Martin E. Atkinson

A quantitative study of neuropeptide immunoreactive cell bodies of primary afferent sensory neurons following rat sciatic nerve peripheral axotomy

Following peripheral axotomy, fluoride resistant acid phosphatase (FRAP) and most neuropeptides are depleted in the central terminals of axotomised nerves and reduced in their corresponding cell bodies (DRG) but vasoactive intestinal polypeptide (VIP) increases. The increase in VIP probably results from a change in gene expression in other ganglion cells which do not normally express VIP. A quantitative study was performed to investigate the proportion of DRG cells immunoreactive for different peptides at increasing times after sciatic nerve section. Retrograde fluorescent neuronal labelling of sciatic nerve cell bodies by injection of fast blue into the proximal stump was combined with unlabelled antibody immunohistochemistry for CGRP and VIP. The proportion of cells immunoreactive for these peptides was quantified between two and fourteen days post-axotomy. The number of VIP immunoreactive profiles increased significantly in the first 4 days post-axotomy, followed by a slight decrease before rising again. In contrast, the number of and CGRP-immunoreactive cell profiles declined to zero by 14 days post-axotomy. 4 days post-axotomy 50% of VIP positive cells were also immunoreactive for CGRP. There was neither colocalisation between VIP and FRAP nor between CGRP and FRAP. It is concluded that many peptidergic DRG cell bodies switch their expression of peptide to VIP after injury, whereas non-peptide-containing subpopulations do not.

Peripheral axotomy of the rat mandibular trigeminal nerve leads to an increase in VIP and decrease of other primary afferent neuropeptides in the spinal trigeminal nucleus.

In the vasoactive intestinal polypeptide (VIP)-rich lumbosacral spinal cord, VIP increases at the expense of other neuropeptides after primary sensory nerve axotomy. This study was undertaken to ascertain whether similar changes occur in peripherally axotomised cranial sensory nerves. VIP immunoreactivity increased in the terminal region of the mandibular nerve in the trigeminal nucleus caudalis following unilateral section of the sensory root of the mandibular trigeminal nerve at the foramen orale. Other primary afferent neuropeptides (substance P, cholecystokinin and somatostatin) were depleted and fluoride-resistant acid phosphatase activity was abolished in the same circumscribed areas of the nucleus caudalis. The rise in VIP and depletion of other markers began 4 days postoperatively and was maximal by 10 days, these levels remaining unchanged up to 1 year postoperatively. VIP-immunoreactive cell bodies were absent from trigeminal ganglia from the unoperated side but small and medium cells stained intensely in the ganglia of the operated side after axotomy. These observations indicate that increase of VIP in sensory nerve terminals is a general phenomenon occurring in both cranial and spinal sensory terminal areas. The intense VIP immunoreactivity in axotomised trigeminal ganglia suggests that the increased levels of VIP in the nucleus caudalis are of peripheral origin, indicating a change in expression of neuropeptides within primary afferent neurons following peripheral axotomy.

The surgical anatomy of the mandibular distribution of the facial nerve

There are many controversies about the course of the mandibular nerve in the submandibular region. In an attempt to resolve these and improve the safety of submandibular approaches a study was undertaken based on anatomical dissection and measurement of 110 facial halves. In over half the specimens the mandibular nerves ran below the mandible and a significant proportion continued below the mandible distal to the facial vessels. The nerves lay in a plane between the platysma and the investing fascia. These findings influence the placement and depth of incisions in the submandibular region and the margins of safety attainable.

The surgical anatomy of the cervical distribution of the facial nerve

Abstract In an attempt to improve the safety of the submandibular approach to the mandible and submandibular gland anatomical dissections of 110 facial halves were undertaken. Observations were made on the course of the cervical branch of the facial nerve in relation to bony and soft tissue landmarks and fascial planes. The course of the nerve and its relation to the platysma muscle and investing fascia dictate the placement and depth of incision used for the submandibular approach.

