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Among 180 units in the solitary tract nucleus (NTS) of rats, 34 solitario-parabrachial relay neurons (SP neurons), were identified by antidromic activation from the parabrachial nucleus. The SP neurons were classified into two groups, fast and slow, according to their antidromic latencies. The responsiveness of the SP in comparison with non-SP neurons was studied by electrical stimulation of three tongue nerves: the lingual (L), chorda tympani (CT) and glossopharyngeal (G) nerves. About half the SP neurons produced a single spike with an orthodromic latency of 2-5 ms, while about one third of them discharged more than two spikes. A few neurons gave rise to a long-lasting discharge consisting of five or six spikes. Some SP neurons were excited by stimulation of the tongue afferents with a low stimulus intensity, but other SP neurons produced spikes at only very high voltages. Fast SP cells were not differentiated from slow SP cells, except that latency of orthodromic responses to CT stimulation was significantly shorter in the former than in the latter (P less than 0.05, Mann-Whitney U-test). Locations of the SP and non-SP neurons, reconstructed histologically, indicate that they do not distribute evenly throughout the mediolateral extent at the rostral pole of the NTS, but clustered in its medial half.

The therapeutic effect of Vitamin B12 or Vitamin B6 on 2,5-hexanedione induced-neuropathy in animals was examined by using our electrodiagnostic technique in order to investigate the mechanism of the development of the neuropathy. Pyridoxal phosphate and two forms of Vitamin B12 were administered to rats intoxicated by the neurotoxin for a period of 18 weeks, and the sensory and motor fiber conduction velocity and the motor distal latency of the tail nerve were periodically determined. None of the groups treated with the therapeutic drugs exhibited a definite improvement in the nerve fiber conduction velocity and motor distal latency of the rat tail nerve, as compared with those of the 2,5-hexanedione-treated controls.

SummaryEighty Recent anatomical studies (NORGREN and LEONARD,1973;NORGREN,1978) have clarified that the rostral part of the solitary tract nucleus(NTS)which receives information from the tongue and oral structures,projects ipsilaterally to the parabrachial nucleus(PB)in rats.In addition, OGAWA et al.(1979)showed that stimulation of tongue afferents evoked field potentials ipsilaterally around the brachium conjunctivum,confirming the previous anatomical studies.The present experiment was conducted to study the physiological characteristics of the NTS neurons which project to the PB and the distribution of such neurons in the NTS.Female albino rats of Sprague-Dawley strain,weighing 260-350 g,were used. The animals were anesthetized by an intraperitoneal injection of amobarbital sodium(80mg/kg body wt.),and anesthesia was maintained by subsequent intravenous injections of the drug when necessary.The lingual nerve(L),the chorda tympani(CT)proper and the lingual branch of the glossopharyngeal nerve(G)were disconnected from the tongue,and the proximal part of each nerve was prepared for electrical stimulation at the left side of the lower jaw, as in the previous experiment (OGAWA et al.,1979).Electrical pulses(pulse duration,0.2 msec;intensity,50V)from a conventional electronic stimulator were delivered to the nerves every 1.5 sec.As previously mentioned (OGAWA et al., 1979),the rats,mounted on a stereotaxic instrument,were cerebellectomized by gentle aspiration to expose the dorsal surface of the pons and medulla.The animals were paralyzed with gallamine triethiodide and artificially ventilated.

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