Influence of age on accumulation of α-actin in satellite-cell-derived myotubes in vitro

Because muscle satellite cells have been implicated in the process of muscle growth and mass regulation, as well as regeneration, alterations in the capacity of satellite cells to differentiate and accumulate muscle specific proteins during aging could play a role in the process of senile muscle atrophy. Skeletal muscle satellite cells were cultured from male rats from the following four age groups: neonatal rats (less than 5 days of age), growing rats (1–3 months of age), adult rats (9–12 months of age) and old rats (more than 24 months of age). A series of experiments was conducted in which cultures were harvested at daily intervals following fusion, and the amount of α-actin per myotube nucleus was determined. Analysis of maximum actin accumulation in myotubes from each experiment within each age group revealed no significant differences among cells derived from growing, adult or old rats; however, myotubes differentiating from neonatal muscle cells were able to accumulate more than three times as much α-actin per myotube nuclei as cells from the other three age groups. This result may reflect fundamental differences between authentic satellite cells and myogenic cells of prenatal origin. Aside from differences between neonatal cells and satellite cells, satellite cells from old muscle do not appear to have a diminished capacity to accumulate muscle-specific proteins following differentiation into muscle fibers.     

Age-related decrease in proopiomelanocortin gene expression in the arcuate nucleus of the male rat brain.

The decline in reproductive function with aging is due in part to decreased gonadotropin-releasing hormone (GnRH) secretion. beta-Endorphin (beta E), an endogenous opioid peptide derived from proopiomelanocortin (POMC), is thought to exert a tonic inhibitory effect upon hypothalamic GnRH secretion. We tested the hypothesis that the age-related decrease in GnRH secretion in male rats is due to increased beta E synthesis, by comparing POMC mRNA levels in the arcuate nucleus (ARC) of intact young, middle-aged and old male rats. In an initial study (Study 1), sixteen 20-microns coronal sections each from the ARC of 3- (n = 5) and 23-month-old (n = 4) male Fischer 344 rats were anatomically matched and analyzed. In a second study (Study 2), four anatomically matched sections of caudal arcuate nucleus from 3- (n = 4), 11- (n = 7) and 23-month-old (n = 5) male rats were compared. POMC mRNA levels were quantitated by in situ hybridization histochemistry, using a 35S-labeled oligodeoxynucleotide probe complementary to a portion of rat POMC cDNA and computerized image analysis. The number of grains per cell and cells per section were used as indices of cellular POMC mRNA content and the number of neurons expressing the POMC gene, respectively. Cellular POMC mRNA content was significantly lower in old compared to young animals (Study 1: 54 +/- 3 vs. 74 +/- 2 grains/cell, p less than 0.01; Study 2: 59 +/- 2 vs. 71 +/- 2 grains/cell, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Ultrastructural and light microscopic evidence of apoptosis after middle cerebral artery occlusion in the rat.

Brains from eight rats subjected to transient focal ischemia (2 hours) and reperfusion (22 hours) revealed an ultrastructural appearance of apoptosis and light microscopic features of cells exhibiting DNA fragmentation. The number of cells exhibiting DNA fragmentation was significantly higher (P < 0.01) in the ipsilateral hemisphere (216 +/- 43 per section) than in the contralateral hemisphere and in normal (n = 4) and sham operated (n = 4) rats (0 to 3 positive cells per section in controls). Cells exhibiting DNA fragmentation were primarily located in the inner boundary zone to the infarct. Cells exhibiting DNA fragmentation provided morphological information of apoptosis. Apoptosis may contribute to the development of infarct after transient focal cerebral ischemia.     

