Nitric oxide (NO) is a unique biological messenger molecule. It serves, in part, as a neurotransmitter in the central and peripheral nervous systems. Neurons containing NO have been identified histochemically by the presence of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) reactivity or immunohistochemically by the antibody for neuronal NO synthase (n-NOS). Previous histochemical or pharmacological studies have raised the possibility that NO may play an important role in the neural pathways of the lower urinary tract. There is also considerable evidence to suggest that n-NOS is plastic and could be upregulated following certain lesions in the lower urinary tract. The present review summarises the distribution of n-NOS containing neurons innervating the urinary bladder and the changes of the enzyme expression in some experimentally induced pathological conditions.

The distribution of glycoconjugates was examined in the nonsensory regions of the rat cochlea during postnatal development using biotin-conjugated lectins. Temporal bones of rats at postnatal d 1 and at wk 2, 4 and 6 were fixed in 4% paraformaldehyde and 0.1% glutaraldehyde and processed for paraffin wax embedding. The dewaxed sections were incubated with 7 biotinylated lectins, followed by avidin-biotin- peroxidase complex. A different staining pattern was observed in the stria vascularis, spiral ligament and spiral limbus in the age groups examined. The staining intensity varied between lectins and the reaction product exhibited limited disparity. The staining intensity for WGA increased with age in all the 3 nonsensory regions. The staining patterns for the other lectins differed in the various nonsensory regions examined indicating tissue specificity. The limited variations in the lectin binding patterns after 2nd wk of postnatal life also indicate that the changes in the carbohydrate moieties are established during the fetal period of cochlear development and limited changes take place during postnatal maturation of the nonsensory regions.

The anatomy of the lymphoid organs was studied during the course of detailed dissections of 50 beach-stranded bottlenose dolphins, Tursiops truncatus. Constant lymph nodes occur in 4 groups, based on their location and structure. These groups are somatic, including nodes of the cervical region and pelvic recess; lung-associated, included marginal, diaphragmatic and hilar nodes; visceral, including the mesenteric, pancreatic, pericolic and porta hepatis nodes; and aortic arch nodes. Lymphatic drainage of the lung is primarily to the marginal and diaphragmatic nodes. The mesenteric node mass is well-endowed with capsular and trabecular smooth muscle, and a network of muscle fascicles within the organ implies an important contractile function in the circulation of lymph. In addition to constant nodes, occasionally nodes are found in relation to the thoracic aorta, the kidney, and under the scapula. Gut-associated structures include dorsal and ventral oropharyngeal tonsils, mucosal aggregates in the straight segment of the intestine (colon) and anal tonsils; this gut-associated lymphoid tissue tends to involute with age, being greatly reduced by puberty. Formed lymphoid organs include the thymus and the spleen, the latter being relatively small in relation to body size. None of these structures is unique among cetaceans, but the anal tonsils are particularly well developed in T. truncatus. The lymphoid aggregates in the colon resemble the arrangement in the vermiform appendix, which is lacking in most cetaceans, and may have functions analogous to that organ.

Angiogenesis is essential for the replacement of cartilage by bone during growth and repair. In order to obtain a better understanding of the mechanisms regulating vascular invasion at sites of endochondral ossification we have investigated the expression of the endothelial cell-specific mitogen, vascular endothelial growth factor (VEGF), by chondrocytes in human neonatal growth plates. VEGF was absent from chondrocytes in the resting zone and only weakly expressed by occasional chondrocytes in the proliferating region. In the hypertrophic zone the number of chondrocytes stained and the intensity of staining for VEGF increased with chondrocyte hypertrophy, maximum expression of VEGF being observed in chondrocytes in the lower hypertrophic and mineralised regions of the cartilage. These observations provide the first demonstration of the presence of VEGF in situ in developing human bone and are consistent with in vitro observations demonstrating the upregulation of proangiogenic growth factor production with increasing chondrocyte hypertrophy. The presence of numerous small blood vessels and vascular structures in the subchondral region where VEGF expression was maximal indicates that VEGF produced by hypertrophic chondrocytes may play a key role in the regulation of vascular invasion of the growth plate.

The interosseous nerve of birds innervates a string of Herbst corpuscles located near the interosseous membrane between the tibia and fibula. Fibre composition of this nerve was assessed including both myelinated and unmyelinated axons. The diameter of the whole nerve is ∼100 μm. Complete data were obtained for 3 nerves. The mean total number of myelinated fibres and unmyelinated axons was 2872±53. The mean number of myelinated fibres was 280±20 and that for unmyelinated axons was 2600±47. There was a broad distribution of diameters for myelinated fibres ranging from ∼2 μm to 10 μm with a distinct peak at ∼3–5 μm and a less prominent second peak at 6–8 μm. Similarly, myelin sheath thickness distribution showed 2 peaks, one at 0.6–0.8 μm and another at 1.4–1.6 μm. It is suggested that the group represented by the second peak innervates the Herbst corpuscles. The group of smaller myelinated fibres and the unmyelinated axons are assumed to innervate other types of receptors, some of which may be nociceptors.

