Epithelial cell renewal and turnover and relationship to morphologic abnormalities in jejunal mucosa in tropical sprue

A morphometric study confirmed that increasing severity of the jejunal mucosal morphologic lesion is accompanied by increased crypt height and reduced villus length in patients with tropical sprue. Mitotic activity in the crypts was increased. Pulse labeling of jejunal mucosal biopsies cultured in vitro with [3H]thymidine confirmed that there was increased uptake of label in tropical sprue with more rapid migration of labeled cells to the villi. The label was also lost more rapidly. Earlier ultrastructural studies have shown enterocyte damage and extrusion in the crypt and villus epithelium. The present data suggest that in the jejunal mucosa of patients with tropical sprue, the loss of damaged enterocytes leads to villus shortening and increased cell production in the crypts, with hypertrophy of the crypts.     

HIV enteropathy: comparative morphometry of the jejunal mucosa of HIV infected patients resident in the United Kingdom and Uganda

Aims—To compare jejunal mucosalmorphometry in HIV infected patients resident in London and Uganda.
Patients—Twenty HIV positivepatients from London and 16 from Uganda were studied, and compared withHIV negative control subjects from both sites.
Methods—Stools and biopsy specimenswere examined for enteropathogens. Surface area to volume (S:V) ratiowas estimated morphometrically, mean crypt length of jejunal biopsyspecimens was measured, and HIV infected cells detectedimmunohistochemically were quantified.
Results—Enteric pathogens weredetected in none of the London patients, and in three Ugandan patients.S:V ratio was lower, and mean crypt length higher, in the specimens ofLondon patients than in normal subjects, but there was no difference inS:V ratio or mean crypt length between Ugandan patients and controls. A negative correlation was present between S:V ratio and mean crypt length in all biopsy specimens analysed. HIV infected cells were detected only in lamina propria.
Conclusion—Infection of cells inthe lamina propria of the jejunum with HIV stimulates crypt cellproliferation, and a fall in villous surface area. The mucosal responseto HIV is masked by other pathogens in the African environment.

Keywords:HIV; jejunum; AIDS; enteropathy

     

Study of the proliferation in human gastric mucosa after in vivo bromodeoxyuridine labelling.

Studies to measure human gastric crypt or gland cell proliferation may have a number of practical clinical applications in relation to both benign and malignant gastric conditions. Bromodeoxyuridine (BrdUrd) labels human gastric mucosal cells in the S phase. Computer aided data analysis of labelled mucosa allows static proliferative indices to be estimated, including the crypt labelling index (LI), the peak labelling position, the distribution of labelled cells and indirectly the crypt growth fraction. Multiparameter flow cytometric analysis of labelled nuclei allows the S phase duration (Ts) of mucosal cells to be estimated. Specimens of histologically normal gastric body (GB, n = 16) and antral mucosa (GA, n = 10) were obtained from 25 patients with gastric carcinomas who received a bolus dose of 250 mg BrdUrd between 3.0 and 15.7 hours before surgery. Tissue sections were stained by an immunohistochemical method and subjected to detailed counting of up to 50 longitudinal crypts per specimen. The total crypt labelling index was calculated by a grid counting method. A significant difference existed between the proliferative compartments of gastric antral and body mucosa measured by a number of criteria. The median lengths of the crypts were 137 cells (GB) and 188 cells (GA). The median peak labelling positions were cell 26 (GB) and cell 61 (GA) from the crypt orifice. The mean crypt labelling indices were 2.8% (GB) and 4.8% (GA). The mean Ts of GA cells was 7.7 hours and of GB cells was 10.8 hours.     

Are the focal microscopic jejunal lesions in Crohn's disease produced by a T-cell-mediated immune response?

In animal models of intestinal hypersensitivity, lymphocyte-mediated damage to the small-bowel mucosa produces a characteristic pattern of morphologic abnormalities. Similar findings in human jejunal biopsy specimens may also indicate that T cells are involved in a disease process. To test the hypothesis that there is a generalized activation of mucosal T cells throughout the small-intestinal mucosa in Crohn's disease, measurements of the lengths of crypts and villi and intraepithelial lymphocyte (IEL) counts were made on jejunal specimens from 33 patients with this condition, and the results compared with the established reference values and with results of specimen measurements in a group of normal subjects. Taken as a group, the specimens from Crohn's patients had abnormal villus length, crypt length, and IEL counts. Focal histologic abnormalities such as ulcers, fissures, or granulomas were present in 10 of the specimens. When specimens with and without a focal abnormality were compared, the former showed shorter villi (median, 249.6 versus 331 microns, p less than 0.01), longer crypts (median, 330.4 versus 108.2 microns, p less than 0.01) and higher IEL counts (60.5 versus 32 IEL/100 enterocytes, p less than 0.01). These findings suggest that there is a mucosal cell-mediated immune response in the jejunum in Crohn's disease and that this is pronounced in the vicinity of microscopic, focal lesions.     