The pattern and timing of lymphatic metastasis of the rat carcinoma LMC1

The distribution pattern and latency of lymphatic metastases naturally disseminated by the Leeds Mammary Carcinoma (LMCI) when transplanted subcutaneously in isogeneic Johns' Strain Wistar rats has been determined. After the curative local irradiation and excision of the primary tumour in 210 rats, 55 ± 3 per cent developed either local (26 ± 3 per cent), and/or regional (28 ± 3 per cent) and/or distant (37 ± 3 per cent) lymph node metastases.Analysis of their pattern of distribution suggests that metastasis to local (inguinal and lumbar) and distant (axillary and mediastinal) nodes results mainly from the radial dissemination, trapping and nodal proliferation of cells released by the primary tumour. Although direct metastasis to the para-aortic node may have occurred, in the main seeding of this site and thence to other, regional, i.e. iliac and/or adrenal nodes, resulted from the dissemination of tumour cells from the local nodes.The latency of metastases appearing at different sites after primary tumour ablation, although highly variable, was site dependent and for local, regional and distant nodes was 30 ± 14, 48 ± 16, 56 ± 17 days respectively. In addition, the latency of metastases at regional and distant nodes was directly correlated with the latency of local metastases. The latency of adrenal and iliac metastases also correlated with para-aortic node metastasis, as did mediastinal with axillary lymph node metastasis. From the data, a semi-quantitative model of lymphatic metastasis has been developed for further evaluation and adjuvant chemotherapy testing.     

Effects of serum collected from rats of different ages on in vitro cell proliferation

It has been reported by Carrel and his co-workers that serum from old hens inhibits cell growth in culture. However, as we had previously demonstrated contradictory results using serum from old rabbits, we examined whether serum from old rats would also show strong induction of cell proliferation. Sera from young and adult rats of either sex strongly stimulated the growth of rat fetal skin fibroblasts and human fetal lung fibroblasts (TIG-1). Sera of old female and male rats (24-29 months old) produced much greater fluctuations in growth-stimulatory activity than sera from young animals. Most samples of serum from old rats stimulated the growth of TIG-1 cells, as did fetal bovine serum and samples from younger rats, even when a higher concentration of serum (up to 50%) was used. On the other hand, a small proportion of samples repressed the growth of the cells. A study on the effects of serial mixtures of both different types of serum samples from old rats on cell growth suggested that this minor proportion of serum samples contain a large amount of inhibitory factor(s). The cell growth-stimulatory activity of serum did not correlate with the total protein and albumin concentrations, albumin/globulin ratio, and the levels of lipid peroxide in the sample. These results therefore seemed to imply that serum induced a striking increase in the heterogeneity of cell growth stimulatory activity with age, although most samples of serum from old rats of either sex stimulated cell proliferation as effectively as samples from younger rats. The biological significance of the small proportion of serum samples from old rats which do inhibit cell proliferation was discussed.     

Age-related toxicity to lactate, glutamate, and beta-amyloid in cultured adult neurons

The age-related susceptibility of the brain to neurodegenerative disease may be inherent in the susceptibility of individual neurons to various stressors. Neurons were isolated from embryonic, young- and old-aged rat hippocampus, cultured in serum-free medium and exposed to lactic acid, glutamate or beta-amyloid. Yields of isolated adult cells were 1 million cells/hippocampus, 12,000 cells/mg tissue, independent of age. For lactic acidosis, there was a non-significant 10% increment in killing of neuron-like cells from old rats compared to young. For glutamate, there was a 5-10% increment in killing of neuron-like cells from old rats compared to young rats and embryonic neurons. For cells exposed to the toxic fragment of beta-amyloid, A beta (25-35), toxicity was age, dose and time-dependent. Maximum toxicity in cells treated for 1 day with 25 microM A beta (25-35) was 16%, 24%, and 33% for embryonic, young and old cells. Similar results were found for A beta (1-40) (LD50 = 2 microM). These results suggest that aging imparts to individual cells an increased susceptibility to toxic substances relevant to neurodegenerative diseases.     