As part of a large comparative study on the development of reptilian skin, we provide the first ultrastructural description of differentiation of the epidermis of the carapace and plastron in the Chelonia, using the Australian pleurodiran turtle Emydura macquarii as a model. The epidermis is initially composed of an external flat peridermis and a basal layer of cuboidal cells. During differentiation, the peridermis darkens, flakes off and is partially lost before hatching. Four to 6 layers of flat cells containing lipids and mucus form from the basal layer beneath the external peridermis. Because such cells are found only during embryogenesis, we have referred to these layers as embryonic epidermis. They contain reticulate bodies made of a meshwork of coarse filaments similar to those described in the inner peridermis of lizard and bird embryos. In advanced embryos, cells of the embryonic epidermis condense into a thin dark stratum which is subsequently lost after hatching. The lowermost 2 layers of the embryonic epidermis keratinise, as for a typical lepidosaurian α-layer. A splitting zone is progressively formed beneath the α-layer to separate the embryonic epidermis from the underlying β-layer. Patterns of cytodifferentiation of the β-synthesising cells over the carapace and plastron essentially resemble those of the lepidosaurian epidermis. The β-keratin matrix initially accumulates among ribosomes as round bodies not clearly surrounded by a membrane. These bodies appear not to be derived from the Golgi apparatus. Melanosomes and other dark granules of uncertain nature are present among early differentiating β-cells. The round β-keratin bodies merge with the dense bodies to produce the definitive variegated pattern of the mature β-keratin layer. The histochemistry suggests that calcium combines with organic molecules within β-keratinising cells to harden the tissue. In contrast to the β-keratin cells of lizards and snakes, cells of the mature β-keratin layer of E. macquarii maintain their cell boundaries in part or completely, a characteristics shared with the β-keratin layer of Sphenodon and crocodilians.

Neuronal nitric oxide synthase immunoreactivity (NOS1-ir) in sacral motor neurons of normal adult cats was compared with that in cats surviving 1–10 wk after unilateral transection and ligation of the pudendal nerve. Levels of immunostaining were measured by microdensitometry. In nonoperated cats 60% of motor neurons in the ventrolateral nucleus (VL) and Onuf's nucleus (ON) showed high levels of NOS1-ir with lower NOS1-ir in 40%. Following axotomy, motor neurons in ON on both sides of the cord showed an acute rise in mean level of NOS1-ir at 1 wk, with a further increase at 2 wk. Mean levels of NOS1-ir in the ipsilateral and contralateral ON remained elevated at 10 wk after axotomy. Elevation of NOS1-ir occurred in the VL with a similar time-course to that in ON, implying a wider response in motor nuclei synaptically coupled to ON. Measurements of neuronal size in ON and VL revealed an increase in neuronal size in ON but not VL, indicating increased NOS1-ir in ON was not an artifact of neuronal atrophy. The proportion of motor neurons in ON and VL possessing higher levels of NOS1-ir increased from 60% in controls to 100% at 2–3 wk postaxotomy. The proportion slightly declined by 8 wk due to re-emergence of motor neurons exhibiting low NOS1-ir, but remained greater than normal at 10 wk in both nuclei. Based on evidence from related analyses of synaptology, we argue that acute axotomy induced alterations in presynaptic complement which increased overall Ca2+ influx and thereby stimulated NOS1-ir.

