Oligodendrocytes, derived from stem cell precursors which arise in subventricular zones of the developing central nervous system, have as their specialist role the synthesis and maintenance of myelin. Astrocytes contribute to the cellular architecture of the central nervous system and act as a source of growth factors and cytokines; microglia are bone-marrow derived macrophages which function as primary immunocompetent cells in the central nervous system. Myelination depends on the establishment of stable relationships between each differentiated oligodendrocyte and short segments of several neighbouring axons. There is growing evidence, especially from studies of glial cell implantation, that oligodendrocyte precursors persist in the adult nervous system and provide a limited capacity for the restoration of structure and function in myelinated pathways damaged by injury or disease.

Skull morphology and histology in the heterozygous offspring of a transgenic founder mouse Del1, harbouring 6 copies of deletion mutation in Col2a1 gene, were compared with those in normal siblings. On visual observation and roentgenocephalometric examination the heads of heterozygous Del1 mice were smaller than normal. Histologically the sizes of cartilaginous structures of the cranial base were reduced. Severe defects were seen in the temporomandibular joint as progressive osteoarthritic lesions. These observations elucidate the relationship between the genotype and phenotype and demonstrate that heterozygous Del1 mice are a useful model for studies on a genetic disturbance where ‘clinical’ manifestations are not evident until adult age.

The projections of different subpopulations of myenteric neurons in the mouse small and large intestine were examined by combining immunohistological techniques with myotomy and myectomy operations. The myotomies were used to examine the polarity of neurons projecting within the myenteric plexus and showed that neurons containing immunoreactivity for nitric oxide synthase (NOS), vasoactive intestinal peptide (VIP), calbindin and 5-HT projected anally, while neurons with substance P (SP)-immunoreactivity projected orally, in both the small and large intestine. Neurons containing neuropeptide Y (NPY)- and calretinin-immunoreactivity projected locally. In the large intestine, GABA-immunoreactive neurons projected both orally and anally, with more axons tending to project anally. Myectomy operations revealed that circular muscle motor neurons containing NOS/VIP/±NPY and calretinin neurons projected anally both in the small and large intestine, while SP-immunoreactive circular muscle motor neurons projected orally. In the large intestine, GABA-IR circular muscle motor neurons projected both orally and anally. This study showed that although some neurons, such as the NOS/VP inhibitory motor neurons and interneurons, SP excitatory motor neurons and 5-HT interneurons had similar projections to those in other species, the projections of other chemical classes of neurons in the mouse intestine differed from those reported in other species.

MyoD1 alleles distinguish between the Mm musculus and Mm domesticus subspecies of Mus musculus. SJL/J mice, which belong to the Mm musculus subspecies, are able to regenerate skeletal muscle more efficiently than BALB/c mice which possess the Mm domesticus MyoD1 allele. Hence the possibility that regeneration responses are due to species-specific genetic differences including MyoD1 was investigated in this study. Quantitative morphometric analysis following muscle crush injury of 2 Mm musculus strains, MBK and MGL, has indicated that regeneration phenotype is not species-specific and may not be directly related to MyoD1 alleles. These results contrast with prior investigations conducted in SJL/J and BALB/c mice, and indicate that other genes may have a direct influence on skeletal muscle regeneration.

Using antiserum to human parathyroid hormone-related protein (1–16) [PTHrP(1–16)] we have examined tissues of the common frog (Rana temporaria) for the presence of immunoreactive PTHrP (irPTHrP) at the stage of emergence from water to land. irPTHrP was detected in dorsal and ventral stratum granulosum of the skin, in the developing ovary, striated muscle and the choroid plexus epithelium of the brain as well as in the olfactory gland epithelium and olfactory lobe neurons of the brain. In the pituitary and hypothalamus irPTHrP protein could be demonstrated in the median eminence, infundibular stem and principally in the neural lobe and pars distalis of the pituitary with weak reaction in the pars intermedia. In situ hybridisation of the same tissues with an oligonucleotide probe to chicken PTHrP 55–65 clearly showed the presence of mRNA for PTHrP-like molecule in all the tissues containing irPTHrP. There was a major inconsistency in the pituitary in that the highest level of gene expression, assessed by in situ hybridisation, was found in the pars intermedia with only very low expression in the pars distalis and neural lobe and undetectable levels in the infundibular stem and median eminence. These observations suggest that tissues of the frog synthesise a PTHrP-like molecule but that in the pituitary the pars intermedia cells may export the protein to cells in other regions of the pituitary and hypothalamus.