雷公藤甲素PG490-88联合环孢素A免疫抑制诱导肾移植急性排斥反应模型大鼠的免疫耐受

背景：近年来的研究发现雷公藤甲素具有很好的抗排异、抗肿瘤作用。PG490-88是雷公藤甲素的提取物,能够预防移植物抗宿主病和诱导免疫耐受。 目的：探讨雷公藤甲素PG490-88联合环孢素A在大鼠肾移植急性排斥反应中诱导免疫耐受的作用。 方法：改良法建立大鼠肾移植动物模型。40只Wistar大鼠做供体、40只SD大鼠做受体,随机数字表法均分为4组：对照组给予常规饮食。雷公藤甲素组给予雷公藤甲素PG490-88 20 mg/(kg•d)灌胃。环孢素A组给予环孢素A 15 mg/(kg•d)灌胃;联合治疗组：PG490-88 20 mg/(kg•d)+环孢素A 15 mg/(kg•d)灌胃。分别检测肾移植后各组1,3,5,7,14 d外周血白细胞介素2受体水平和肾移植后大鼠的脾脏淋巴细胞组织中的白细胞介素2活性蛋白表达。 结果与结论：3个治疗组的白细胞介素2活性和白细胞介素2受体均明显低于对照组(P < 0.05)。其中,联合治疗组低于雷公藤甲素组和环孢素A组,差异有显著性意义(P < 0.05)。提示,雷公藤甲素PG490-88通过对白细胞介素2、白细胞介素2受体的影响,来达到免疫抑制作用,不但具有免疫抑制作用,而且还能够诱导一定程度的免疫耐受,联合环孢素A效果会更好。     

The effect of increased longevity, produced by dietary restriction, on the neuronal population of area 17 in rat cerebral cortex

Area 17 of the brains of Sprague-Dawley derived rats, maintained on a limited ration of food to maintain their weights at the levels attained by two months of age, was compared with area 17 in control groups of rats fed ad lib. The oldest rats in the diet restricted group were sacrificed at 46 and 48 months of age, by which time their life spans had been extended about 12 months beyond the oldest age that rats fed ad lib achieve, for only few of the latter live as long as 33 months. In this study, the rats which were compared consisted of two groups of ad lib fed rats, one 3 and 6 months of age, and the other 33 months old, and two groups of diet restricted rats, one 26 months old and the other 46 to 48 month old rats (designated as 47 month old rats). Two indices were used to assess whether age affects the volume of area 17. One, the number of clusters of apical dendrites of layer V pyramidal cells per unit area of tangential sections, was the same in all groups, indicating that the lateral spread of area 17 did not alter with age. However, the other index, the thickness of area 17, did change with age, for area 17 was significantly thinner in the 47 month old diet restricted rats than in the other three groups. It was also found that the number of neuronal profiles in strips of sections passing through the entire depth of area 17 is decreased in the 47 month old rats, indicating that neurons had been lost from their cortices. This decrease in the number of neuronal profiles in the 47 month old rats was not due to nuclear shrinkage since the sizes of neuronal nuclei were not significantly different in the older ad lib and diet restricted rats. Determinations of neuronal packing densities in layers II/III, IV, V and VIa suggest that neurons are most frequently lost from the deeper cortical layers of the 47 month old rats, and in these layers large vacuolated spaces, the sizes of neuronal cell bodies, have been encountered. It is suggested that these spaces represent places from which neurons have been lost. It is concluded, therefore, that neurons are lost from area 17 in rats whose longevity is increased by diet restriction.     