Glutamine synthetase (GS) is a glucocorticoid-inducible enzyme that has a key role for glutamate metabolism in the central and peripheral nervous system. In this study GS activity was measured and the amount of immunoreactive GS (ir-GS) cells in the rat anterior pituitary gland was quantified as a function of age. In addition, the effects of GS inhibitors, glucocorticoid administration, and adrenalectomy on GS activity were examined. Some of the ir-GS cells were also immunoreactive for S100 protein (ir-S100) which is a known marker for folliculostellate cells (FS) in the anterior pituitary. FS cells expressing GS were first detected in 3-d-old rats, and this cell population, expressed as the immunostained cell area divided by a standard unit area, increased as a function of age. The percentages of FS cells also expressing GS were 0.2, 6.4, 25 and 74% at 3 d, 30 d, 60 d and 2 y of age, respectively. GS enzyme activity also increased in parallel with the increase of ir-GS cell population maturation. The subcutaneous injection of methionine sulphoximine, a GS and γ-glutamylcysteine synthetase inhibitor, reduced pituitary GS activity by 83%, but increased the population of ir-GS cells 3.5-fold in 30-d-old rats. Buthionine sulphoximine, a specific inhibitor of γ-glutamylcysteine synthetase, had little effect on GS activity or the ir-GS cell population. Neither methionine sulphoximine nor buthionine sulphoximine changed the population of ir-S100 protein cells (FS cells). Dexamethasone and hydrocortisone increased the population of ir-GS cells by 3.1 and 4.2-fold, respectively, within 12 h after administration. A significant increase of GS activity due to the injection of glucocorticoids was observed in the anterior pituitary, but not in the brain, retina or liver of immature rats. Adrenalectomy did not cause decrease of pituitary GS activity, and dexamethasone administration increased GS activity in both adrenalectomised and intact rats. In the monolayer culture of anterior pituitary cells, glucocorticoids increased GS activity by ×1.5, and methionine sulphoximine reduced the activity by over 94%. These results demonstrate that GS in folliculostellate cells is a glucocorticoid-inducible enzyme in vivo and in vitro, and that the age-dependent increase of GS activity is independent of endogenous adrenal glucocorticoids.

The pain of a migraine attack is often described as unilateral, with a throbbing or pulsating quality. The middle meningeal artery (MMA) is the largest artery supplying the dura mater, is paired, and pain-producing in humans. This artery, or its branches, and other large intracranial extracerebral vessels have been implicated in the pathophysiology of migraine by theories suggesting neurogenic inflammation or cranial vasodilatation, or both, as explanations for the pain of migraine. Having previously studied in detail the distribution of the second order neurons that are involved in the transmission of nociceptive signals from intracranial venous sinuses, we sought to compare the distribution of second order neurons from a pain-producing intracranial artery in both monkey and cat. By electrically stimulating the middle meningeal artery in these species and using immunohistochemical detection of the proto-oncogene Fos as a marker of neuronal activation, we have mapped the sites of the central trigeminal neurons which may be involved in transmission of nociception from intracranial extracerebral arteries. Ten cats and 3 monkeys were anaesthetised with α-chloralose and the middle meningeal artery was isolated following a temporal craniotomy. The animals were maintained under stable anaesthesia for 24 h to allow Fos expression due to the initial surgery to dissipate. Following the rest period, the vessel was carefully lifted onto hook electrodes, and then left alone in control animals (cat n = 3), or stimulated (cat n = 6, monkey n = 3). Stimulation of the left middle meningeal artery evoked Fos expression in the trigeminocervical nucleus, consisting of the dorsal horn of the caudal medulla and upper 2 divisions of the cervical spinal cord, on both the ipsilateral and contralateral sides. Cats had larger amounts of Fos expressed on the ipsilateral than on the contralateral side. Fos expression in the caudal nucleus tractus solitarius and its caudal extension in lamina X of the spinal cord was seen bilaterally in response to middle meningeal artery stimulation. This study demonstrates a comparable anatomical distribution of Fos activation between cat and monkey and, when compared with previous studies, between this arterial structure and the superior sagittal sinus. These data add to the overall picture of the trigeminovascular innervation of the intracranial pain-producing vessels showing marked anatomical overlap which is consistent with the often poorly localised pain of migraine.

A joint meeting of the Anatomical Society of Great Britain and Ireland and the British Biophysical Society was held at the School of Biomedical Sciences, University of Leeds, from 5th to 7th January 1999. It included a symposium on ‘Structure and function of molecular motors’ and the Annual General Meetings of both Societies. The following are abstracts of communications and posters presented at the meeting.

Anatomical Society of Great Britain and Ireland

Future meetings

13–15 July 1999. University of Glasgow. This meeting will feature a symposium on the neurobiology of the basal ganglia (to include basic neuronal properties, disease aspects including imaging and transplantation, and evolutionary aspects).

11–16 September 1999. 15th Congress of the International Federation of Association of Anatomists, Rome, Italy.

17 September 1999. Royal Free and University College Medical School, University of London, Royal Free Campus. One-day symposium on the biology of ageing.

5–7 January 2000. Royal Holloway College, University of London. This will include a symposium on phenotypic changes in epithelial development.

24–26 July 2000. University of Cambridge; this will be a tripartite meeting with the Anatomische Gesellschaft and the Nederlandse Anatomen Vereniging.

The Wellcome Trust

An exhibition entitled The New Anatomists will be held in the Two 10 Gallery at the Wellcome Trust Offices, 210 Euston Road, London NW1 2BE from 11 March to 16 July 1999. It is part of a series exploring the relationship between science and art. The exhibition is open from 9 am to 6 pm on weekdays, public holidays excluded. Admission is free.