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Nucleus principalis (PrV) of the brain stem trigeminal complex mediates the processing and transfer of low-threshold mechanoreceptor input en route to the ventroposterior medial nucleus of the thalamus (VPM). In rats, this includes tactile information relayed from the large facial whiskers via primary afferent fibers originating in the trigeminal ganglion (NV). Here we describe the responses of antidromically identified VPM-projecting PrV neurons (n = 72) to controlled ramp-and-hold deflections of whiskers. For comparison, we also recorded the responses of 64 NV neurons under identical experimental and stimulus conditions. Both PrV and NV neurons responded transiently to stimulus onset (ON) and offset (OFF), and the majority of both populations also displayed sustained, or tonic, responses throughout the plateau phase of the stimulus (75% of NV cells and 93% of PrV cells). Average ON and OFF response magnitudes were similar between the two populations. In both NV and PrV, cells were highly sensitive to the direction of whisker deflection. Directional tuning was slightly but significantly greater in NV, suggesting that PrV neurons integrate inputs from NV cells differing in their preferred directions. Receptive fields of PrV neurons were typically dominated by a "principal" whisker (PW), whose evoked responses were on average threefold larger than those elicited by any given adjacent whisker (AW; n = 197). However, of the 65 PrV cells for which data from at least two AWs were obtained, most (89%) displayed statistically significant ON responses to deflections of one or more AWs. AW response latencies were 2.7 +/- 3.8 (SD) ms longer than those of their corresponding PWs, with an inner quartile latency difference of 1-4 ms (+/-25% of median). The range in latency differences suggests that some adjacent whisker responses arise within PrV itself, whereas others have a longer, multi-synaptic origin, possibly via the spinal trigeminal nucleus. Overall, our findings reveal that the stimulus features encoded by primary afferent neurons are reflected in the responses of VPM-projecting PrV neurons, and that significant convergence of information from multiple whiskers occurs at the first synaptic station in the whisker-to-barrel pathway.
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Affiliation(s)
- Brandon S Minnery
- Department of Neurobiology, University of Pittsburgh, Pennsylvania 15261, USA
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14
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Abstract
The spatial organization of the anatomical structures along the trigeminal afferent pathway of the rat conserves the topographical order of the receptor sheath: The brainstem barrelettes, thalamic barreloids, and cortical barrels all reflect the arrangement of whiskers across the mystacial pad. Although both the amount of innervation in the mystacial pad and the size of cortical barrels were shown previously to exhibit increasing gradients toward the ventral and caudal whiskers, whether similar gradients existed in the brainstem and thalamus was not known. Here, the authors investigated the size gradients of the barreloids in the ventral posteromedial nucleus of the rat thalamus. Because the angles used to cut the brain were crucial to this study, the optimal cutting angles were determined first for visualization of individual barreloids and of the entire barreloid field. Individual barreloids, arcs, and rows as well as entire barreloid fields were clearly visualized using cytochrome oxidase staining of brain slices that were cut with the optimal cutting angles. For the first five arcs (including straddlers), the length of barreloids increased in the direction of dorsal-to-ventral whiskers and of caudal-to-rostral whiskers. These gradients reveal an inverse relationship between the size of barreloids and whiskers (length and follicle diameter) along arcs and rows. The largest barreloids in the ventral posteromedial nucleus were those that represent whiskers C2-C4, D2-D4, and E2-E4, which are neither the largest nor the most innervated whiskers in the mystacial pad. This implies that the extended representation is not merely a reflection of peripheral innervation biases and probably serves an as yet unknown processing function.
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Affiliation(s)
- S Haidarliu
- Department of Neurobiology, The Weizmann Institute of Science, Rehovot 76100, Israel.
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