Are the Focal Microscopic Jejunal Lesions in Crohn's Disease Produced by a T-Cell-Mediated Immune Response?

In animal models of intestinal hypersensitivity, lymphocyte-mediated damage to the small-bowel mucosa produces a characteristic pattern of morphologic abnormalities. Similar findings in human jejunal biopsy specimens may also indicate that T cells are involved in a disease process. To test the hypothesis that there is a generalized activation of mucosal T cells throughout the small-intestinal mucosa in Crohn's disease, measurements of the lengths of crypts and villi and intraepithelial lymphocyte (IEL) counts were made on jejunal specimens from 33 patients with this condition, and the results compared with the established reference values and with results of specimen measurements in a group of normal subjects. Taken as a group, the specimens from Crohn's patients had abnormal villus length, crypt length, and IEL counts. Focal histologic abnormalities such as ulcers, fissures, or granulomas were present in 10 of the specimens. When specimens with and without a focal abnormality were compared, the former showed shorter villi (median, 249.6 versus 331 μm, p < 0.01), longer crypts (median, 330.4 versus 108.2 μm, p < 0.01) and higher IEL counts (60.5 versus 32 IEL/100 enterocytes, p < 0.01). These findings suggest that there is a mucosal cell-mediated immune response in the jejunum in Crohn's disease and that this is pronounced in the vicinity of microscopic, focal lesions.     

Measurement of in vivo proliferation in human colorectal mucosa using bromodeoxyuridine.

In vivo bromodeoxyuridine (BrdUrd) labelling of the human large bowel was performed and a detailed histochemical localisation of label in sections of crypts was undertaken using a monoclonal antibody to BrdUrd containing DNA. Flow cytometric studies on extracted nuclei were also performed (data presented elsewhere). The average crypt in the human large bowel (excluding the rectum) was 82 cells in height and 41 cells in circumference, with a total of about 2000 cells (assuming a topographical correction factor of 0.6). Ten per cent of the cells were replicating their DNA--that is, were in the S phase of the cell cycle--and 0.4% were in mitosis. The median position for the labelling index versus cell position frequency plot is at the 20th cell position--at a quarter of the crypt height. The lower and upper limits of the cell proliferation are given by the 5th and 95th percentiles at cell positions 4 and 43 respectively. The peak labelling index is about 30% and it occurs at cell position 15. The labelling index at the crypt base, the probable stem cell zone, is about 14%, suggesting that these cells have a longer cell cycle. Taking a value of 8.6 hours for the duration of the S phase (deduced from the flow cytometric data) and assuming a growth fraction of 1.0 for the mid-crypt, these data provide an estimate of about 30 hours for the cell cycle time. The rectal crypts are about the same size but contain about 30% fewer S phase cells. The data also yielded a per cent BrdUrd labelled mitosis curve.     

Effects of fasting and refeeding on jejunal morphology and cellular activity in rats in relation to depletion of body stores

BACKGROUND: Intestinal mucosa atrophy following a period of starvation characterized by the mobilization of fat stores for energy expenditure (phase II) worsen after a long fast marked by an increase in protein catabolism (phase III). However, the morphology of the jejunum is completely restored after 3 days of refeeding. The aim of this study was to determine the mechanisms involved in the rapid jejunal restoration following the critical phase III. METHODS: Jejunal structure was observed through conventional and environmental scanning electron microscopy, whilst cellular dynamics were studied using classical optic microscopy tools and immunohistochemistry. RESULTS: Mucosal structural atrophy during fasting proved to worsen over the two phases. During phase II, apoptosis is still present at the tip of the villi, the number of mitosis in crypts showed a 30% decrease and a transient drop in cell migration is observed. During phase III, however, an 85% rise in mitosis was noticed along with an increase in cell migration and the disappearance of apoptotic cells at the villus tips. This increased cell renewal continues after food ingestion. CONCLUSIONS: Starved rats appeared to be in a phase of energy sparing in phase II, with depressed cellular events in the intestinal mucosa. In phase III, however, the preservation of functional cells and the early increase in crypt cell proliferation should prepare the mucosa to refeeding and could explain why jejunal repairs are complete after 3 days of refeeding following either phase II or phase III.     

