Light and scanning electron microscopic study of the structure of the ostrich (Strutio camelus) tongue

The ostrich's tongue is situated in the posterior part of the oropharyngeal cavity and its length is only about a quarter of the beak cavity. The triangular shortened tongue has retained the usual division into the apex, the body and the root. There are no conical papillae between the body and the root of the tongue, and the presence of the flat fold with lateral processes sliding over the tongue root in the posterior part of the lingual body is a unique morphological feature. All lingual mucosa covers non-keratinised stratified epithelium, and the lamina propria of the mucosa is filled with mucous glands whose round or semilunar openings are found on both the dorsal and ventral surface of the tongue. The complex glands found in the lingual body are composed of alveoli and/or tubules. Moreover, simple tubular glands seen in the posterior part of the tongue root are an exception. Numerous observations have shown that the ostrich's tongue is a modified structure, though not a rudimentary one, whose main function is to produce the secretion moisturising the beak cavity surface and the ingested semidry plant food in this savannah species.     

Distribution of trigeminothalamic and spinothalamic lamina I terminations in the cat

The distribution in the thalamus of terminal projections from lamina I neurons of the trigeminal, cervical, and lumbosacral dorsal horn was investigated with the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) in the cat. Iontophoretic injections were guided by single- and multi-unit physiological recordings. The injections in particular cases were essentially restricted to lamina I, whereas in others they spread across laminae I-III or laminae I-V. The trigemino- and spinothalamic (TSTT) terminations were identified immunohistochemically. In all cases, regardless of the level of the injections, terminal fibers were consistently distributed in three main locations: the submedial nucleus; the ventral aspect of the basal ventral medial nucleus and ventral posterior nuclei; and, the dorsomedial aspect of the ventral posterior medial nucleus. The terminal fields in the submedial nucleus and the ventral aspect of the ventral posterior group were topographically organized. Terminations along the ventral aspect of the ventral posterior group extended posterolaterally into the caudal part of the posterior nucleus and anteromedially into the ventromedial part of the ventral lateral nucleus. In several cases with trigeminal lamina I injections, a terminal labeling patch was observed within the core of the ventral posterior medial nucleus. In cases with spinal lamina I injections, terminations were also consistently found in the lateral habenula, the parafascicular nucleus, and the nucleus reuniens. Isolated terminal fibers were occasionally seen in the zona incerta, the dorsomedial hypothalamus, and other locations. These anatomical observations extend prior studies of TSTT projections and identify lamina I projection targets that are important for nociceptive, thermoreceptive, and homeostatic processing in the cat. The findings are consistent with evidence from physiological (single-unit and antidromic mapping) and behavioral studies. The novel identification of spinal lamina I input to the lateral habenula could be significant for homeostatic behaviors.     

Distribution of trigeminothalamic and spinothalamic lamina I terminations in the cat

The distribution in the thalamus of terminal projections from lamina I neurons of the trigeminal, cervical, and lumbosacral dorsal horn was investigated with the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) in the cat. Iontophoretic injections were guided by single- and multi-unit physiological recordings. The injections in particular cases were essentially restricted to lamina I, whereas in others they spread across laminae I–III or laminae I–V. The trigemino- and spinothalamic (TSTT) terminations were identified immunohistochemically. In all cases, regardless of the level of the injections, terminal fibers were consistently distributed in three main locations: the submedial nucleus; the ventral aspect of the basal ventral medial nucleus and ventral posterior nuclei; and, the dorsomedial aspect of the ventral posterior medial nucleus. The terminal fields in the submedial nucleus and the ventral aspect of the ventral posterior group were topographically organized. Terminations along the ventral aspect of the ventral posterior group extended posterolaterally into the caudal part of the posterior nucleus and anteromedially into the ventromedial part of the ventral lateral nucleus. In several cases with trigeminal lamina I injections, a terminal labeling patch was observed within the core of the ventral posterior medial nucleus. In cases with spinal lamina I injections, terminations were also consistently found in the lateral habenula, the parafascicular nucleus, and the nucleus reuniens. Isolated terminal fibers were occasionally seen in the zona incerta, the dorsomedial hypothalamus, and other locations. These anatomical observations extend prior studies of TSTT projections and identify lamina I projection targets that are important for nociceptive, thermoreceptive, and homeostatic processing in the cat. The findings are consistent with evidence from physiological (single-unit and antidromic mapping) and behavioral studies. The novel identification of spinal lamina I input to the lateral habenula could be significant for homeostatic behaviors.     

