Central Projections of Trigeminal Afferents Innervating the Face in Naked Mole‐Rats (Heterocephalus glaber)

Abstract

In this study, we examined the topography of projections from facial afferents to the trigeminal brainstem nuclear complex (TBNC) in naked mole-rats using the neuronal tracer CTB-HRP. Tracer injections were made in a ventral to dorsal sequence that included the tooth pulp and dental ligament, ventral buccal pad, vibrissae, and the forehead. Labeled terminals were identified throughout the rostrocaudal extent of the TBNC, including the principal nucleus (Pr5), pars oralis (Sp5O), pars interpolaris (Sp5I), and pars caudalis (Sp5C) of the spinal trigeminal nucleus. Injections that labeled afferents from the tooth pulp and dental ligament resulted in heavy transport to dorsomedial portions of the TBNC, whereas injections made into progressively more dorsal regions of the face resulted in labeled terminals progressively more ventral and lateral in the nuclei. Injections that included dental afferents also labeled the mesencephalic nucleus of V, whereas injections into the skin of the face labeled cell bodies in the facial nucleus, and in most cases the motor nucleus of 5. Dental afferents in more rostral portions of the TBNC were coextensive with a cytochrome oxidase-dense region visible in alternate sections processed for chemoarchitecture. Anat Rec, 291:988-998, 2008. 2008 Wiley-Liss, Inc.Key words: dental; teeth; somatosensory; tooth pulp; pain Abbreviations used: I/II = spinal cord layer 1/2; 4V = fourth ventricle; 7 = facial motor nucleus; 7n = facial nerve; 8n = vestibular root of cranial nerve 8; 10 = dorsal motor nucleus of vagus; 12 = hypoglossal nucleus; Acs5 = accessory motor trigeminal nucleus; Acs7 = accessory facial nucleus; Amb = ambiguus nucleus; CGPn = central gray pons; Cu = cuneate nucleus; DC or DCN = dorsal cochlear nucleus; DM = dorsomedial; DTgC = dorsal tegmental nucleus, central; DTgP = dorsal tegmental nucleus, pericentral; ECu = external cuneate nucleus; g7 = genu of the facial nerve; Ge5 = gelat layer caudal sp5 nuc; Gr = gracile nucleus; icp = inferior cerebellar peduncle; io = inferior olive; LC = locus coeruleus; LPBC = lateral parabracheal nucleus, central; LRt = lateral reticular nucleus; LSO = lateral superior olive; LVe = lateral vestibular nucleus; mcp = middle cerebellar peduncle; Me5 = mesencephalic 5 nucleus; me5 = mesencephalic 5 tract; mlf = medial longitudinal fasciculus; Mo5 = motor trigeminal nucleus; MPB = medial parabrachial nucleus; MVe = medial vestibular nucleus; MVeMC = medial vestibular nucleus, magnocellular; MVePC = medial vestibular nucleus, parvocellular; MVPO = medioventral periolivary nucleus; PCRta = parvicellular reticular nucleus, alpha; PDTg = posterodorsal tegmental nucleus; Pr = prepositus nucleus; Pr5 = principal trigeminal nucleus; Pr5DM = dorsomedial subnucleus of Pr5; Pr5VL = ventrolateral subnucleus of Pr5; py = pyramidal tract; pyx = pyramidal decussation; RtTg = reticulotegmental nucleus of the pons; s5 = sensory root of trigeminal nerve; scp = superior cerebellar peduncle; SGe = supragenual nucleus; SO = superior olive; Sol = solitary n...

Trigeminal intersubnuclear neurons: Morphometry and input‐dependent structural plasticity in adult rats

“…Convergence of inputs from various sources has been repeatedly described in Sp5c neurons, occurring mostly in units recorded in layers I–II and V–VI, although much less in neurons in layers III–IV (Sessle et al, ; Hu, ). Anatomically, there is also a moderate overlap in the trigeminal nuclei between primary afferents from neighboring territories (Henry et al, ; Shigenaga et al, ). Therefore, the possibility cannot be discarded that the effects of the IoN transection on at least some Sp5c–Pr5 neurons, and particularly those displaying more extensive dendritic trees, reflect the deafferentation of the whiskers compounded with the loss of sensory input from other IoN targets, such as the anterior teeth or the intraoral mucosa.…”

Mammalian tactile hair: divergence from a limited distribution

“…This expansion of naked mole‐rat S1 occurs at the expense of auditory, and particularly visual, areas and is thought to be related to the postcranial tactile hair system and to the specialized incisors. A prominent, though less dramatically expanded, ventroposterior nucleus of the thalamus and principal sensory trigeminal nucleus are found in naked mole‐rats, indicating that magnification is not reflected to the same degree throughout different levels of the neuraxis 60,61 . Regarding organization within somatosensory areas, although barrel cortex is present in naked mole‐rats, the barrels are less discrete and occasionally lacked clear septal boundaries 62 .…”

Cutaneous and periodontal inputs to the cerebellum of the naked mole-rat (Heterocephalus glaber)

“…Similar cortical modules representing dentition exist in laboratory rats ( Remple et al, 2003 ) and naked mole-rats ( Heterocephalus glaber ; Henry et al, 2005 , 2006 , 2008 ; Henry and Catania, 2006 ), further indicating that columnar units of differing metabolic, connectional, and computational significance distinguish dentition across mammalian species. Naked mole-rats have a large cortical area dedicated to inputs from the dentition with over 30% of primary somatosensory cortex devoted to the two contralateral incisors alone compared to only 7% in rats ( Catania and Remple, 2002 ; Remple et al, 2003 ).…”