Small intestinal villous pattern and mucosal dynamics in healthy Jamaicans

Twenty intestinal biopsy specimens from Jamaican subjects who did not have evidence of gastrointestinal disease were examined under the dissecting microscope and histologically. The appearances were normal in all 20. The most common finding was a mixture of finger- and leaf-shaped villi. Histologically, the biopsy specimens were also normal, consisting of long slender villi with short crypts and very few inflammatory cells. The crypt length; adult crypt cell ratio, mitotic index and turnover time were normal. These findings indicate that the set of circumstances causing and perpetuating the abnormalities seen in the jejunal biopsies of subjects living in the tropics, do not exist in Jamaica, and that the small intestinal villous appearance and mucosal dynamics in the healthy Jamaican Negro are similar to those of Europeans and North Americans.     

Stimulation and inhibition of proliferation in the small intestinal crypts of the mouse after in vivo administration of growth factors.

The effects of epidermal growth factor (EGF), transforming growth factor alpha (TGF alpha), insulin-like growth factor (IGF) I and II, acidic fibroblast growth factor (FGF), tumour necrosis factor alpha (TNF alpha), macrophage inhibitory protein 1 alpha (MIP-1 alpha) (LD78), and TGF beta-1 on cell proliferation in the crypts of the small intestine of mice were investigated. Various doses and dosing regimens were tested. Three in vivo assays were developed, in each case involving detailed cell positional analysis of methyl tritiated thymidine labelling and mitotic activity. These allowed deductions to be made about the regions of the crypt and hence regions of the proliferative hierarchy (stem cells versus dividing transit cells) that are affected by treatment with growth factors. The assays involved: (1) normal untreated mice (an assay most likely to be effective for detecting inhibitors); (2) mice shortly after whole body irradiation when compensatory proliferation has been endogenously triggered (another assay for inhibitory factors, possibly ones associated specifically with the regenerative process); and (3) mice at late times (96 hours) after irradiation in the regression phase after a proliferative overshoot (an assay designed to detect stimulators). Little effect was seen after treatment with acidic FGF, TNF alpha, or MIP-1 alpha but EGF, IGF-I and II, and TGF alpha can all be seen to exert some stimulatory effects on labelling or mitosis. EGF and IGF-I stimulate both unirradiated mice and 96 hour recipients, while TGF alpha had a greater effect on the 96 hour animals. In all cases, multiple doses were used. TGF beta-1 was an effective inhibitor of proliferation in unirradiated and early regenerating (18 hour) animals. EGF was the most effective of the stimulators, raising the levels of proliferation at all positions in the crypt, but particularly in the upper crypt. IGF-I also exerted its effect predominantly in the upper crypt, while TGF alpha raised proliferation at all cell positions. TGF beta-1 tended to have its strongest inhibitory effects in the lower (stem cell) regions of the crypt.     

Detection of HIV in Enterochromaffin Cells in the Rectal Mucosa of an AIDS Patient

The human immunodeficiency virus (HIV) was detected by in situ hybridization in the bowel crypt and lamina propria in the rectal mucosa of an acquired immune deficiency syndrome (AIDS) patient. More infected cells were noted in the crypts than the lamina propria. The enterochromaffin cell was one cell type showing the presence of virus. HIV may play an important role in some gastrointestinal disorders in infected individuals.     

Effects of fasting and refeeding on jejunal morphology and cellular activity in rats in relation to depletion of body stores

Background: Intestinal mucosa atrophy following a period of starvation characterized by the mobilization of fat stores for energy expenditure (phase II) worsen after a long fast marked by an increase in protein catabolism (phase III). However, the morphology of the jejunum is completely restored after 3 days of refeeding. The aim of this study was to determine the mechanisms involved in the rapid jejunal restoration following the critical phase III. Methods: Jejunal structure was observed through conventional and environmental scanning electron microscopy, whilst cellular dynamics were studied using classical optic microscopy tools and immunohistochemistry. Results: Mucosal structural atrophy during fasting proved to worsen over the two phases. During phase II, apoptosis is still present at the tip of the villi, the number of mitosis in crypts showed a 30% decrease and a transient drop in cell migration is observed. During phase III, however, an 85% rise in mitosis was noticed along with an increase in cell migration and the disappearance of apoptotic cells at the villus tips. This increased cell renewal continues after food ingestion. Conclusions: Starved rats appeared to be in a phase of energy sparing in phase II, with depressed cellular events in the intestinal mucosa. In phase III, however, the preservation of functional cells and the early increase in crypt cell proliferation should prepare the mucosa to refeeding and could explain why jejunal repairs are complete after 3 days of refeeding following either phase II or phase III.     