Ascending and descending projections of the lateral vestibular nucleus in the rat

The tracer neurobiotin was injected into the lateral vestibular nucleus in rat and the efferent fiber connections of the nucleus were studied. The labeled fibers reached the diencephalon rostrally and the sacral segments of the spinal cord caudally. In the diencephalon, the ventral posteromedial and the gustatory nuclei received the most numerous labeled fibers. In the mesencephalon, the inferior colliculus, the interstitial nucleus of Cajal, the nucleus of Darkschewitch, the periaqueductal gray matter and the red nucleus received large numbers of labeled fibers. In the rhombencephalon, commissural and internuclear connections originated from the lateral vestibular nucleus to all other vestibular nuclei. The medioventral (motor) part of the reticular formation was richly supplied, whereas fewer fibers were seen in the lateral (vegetative) part. In the spinal cord, the descending fibers were densely packed in the anterior funiculus and in the ventral part of the lateral funiculus. Collaterals invaded the entire gray matter from lamina IX up to lamina III; the fibers and terminals were most numerous in laminae VII and VIII. Collateral projections were rich in the cervical and lumbosacral segments, whereas they were relatively poor in the thoracic segments of the spinal cord. It was concluded that the fiber projection in the rostral direction was primarily aimed at sensory-motor centers; in the rhombencephalon and spinal cord, fibers projected onto structures subserving various motor functions.     

Reconstruction of the musculature of <Emphasis Type="Italic">Magelona</Emphasis> cf. <Emphasis Type="Italic">mirabilis</Emphasis> (Magelonidae) and <Emphasis Type="Italic">Prionospio cirrifera</Emphasis> (Spionidae) (Polychaeta,Annelida) by phalloidin labeling and cLSM

Recent investigations have suggested that a lack of circular muscle fibers may be a common situation rather than a rare exception in polychaetes. As part of a comparative survey of polychaete muscle systems, the F-actin musculature subset of Magelona cf. mirabilis and Prionospio cirrifera were labeled with phalloidin and three-dimensionally analyzed and reconstructed by means of cLSM. Obvious similarities are sublongitudinal lateral, circumbuccal, palp retractor, dominating dorsal longitudinal, perpendicular lateral and ventral transverse muscles. Differences between M. cf. mirabilis and P. cirrifera are: (1) two types of prostomial muscles (transversal and longitudinal) in M. cf. mirabilis versus one type (diagonal) in P. cirrifera; (2) one type of palp muscles (longitudinal) in M. cf. mirabilis versus three types (longitudinal, diagonal, circular) in P. cirrifera; (3) five ventral longitudinal muscles (ventromedian, paramedian, ventral) in M. cf. mirabilis versus four (two paramedian, two ventral) in P. cirrifera. Ventral and lateral transverse fibers are present in the thorax, but absent in the abdomen of M. cf. mirabilis. The triangular lumen of the pharynx in M. cf. mirabilis is surrounded by radial muscle fibers; three sets of pharynx diductors attach to its dorsal side. The unique features of P. cirrifera are one pair of brain muscles and segmentally arranged dorsal transverse muscles, the latter located outside the longitudinal muscles. The transverse lateral muscles are restricted to the sides and lie beneath the longitudinal muscles, a pattern described here for the first time. A true, outer layer of circular fibers is absent in both species of Spionida that were investigated.     

Scanning electron microscope study of tongue development in the CD-1 mouse fetus

The objective of this study was to examine three dimensionally the embryonic and fetal stages of tongue development with scanning electron microscopy. Time-bred CD-1 mice were sacrificed at quarter-day intervals on days 10-13, and at half-day intervals on days 13.5-16.5 of gestation. Fetal tongues were dissected and fixed in s-collidine buffered 4% glutaraldehyde at pH7.4, and subsequently processed for SEM viewing. Tongue development was initiated on the 11th day by the appearance of the tuberculum impar and the two lateral lingual swellings on arch I. This was followed by the elevation of the hypobranchial eminence, which unites arches III and IV in the ventral midline, and overgrows arch II anteriorly. During the 12th day, remodeling occurred in areas of arches II and III, forming the root of the tongue. A cone-shaped midline swelling, the epiglottis, appeared in the ventral midline of arches III and IV. By the 13th day, the general proportions of the tongue, occupied by the body, root, and epiglottis, were established. The single circumvallate papilla and fungiform papillae were initiated during the early part of the 13th day, followed on the 15th day by differentiation of filiform and foliate papillae and raised nodules of lingual tonsilar tissue. The SEM study documented the temporal and morphological sequence of events during mouse tongue development. The tuberculum impar persisted to the late fetal stages and may therefore contribute largely to the dorsum of the tongue anterior to the circumvallate papilla.     

