Physiological properties of the penis retractor muscle of Aplysia

The properties of the penis retractor muscle of Aplysia have been studied using intracellular, sucrose gap and tension recording. The fibers are of the invertebrate smooth muscle type and exhibit slow contractions which occur spontaneously or in response to stretch in isolated preparations. Individual muscle fibers are innervated by excitatory and inhibitory axons. A variety of sizes of excitatory and inhibitory junctional potentials can be recorded from them. The innervation is probably diffuse and functionally polyneuronal. The fibers are electrically coupled, permeable to potassium and chloride at rest, and exhibit no overshooting active responses. The muscle shows graded responses of depolarization and contraction proportional to strength of nerve stimulation. Facilitation and depression of junctional potentials are seen with various frequencies of nerve stimulation. Post-tetanic potentiation occurs with nerve stimulation at frequencies from 2 to 50 Hz and is suppressed in the presence of increased extracellular calcium concentrations.     

In Vivo Studies on Fast and Slow Muscle Fibers in Cat Extraocular Muscles

In anesthetized in vivo preparations, responses of two types of extraocular muscle fibers have been studied. The small, multiply innervated slow fibers have been shown to be capable of producing propagated impulses, and thus have been labeled slow multi-innervated twitch fibers. Fast and slow multi-innervated twitch fibers are distinguished by impulse conduction velocities, by ranges of membrane potentials, by amplitudes and frequencies of the miniature end plate potentials, by responses to the intravenous administration of succinylcholine, by the frequency of stimulation required for fused tetanus, and by the velocities of conduction of the nerve fibers innervating each of the muscle fiber types.     

Inhibitory innervation to the guinea pig trachealis muscle

The inhibitory innervation of the cervical trachea was studied in situ in anesthetized male guinea pigs. We measured effects of electrical stimulation of vagal motor and sympathetic trunk nerve fibers, during atropine, on trachealis muscle tension. Effects of direct transmural stimulation of trachealis muscle were also determined. We confirmed the dual nature of the inhibitory innervation to this muscle. Vagal motor inhibitory nerves are shown to be preganglionic. Neural transmission at the level of the ganglia is characterized by filtering of high frequency action potentials. The neurotransmitter at the myoneural junction is unidentified but is not norepinephrine. Maximal relaxation accounts for about 20-40% of maximal relaxations seen with transmural stimulation of trachealis muscle in the presence of atropine. Sympathetic trunk nerve fibers are also preganglionic. Neurotransmission at the level of the ganglia is apparently 1:1 at high-action potential frequencies. Norepinephrine released presynaptically has access to smooth muscle beta- but not alpha-receptors. Maximal adrenergic relaxations account for 60-80% of total transmural stimulation relaxations. Transmural stimulation relaxations appear to be accounted for by release of neurotransmitter from sympathetic adrenergic plus vagal nonadrenergic postganglionic nerve fibers.     

Nerve,spinal cord and brain somatosensory evoked responses: a comparative study during electrical and magnetic peripheral nerve stimulation

Somatosensory evoked potentials (SEPs) and compound nerve action potentials (cNAPs) have been recorded in 15 subjects during electrical and magnetic nerve stimulation. Peripheral records were gathered at Erb's point and on nerve trunks at the elbow during median and ulnar nerve stimulation at the wrist. Erb responses to electrical stimulation were larger in amplitude and shorter in duration than the magnetic ones when ‘electrical’ and ‘magnetic’ compound muscle action potentials (cMAPs) of comparable amplitudes were elicited. SEPs were recorded respectively at Cv7 and on the somatosensory scalp areas contra- and ipsilateral to the stimulated side. SEPs showed a statistically significant difference in amplitude only for the brachial plexus response and for the ‘cortical’ N20-P25 complex; differences were not found between the magnetic and electrical central conduction times (CCTs) or for the peripheral nerve response latencies. Magnetic stimulation preferentially excited the motor and proprioceptive fibres when the nerve trunks were stimulated at motor threshold intensities.     