Maturation of the rat small intestine at weaning: changes in epithelial cell kinetics, bacterial flora, and mucosal immune activity.

The relationship between maturation of the small intestine and change in mucosal immune activity was examined in the DA rat during the weaning period from 12 to 30 days. Two stages of jejunal maturation were observed: an initial stage of morphological development and crypt proliferation (days 12 to 22), followed by a period of stabilisation (days 24 to 30). By day 22 of the initial phase, villi increased principally in width but not in length, crypt length increased, and crypt cell production rate increased from 0.5 (day 12) to 11.1 (day 22) cells/crypt/hour. Various measures of mucosal immune activity showed a biphasic response. Up to days 20 to 22, the weight of the mesenteric lymph node increased seven-fold (p less than 0.0001), counts of jejunal eosinophils and goblet cells increased 3- (p less than 0.0001) and 19-fold (p less than 0.0001) respectively, and mean serum rat mucosal mast cell protease II, released from mucosal mast cells, increased from 24 (day 12) to 313 (day 22) ng/ml (p less than 0.0001). After day 22, mesenteric lymph node weight stabilised, eosinophil count stabilised and goblet cells decreased, serum rat mucosal mast cell protease II decreased three-fold (p less than 0.0001), and mean jejunal count of intraepithelial lymphocytes increased from 26 (day 22) to 54 (day 24) cells per mm of muscularis mucosae (p less than 0.0001), before stabilising. These results demonstrated a close association between maturation of the small intestine and change in activity of the mucosal immune system.     

Myenteric neurons and intestinal mucosa of diabetic rats after ascorbic acid supplementation

AIM： To investigate the effect of ascorbic acid （AA） dietary supplementation on myenteric neurons and epithelial cell proliferation of the jejunum of adult rats with chronic diabetes mellitus. METHODS： Thirty rats at 90 d of age were divided into three groups： Non-diabetic, diabetic and diabetic treated with AA （DA） （1 g/L）. After 120 d of treatment with AA the animals were killed. The myenteric neurons were stained for myosin-V and analyzed quantitatively in an area of 11.2 mm2/animal. We further measured the cellular area of 500 neurons per group. We also determined the metaphasic index （MI） of the jejunum mucosa layer of about 2500 cells in the intestinal crypts, as well as the dimensions of 30 villi and 30 crypts/animal. The data area was analyzed using the Olympus BX40 microscope. RESULTS： There was an increase of 14% in the neuronal density （792.6 ± 46.52 vs 680.6 ± 30.27） and 4.4% in the cellular area （303.4 ± 5.19 vs 291.1 ± 6.0） respectively of the diabetic group treated with AA when compared to control diabetic animals. There were no significant differences in MI parameters, villi height or crypt depths among the groups.CONCLUSION： Supplementation with AA in the diabetic animal promoted moderate neuroprotection. There was no observation of alteration of the cellular proliferation of the jejunum mucosa layer of rats with chronic diabetes mellitus with or without supplementation with AA.     

Post-irradiation somatic mutation and clonal stabilisation time in the human colon.

BACKGROUND: Colorectal crypts are clonal units in which somatic mutation of marker genes in stem cells leads to crypt restricted phenotypic conversion initially involving part of the crypt, later the whole crypt. Studies in mice show that the time taken for the great majority of mutated crypts to be completely converted, the clonal stabilisation time, is four weeks in the colon and 21 weeks in the ileum. Differences in the clonal stabilisation time between tissues and species are thought to reflect differences in stem cell organisation and crypt kinetics. AIM: To study the clonal stabilisation time in the human colorectum. METHODS: Stem cell mutation can lead to crypt restricted loss of O-acetylation of sialomucins in subjects heterozygous for O-acetyltransferase gene activity. mPAS histochemistry was used to visualise and quantify crypts partially or wholly involved by the mutant phenotype in 21 informative cases who had undergone colectomy up to 34 years after radiotherapy. RESULTS: Radiotherapy was followed by a considerable increase in the discordant crypt frequency that remained significantly increased for many years. The proportion of discordant crypts showing partial involvement was initially high but fell to normal levels about 12 months after irradiation. CONCLUSIONS: Crypts wholly involved by a mutant phenotype are stable and persistent while partially involved crypts are transient. The clonal stabilisation time is approximately one year in the human colon compared with four weeks in the mouse. The most likely reason for this is a difference in the number of stem cells in a crypt stem cell niche, although differences in stem cell cycle time and crypt fission may also contribute. These findings are of relevance to colorectal gene therapy and carcinogenesis in stem cell systems.     