Demonstration of primary and secondary muscle fiber architecture of the bovine tongue by diffusion tensor magnetic resonance imaging

The myoarchitecture of the tongue is comprised of a complex array of muscle fiber bundles, which form the structural basis for lingual deformations during speech and swallowing. We used magnetic resonance imaging of the water diffusion tensor to display the primary and secondary fiber architectural attributes of the excised bovine tongue. Fiber orientation mapping provides a subdivision of the tongue into its principal intrinsic and extrinsic muscular components. The anterior tongue consists of a central region of orthogonally oriented intrinsic fibers surrounded by an axially oriented muscular sheath. The posterior tongue consists principally of a central region of extrinsic fibers, originating at the inferior surface and projecting in a fan-like manner in the superior, lateral, and posterior directions, and lateral populations of extrinsic fibers directed posterior-inferior and posterior-superior. Analysis of cross-fiber anisotropy indicates a basic contrast of design between the extrinsic and the intrinsic fibers. Whereas the extrinsic muscles exhibit a uniaxial architecture typical of skeletal muscle, the intrinsic core muscles, comprised of the verticalis and the transversus muscles, show strong cross-fiber anisotropy. This pattern is consistent with the theory that the tongue's core functions as a muscular hydrostat in that conjoint contraction of the transverse and vertical fibers enable the tissue to expand at right angles to these fibers. These findings suggest that three-dimensional analysis of diffusion tensor magnetic resonance imaging provides a structural basis for understanding the micromechanics of the mammalian tongue.     

The fine structure of myotendinous and myo-epithelial junctions in the guinea pig tongue (author's transl)]

The insertion of muscle fibers in the subepithelial connective tissue layer of the guinea pig tongue was studied light and electron microscopically. Fibers of the tractus verticalis approach the epithelium penetrating the lamina propria, both the reticular and papillar layer. Terminating muscle fibers split up and form branching finger-like cytoplasmic processes. The myotendinous junctions of such terminal processes fine structurally correspond to myotendinous junctions generally observed in skeletal or smooth muscles. The entire brush-like formation, however, is more far-reaching and highly differentiated. Filament bundles (spine-like profiles) originate from the plasmalemma and extend to the lamina densa of the basal lamina, especially in those regions where actin filaments are attached to the plasmalemma. Microfibrils (10 to 12 nm diameter) reach the lamina densa of the basal lamina. They form bundles which are continuous with fibrotubular strands of elaunin fibers and elastic fiber microfibrils. Furthermore, microfibrils are interwoven with collagen fibrils.     

Substance-P-containing fibers in the incisive papillae of the rat hard palate. Light- and electron-microscopic immunohistochemical study

Substance P (SP)-containing fibers in the incisive papillae of rat hard palates, which include various components of sensory receptors, i.e. mechanoreceptors, free nerve endings and chemosensory corpuscles (taste buds), were examined using immunoperoxidase techniques and light and electron microscopes. Immunolabeled fibers were consistently distributed in the medial part of the orifice of the incisive canals, i.e. in the taste-bud-enriched region. Dense immunolabeled fibers were found in subgemmal regions and in the lamina propria papillae. Some fine fibers entered and ascended the taste buds or occasionally the epithelium outside the taste buds. In addition, a rich innervation by SP-containing fibers close to blood capillaries was clearly identified. Electron microscopy revealed no specialized synaptic contact between the immunolabeled fibers and taste bud cells. Synaptic-like images could be found only between nonimmunolabeled nerve endings and the underlying taste bud cells. In the lamina propria papillae, mechanoreceptors observed in the present study contained no immunoperoxidase end products, whereas free nerve endings with an immunolabeled small-diameter axon (630-730 nm in diameter) were frequent. Similar axons were located at the adventitia of the blood capillaries. The possible functional role of SP-containing fibers in the incisive papillae was given attention.     