A radioautographic study of the proliferative activity of adrenocortical and hypophyseal cells of the rat at different periods of the estrous cycle

The hypophysis and adrenal glands of Long-Evans female rats about two months old were examined after receiving thymidine-H³ at different phases of the estrous cycle. Radioautographs showed labeled cells preparing for or in division. In the hypophysis, where labeled cells were uniformly distributed in the anterior lobe, greatest activity was at estrus about 12 to 24 hours after ovulation. An average of about 300 labeled cells per mm² occurred but some individuals had over 700 per mm². At other periods of the cycle the average was less than 40 labeled cells per mm². The greatest proliferative activity in the adrenal cortex was found the first day of diestrus when an average of 92 labeled cells per section occurred compared with fewer than 50 per section at other stages. About 80% of the activity in early diestrus occurred in the outer zona fasciculata where it was four and eight times that at proestrus and estrus respectively. In the glomerulosa the number of labeled cells remained about the same on different days of the cycle and in the reticularis the average number was somewhat greater during diestrus when there were 3.4 labeled cells per section.     

Ultrastructural quantitative analysis of the innervation of axillary lymph nodes in juvenile and old rats

Background: Earlier studies have shown that the innervation of axillary lymph nodes is increased in old animals, compared to juvenile rats. The question thus arose, whether changes are also observable at an ultrastructural level for varicosities which form the actual transmission units. Methods: Ensheathed (axons) and unensheathed axonal profiles (open areas), were quantified with their spatial relationships to cells at the ultrastructural level in the axillary lymph nodes of juvenile ( < 6 weeks) and old ( > 2 years) Wistar rats. Results: In both groups of animals the majority of open areas, irrespective of their content of vesicles, lie at distances of more than 1,000 nm from cells in the plane of the section. Almost all open areas, located within 1,000 nm of a cell, are related to reticular cells, a small minority to plasma cells, and even fewer to lymphocytes. In the old animals there is a highly significant increase in the total number of sections of open areas with and without vesicles per unit area of medulla. The number of open areas related to cells does not change significantly in the old animals, as also the percentage of profiles containing vesicles. Only the percentages of open areas with and without vesicles related to plasma cells increase significantly in the old animals. This change is paralleled by a highly significant increase in the percentage volume of plasma cells in the old animals. On average, the profiles related to cells are closer to the cells in the older animals. Conclusions: The observed changes indicate that the innervation of lymph nodes of the rat is absolutely increased in the old animals, but that the relations between the various categories of profiles and their relations to cells tend to remain constant. © 1995 Wiley-Liss, Inc.     

Changes in immunological activity of rat lymphoid organs during pregnancy.

Immune reactivity in lymhoid organs of rats during the last week of syngeneic (Lewis: L x L) or allogeneic (females Lewis x males Wistar: L x W) pregnancy was compared with that found in non-pregnant animals. The thymus weight was slightly reduced and the response of thymic lymphocytes to phytohaemagglutinin and concanavalin A was slightly, but not significantly, elevated in pregnant rats. By contrast, the response of lymphoid cells from spleen and mesenteric lymph nodes to the mitogens was reduced in rats during advanced pregnancy. The immune response of lymphocytes from pregnant L x W rats to allogenic (Brown-Norway: BN) or semiallogeneic (W) irradiated cells was tested by the mixed lymphocyte culture (MLC) assay. The MLC response of para-aortic lymph nodes towards the unrelated BN cells was elevated over that of non-pregnant rats on day 15 of pregnancy. No significant enhancement was observed at the same time in the MLC response of mesenteric lymph nodes. On day 20 of pregnancy, a reduced MLC response towards BN cells was found in the mesenteric and para-aortic lymph nodes. On day 15 of pregnancy, the MLC response of mesenteric and, more markedly, that of para-aortic lymph nodes to paternal (W) cells was enhanced, as compared to that of non-pregnant rats. On day 20 of pregnancy, the response of mesenteric lymph nodes was suppressed, while the response of para-aortic lymph nodes was similar to that found in non-pregnant rats. Since the latter lymph nodes are the most directly exposed to antigenic stimulation from the uterus, it seems unlikely that the suppression in response to T-cell mitogens observed in the spleen and mesenteric lymph nodes during pregnancy accounts for the survival of the foetus. It seems more plausible that local factors in the vicinity of the uterus protect the foetus from being rejected.     

