A comparison of the postnatal development of muscle-spindle and periodontal-ligament neurons in the mesencephalic trigeminal nucleus of the rat.
The trigeminal mesencephalic nucleus (Vmes) is known to include primary afferent neurons of jaw muscle spindles (MS neurons) and periodontal ligament receptors (PL neurons). The aim of this study was to clarify the postnatal development of Vmes neurons by comparing MS neurons with PL neurons using horseradish peroxidase labeling. We measured somal diameter and somal shape of MS and PL neurons in rats from postnatal day (P)7 to P70. No significant changes were seen between postnatal day P7 and P70 in somal diameter or somal shape of MS neurons. Conversely, PL neurons showed a larger somal diameter at P7 than at P14, and in terms of somal profile, multipolar neurons comprised 0% at P7, but 4.8% at P14 and 16.9% at P70. These findings suggest that PL neurons develop with the eruption of teeth, taking into account the fact that tooth eruption occurs from around P14 in rats. Conversely, the lack of postnatal changes in MS neurons is due to the fact that these neurons have been active since the embryonic period, as swallowing starts in utero.
Umemura
Tetsuhiro
T
Department of Oral and Maxillofacial Surgery, Institute for Oral Science, Division of Maxillofacial Biology, Matsumoto Dental University, 1780 Hirooka, Shiojiri, Nagano 399-0781, Japan.
Yasuda
Kouichi
K
Ishihama
Kohji
K
Yamada
Hidefumi
H
Okayama
Masaki
M
Hasumi-Nakayama
Yoko
Y
Furusawa
Kiyofumi
K
D000818:Animals; D048430:Cell Shape; D048429:Cell Size; D005260:Female; D008297:Male; D008636:Mesencephalon / Q000166:cytology* / Q000254:growth & development; D009470:Muscle Spindles / Q000166:cytology* / Q000254:growth & development; D009474:Neurons / Q000166:cytology*; D010513:Periodontal Ligament / Q000254:growth & development / Q000294:innervation*; D010519:Periodontium / Q000254:growth & development / Q000294:innervation*; D051381:Rats; D017208:Rats, Wistar; D014278:Trigeminal Nuclei / Q000166:cytology* / Q000254:growth & development