The effect of tetanus toxin in the goldfish

1. The effects of tetanus toxin have been investigated both on central nervous and peripheral neuromuscular systems of goldfish.2. Tetanus toxin kills goldfish when administered in minute doses. The lethal effect is temperature dependent. Unlike mammals, in which tetanus toxin produces spastic paralysis and convulsions, the tetanus-intoxicated goldfish die with an apparently flaccid paralysis.3. Inhibition and excitation were investigated on the Mauthner cells of goldfish which had been paralysed with tetanus toxin for at least 24 hr, and which were subsequently kept alive for up to 3 days by perfusing the gills with oxygenated water. In such fish, antidromically and orthodromically excited Mauthner cells were quite normal, and there was no apparent effect on either the collateral inhibition or the crossed VIIIth nerve inhibition.4. Local injection of sublethal doses of tetanus toxin into the pectoral fin muscles produced local paralysis of the fin. Nerve-muscle preparations were isolated from such goldfish; in tetanus toxin-paralysed fins, the muscle no longer responded to stimulation of its nerve. The nerve compound action potential was still present and the muscle still responded vigorously to direct electrical stimulation.5. It is concluded that the major part of the lethal action of the toxin in the fish must be ascribed to a peripheral effect, the blocking of neuromuscular transmission. The inhibitory neuronal systems acting on the Mauthner cells of the goldfish, in apparent contrast to those acting on mammalian spinal neurones, are highly insensitive to tetanus toxin.

Observations on the site & mode of action of pyrogens in the rabbit brain

1. Leucocyte pyrogen has been injected bilaterally into various parts of the rabbit brain. It caused fever when injected into the pre-optic area and the anterior hypothalamus, but not when injected into the posterior hypothalamus, the mid-brain, the pons, the cerebellum or the cerebral cortex.2. The mean time which elapsed between a leucocyte pyrogen injection into the anterior hypothalamus and the onset of fever was 7.8 min. For similar injections of bacterial pyrogen the time lag was 24.8 min. The mean time lag between bilateral injections of noradrenaline into the anterior hypothalamus and the onset of fever was 7.4 min.3. The amount of leucocyte pyrogen required to cause fever when injected into the anterior hypothalamus was less than 1/100 of that required to cause a similar fever on intravenous injection. The quantity of bacterial pyrogen injected into the hypothalamus was of the same order as that which would cause a similar fever on intravenous injection.4. Control injections of saline, plasma, cerebrospinal fluid, heated leucocyte pyrogen and red cells into the anterior hypothalamus did not cause fever.5. After attempts to deplete the hypothalamus of its monoamine stores by intraventricular injections of reserpine, the rabbit had fever as a result of an intravenous injection of bacterial pyrogen.6. We conclude that the anterior hypothalamus and the pre-optic area are sites at which leucocyte pyrogen acts to cause fever in the rabbit. The mechanism of this febrile response is not clear, but it appears that part, at least, of the response could be mediated by a mechanism other than release of noradrenaline or failure to release 5-HT.

Pharmacological properties of cholinoceptive neurones in the medulla and pons of the cat

1. Iontophoretic application of acetylcholine to neurones in the medulla and pons of the unanaesthetized decerebrate cat excited 35.5% and inhibited 22%. This was not a representative sample of lower brain stem neurones, since most penetrations were made medially. Some cholinoceptive neurones were in the medial reticular formation.2. The time course of the response to different doses has been described.3. Nicotine and nicotinic agents 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP) and choline phenyl ether (TM1) excited neurones excited by acetylcholine but, with one exception, did not inhibit neurones inhibited by acetylcholine.4. Muscarinic agents mimicked both the excitatory and inhibitory responses to acetylcholine. (+/-)-muscarine and bethanechol (beta-methylcholine carbamate) had a prolonged and powerful inhibitory action.5. Oxotremorine [1-(2-oxopyrrolidino)-4-pyrrolidino-butyne-2] had a long-lasting excitatory action on neurones excited by acetylcholine.6. Eserine and neostigmine potentiated the action of acetylcholine but in addition they had a strong excitatory effect on many brain stem neurones, independently of the action of acetylcholine.7. Excitatory and inhibitory responses to acetylcholine could be antagonized by gallamine, hexamethonium and atropine. Dihydro-beta-erythroidine (DHbetaE) antagonized only excitatory responses. (+)-Tubocurarine was a weak antagonist.8. It is concluded that the excitatory responses have both nicotinic and muscarinic properties but the inhibitory responses are only muscarinic. Since the pharmacology of these two types of response is different, it is concluded that the inhibitory action is not due to an indirect effect from excitation of a neighbouring inhibitory neurone.