Prion infection of skeletal muscle cells and papillae in the tongue

The presence of the prion agent in skeletal muscle is thought to be due to the infection of nerve fibers located within the muscle. We report here that the pathological isoform of the prion protein, PrP(Sc), accumulates within skeletal muscle cells, in addition to axons, in the tongue of hamsters following intralingual and intracerebral inoculation of the HY strain of the transmissible mink encephalopathy agent. Localization of PrP(Sc) to the neuromuscular junction suggests that this synapse is a site for prion agent spread between motor axon terminals and muscle cells. Following intracerebral inoculation, the majority of PrP(Sc) in the tongue was found in the lamina propria, where it was associated with sensory nerve fibers in the core of the lingual papillae. PrP(Sc) staining was also identified in the stratified squamous epithelium of the lingual mucosa. These findings indicate that prion infection of skeletal muscle cells and the epithelial layer in the tongue can be established following the spread of the prion agent from nerve terminals and/or axons that innervate the tongue. Our data suggest that ingestion of meat products containing prion-infected tongue could result in human exposure to the prion agent, while sloughing of prion-infected epithelial cells at the mucosal surface of the tongue could be a mechanism for prion agent shedding and subsequent prion transmission in animals.     

Time-related changes in the labeling pattern of motor and sensory neurons innervating the gastrocnemius muscle,as revealed by the retrograde transport of the cholera toxin B subunit

Summary Morphological changes in the motor and sensory neurons in the lumbar spinal cord and the dorsal root ganglia were investigated at different survival times following the injection of the B subunit of cholera toxin (CTB) into the medial gastrocnemius muscle. Unconjugated CTB, visualized immunohistochemically, was found to be retrogradely transported through ventral and dorsal roots to motor neurons in the anterior horn, each lamina in the posterior horn, and ganglion cells in the dorsal root ganglia at L₃–L₆. The largest numbers of labeled motor neurons and ganglion cells were observed 72 h after the injection of CTB. Thereafter, labeled ganglion cells were significantly decreased in number, whereas the amount of labeled motor neurons showed a slight reduction. Motor neurons had extensive dendritic trees filled with CTB, reaching lamina VII and even the pia mater of the lateral funiculus. Labeling was also seen in the posterior horn, but the central and medial parts of laminae II and III had the most extensively labeled varicose fibers, the origin of which was the dorsal root ganglion cells. The results indicate that CTB is taken up by nerve terminals and can serve as a sensitive retrogradely transported marker for identifying neurons that innervate a specific muscle.     

The Distribution of TRPV1 and TRPV2 in the Rat Pharynx

Immunohistochemistry for two nociceptive transducers, the transient receptor potential cation channel subfamily V members 1 (TRPV1) and 2 (TRPV2), was performed on the pharynx and its adjacent regions. TRPV1-immunoreactivity (IR) was detected in nerve fibers beneath and within the epithelium and/or taste bud-like structure. In the pharynx, these nerve fibers were abundant in the naso-oral part and at the border region of naso-oral and laryngeal parts. They were also numerous on the laryngeal side of the epiglottis and in the soft palate. TRPV2-IR was expressed by dendritic cells in the pharynx and epiglottis, as well as in the root of the tongue and soft palate. These cells were located in the epithelium and lamina propria. TRPV2-immunoreactive (IR) dendritic cells were numerous in the naso-oral part of the pharynx, epiglottis, and tongue. Abundance of TRPV2-IR dendritic processes usually obscured the presence of TRPV2-IR nerve fibers in these portions. However, some TRPV2-IR nerve fibers could be observed in the epithelium of the soft palate. Retrograde tracing method also revealed that sensory neurons which innervate the pharynx or soft palate were abundant in the jugular–petrosal ganglion complex and relatively rare in the nodose ganglion. In the jugular–petrosal ganglion complex, TRPV1- and TRPV2-IR were expressed by one-third of pharyngeal and soft palate neurons. TRPV2-IR was also detected in 11.5 % pharyngeal and 30.9 % soft palate neurons in the complex. Coexpression of TRPV1 and CGRP was frequent among pharyngeal and soft palate neurons. The present study suggests that TRPV1- and TRPV2-IR jugular–petrosal neurons may be associated with the regulation of the swallowing reflex.     