Cell cycle distribution of proliferative and functional cells of the rat jejunum after treatment with oral E2 prostaglandins

Proliferative and functional epithelial cells were isolated from jejunal specimens of the rat by means of vibrational treatment combined with differential air insufflation. This method gave a good separation between superficial cells of the villi and the crypt cells, as evaluated by flow cytometry, morphology, cytology, and incorporation of radioactive thymidine into DNA. Groups of Sprague-Dawley rats (260 g) were treated twice daily for 11 days with oral placebo, 15(R)15-methyl-prostaglandin E2 in the range of 0.125-2 mg X kg-1, or 5 mg X kg-1 natural PGE2. Isolated crypt cells and superficial cells of the jejunal villi were then analysed by flow cytometry. Morphometric measurements were performed on sections of some jejunal specimens not submitted to vibrational treatment. The cell cycle distribution of crypt cells was unaffected by treatment with the prostaglandin analogue despite the presence of trophic changes. The proportion of crypt cells in G2/M phase was slightly but significantly reduced in rats given natural PGE2 compared with controls. The cell cycle distribution of villus cells was not affected by prostaglandin treatment. Trophic changes in the absence of increased DNA synthesis (S phase) or increased mitotic activity suggests that the hyperplasia observed after prostaglandin treatment is due to a reduced cell loss and/or slower migration time of epithelial cells.     

Effect of acute and chronic glucocorticoid treatments on epithelial cell proliferation in the esophagus and small intestine of rats

Data about glucocorticoid influence on proliferation in the esophagus and small intestine are very contradictory and need to be reexamined. Moreover, only the effects of acute or short-term treatments with glucocorticoids have been demonstrated, whereas nothing is known about their effects under chronic exposure. This work was therefore carried out to examine proliferative activity in the esophagus and small intestine under conditions of acute and chronic glucocorticoid exposure. Rats were treated with either glucocorticoid triamcinolone acetonide or vehicle for 3, 33, or 63 days. Proliferation was assessed in the basal layer of esophageal epithelium and in the epithelium of jejunal crypts, using three criteria, as the number of mitotic, bromodeoxyuridine-labelled, and proliferating cell nuclear antigen-labelled cells. Treatment with glucocorticoid for 3 days led to a slight decrease in all parameters in the esophageal epithelium and had almost no effect on proliferation in the epithelium of jejunal crypts. Long-term treatment with glucocorticoid for either 33 or 63 days resulted in an increase in all parameters tested in both esophageal and jejunal crypt epithelia. Sixty-three-day treatment had a more prominent and significant (P < 0.05) effect. These results suggest that acute glucocorticoid treatment nonsignificantly reduces the number of cells in the cell cycle in the esophageal epithelium, whereas chronic treatment increases the number of proliferating cells in both esophageal and jejunal crypt epithelia. Received: February 22, 1999 / Accepted: June 25, 1999     

Influence of a highly purified senna extract on colonic epithelium

BACKGROUND: Chronic use of sennoside laxatives often causes pseudomelanosis coli. A recent study suggested that pseudomelanosis coli is associated with an increased colorectal cancer risk. A single high dose of highly purified senna extract increased proliferation rate and reduced crypt length in the sigmoid colon compared to historical controls. AIMS: To evaluate in a controlled study the effects of highly purified senna extract on cell proliferation and crypt length in the entire colon and on p53 and bcl-2 expression. METHODS: Addition of a senna extract to colonic lavage was studied in 184 consecutive outpatients. From 32 randomised patients, 15 with sennosides (Sen), 17 without (NSen), biopsies were taken. Proliferative activity was studied in 4 areas of the colon, using 5-bromo-2'-deoxyuridine labelling and immunohistochemistry (labelling index, LI). Expression of p53 and bcl-2 in the sigmoid colon was determined immunohistochemically. RESULTS: Crypts were shorter in Sen than in NSen in the transverse and sigmoid colon. LI was higher in Sen than in NSen in the entire colon. No difference in p53 expression was seen. Bcl-2 expression was higher in both groups when crypts were shorter and/or proliferation was increased. CONCLUSION: Sennosides induce acute massive cell loss probably by apoptosis, causing shorter crypts, and increased cell proliferation and inhibition of apoptosis to restore cellularity. These effects may reflect the mechanism for the suggested cancer-promoting effect of chronic sennoside use.     

