In the preceding paper (Buller, Eccles & Eccles, 1960) evidence was presented which suggested that the differentiation of slow muscles of the cat hind limb to a large extent failed to occur after certain operative procedures on the spinal cord. This finding indicates that in some way the central nervous system controls muscle differentiation. A more analytic investigation into this postulated influence of nerve on muscle has been accomplished by dividing and cross-uniting nerves to fast and slow muscles, so that motoneurones formerly innervating the fast muscle come to innervate the slow muscle by virtue of the regenerative outgrowth of their fibres, and vice versa for the motoneurones of the slow muscle. The effect of this crossed innervation on the speed of muscle contraction has been tested at varying times after the cross-union. These investigations have also been carried out on animals subjected to the operative procedures on the spinal cord, as previously described (Buller et al. 1960). Cross-union experiments allow in addition an investigation into the possible effects in the reverse direction, i.e. of speed of muscle contraction on the conduction velocity of the axons and the after-hyperpolarization of the motoneurones which innervate it. A preliminary account of part of this investigation has already been published (Bulier, Eccles & Eccles, 1958).

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.1960.sp006395

Interactions between motoneurones and muscles in respect of the characteristic speeds of their responses.

Publisher Summary This chapter takes a view of biogenic amines in the insect nervous system and to assess critically the evidence for their roles as neurotransmitters, neuromodulators and neurohormones. It attempts to answer several questions such as where biogenic amines are located in the insect nervous system; how are they synthesized and inactivated; and what physiological roles do they perform and how do they bring about their effects. Particular emphasis is placed on the correlation of biochemical, physiological, pharmacological and anatomical information from systems containing identified aminergic neurones. The chapter points out instances where data from one or more of the approaches is either missing or conflicts with that from another and suggests experiments to resolve these points. The function of biogenic amines in the insect nervous system has been compared with that in the vertebrate nervous system. In this context the chapter mentions the role of biogenic amines as chemical messengers in the vertebrate nervous system.

Biogenic Amines in the Insect Nervous System

I. We have studied the central and peripheral functions of the metacerebral cell (MCC) ofAplysia. This research concentrated on the role of the MCC in controlling the ARC muscle, which is representative of a group of muscles that effect the biting and swallowing response of Aplysia. 2. Firing of the MCC produced a slowly rising and slowly decaying excitatory synaptic potential in motoneurons of the ARC muscle and other muscles of the buccal mass. The excitatory synaptic potential was not sufficient to fire motoneurons unless they received another source of depolarization. 3. In isolated buccal ganglia that exhibit periodic burst output, firing of the MCC at low, physiological rates, increased the frequency of occurrence of the burst output. Firing of the MCC was never effective in eliciting sustained burst output from nonbursting ganglia. 4. Although the MCC sends axonal branches to nerves innervating the accessory radula closer (ARC) and other muscles, firing of the MCC produced neither an increase nor decrease of the resting tension of the ARC muscle. Furthermore, firing of the ARC was never associated with any direct depolarizing or hyperpolarizing responses in muscle fibers. 5. Brief firing of the MCC enhanced the muscle contraction produced by firing of ARC motoneurons. The enhancement of contraction was maximum approximately 30 s after termination of a brief burst of MCC spikes (e.g., 30 spikes at 5/s), and the process then gradually decayed over a period of a minute or more. Physiological rates of MCC firing (see below) also enhanced contraction of ARC muscles. 6. The above data suggested that the MCCs might be involved in feeding behavior. To explore this hypothesis, chronic extracellular recordings from a MCC were obtained while ani-

Modulatory control of buccal musculature by a serotonergic neuron (metacerebral cell) in Aplysia

1. Spikes in the octopaminergic dorsal unpaired median (DUM) neurone which innervates the extensor tibiae muscle of the locust metathoracic leg (DUMETi) produce direct and indirect effects on muscle tension. 2. Direct effects include a slowing of an intrinsic rhythm of contraction and relaxation, a relaxation of muscle tone and a small hyperpolarization of the muscle membrane potential. The latter two effects are weak and variable. All three effects are mimicked by superfusion of octopamine and are mediated by octopamine receptors on the muscle fibres. 3. Indirect effects are found when the DUMETi neurone is stimulated at the same time as the motoneurones innervating the extensor muscle. They include (a) potentiation of tension generated in the extensor muscle by spikes in the slow excitatory motoneurone (SETi), (b) reduction in duration of each twitch contraction generated by SETi due to an increase in the rate at which the muscle relaxes, (c) increase in the amplitude of the synaptic potential generated by SETi. These various effects have a time course of several minutes and far outlast the duration of DUMETi stimulation. They can be mimicked by superfusion of octopamine. 4. The effect of DUMETi on neuromuscular transmission is mediated by receptors with a high affinity for octopamine located both on the muscle and on the terminals of the slow motoneurone. The presence of the presynaptic receptors is revealed by the increase in the frequency of spontaneous miniature end plate potentials recorded in the muscle in the presence of octopamine. 5. DUMETi is a member of a group of similar aminergic neurones and it is suggested that they may share a role in modulating transmission at peripheral neuromuscular synapses, and possibly central synapses.

Potentiation of Neuromuscular Transmission by an Octopaminergic Neurone in the Locust

Relaxation of vertebrate skeletal muscle. A synthesis of the biochemical and physiological approaches.

Adrenaline, noradrenaline and other sympathomimetic amines have been shown to increase the maximal twitch tension of unfatigued skeletal muscles (Oliver & Schaefer, 1895; Gruber, 1922a, b; Goffart & Brown, 1947; West & Zaimis, 1949; Brown, Goffart & Vianna Dias, 1950; Goffart & Ritchie, 1952; Huidobro, Cubillos & Eyzaguirre, 1952; Goffart, 1952, 1954; Montagu, 1955). This response, however, is not characteristic of all skeletal muscles. In fact the present experiments show that, in the cat, slow contracting muscles such as the soleus respond in a completely opposite way. A short account of the results has already been published (Bowman & Zaimis, 1955).

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.1958.sp006088

W. C. Bowman

Papers

The effects of adrenaline, noradrenaline and isoprenaline on skeletal muscle contractions in the cat