THE SELECTIVITY OF DRUGS BLOCKING GANGLIONIC TRANSMISSION IN THE RAT

By comparing the effects on ganglionic transmission and on the pre- and post-ganglionic nerves in the isolated superior cervical ganglion preparation of the rat, the selectivity of several drugs was assessed quantitatively. Hexamethonium, tetraethylammonium, nicotine and tubocurarine blocked transmission in concentrations which did not affect nervous conduction and were considered to be highly selective in action. Atropine, amylobarbitone and paraldehyde depressed nervous conduction appreciably in ganglion-blocking doses, but not enough to account wholly for the block in transmission and they were therefore considered as being moderately selective. The ganglion blocking actions of mephenesin, procaine, methylpentynol, methylpentynol carbamate and benactyzine were nonspecific, showing general depression of neuronal activity. Ganglion block with bretylium was nonselective in its site of depression of the postganglionic neurone in concentrations which only partly depressed the preganglionic nerve.

NONSPECIFIC DEPRESSANT ACTION OF GAMMA-AMINOBUTYRIC ACID ON SOMATIC REFLEXES

The effects of gamma-aminobutyric acid (GABA) on central integration of somatic reflexes in the cat have been studied by topical application, and by intrathecal or intracerebroventricular injection. Intrathecal injection of GABA inhibited the monosynaptic patellar reflex. The facilitation of the patellar reflex induced by strychnine, leptazol, tubocurarine and tetanus toxin was also inhibited. Polysynaptic facilitation of the patellar reflex induced in the spinal cat by electrical stimulation of the contralateral sciatic nerve was depressed by intrathecal GABA. Similarly, the supraspinal facilitation of the patellar reflex by electrical stimulation of the brain stem reticular formation was inhibited by application of GABA to the floor of the 4th ventricle. The polysynaptic inhibition of the patellar reflex at both levels was intensified by GABA. The flexor (tibialis anterior) reflex was depressed in the same manner as the extensor patellar reflex. The polysynaptic linguomandibular reflex was depressed by intracerebroventricular GABA. The depressant action of GABA at spinal and supraspinal levels of the neuraxis is discussed in relation to the role of GABA as an inhibitory transmitter in the central nervous system.

ACTIONS OF HEMICHOLINIUM (HC-3) ON NEUROMUSCULAR TRANSMISSION

Hemicholinium No. 3 (HC-3; alpha,alpha'-dimethylaminoethanol-4, 4'-biacetophenone) produced neuromuscular block of the tibialis anterior muscle-sciatic nerve preparation of the anaesthetized cat which was of slow onset, of long duration and dependent on the nerve stimulus frequency. The failure of the compound to modify the response of the tibialis muscle to close-arterial injections of acetylcholine suggested that the sensitivity of the motor endplate was not changed by it. The neuromuscular block produced by hemicholinium was antagonized by choline but only partly relieved by anticholinesterase drugs. The response to tetanic stimulation of the nerve during the neuromuscular block was well sustained and was followed by a slight posttetanic potentiation. The neuromuscular blocking action of hemicholinium could be relieved by temporary suspension of stimulation. These results suggest that the mode of action of hemicholinium at the neuromuscular junction is different from that of tubocurarine, and indicate that the action of hemicholinium is presynaptic, probably arising from a reduction in acetylcholine released by nerve stimulation.

ACTIONS OF MECAMYLAMINE, DIMECAMINE, PEMPIDINE AND THEIR TWO QUATERNARY METHO-SALTS AT THE NEUROMUSCULAR JUNCTION

Mecamylamine, dimecamine and pempidine differed in neuromuscular-blocking activity on the isolated phrenic nerve-diaphragm preparation of the rat from the corresponding methiodides by a factor of less than two. It was concluded that the active component of each amine was the cation acting extracellularly. The finding that the neuromuscular-blocking activity of mecamylamine at pH 6.7 was similar to the activity at pH 7.7 did not refute this conclusion. Mecamylamine, dimecamine methiodide, dimecamine and pempidine, at concentrations insufficient to cause block, could increase the twitch response of the rat diaphragm; the ability to do this increased in the above order. With pempidine (the most active compound) this effect, on the isolated sartorius muscle of the frog, was a direct action. During steady partial block by each of the compounds, the responses to brief tetanic stimulation, to neostigmine and to an increase in calcium concentration were similar to those observed during block by tubocurarine. From indirect evidence, pempidine methiodide appeared both to enhance the release of acetylcholine from motor-nerve terminals and to cause postsynaptic block.

THE RELATIONSHIP BETWEEN ANICURARE ACTIVITY AND TIME COURSE OF THE ENDPLATE POTENTIAL; A STRUCTURE-ACTIVITY APPROACH

A comparison of the effects of several quaternary ammonium ions has been made on the intracellularly recorded endplate potential of curarized frog muscle. The hydroxyanilinium ions usually caused an increase in endplate potential amplitude, a slowing of rate of rise and marked prolongation, but rarely caused spike generation. Contrariwise, tetraethylammonium and triethylphenylammonium consistently caused an increase in both amplitude and rate of rise of the endplate potential but no prolongation; these endplate potentials generated muscle spikes. The results suggest a relationship between rate of rise of the endplate potential and the probability of spike generation. Using the neurally evoked contractile response as a signal of transmitter action, the hydroxyanilinium ions were found to be relatively weak antagonists of tubocurarine at deep levels of curarization, indicating a ceiling effect. There was also a ceiling to the effect of hydroxyaniliniums on endplate potential amplitude. Thus, in the presence of high concentrations of tubocurarine, tetraethylammonium is a more potent anticurare agent than is triethyl(3-hydroxyphenyl) ammonium.