Compartmentalisation of the developing trigeminal ganglion into maxillary and mandibular divisions does not depend on target contact

During development axons contact their target tissues with phenomenal accuracy but the mechanisms that control this homing behaviour remain largely elusive. A prerequisite to the study of the factors involved in hard‐wiring the nervous system during neurogenesis is an accurate calendar of developmental events. We have studied the maxillary and mandibular components of the trigeminal system to determine the stages during embryogenesis when a gross somatotopic order is first established within the trigeminal ganglion and the axons projecting to the brainstem. The retrograde transganglionic fluorescent tracers DiO and DiI were injected into the maxillary and mandibular arches or their derivatives in fixed mouse embryos staged between 13 and 40 somites (E9–E11). After 1–4 wk, the distribution of the 2 tracers was determined using confocal laser scanning microscopy. The first maxillary nerve cell bodies and their developing axons were labelled at the 30 somite stage (E10). This was 2 somite stages earlier than the mesencephalic nucleus and the ganglion cell bodies of the mandibular nerve. The gross somatotopic division of cells within the trigeminal ganglion projecting to the maxillary and mandibular targets was established by the 32 somite stage (E10). This arrangement was evident as 2 groups of cell bodies occupying adjacent but separate regions of the trigeminal ganglion. The central branches of the maxillary and mandibular cell bodies entered the metencephalon as 2 distinct bundles at the same stage. The trigeminal motor nucleus was first detected at the 38 somite stage (E10.5).

The ontogeny of substance P-containing nerve fibres in the developing mouse dentition

SummaryThe putative neurotransmitter, substance P, was localised in the developing teeth and periodontium of mice by indirect immunofluorescence. Substance P-containing fibres were visible in the incisor dental follicle eighteen days post-conception and entered the pulp two days after birth. The first molar pulp was innervated four days after birth and the second molar six days after birth. Innervation of the teeth by substance P fibres was delayed compared with the mucous and cutaneous innervation of adjacent areas and correlated with the stage of development of the teeth rather than the chronological age of the animal. The innervation of developing dental structures by substance P probably represents the establishment of a sensory supply prior to function of the tooth.

The effects of prenatal capsaicin on the distribution of substance P in developing primary afferent neurons.

Capsaicin was injected subcutaneously into 15-day pregnant mice and by transuterine injection into foetuses of the same age. Indirect immunofluorescence was used to assess its effects on the distribution of substance P. Capsaicin administered to either the mother or the foetus crossed the placenta and depleted substance P from the primary afferent terminal field in the spinal cord and abolished reactivity in the dorsal root ganglia and peripheral terminals of spinal nerves. Subcutaneous capsaicin administration to the pregnant female is, operationally, the easiest method providing low doses are used; otherwise pregnant females seem highly susceptible to respiratory failure. These results suggest the use of capsaicin to study prenatal ontogeny of sensory nerves.

A histochemical study of the cholinergic and adrenergic innervation of the developing teeth and oral tissues in the mouse

The dental follicle and papilla are innervated at different stages of tooth development. The type of nerves innervating these structures at different stages was investigated using an enzymic method for acetylcholinesterase (AChE) and direct visualization for noradrenaline on fetal and neonatal stages up to 7 days after birth. Glandular and muscular tissue were positive for AChE in 17-day fetuses but no reaction was observed in the teeth or supporting tissues up to 7 days after birth. Noradrenaline was detected in blood vessels at 18 days and in glandular tissue at birth but was not observed in the teeth within the period covered. It is unlikely that AChE plays any role in the innervation of teeth; the adrenergic nerve supply probably develops later.

The ontogeny of substance P fibers in the mouse trigeminal nerve.

The putative neurotransmitter substance P was localized in the embryonic and neonatal mouse trigeminal nerve by indirect immunofluorescence. Central terminals in the nucleus caudalis gave a positive substance P-like immunofluorescence (SPLI) reaction of E13-E14. SPLI subsequently appeared in the peripheral mucous and cutaneous nerves at E16-17 at which time trigeminal nucleus cell bodies were also positive. These findings indicate the early development of primary afferent nociceptive pathways.

THE ANGULAR TRACT: AN ANATOMICAL STRUCTURE OF SURGICAL SIGNIFICANCE

Abstract During the course of anatomical studies of the submandibular region, the presence of a strong fascial band running deep from the investing fascia to the fascia of the posterior belly of the digastric was repeatedly encountered. This angular tract is described in detail. Its position as a division between the submandibular gland and lower portion of the parotid gland suggests that the tract is potentially useful as a landmark and as protection for the glands and their contents in submandibular surgical approaches.