Timing and pattern of expression of alkaline phosphatase was examined during early differentiation of the 1st arch skeleton in inbred C57BL/6 mice. Embryos were recovered between 10 and 18 d of gestation and staged using a detailed staging table of craniofacial development prior to histochemical examination. Expression of alkaline phosphatase is initiated at stage 20.2 in the plasma membrane of mesenchymal cells in the distal region of the first arch. Expression is strongest in osteoid (unmineralised bone matrix) and presumptive periosteum at stage 21.32. Mineralisation begins at stage E23. Expression is present in the mineralised bone matrix. Secondary cartilages form in the condylar and angular processes by stage M24. The cartilaginous cells and surrounding cells in the processes are all alkaline phosphatase-positive and surrounded by the common periosteum, suggesting that progenitor cells of the processes, dentary ramus and secondary cartilages all originate from a common pool. Nonhypertrophied chondrocytes of Meckel's cartilage express alkaline phosphatase at stage M23. Expression in these chondrocytes is preceded by the expression in their adjacent perichondrium. This is true of chondrocytes in all other cranial cartilages examined. 3-D reconstruction of expression in Meckel's cartilage also revealed that the chondrocytes of Meckel's cartilage which express alkaline phosphatase and the matrix of which undergoes mineralisation are those surrounded by the alkaline phosphatase-positive dentary ramus. By stage 25, coincident with mineralisation in the distal section of Meckel's cartilage, most chondrocytes are strongly positive. The perichondria of malleus and incus cartilages express alkaline phosphatase at stage M24. Nonhypertrophied chondrocytes along these perichondria also express alkaline phosphatase. Superficial and deep cells in the dental laminae of incisor and 1st molar teeth become alkaline phosphatase-positive at the bud stage, stages 21.16 and 21.32, respectively. Dental papillae are negative until stage M24 when alkaline phosphatase expression begins in the dental papillae and follicles of the incisor teeth and the dental follicles of the 1st molar teeth. The dental papillae of the 1st molar teeth express alkaline phosphatase at stage 25. Expression in the dental papillae and follicles appears to coincide with cellular differentiation of follicle from papilla. The presumptive squamosal, ectotympanic and gonial membrane bones, lingual oral epithelial cells connected to the dental laminae of the incisor teeth, hair follicle papillae and sheath and surrounding dermis all express alkaline phosphatase in a stage-specific manner.

Adult muscle is highly vascularised, with blood vessels being essential for adequate oxygenation of the tissue and for supporting increased metabolic demands. Whether this is the case during muscle development has not been examined. Resin histology was used to map the muscle splitting process and conventional transmission electron microscopy to examine early muscle differentiation at the midlimb level or later at the mid radius/ulna level in the chick wing bud from stages 24 (4.5 d) to 36 (10 d) (Hamburger & Hamilton, 1951). Microinjection of India Ink into the extra-embryonic vasculature was used to visualise the patent muscle microcirculation. The results showed that the premuscle masses are present at stage 24 and initial splitting of the muscle masses commences at stage 28. The final muscle pattern is not established until stage 36. At stage 26 the cells within the premuscle masses exhibited a mesenchymal morphology, but at stage 28 overt muscle differentiation was evident with myofibrils present within myoblasts. Undifferentiated mononucleated cells were interspersed with the differentiating myoblasts. The ratio of mononucleated cells[ratio ]myoblasts decreased and the myoblasts became plumper and increasingly packed with myofibrils with age. There was no evidence of secondary myotube formation at any of the stages examined. Vascular invasion of the limb occurred at stage 35 just prior to the establishment of the final muscle pattern. This was surprising as it was assumed that myogenic differentiation would be both oxygen and nutrient dependent. The results of this study provide descriptions of the splitting of the premuscle masses through to the establishment of the final muscle pattern at the midlimb or mid radius/ulna level of the chick wing bud together with the differentiation of the myogenic cells within the developing muscles. However, the relationship between muscle patterning at the tissue level and muscle differentiation at the cellular level with vascularisation remains unclear. It is hoped that the results of the study may provide the basis for future investigations into mechanisms involved in muscle patterning and the signalling mechanisms for vascular invasion.

Tammar wallaby spermatozoa undergo maturation during transit through the epididymis. This maturation differs from that seen in eutherian mammals because in addition to biochemical and functional maturation there are also major changes in morphology, in particular formation of the condensed acrosome and reorientation of the sperm head and tail. Of spermatozoa released from the testes, 83% had a large immature acrosome. By the time spermatozoa reached the proximal cauda epididymis 100% of sperm had condensed acrosomes. Similarly 86% of testicular spermatozoa had immature thumb tack or T shape head-tail orientation while only 2% retained this immature morphology in the corpus epididymis. This maturation is very similar to that reported for the common brush tail possum, Trichosurus vulpecula. However, morphological maturation occurred earlier in epididymal transit in the tammar wallaby. By the time spermatozoa had reached the proximal cauda epididymis no spermatozoa had an immature acrosome and thumbtack orientation. Associated with acrosomal maturation was an increase in acrosomal thiols and the formation of disulphides which presumably account for the unusual stability of the wallaby sperm acrosome. The development of motility and progressive motility of tammar wallaby spermatozoa is similar to that of other marsupials and eutherian mammals. Spermatozoa are immotile in the testes and the percentage of motile spermatozoa and the strength of their motility increases during epididymal transit. During passage through the caput and corpus epididymis, spermatozoa first became weakly motile in the proximal caput and then increasingly progressively motile through the corpus epididymis. Tammar wallaby spermatozoa collected from the proximal cauda epididymis had motility not different from ejaculated spermatozoa. Ultrastructural studies indicated that acrosomal condensation involved a complex infolding of the immature acrosome. At spermiation the acrosome of tammar wallaby spermatozoa was a relatively large flat or concave disc which projected laterally and anteriorly beyond the limits of the nucleus. During transit of the epididymal caput and proximal corpus the lateral projections folded inwards to form a cup like structure the sides of which eventually met and fused. The cavity produced by this fusion was lost as the acrosome condensed to its mature form as a small button-like structure contained within the depression on the anterior end of the nucleus. During this process the dorsal surface of the immature acrosome and its outer acrosomal membrane and overlying plasma membrane were engulfed into the acrosomal matrix. This means that the dorsal surface of the acrosomal region of the testicular tammar wallaby sperm head is a transient structure. The dorsal acrosomal surface of the mature spermatozoon appears ultrastructurally to be the relocated ventral surface of the acrosomal projections which previously extended out beyond the acrosomal depression on the dorsal surface of the nucleus of the immature spermatozoon.