Clinical heterogeneity of seronegative myasthenia gravis

We studied 38 patients affected by seronegative myasthenia gravis (SNMG) with age at the onset of the disease ranging from 6 to 66 yr. Clinical follow-up lasted at least 2 yr. Patients' lymphocyte cultures showed in no case anti-acetylcholine receptor antibody production; HLA associations did not differ significantly from those in seropositive MG. In most cases (33 out of 38) the disease differed from seropositive MG only in the low incidence of thymic pathology. In five cases the clinical picture was characterized by prevalent involvement of ocular and bulbar muscles and by a more stable course. These last group of patients did not respond satisfactorily to immunosuppressants, but they clearly improved with plasma-exchange. Mice injected with plasma IgG from four patients (two with typical clinical picture and two with prevalent oculobulbar involvement) showed a defect of neuromuscular transmission. In our experience, SNMG is a heterogeneous disease. A humorally mediated pathogenesis appears to be operating in both groups of patients we described.

Ontogeny and effect of activity on proenkephalin mRNA expression during development of the chick spinal cord

Numerous studies have shown in the adult nervous system that mRNA expression can be regulated by neuronal activity. To examine the effect of activity during embryogenesis, the ontogeny of proenkephalin mRNA expression and expression following activity blockade was investigated during development of chick spinal cord. A cDNA fragment (ca. 0.5 kb) coding for chick proenkephalin was cloned and sequenced. With this cDNA, a cRNA probe was made to examine proenkephalin mRNA expression in the spinal cord during embryogenesis. Proenkephalin mRNA was expressed in spinal cord in clusters of cells located in the developing dorsal horn and intermediate lamina at the earliest stages examined (stage 22; E4). Proenkephalin-positive cells in the intermediate lamina were located immediately adjacent to the ventricular zone. At stage 28 (E6) an additional cluster of proenkephalin mRNA-positive cells was seen at the lateral border of the developing intermediate lamina. At stage 33 (E7.5-5-8) the pattern of hybridization positive cells was similar to earlier stages, but individual cells could be identified. At stage 39 (E13) densely labeled cells were seen throughout the dorsal horn and intermediate laminae including the column of Terni. To determine whether neural activity affects proenkephalin mRNA expression, d-tubocurarine (an inhibitor of neural activity) was injected into developing embryos. Following administration of d-tubocurarine a dramatic decrease was seen in proenkephalin mRNA hybridization in the dorsal horn and intermediate lamina of the spinal cord. This study demonstrates in vivo that changes in the level of neural activity can alter gene expression during embryogenesis and suggests that activity is required for expression of nervous system-specific genes.

Characterization of slow postsynaptic K+ current of Aplysia LUQ neurons in culture

We have characterized the slow inhibitory synaptic connection between an left upper quadrant (LUQ) neuron and neuron L10, L12 or L13 in culture. A slow postsynaptic outward current in the LUQ neuron was elicited by repetitive firing of the co-cultured cholinergic neuron L10 as well as neuron L12 or L13 which were not cholinergic but FMRFamide synthesizing neurons. This outward current was due to an increase in K+ conductance and was relatively insensitive to external application of tetraethylammonium and 4-aminopyridine. We also investigated the effects of injection of a guanosine 5'-triphosphate (GTP) analogue into the LUQ neuron and extracellular application of serotonin and an adenosine 3',5'-cyclic monophosphate (cAMP) analogue on the current. In all the investigated properties, no significant difference was found among neuron L10, L12 and L13 as a presynaptic neuron. The slow postsynaptic current appeared to be virtually identical to the FMRFamide or acetylcholine (ACh)-induced K+ current reported in vivo, which resembled the 'S' current in Aplysia sensory neurons. We performed experiments to see the effect of phenyltrimethylammonium, an ACh antagonist, on the postsynaptic, ACh-, and FMRFamide-induced currents, clearly indicating that the neurotransmitter used in the cultured synapses was not ACh.

Muscle pain after outpatient laparoscopy--influence of propofol versus thiopental and enflurane

The incidence and pattern of postoperative muscle pains was studied in 155 healthy women undergoing outpatient laparoscopic surgery who were assigned randomly to one of five treatment groups. Group 1 (control) received thiopental and succinylcholine, 1 mg/kg, followed by enflurane and nitrous oxide. Group 2 received d-tubocurarine, 3 mg, followed by succinylcholine, 1.5 mg/kg, but was otherwise similar to Group 1. Groups 3 and 4 were similar to Group 1, but received propofol instead of thiopental, and Group 4 also received a variable-rate propofol infusion instead of enflurane. Finally, Group 5 was similar to Group 3, but received atracurium instead of succinylcholine. Muscle fasciculations were often observed in Groups 1, 3, and 4, but were attenuated in Group 2 and absent in Group 5. Overall, postoperative shoulder pain occurred in 81%, 72%, and 29% of patients on the first, second, and third postoperative days, respectively. The incidence of this symptom did not differ among the five groups. Neck pain occurred less frequently than shoulder pain in each group, and also occurred less often in Group 5 than in Group 1. Muscle stiffness occurred less often than muscle pain, and also occurred less frequently in Group 5 than in Group 1. In conclusion, succinylcholine contributes to neck pain and muscle stiffness after laparoscopic procedures. Compared to thiopental and enflurane, the use of propofol for induction and/or maintenance of anesthesia failed to alter the incidence of postlaparoscopic muscle pain or stiffness.