Failure of neuromuscular propagation during human maximal voluntary contraction

The mechanism for fatigue of the adductor pollicis was studied in normal subjects during maximal voluntary contractions (MVC) sustained for 90-100 s, by comparing the force and electrical response of this muscle to voluntary motor drive with that obtainable with artificial stimulation of the ulnar nerve. The adequacy of nerve stimulation was checked by recording simultaneously the electrical response of a nonfatiguing muscle, the abductor of the small finger. The decrease in force and in the natural electrical activity with fatigue was accompanied by a parallel decrease in the amplitude of synchronous muscle action potentials (M waves) evoked by artificial stimulation of the ulnar nerve at different frequencies. The decline in M-wave amplitude in the adductor pollicis was not due to a submaximal nerve stimulation, since the amplitudes recorded simultaneously from the nonfatiguing abductor digiti minimi remained unchanged. The force and the electrical responses from the adductor pollicis recovered in parallel with a half time of approximately 1 min. These results suggest that the loss of force of the adductor pollicis with fatigue and its subsequent recovery are largely determined by the extent of neuromuscular propagation failure. The slow recovery of the M-wave amplitude during repetitive stimulation suggests that it may be related to some aspect of muscle metabolism.     

The origin of slow potentials on the tongue surface induced by frog glossopharyngeal efferent fiber stimulation

When the glossopharyngeal (GP) nerve of the frog was stimulated electrically, electropositive slow potentials were recorded from the tongue surface and depolarizing slow potentials from taste cells in the fungiform papillae. The amplitude of the slow potentials was stimulus strength- and the frequency-dependent. Generation of the slow potentials was not related to antidromic activity of myelinated afferent fibers in the GP nerve, but to orthodromic activity of autonomic post-ganglionic C fibers in the GP nerve. Intravenous injection of atropine abolished the positive and depolarizing slow potentials evoked by GP nerve stimulation, suggesting that the slow potentials were induced by the activity of parasympathetic post-ganglionic fibers. The amplitude and polarity of the slow potentials depended on the concentration of adapting NaCl solutions applied to the tongue surface. These results suggest that the slow potentials recorded from the tongue surface and taste cells are due to the liquid junction potential generated between saliva secreted from the lingual glands by GP nerve stimulation and the adapting solution on the tongue surface.     

Depression of gustatory receptor potential in frog taste cell by parasympathetic nerve-induced slow hyperpolarizing potential

Parasympathetic nerve (PSN) innervates taste cells of the frog taste disk, and electrical stimulation of PSN elicited a slow hyperpolarizing potential (HP) in taste cells. Here we report that gustatory receptor potentials in frog taste cells are depressed by PSN-induced slow HPs. When PSN was stimulated at 30 Hz during generation of taste cell responses, the large amplitude of depolarizing receptor potential for 1 M NaCl and 1 mM acetic acid was depressed by approximately 40% by slow HPs, but the small amplitude of the depolarizing receptor potential for 10 mM quinine-HCl (Q-HCl) and 1 M sucrose was completely depressed by slow HPs and furthermore changed to the hyperpolarizing direction. The duration of the depolarizing receptor potentials depressed by slow HPs prolonged with increasing period of PSN stimulation. As tastant-induced depolarizing receptor potentials were increased, the amplitude of PSN-induced slow HPs inhibiting the receptor potentials gradually decreased. The mean reversal potentials of the slow HPs were approximately -1 mV under NaCl and acetic acid stimulations, but approximately -14 mV under Q-HCl and sucrose stimulations. This implies that when a slow HP was evoked on the same amplitude of depolarizing receptor potentials, the depression of the NaCl and acetic acid responses in taste cells was larger than that of Q-HCl and sucrose responses. It is concluded that slow HP-induced depression of gustatory depolarizing receptor potentials derives from the interaction between gustatory receptor current and slow hyperpolarizing current in frog taste cells and that the interaction is stronger for NaCl and acetic acid stimulations than for Q-HCl and sucrose stimulations.     

Motor innervation of the pharynx levator muscle of the snail, Helix pomatia: physiological and histological properties

(1) Motor innervation of the pharynx levator muscle of Helix pomatia was investigated with intracellular recording and axonal iontophoresis of cobalt chloride. (2) Muscle fibers respond to direct electrical stimulation of the muscle with active graded responses or non-overshooting spike potentials. (3) Each fiber is innervated via the external and internal lip nerves by several (mostly 3) excitatory nerve fibers each. Two types of EPSPs can be distinguished according to amplitude, duration, and facilitation. (4) Axonal CoCl2-staining via an external lip nerve branch revealed many nerve fibers entering the muscle and branching there into a rich network of blebbed fibers of various diameters.     

