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

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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 asstronglystained orweaklystained, 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%. J. Comp. Neurol. 493:538–553, 2005.

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