Martínez-Marcos A, Ubeda-Bañón I, Halpern M
Department of Anatomy and Cell Biology, Health Science Center at Brooklyn, State University of New York, Brooklyn, New York 11203, USA.
J Comp Neurol. 2001 Mar 26;432(1):75-87. doi: 10.1002/cne.1089.
Snakes deliver odorants to the vomeronasal organ by means of tongue-flicks. The rate and pattern of tongue-flick behavior are altered depending on the chemical context. Accordingly, olfactory and vomeronasal information should reach motor centers that control the tongue musculature, namely, the hypoglossal nucleus (XIIN); however, virtually nothing is known about the circuits involved. In the present work, dextran amines were injected into the tongue of garter snakes (Thamnophis sirtalis) to identify the motoneurons of the XIIN. Tracers were then delivered into the XIIN to identify possible afferents of chemical information. Large injections into the XIIN yielded retrograde labeling in two chemosensory areas: the medial amygdala (MA) and the lateral posterior hypothalamic nucleus (LHN). Smaller injections only yielded labeled neurons in the LHN. In fact, the MA, which receives afferents from the accessory olfactory bulb, the rostroventral lateral cortex, and the nucleus sphericus, projects to the LHN. Injections into the MA did not show terminal labeling in the XIIN but in an area lateral to it. However, injections into the LHN gave rise not only to labeled fibers in the XIIN but also to retrograde labeling in the MA, thus confirming the chemosensory input to LHN. Injecting different fluorescent tracers into the tongue and into the LHN corroborated the projection from the LHN to the XIIN. The present report investigates further connections of the olfactory and vomeronasal systems and describes the afferent connections to XIIN in a nonmammalian vertebrate. The circuit for tongue-flicking behavior described herein should be evaluated using functional studies.
蛇通过舔舌将气味剂传递到犁鼻器。舔舌行为的速率和模式会根据化学环境而改变。因此，嗅觉和犁鼻器信息应该会到达控制舌肌的运动中枢，即舌下神经核（XIIN）；然而，对于其中涉及的神经回路几乎一无所知。在本研究中，将葡聚糖胺注射到束带蛇（美洲束带蛇）的舌头中，以识别XIIN的运动神经元。然后将示踪剂注入XIIN，以识别化学信息的可能传入神经。向XIIN进行大量注射在两个化学感受区域产生了逆行标记：内侧杏仁核（MA）和下丘脑外侧后核（LHN）。较小的注射仅在LHN中产生标记神经元。事实上，从副嗅球、吻腹外侧皮质和球状核接收传入神经的MA投射到LHN。向MA注射未在XIIN中显示终末标记，而是在其外侧区域显示。然而，向LHN注射不仅在XIIN中产生标记纤维，还在MA中产生逆行标记，从而证实了向LHN的化学感受输入。将不同的荧光示踪剂分别注射到舌头和LHN中，证实了从LHN到XIIN的投射。本报告进一步研究了嗅觉和犁鼻器系统的连接，并描述了非哺乳类脊椎动物中与XIIN的传入连接。本文所述的舔舌行为神经回路应通过功能研究进行评估。