Chronic Low-Frequency Stimulation Transforms Cat Masticatory Muscle Fibers into Jaw-Slow Fibers

Cat masticatory muscle during regeneration expresses masticatory-specific myofibrillar proteins upon innervation by a fast muscle nerve but acquires the jaw-slow phenotype when innervated by a slow muscle nerve. Here, we test the hypothesis that chronic low-frequency stimulation simulating impulses from the slow nerve can result in masticatory-to-slow fiber–type transformation. In six cats, the temporalis muscle was continuously stimulated directly at 10 Hz for up to 12 weeks using a stimulator affixed to the skull. Stimulated muscles were analyzed by immunohistochemistry using, among others, monoclonal antibodies against masticatory-specific myosin heavy chain (MyHC), myosin binding protein-C, and tropomyosins. Under the electrodes, stimulation induced muscle regeneration, which generated slow fibers. Deep to the electrodes, at two to three weeks, two distinct populations of masticatory fibers began to express slow MyHC: 1) evenly distributed fibers that completely suppressed masticatory-specific proteins but transiently co-expressed fetal MyHCs, and 2) incompletely transformed fibers that express slow and masticatory but not fetal MyHCs. SDS-PAGE confirmed de novo expression of slow MyHC and β-tropomyosin in the stimulated muscles. We conclude that chronic low-frequency stimulation induces masticatory-to-slow fiber–type conversion. The two populations of transforming masticatory fibers may differ in their mode of activation or lineage of their myogenic cells.     

Effects of Q-switched Nd:YAG laser irradiation on neural impulse propagation: II. Dorsal roots and peripheral nerves.

We have studied the effects of Q-switched Nd:YAG laser irradiation on transmission of neural impulses in sensory nerve fibers in anesthetized rats and cats. Laser light was applied to dorsal roots (rat, cat) and to the sciatic nerve (rat) at increasing pulse energies ranging from 10 to 100 mJ/pulse for 5 minutes each. Compound action potentials recorded from dorsal roots and the sciatic nerve in response to high intensity electrical stimulation during laser application at increasing pulse energies showed a progressive preferential reduction of the slow late component of the electrically evoked response. Preliminary data from multifilament recordings from dorsal roots in cats demonstrated that conduction in small slow conducting fibers was blocked at lower laser pulse energies than in fibers with faster conduction velocities. These results imply, that laser light might have differential effects on slow versus fast conducting sensory nerve fibers. It is most likely that the preferential effect of laser irradiation on slow conducting fibers is mediated by photothermal mechanisms, since temperature increased substantially during laser application.     

Increased effectiveness of a motorneuron after partial denervation of its target muscle in the cricket Teleogryllus oceanicus

Fibers of the metathoracic extensor tibia muscle of the cricket Teleogryllus oceanicus are innervated by a slow excitatory axon (slow fibers), a fast excitatory axon (fast fibers), or by both slow and fast axons (dual fibers). Sectioning metathoracic nerve 5 removes the fast axon input to the muscle but not that of the slow axon. Following such partial denervation, the mechanical responses initiated by the slow axon increase progressively for at least 30 days; twitch tensions reach 5–10 times those of control muscles and tetanic tensions 10–30 times control values. After sectioning nerve 5, resting membrane potentials decrease in those fibers which originally received fast axon input and the input resistance of all fiber types increases, including that of slow fibers which are not innervated through nerve 5. Excitatory junctional potentials (EJPs) initiated by the slow axon become larger following partial denervation, accounting in part for the larger contraction amplitudes. The increased input resistance is adequate to account for the larger EJPs in slow fibers but not for the proportionally greater increase in EJP amplitude in fibers which were formerly dually innervated. The change in EJP amplitude is abrupt in slow fibers and gradual in formerly dual fibers.     