大鼠视上核神经分泌细胞的衰老形态变化

本文选用青年(3个月)、成年(10—12个月)和老年(28—30个月)雄性Wistar大鼠,对其下丘脑视上核神经分泌细胞分别作了光镜和电镜观察与测定。结果表明:老年大鼠视上核前部的神经分泌细胞密度与细胞核体积明显低于青年和成年大鼠,提示老年大鼠视上核有神经元消失和细胞活性降低的表现;神经分泌细胞核周质内的醛复红阳性颗粒未测出三个年龄组大鼠间的差异,含醛复红阳性颗粒的胞突在老年时却显示增粗和膨大;老年动物神经分泌细胞超微结构的主要变化为神经分泌颗粒和脂褐素增加,尤以后者为甚。老年大鼠少数神经分泌细胞还表现有粗面内质网和核蛋白体减少,排列紊乱,池囊扩张和脱颗粒,高尔基复合体池囊变窄或扩张,胞质和胞突内有自噬体样物质出现等衰老改变;多数细胞胞质内的其他结构同青年和成年大鼠者相似。此外。老年大鼠视上核神经毡结构中有多层膜包绕胞突,终末和突触等的鞘样结构出现增多。本研究表明大鼠衰老时视上核神经分泌细胞活性降低。     

A comparison of DNA repair synthesis in primary hepatocytes from young and old rats

DNA repair synthesis has been compared in primary hepatocyte cultures obtained from 3-month-old and 16-20-month-old rats. Several morphological and metabolic characteristics were determined to assure cultures of comparable quality. DNA damage was induced by the addition of bleomycin or the exposure of the culture to UV irradiation. DNA repair (unscheduled DNA synthesis) was determined by measuring [3H]thymidine incorporation. After UV irradiation, there was almost twice as much [3H]thymidine incorporation in cells obtained from young rats as in those obtained from old rats. Equal amounts of bleomycin resulted in substantially greater damage to DNA in cells from old rats than from young rats. For equal amounts of DNA damage there was again diminished [3H]thymidine incorporation in cells obtained from old rats. Finally equal amounts of bleomycin resulted in equal damage to DNA when the bleomycin was added to isolated rat liver nuclei from young or old rats. Bleomycin treated nuclei from young rats incorporated substantially more [3H]thymidine triphosphate (TTP) than bleomycin treated nuclei from old rats. The results indicate that hepatocytes from old rats are much more susceptible to bleomycin than hepatocytes from young rats and that the capacity for DNA repair synthesis is impaired in hepatocytes from old rats.     

Protein production and processing in young adult and aged rat submandibular gland cells in vitro

Protein production and processing were evaluated in vitro in dispersed submandibular gland cells from young adult (4–6 month) and aged (24 month) rats. A modest decrease (approx. 25%) in protein production (incorporation of radiolabeled amino acids into 10% CCl₃COOOH-insoluble material) was found with old cells in both continuous-pulse and pulse-chase studies. Also new protein processing, followed by gel electrophoresis and autofluorography of radiolabeled samples, showed specific, marked alterations in old cells. In particular a significant difference in the processing of a 225 000 molecular weight glycoprotein (likely the major rat submandibular muciN) was detected.     

Age-related toxicity to lactate, glutamate, and β-amyloid in cultured adult neurons

The age-related susceptibility of the brain to neurodegenerative disease may be inherent in the susceptibility of individual neurons to various stressors. Neurons were isolated from embryonic, young- and old-aged rat hippocampus, cultured in serum-free medium and exposed to lactic acid, glutamate or β-amyloid. Yields of isolated adult cells were 1 million cells/hippocampus, 12,000 cells/mg tissue, independent of age. For lactic acidosis, there was a non-significant 10% increment in killing of neuron-like cells from old rats compared to young. For glutamate, there was a 5–10% increment in killing of neuron-like cells from old rats compared to young rats and embryonic neurons. For cells exposed to the toxic fragment of β-amyloid, Aβ (25–35), toxicity was age, dose and time-dependent. Maximum toxicity in cells treated for 1 day with 25 μM Aβ (25–35) was 16%, 24%, and 33% for embryonic, young and old cells. Similar results were found for Aβ (1–40) ( ₅₀ = 2 μM). These results suggest that aging imparts to individual cells an increased susceptibility to toxic substances relevant to neurodegenerative diseases.     

