終神経(Nervus terminalis) は、脊椎動物の多くに見られ、その神経節細胞（ＮＴ細胞）及び神経線維は嗅覚神経路に近接して存在する。しかし、これまで、いずれの動物においても電気生理学的研究はなく、その生理学的性質および機能は不明である。今回、我々は、コイのＮＴ細胞から細胞内記録を行ない、嗅索および嗅神経の電気刺激に対する応答を調べた。ＮＴ細胞は、嗅球最吻側部の嗅神経層内側部に位置する細胞という基準で同定した。全てのＮＴ細胞は、外側嗅索刺激には応答せず、内側嗅索刺激には過分極応答を示した。約半数の細胞は、内側嗅索刺激により逆行性活動電位を生じ、その伝導速度は約0.5m/sであった。嗅神経刺激に対しては、無応答の細胞と、過分極応答を示す細胞とがあった。
Proc. Jap. Soc. Gen. Comp. Physiol., 5 (1983), 78.
The nervus terminalis system in the carp (Cyprinus carpio L.): analysis of intracellular potentials in the ganglion cells
Ichiro FUJITA, Masahiko SATOU and Kazuo UEDA
Zool. Inst., Fac. Sci., Univ. Tokyo
The nervus terminalis and its ganglion cells are found within or along the olfactory pathway of various vertebrate species. Although there are relatively many histological and immunohistochemical studies, no electrophysiological study of the nervus terminalis system has been carried out so far. In the present study, intracellular potentials were analyzed in the ganglion cells of the nervus terminalis (NT cells) in the carp.
Twenty-five cells impaled in the medial part of the ON at or near the rostral level of the olfactory bulb (OB) were identified as NT cells. The responses of these cells to single shocks of 100 µs, applied to the medial or lateral olfactory tract (MOT or LOT respectively), or the olfactory nerve (ON), were analyzed. Strength of stimuli was adjusted to elicit the maximal field potential responses in the OB. Four of these cells were stained by intracellular injection of horseradish peroxidase. It was confirmed that these four cells were located among the ON fibers and morphologically distinct from other neurons (e.g., mitral cells or granule cells) in the OB.
The resting membrane potentials of the analyzed NT cells ranged from -30 to -63 mV. In all NT cells, MOT shocks evoked a long-lasting hyperpolarizing potential (3-20 mV in amplitude, 950-1600 ms in duration), while LOT shocks elicited no response. In addition, 12 out of 25 NT cells showed an antidromic action potential after MOT shocks. The conduction velocities of the axons ranged from 0.33 to 0.53 m/s (0.46±0.06 m/s, mean ± S.D.). When electrical shocks were applied to the ON, 17 NT cells showed a long-lasting hyperpolarizing potential (4-15 mV in amplitude, 650-1300 ms in duration), while the remaining 8 NT cells showed no response. Some cells showed spontaneous firing, which was suppressed during the MOT- or ON- evoked hyperpolarizing potentials.
The intracellular potential responses of the NT cells were similar to those of mitral cells in the medial part of the OB in that both showed a long-lasting hyperpolarizing potential (or IPSP in the case of mitral cells) after MOT or ON shocks, but no response to LOT shocks (cf. Satou, Fujita, Ichikawa, Yamaguchi and Ueda, J. Comp. Physiol., 152:319-333, 1983). However, the onset latencies of the hyperpolarizing potentials evoked by MOT or ON shocks in the NT cells were longer than those of the IPSPs evoked by MOT or ON shocks in the mitral cells in the medial part of the OB.
The present study characterizes the responses of the NT cells evoked by MOT, LOT or ON shocks and provides an
electrophysiological basis for the elucidation of the funcions of the nervus terminalis system.