Changes in the electrical activity of the rabbit proximal colon in vivo by stimulation of the vagus and splanchnic nerves]

1. Using extracellular electrodes placed on the serosa, we recorded the modifications of the electrical activity of the colonic muslce fibers caused by the stimulation of vagal and splanchnic nerve fibers. 2. Vagal stimulation produces two types of junction potentials: excitatory junction potentials (EJPs) and inhibitory junction potentials (IJPs). The IJPs are elicited by stimulation of vagal fibers which innervate intramural non-adrenergic inhibitory neurons. 3. The conduction velocity of the nerve impulse along the vagal pre-ganglionic fibers is 1.01 m/sec for excitatory fibers and 0.5. m/sec for inhibitory fibers. 4. Splanchnic fiber stimulation causes EJP disappearance, blocking transmission between preganglionic fibers and intramural excitatory neurons, and a decrease in IJP amplitude that most likely indicates a previous hyperpolarization of the smooth muscle. 5. IJP persistence during splanchnic stimulation proves that sympathetic inhibition does not modify the transmission of the vagal influx onto the non-adrenergic inhibitory neurons of the intramural plexuses. 6. Through a comparative study of proximal and distal colonic innervation, we are able to show that there is a similar organization of both regions, that is a double inhibitory innervation: an adrenergic one of a sympathetic origin, and a non adrenergic one of a parasympathetic origin.     

Studies on the mid-gut of the desert locust, Schistocerca gregaria.

ABSTRACT. The gross morphology of the mid-gut musculature of the desert locust, Schistocerca gregaria is described. Some of the electrophysiological characteristics of the external longitudinal muscle fibres were examined. The membrane potentials have mean values of -24.7mV (SE ± 7.3). Spontaneous post-synaptic potentials were recorded, and the responses of the muscle fibres to electrical stimulation of their nerve supply studied.     

Slow potentials in taste cells induced by frog glossopharyngeal nerve stimulation

Intracellular recordings were made from the taste cells of atropinized bullfrogs while the glossopharyngeal (GP) nerve fibres were electrically stimulated. Two types of slow potential, slow hyperpolarizing potentials (HPs) and slow depolarizing potentials (DPs), were induced in the taste cells. The slow HPs appeared when the lingual capillary blood flow was kept above 0.7 mm/s, whereas the slow DPs appeared when the blood flow was slowed down below 0.7 mm/s. The membrane resistance of a taste cell increased during the generation of a slow HP, but decreased during the generation of a slow DP. The reversal potentials for the slow HPs and the slow DPs were recorded at the same membrane potential (-11 to approximately -13 mV). Activation of non-selective cation channels possibly induced the slow DP and inactivation of those channels possibly induced the slow HP in the taste cell membrane. Electrical stimulation of the GP nerve activated a population of C fibres in the nerve and possibly released neurotransmitters from the nerve terminals. Released neurotransmitters might cause modulation of the membrane conductance in taste cells that leads to generation of the slow potentials. The present data suggest that slow HPs and slow DPs evoked in the taste cells of atropinized frogs by GP nerve stimulation are induced by putative neurotransmitters in the taste disc.     

Characteristics of biphasic slow depolarizing and slow hyperpolarizing potential in frog taste cell induced by parasympathetic efferent stimulation

When the velocity of capillary blood flow in the frog tongue declined to an intermediate range of 0.2-0.7 mm/s, the glossopharyngeal nerve stimulation induced a biphasic slow depolarizing and slow hyperpolarizing potential (HP) in taste cells. The objective of this work was to examine the generative mechanisms of the biphasic slow potentials. The biphasic slow response was always preceded by a slow depolarizing potential (DP) component and followed by a slow HP component. Intravenous injection of tubocurarine completely blocked the biphasic slow responses, suggesting that both components of the biphasic slow potentials are evoked by the parasympathetic nerve (PSN) fibers. Membrane conductance of taste cells increased during slow DPs and decreased during slow HPs. The reversal potential of either component of a biphasic slow response was the almost same value of -12 mV. An antagonist, L-703,606, for neurotransmitter substance P neurokinin(1) receptor completely blocked both components of the biphasic slow responses. An antagonist, flufenamic acid, for nonselective cation channels on the taste cell membrane completely blocked the biphasic slow responses. These results suggest that PSN-induced biphasic slow responses are postsynaptically elicited in taste cells by releasing substance P at the PSN axon terminals. It is concluded that the slow DP component may be generated by opening one type of nonselective cation channel on taste cells and that the slow HP component may be generated by closing the other type of nonselective cation channel. We discussed that a second messenger inositol 1,4,5-trisphosphate might be related to a slow DP component and another second messenger diacylglycerol might be related to a slow HP component.     