Complete sciatic nerve transection induces increase of neuropeptide Y-like immunoreactivity in primary sensory neurons and spinal cord of frogs

Neuropeptide Y (NPY) was immunohistochemically investigated in the frog spinal cord and dorsal root ganglia after axotomy. In normal ganglia, moderate NPY-like immunoreactivity (NPY-IR) prevailed in large and medium cells. In the spinal cord, the NPY-IR was densest in the dorsal part of the lateral funiculus. Other fibers and neurons NPY-IR were observed in the dorsal and ventral terminal fields and mediolateral band. NPY-IR fibers were also found in the ventral horn and in the ventral and lateral funiculi. The sciatic nerve transection increased the NPY-IR in large and medium neurons of the ipsilateral and contralateral dorsal root ganglia at 3 and 7 days, but no clear change was found at 15 days. In the spinal cord, there was a bilateral increase in the NPY-IR of the dorsal part of the lateral funiculus. In the ipsilateral side, the NPY-IR was increased at 3 and 7 days but was decreased at 15 days. In the contralateral side, a significant reduction at 15 days occurred. These findings seem to favor the role of NPY in the modulation of pain-related information in frogs, suggesting that this role of NPY may have appeared early in vertebrate evolution.     

Immunocytochemical localization of prostaglandin endoperoxide synthase in the bovine intestine

The localization of prostaglandin (PG) endoperoxide synthase in bovine intestine was examined immunocytochemically with polyclonal antibody raised against PG endoperoxide synthase purified from bovine seminal glands. The most intense positive staining reaction for the enzyme was present in mast cells. Mast cells were found to be widely distributed in the intestinal wall, and were particularly numerous in the lamina propria. Most of the mast cells in the lamina propria of the intestinal villi were elongated and oriented with their long axis parallel to the plane of the absorptive epithelium. In whole mount preparations of jejunal villi, mast cells were seen to form a two-dimensional network in the lamina propria. In addition to mast cells, smooth muscle cells of the inner circular muscle layer and muscularis mucosae, nerve cells and fibers, endothelial cells of arterioles, and serosal epithelial cells also showed faint to moderate staining for the enzyme. These results suggested that mast cells are the major source of PGs in the bovine intestinal wall. The characteristic arrangement of mast cells in the intestinal villi may be related to their functions in this portion of the bovine intestine.     

A Pacinian corpuscle in the human bladder lamina propria

The fortuitous finding of a complex Pacinian corpuscle within the lamina propria of the human urinary bladder is described. It consisted of a complex of encapsulated nerve endings within the areolar connective tissue of the lamina propria immediately adjacent to the inner aspect of the detrusor muscle. It showed no structural evidence of directional sensitivity and was associated on its outer aspect with small unmyelinated axons containing small clear and dense-cored vesicles. This appears to be the first report of an encapsulated nerve ending within the lining of the adult human urinary bladder.     

The Topography of the Superficial Roots and Ganglia of the Anterior Lateral Line Nerve of the Smooth Dogfish,Mustelus canis

The topographic relationships of the superficial roots and ganglia of the anterior lateral line nerve (NLLa) to each other and to cranial nerves V, VII and VIII were studied, in the smooth dogfish Mustelus canis, by dissection of Sudan Black Bstained specimens. NLLa consists of four branches: namely, superficial ophthalmic, buccal, otic and external mandibular. Each branch carries lateral line neurons exclusively and forms a dorsal root and a ventral root which enter the anterior lateral line lobe and posterior lateral line lobe of the medulla respectively. It is estimated that slightly more than 50% of the fibers of the superficial opthalmic, approximately 60% of the fibers of the buccal, at least 35% of the fibers of the otic and about 20% of the fibers of the external mandibular constitute the dorsal root. The ventral root is comprised of less than 50% of the fibers of the superficial ophthalmic, 40% of the fibers of the buccal, at least 50% of the fibers of the otic, and 80% of the fibers of the external mandibular. These results are correlated with the peripheral distribution and central termination of NLLa and it is concluded that the dorsal root carries axons from ampullary receptors and the ventral root carries fibers that innervate ordinary lateral line sense organs.     

Histomorphometric study of the lower urogenital tract in pre- and post-menopausal women

In this study 22 histomorphometric parameters were used to quantify the histologic changes in the vagina, trigone of the bladder, and the proximal and distal urethra of 37 women aged between 18 and 82 years. The results of this quantitative study revealed a hormonally induced, age-independent atrophy of smooth muscle in the lamina propria of the mucosa and the longitudinal part of the muscular layer in the aforementioned anatomical sites in post-menopausal women. In the lamina propria of the mucosa of the lower urogenital tract in post-menopausal women hormonally induced quantitative changes of blood vessels were not observed. Senile atrophy of smooth muscles was only observed in the deeper part of the muscular layer of the vagina and the trigone of the urinary bladder and was less prominent than the hormonally induced smooth muscle atrophy.     

