Kolta A, Dubuc R, Lund J P
Centre de recherche en sciences neurologiques, Université de Montréal, Canada.
Neuroscience. 1993 Apr;53(4):1113-26. doi: 10.1016/0306-4522(93)90494-z.
The results of a previous experiment suggest that the cell bodies of many jaw closing muscle spindle afferents in the trigeminal mesencephalic nucleus of the rabbit are phasically inhibited during fictive mastication. The aim of this study was to investigate one possible neurotransmitter system that could be involved in this modulation, serotonin, by use of receptor autoradiography techniques and immunofluorescence combined with retrograde labelling of masseteric spindle afferents and motoneurons. A second objective was to compare the serotonin innervation of neurons in the trigeminal mesencephalic nucleus with that of masseteric motoneurons. Serotoninergic fibres were seen surrounding labelled masseteric spindle afferents, as well as unlabelled neurons, in the trigeminal mesencephalic nucleus. These fibres were close to the cell bodies and sometimes to the axon hillocks of the neurons. Although it has been reported that many neurons of the trigeminal nucleus are multipolar in some species, none of the labelled spindle afferent in this study had more than one process. Throughout the motor trigeminal nucleus, serotonin fibres were found in close proximity with cell bodies and with the proximal portions of axons and dendrites of labelled and unlabelled motoneurons. Serotonin fibres were also seen adjacent to cell bodies and processes of efferent neurons in cell group k. Autoradiography with several tritiated ligands was used to reveal the presence of receptors for serotonin as well as its uptake sites. Only serotonin2 receptors were found to be abundant in the trigeminal mesencephalic nucleus. The motor nucleus and cell group k contained serotonin2 and serotonin3 receptors, as well as serotonin uptake sites. Serotonin1A receptors appear to be absent from both nuclei. The findings suggest that release of serotonin from fibres in close proximity to trigeminal primary afferent somata could modify the transmission of action potentials from muscle spindle receptors during mastication through an action on serotonin2 receptors. In the motor nucleus and cell group k, serotonin may alter neuronal properties through actions on at least two receptor subtypes (serotonin2 and serotonin3).
先前一项实验的结果表明，在假咀嚼过程中，兔三叉神经中脑核内许多闭口肌梭传入纤维的细胞体受到相位性抑制。本研究的目的是通过受体放射自显影技术以及免疫荧光结合咬肌梭传入纤维和运动神经元的逆行标记，来研究一种可能参与这种调节的神经递质系统——5-羟色胺。第二个目的是比较三叉神经中脑核内神经元与咬肌运动神经元的5-羟色胺神经支配情况。在三叉神经中脑核内，可见5-羟色胺能纤维围绕着标记的咬肌梭传入纤维以及未标记的神经元。这些纤维靠近神经元的细胞体，有时也靠近轴丘。尽管有报道称在某些物种中三叉神经核的许多神经元是多极的，但本研究中标记的梭传入纤维都没有超过一个突起。在整个三叉神经运动核中，发现5-羟色胺纤维与标记和未标记运动神经元的细胞体以及轴突和树突的近端部分紧密相邻。在细胞群k中，也可见5-羟色胺纤维与传出神经元的细胞体和突起相邻。使用几种氚标记配体进行放射自显影，以揭示5-羟色胺受体及其摄取位点的存在。仅发现5-羟色胺2受体在三叉神经中脑核中大量存在。运动核和细胞群k含有5-羟色胺2和5-羟色胺3受体以及5-羟色胺摄取位点。两个核中似乎都不存在5-羟色胺1A受体。这些发现表明，靠近三叉神经初级传入纤维细胞体的纤维释放的5-羟色胺，可能通过作用于5-羟色胺2受体来改变咀嚼过程中肌肉梭受体动作电位的传递。在运动核和细胞群k中，5-羟色胺可能通过作用于至少两种受体亚型（5-羟色胺2和5-羟色胺3）来改变神经元特性。