Taste cell responses in the frog are modulated by parasympathetic efferent nerve fibers

We studied the anatomical properties of parasympathetic postganglionic neurons in the frog tongue and their modulatory effects on taste cell responses. Most of the parasympathetic ganglion cell bodies in the tongue were found in extremely small nerve bundles running near the fungiform papillae, which originate from the lingual branches of the glossopharyngeal (GP) nerve. The density of parasympathetic postganglionic neurons in the tongue was 8000-11,000/mm(3) of the extremely small nerve bundle. The mean major axis of parasympathetic ganglion cell bodies was 21 microm, and the mean length of parasympathetic postganglionic neurons was 1.45 mm. Electrical stimulation at 30 Hz of either the GP nerve or the papillary nerve produced slow hyperpolarizing potentials (HPs) in taste cells. After nicotinic acetyl choline receptors on the parasympathetic ganglion cells in the tongue had been blocked by intravenous (i.v.) injection of D-tubocurarine (1 mg/kg), stimulation of the GP nerve did not induce any slow HPs in taste cells but that of the papillary nerve did. A further i.v. injection of a substance P NK-1 antagonist, L-703,606, blocked the slow HPs induced by the papillary nerve stimulation. This suggests that the parasympathetic postganglionic efferent fibers innervate taste cells and are related to a generation of the slow HPs and that substance P is released from the parasympathetic postganglionic axon terminals. When the resting membrane potential of a taste cell was hyperpolarized by a prolonged slow HP, the gustatory receptor potentials for NaCl and sugar stimuli were enhanced in amplitude, but those for quinine-HCl and acetic acid stimuli remained unchanged. It is concluded that frog taste cell responses are modulated by activities of parasympathetic postganglionic efferent fibers innervating these cells.     

Penis-retractor muscle of Aplysia: excitatory motor neurons

Cobalt axonal iontophoresis and intracellular recordings were used to identify a cluster of several motor neurons innervating the penis-retractor muscle of Aplysia. Intracellularly recorded motor neuron action potentials elicited direct, one-for-one, constant latency excitatory junctional potentials (ejps) in individual muscle fibers. The axons of motor neurons could be recorded extracellularly in the penis-retractor nerve and stimulation of the nerve backfired the motor neurons. Perfusion of the ganglion, the muscle, or both with solutions of either increased Mg++/decreased Ca++ or increased Ca++ sea water indicated that the presumed motor neuron impaled was not a sensory cell and that interneurons were not intercalated in the pathway. Innervation of muscle fibers was found to be functionally polyneuronal and diffuse. The ejps were found to undergo marked facilitation with repetitive motor-neuron stimulation. The motor neurons were isolated in a distinct cluster in the right pedal ganglion. Their electrical activity was characterized by spontaneous irregular action potentials and a moderate input of postsynaptic potentials.     

Certain functional connections of neurons control the walking of the cockroach Periplaneta americana

On isolated abdominal nervous chain of the cockroach studies have been made of the responses of motoneurones of the thoracic ganglion to electrical stimulation of afferent axons of the leg nerve under normal conditions and during application of an anticholinesterase drug, GD-7. Depending on the type of stimulated axons, monosynaptic response, as well as polysynaptic phasic and tonic responses of motoneurones were recorded. A scheme of activation of motoneurones is suggested which evokes slow contractions of muscles in cockroach extremities.     

Synapse elimination by fiber type and maturational state in rabbit soleus muscle

We have compared the development of fast and slow motor innervation in the neonatal rabbit soleus, a muscle which contains two distinct motor unit types during the early period of polyneuronal innervation. The innervation state of individual muscle fibers was ascertained using an intracellular electrode; a fluorescent dye was then injected into particular fibers to permit subsequent identification of histochemical type. We found no significant difference in the time course of synapse elimination for fast and slow motor units as judged by the percentage of fibers remaining polyneuronally innervated at two ages: 7-8 days, when most fibers are multiply innervated, and 10-11 days, when the level of polyinnervation is low. In a second experiment, we examined a phenomenon in which compound end-plate potentials were occasionally seen in muscle fibers at an age (17-23 days) well past the major episode of synapse elimination. We present evidence that this apparent polyinnervation in fact derives from an electrode-induced electrical coupling artifact and that genuinely polyinnervated fibers are very rare at this stage, if present at all.