Neuron numbers in the sensory trigeminal nuclei of the rat: A GABA‐ and glycine‐immunocytochemical and stereological analysis

One of the most salient features of primary vibrissal afferents is their sensitivity to the direction in which the vibrissae move. Directional sensitivity is also well conserved in brainstem, thalamic, and cortical neurons of the lemniscal pathway, indicating that this property plays a key role in the organization of the vibrissal system. Here, we show that directional tuning is also a fundamental feature of second-order interpolaris neurons that give rise to the paralemniscal pathway. Quantitative assessment of responses to vibrissa deflection revealed an anisotropic organization of receptive fields with regard to topography, response magnitude, and the degree of angular tuning. Responses evoked by all vibrissae within the receptive field of each cell exhibited a high consistency of direction preference, but a striking difference in angular tuning preference was found among cells that reside in the rostral and caudal divisions of the interpolaris nucleus. Although in caudal interpolaris vectors of angular preference pointed in all directions, in rostral interpolaris virtually all vectors pointed upward, revealing a strong preference for this direction. Control experiments showed that the upward bias did not rely on a preferential innervation of rostral cells by upwardly tuned primary vibrissa afferents, nor did it rely on a direction-selective recruitment of feedforward inhibition. We thus propose that the upward preference bias of rostral cells, which project to the posterior group of the thalamus, emerges from use-dependent synaptic processes that relate to the kinematics of whisking.

Section: Local Circuit Cellsmentioning

confidence: 99%

Angular Tuning Bias of Vibrissa-Responsive Cells in the Paralemniscal Pathway

Furuta

Nakamura²,

Deschênes³

2006

“…Lesion of SpVi projections, although extensive, did not totally suppress whisker-evoked inhibition in the PrV, suggesting that residual inhibition was mediated by local circuit inhibitory neurons within the PrV (Avendaño et al, 2005;Furuta et al, 2008). We examined how pharmacological blockade of inhibition by local injection of gabazine (a GABAa receptor antagonist) and strychnine (a glycinergic receptor antagonist) affects the angular tuning of PrV cells.…”

Section: Origin Of Inhibition-effect Of Gabaergic and Glycinergic Antmentioning

confidence: 99%

“…Prior studies have shown that the PrV contains GABAergic and glycinergic neurons (Avendaño, et al, 2005), and that it also receives profuse inhibitory input from the SpVi (Furuta et al, 2008). We first examined how lesion of the interpolaris input affected the angular tuning of PrV neurons.…”

Section: Origin Of Inhibition-interpolaris Lesionmentioning

confidence: 99%

“…The PrV contains local circuit inhibitory cells and receives inhibitory input from the interpolar trigeminal nucleus (SpVi) (Avendaño et al, 2005;Furuta et al, 2008), but the contribution of inhibition in sharpening directional selectivity of vibrissal responses has never been investigated. In the present study we provide a comprehensive assessment of the mechanisms underlying directional tuning in the PrV, and we show that pharmacological blockade of inhibition markedly reduces the directional selectivity of PrV cells.…”

Section: Introductionmentioning

confidence: 99%

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Feedforward Inhibition Determines the Angular Tuning of Vibrissal Responses in the Principal Trigeminal Nucleus

Bellavance¹,

Demers²,

Deschênes³

2010

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.

“…Because variability in section thickness is potentially a significant source of bias, we systematically weighted the contribution of each section to the final number estimate by the number of cells counted in each section (Avendaño et al, 2005). Nevertheless, celloidin sections exhibit a negligible amount of vertical compression and, consequently, low thickness variability within and among sections (Avendaño and Dykes, 1996;West, 1999).…”

Section: Quantitative Studies In Adult Rat Tg In Vivomentioning

confidence: 99%

Primary Sensory Neuron Addition in the Adult Rat Trigeminal Ganglion: Evidence for Neural Crest Glio-Neuronal Precursor Maturation

Lagares¹,

Li²,

Zhou³

et al. 2007

It is debated whether primary sensory neurons of the dorsal root ganglia increase the number in adult animals and, if so, whether the increase is attributable to postnatal neurogenesis or maturation of dormant, postmitotic precursors. Similar studies are lacking in the trigeminal ganglion (TG). Here we demonstrate by stereological methods that the number of neurons in the TG of adult male rats nearly doubles between the third and eighth months of age. The increase is mainly attributable to the addition of small, B-type neurons, with a smaller contribution of large, A-neurons. We looked for possible proliferative or maturation mechanisms that could explain this dramatic postnatal expansion in neuron number, using bromodeoxyuridine (BrdU) labeling, immunocytochemistry for neural precursor cell antigens, retrograde tracing identification of peripherally projecting neurons, and in vitro isolation of precursor cells from adult TG explant cultures. Cell proliferation identified months after an extended BrdU administration was sparse and essentially corresponded to glial cells. No BrdU-labeled cell took up the peripherally injected tracer, and only a negligible number coexpressed BrdU and the pan-neuronal tracer neuron-specific enolase. In contrast, a population of cells not recognizable as mature neurons in the TG and neighboring nerve expressed neuronal precursor antigens, and neural crest glioneuronal precursor cells were successfully isolated from adult TG explants. Our data suggest that a protracted maturation process persists in the TG that can be responsible for the neuronal addition found in the adult rat.