Mucosal cell proliferation in duodenal ulcer and duodenitis.

Mucosal cell proliferation in the first part of the duodenum was studied in 24 patients using a tissue culture technique in which endoscopic biopsies were subjected to autoradiography after exposure to tritiated thymidine. Eight patients had a normal duodenum, eight had duodenal ulcer, and eight had symptomatic chronic non-specific duodenitis. The mean crypt labelling index (LI) in normal duodenum was 8.8 0.4% (SEM). Increased labelling indices of 15.6 +/- 1.7% were found near the edge of duodenal ulcers and 17.8 1.8% in duodenitis. Treatment with cimetidine reduced both the severity of duodenitis and the mean crypt LI. The LI of histologically normal duodenal mucosa distal to ulcer of duodenitis was similar to that of the control subjects' mucosa. The increased mucosal cell proliferation seen in severe duodenitis, either alone or associated with duodenal ulceration, suggested that erosions and ulcers arose when the crypts passed into 'high output failure' and were unable to compensate for further epithelial cell loss. There was no evidence in out study for a generalised failure of mucosal cell proliferation in duodenal ulcer or duodenitis.     

Identification and isolation of candidate human colonic clonogenic cells based on cell surface integrin expression

BACKGROUND & AIMS: The surface epithelium of the colon is being replaced constantly with cells derived from the stem cells of the crypt. Although the location of the stem cells is known, there are no markers for these cells. This study tested the hypothesis that colonic stem cells might be isolated and cultured on the basis of specific integrin expression patterns in normal human colonic epithelium. METHODS: Integrin expression in normal human colonic mucosa was determined by using indirect immunofluorescence. Crypt cells were then isolated as single cells from normal colon tissues and the expression pattern of integrins was analyzed by flow cytometry. Based on the specific expression of integrin beta1 in colonic crypts, the cells were sorted by using a flow cytometer, and colony assays in soft agar were performed to evaluate the clonogenicity of the sorted cells. RESULTS: By immunofluorescence, the cells located in the lower one third of crypts expressed higher levels of beta1-integrin than the cells in the remainder of the crypt. When isolated crypt cells were stained with the beta1-integrin antibody and examined in a flow cytometer, there were 2 peaks of fluorescence. Sorting of crypt cells based on staining with anti-beta1 integrin antibody produced a cell population with a significantly enhanced ability to form colonies. CONCLUSIONS: beta1-integrin is a candidate surface marker for the proliferative zone of the human colonic crypt. Our in vitro culture system for the clonal growth of a single colonic crypt cell suspension could facilitate the identification of other candidate stem cell markers.     

Reinnervation of villi of rat jejunum following severe mucosal damage

We studied the time course of the regeneration of the jejunal mucosa of the rat after it was damaged by exposure to the surfactant, benzalkonium chloride. We placed particular emphasis on assessing the morphology of the nerve fibers within the villi during and after regeneration. The application of benzalkonium chloride resulted in virtually complete loss of villi within the treated segment; however, the crypts were only partially damaged. The mucosa began to regenerate within 6 hr of the insult. The villus lengths and crypt depths returned to pretreatment values within two to four days. The mucosal innervation was assessed through immunohistochemistry for vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), and neuron-specific enolase (NSE). At all stages of regeneration, VIP, NPY, and NSE immunopositive fibers within the lamina propria extended to the tips of the villi. The density of the immunopositive fibers in the lamina propria at four days after mucosal insult was similar to that in control tissues regardless of the neuronal marker visualized. We conclude that the nerve fibers innervating the small intestinal mucosa grow at a rate of approximately 100 m/day and that the entire length of each villus contains nerve fibers throughout the regeneration process. The innervation of the regenerated mucosa appears identical to that of control mucosa.Norman A. See is a Fellow of the American Foundation for Pharmaceutical Education.Supported by NIH grant AM32594 (P.B.) and NSF grant BNS-8820658 (M.E.).