Distribution and innervation of short, interdigitated muscle fibers in parallel-fibered muscles of the cat hindlimb

The cat hindlimb contains several long, biarticular strap muscles composed of parallel muscle fascicles that attach to short tendons. Three of these muscles--sartorius, tenuissimus, and semitendinosus--were studied by dissecting individual gold-stained fibers and determining the surface distribution of acetylcholinesterase-stained end-plate zones. In each muscle, fascicles were composed of muscle fibers that ran only part of the fascicle length and tapered to end as fine strands that interdigitated with other tapering fibers within the muscle mass. Most muscle fibers measured 2-3 cm in length. Fascicles of muscle fibers were crossed by short transverse bands of endplates (1 mm wide by 1-5 mm long) that were spaced at fairly regular intervals from the origin to the insertion of the muscle. The endplate pattern suggested that the fiber fascicles were organized into multiple longitudinal strips. In the sartorius, the temporospatial distribution of electromyographic (EMG) activity evoked by stimulating fine, longitudinal branches of the parent nerve confirmed that each strip was selectively innervated by a small subset of the motor axons. These axons appeared to distribute their endings throughout the entire length of the fascicles, providing for synchronous activation of their in-series fibers.     

Peptide-containing nerve fibers in the respiratory tract of the ferret

Summary The ferret is widely used in functional and neuromorphological studies on the respiratory tract. We have examined the occurrence and distribution of peptide-containing and adrenergic nerve fibers (using dopamine--hydroxylase as a marker). Adrenergic nerve fibers and fibers storing vasoactive intestinal peptide have a widespread distribution along the entire respiratory tract. Adrenergic nerve fibers were found in the lamina propria, as well as around blood vessels and glands and in smooth muscle. Nerve fibers storing vasoactive intestinal peptide occurred in the epithelium, the lamina propria, around blood vessels and glands, and among muscle bundles. Substance P-, neurokinin A- and calcitonin gene-related peptide-containing nerve fibers predominated beneath and within the epithelium along the entire respiratory tract. Neuropeptide Y-containing nerve fibers were prominent among smooth muscle bundles and around glands. The blood vessels in the wall of the airways were richly supplied with peptidecontaining nerve fibers and adrenergic fibers. Ganglia located over the outer or dorsal surface of the tracheal wall harbored vasoactive intestinal peptide-containing nerve cell bodies. Substance P and neurokinin A invariably coexisted in the same nerve fibers. Further, coexistence of substance P/neurokinin A and calcitonin gene-related peptide was observed in the nerve fibers associated with the epithelium. Vasoactive intestinal peptide, neuropeptide Y and occasionally also substance P coexisted in the population of nerve fibers associated with blood vessels and smooth muscle. Many adrenergic nerve fibers contained neuropeptide Y.     

A nude mouse xenograft model of fetal intestine development and differentiation.

This report describes a novel in vivo model of intestinal differentiation. Fourteen day, undifferentiated fetal rat small intestine, stripped of the major part of its mesenchyme, suspended in a type I collagen gel and then xenografted into a nude mouse, undergoes small intestinal morphogenesis and cytodifferentiation. All four major epithelial lineages, namely Paneth, goblet, columnar and endocrine are present. Double-label nonisotopic in situ hybridization, employing biotinylated and digoxigenin-labelled whole rat DNA and whole mouse DNA probes, was performed to distinguish donor cells from host cell types. The outer longitudinal smooth muscle layer, and the major part of the lamina propria, including pericryptal fibroblasts, are of host mouse origin; the inner circular smooth muscle layer is of donor rat origin. Cells of the muscularis propria and lamina propria acquired smooth muscle alpha-actin, presumably under the influence of the donor endoderm. Furthermore, this xenograft develops a host vascular network, and cells with the morphological appearance of lymphocytes are present within the intestinal epithelium. The production of chemotactic factors by the endoderm is postulated because grafting of collagen gel alone results in a minimal invasion by stromal cells which do not express smooth muscle alpha-actin.