Wheat germ agglutinin–horseradish peroxidase conjugate (WGA–HRP) was injected into the dorsal root ganglia (L5–S1) of the cat and used as an anterograde tracer substance for intra-axonal labelling of peripheral nerve endings in joint capsule and cranial (anterior) cruciate ligament (CCL). We believed that the high specificity of WGA–HRP for neural tissue along with the high visibility of its reaction product could help resolve controversies concerning the sensory innervation of the cruciate ligaments. Substantial amounts of WGA–HRP were transported in tibial nerve axons to the level of the knee. However, using standard HRP histochemistry we found that the capsular tissue and ligament synovia disintegrated during the incubation reaction. This problem was avoided by air drying the tissue slices on glass slides prior to reaction. Abundant labelling occurred in the posterior capsule with dense filling of axons and terminal endings. Sensory endings displayed features consistent with Ruffini endings and pacinian corpuscles. Sensory endings were located throughout the CCL in its sagittal plane, in the subsynovial layers and between collagen fascicles. In each CCL we observed 5–17 ovoid and elongated endings with dense terminal arborisations. These endings were between 100 and 150 μm long, were encapsulated, and gave rise to 1 or 2 axons. Large (up to 1.5 mm in maximum extent) elongated regions of dense, inhomogeneous labelling were found in the body of several CCLs. These resembled Golgi tendon-like endings, with the exception of their large size. We conclude that anterograde transport of HRP to the knee is a useful technique for labelling mechanoreceptors and axons in knee tissue. However, recently developed immunohistochemical analysis of peripheral tissue using protein gene product 9.5 appears to be the method of choice and should be employed for further study of human and animal cruciate ligament innervation.

Important functions of the oviduct during reproduction include the provision of an optimal environment for gametes and zygotes and nutrition of the early embryo. These functions are ensured by the secretion of an oviductal fluid which is known to contain organ-specific glycoproteins. Glycoconjugates of the apical glycocalyx are considered to play a major role in cell recognition and interaction processes. In the present investigation, binding patterns of Con A, HPA, LTA, RCA I, UEA I, and WGA were studied in defined segments of the oviduct (infundibulum, ampulla, isthmus) and in the uterus during the oestrous cycle. The carbohydrate distribution showed regional as well as time dependent differences. LTA, HPA and WGA reacted strongly with Golgi regions and secretory granules in the oviduct epithelium during the follicular phase, indicating high secretory activity. LTA, HPA, and UEA I also revealed a varying carbohydrate composition of the glycocalyx during the oestrous cycle. Prominent regional differences in glycoconjugate expression were shown in oviductal segments by LTA and HPA binding: during the follicular phase, LTA binding sites were only present on epithelial cells of the isthmic segment, the ampulla and infundibulum being unreactive. D-N-acetyl-galactosamine residues were demonstrated on ciliated epithelial cells of the ampulla and infundibulum exclusively during oestrus. The glycocalyx of uterine epithelial cells was clearly defined by HPA, WGA, LTA, RCA I and UEA I; LTA binding was restricted to the secretory phase. The observation of regional and time dependent variability in glycoconjugate distribution strongly indicates their specific physiological functions in reproductive processes.

A correspondence item entitled ‘A warning against revival of the classic tenets of gross anatomy related to nerve–muscle specificity’ was recently published in the Journal of Anatomy (Shinohara, 1996a). The present correspondent fully agrees with some aspects of his opinion, in particular, the 3 laws about applications which he described, and he also appreciates his approach to the argument based on the results of embryology and experimentation. However, his denial of morphological interpretations based on the theory of nerve–muscle specificity may be due to an incomplete understanding of the current status of the theory.

A symposium on extramedullary haematopoiesis was held on 11–12 September 1996 at the University of St Andrews. The following are abstracts of papers and posters presented at the meeting.

Anatomical Society of Great Britain and Ireland

15–17 July 1997. Medical School, University of Edinburgh.

6–8 January 1998. University of Newcastle upon Tyne.

24–26 July 2000. University of Cambridge.

Anatomical Society Research Studentchips

Grant funding is available for Research Studentships in the anatomical sciences, commencing October 1997. Project applications are invited from members of academic staff in departments of anatomical sciences in the UK and Ireland.