The response of motor neurones to intramuscular injection of botulinum toxin

Abstract

SUMMARY1. The dry mass and nucleic acid content of both nerve cell bodies and their nucleoli were measured by interference microscopy and ultra-violet absorption microspectrography respectively: succinoxidase and acetylcholine hydrolase activities were also determined. Autoradiography was used to follow synthesis of deoxyribonucleic acid (DNA) by glial cells, and to follow nucleic acid and protein metabolism in muscle fibres.2. After injection of botulinum toxin the synthesis of ribosomal RNA by the neurone followed closely the pattern found after axotomy.3. After injection of toxin neuronal dry mass increased before the rate of ribosomal RNA synthesis was raised. This early increase, which was not due to increased protein synthesis, probably represents a 'damming back' of proteins within the nerve cell body.4. After injection of toxin no local accumulation of microglial cells synthesizing DNA was found around the affected neurones: it is suggested that this reflects the intact system for intra-axonal transport under these conditions. 5. The affected muscles show increased nucleic acid and protein synthesis.6. It is suggested that the results obtained indicate that membrane expansion or synthesis which occurs both in muscle and in neurone under these circumstances is the factor responsible for inducing directly or indirectly the changes found in nucleic acid metabolism after injection of botulinum toxin and after axotomy.

Some quantitative observations upon the responses of neuroglial cells which follow axotomy of adjacent neurones

“…Rats were killed 90 min after injecting uridine and 60 min after leucine: previous unpublished studies had indicated that these intervals were optimum for detecting the altered uptake and incorporation which accompanied altered nucleolar nucleic acid content and dry mass. The autoradiographic techniques have been described previously (Watson, 1965;Sumner & Watson, 1972 (Watson, 1966b) Unlike such measurements in isolated neuronal nuclei (Watson, 1968(Watson, , 1969(Watson, , 1970, the nucleolar dry mass and nucleic acid content of neuroglial cells had to be measured within the total isolated cell, including thin covering and underlying layers of perinuclear cytoplasm in addition to nucleoplasin. Initial studies indicated that the values obtained for nucleolar dry mass and nucleic acid content were over-estimated by 18 and by 12 % respectively: similar values were obtained in cells reacting after axotomy.…”

“…Study of groups two and four allowed the significance of metabolic change in the nerve cell, which occurred under these circumstances (Watson, 1970) to be distinguished from the significance of retraction and re-expansion of the dendritic tree, which was already retracted following the previous axotomv, and underwent no re-expansion until the axon reinnervated denervated muscle (Summer & Watson, 1971). In the fifth group 250 pg botulinum toxin type D was injected into the extrinsic and intrinsic muscles of the left half of the tongue (Watson, 1969) to impede neuromuscular transmission without loss of axoplasm.…”

“…The part of the hypoglossal nucleus rostral to the obex was removed rapidly and glial cells prepared as described previously (Summer & Watson, 1972). The dry mass of the cell or of its nucleolus was measured by interference microscopy (Watson, 1969): the nucleic acid content was determined by ultraviolet absorption microspectrography (Watson, 1968). In autoradiographic studies tritiated [5-3H] Severinghaus, 1963): the final activity of the amino acid or uridine solution was 0-8 mCi/ml.…”

“…Changes in neuronal metabolism have been measured under these circumstances using quantitative techniques of cell biology (Watson, 1965(Watson, , 1966a(Watson, , 1968(Watson, , 1969. Concurrent changes in perineuronal glial cells have been observed histologically (Cammermeyer, 1955;Rapos & Bakos, 1959;Watson, 1965;Kreutzberg, 1966Kreutzberg, , 1967Sjbstrand, 1966;Friede & Johnstone, 1967;Roessmann & Friede, 1968;Adrian, 1969;Adrian & Smothermon, 1970), but are difficult to interpret because of the limited reproducibility of metal impregnation techniques, and because of the problems of classifying glial cells by nuclear morphology when basophilic stains are used, especially when the nuclei are partially obscured in autoradiographs.…”

Regulation of Motoneuron Excitability via Motor Endplate Acetylcholine Receptor Activation

“…An example is axotomy itself, in which premature return to the cell body of material normally transported along the axon in an anterograde direction could, in principle, trigger the effects of axotomy (Grafstein, 1983). Another example is intramuscularly injected botulinum toxin (botox), which can evoke axotomy-like changes in motoneurons after 2-3 weeks (Watson, 1969;Pinter et al, 1991) but exerts its primary action presynaptically, in which it inhibits acetylcholine (ACh) release (Molgo et al, 1990;Meunier et al, 2002).…”