Proliferation and differentiation of thyrotrophs in the pars distalis of the rat pituitary gland during the fetal and postnatal period

Pituitary glands from rat fetuses (gestational age 17.5-21.5 days) and rat pups (3, 7, 10, 14, 28 days old) were labeled with bromodeoxyuridine (BrdU) 2 h prior to sacrifice and embedded in paraffin. Sections were consecutively immunostained with anti-BrdU and anti-rat TSH. The number of cells stained with anti-BrdU, anti-rTSH, or both of them were counted. The area of the section and the volume of the pituitary were measured and the number of immunostained cells per mm3 or per pituitary was calculated. Thyrotrophs were few in 17.5 day-fetuses but increased thereafter, with a rapid increase during the 2nd week after birth. The number of cells labeled with both BrdU and TSH peaked at 7 days after birth. It was estimated that about 1/5 of the thyrotrophs increased during this period was derived from the mitosis of existing thyrotrophs.     

Cellular immunosenescence in F344 rats: decreased natural killer (NK) cell activity involves changes in regulatory interactions between NK cells, interferon, prostaglandin and macrophages

Natural killer (NK) activity of F344 rat spleen cells remained constant between 1 and 18 months of age under specific pathogen-free (SPF) conditions. Between 18 and 24 months of age, however, there was a dramatic decline in activity which remained at a low baseline throughout the normal lifespan. Removal of adherent cells on G-10 Sephadex columns revealed age-related changes in adherent cell regulation of NK activity. Young (4-6 week) NK activity was consistently decreased by adherent cell removal while old (24-30 month) NK activity was slightly but reproducibly increased. Moreover, splenic macrophages from old rats purified by adherence to microexudate-coated surfaces were highly suppressive to young nonadherent NK activity. A role for endogenous prostaglandin (PG) in suppressed old rat NK activity was suggested by the effectiveness of anti-PGE2 in vivo to boost old NK activity. Although old rat NK activity was boosted to a relatively greater extent by interferon (IFN) in vitro than was young NK activity, IFN-boosted NK activity of old rats was much more sensitive to PGE2 inhibition than was IFN-boosted young rat NK activity. IFN treatment in vitro or poly(I:C) treatment in vivo induced protection against PGE2 inhibition of NK activity in young rats, while no resistance to PGE2 inhibition was induced in old rat NK cells by similar treatments. In vivo, the same protocol of IFN administration which boosted young rat NK activity further suppressed old rat activity. These results support the hypothesis that immunosuppression related to aging, which supersedes the boosting effect of IFN, involves the combined effects of suppressor macrophages (via PGE2) and intrinsic changes in effector (NK) cells which render them more sensitive to PGE2 inhibition.     

Quantitative analysis of the Purkinje cell population during extreme ageing in the cerebellum of the Wistar/Louvain rat.

The loss of neurons is viewed as one of several causes of the deterioration of neural function during ageing. However, the existing experimental evidence for an age-related decrease in the neuronal number may be misinterpreted due to the way the cells are counted and to the interference of unsuspected degenerative pathology of the animals studied. To reinvestigate this question we have quantified an easily identifiable population of neurons, the cerebellar Purkinje cells, in very old but healthy rats. The number of Purkinje cells in the cerebellum was assessed in two populations of rats: control (10 months) and old (42 months) rats from the Wistar/Louvain strain. In both groups, paraffin-embedded brains were cut serially in the sagittal plane. Purkinje cells were counted every 15 or 22 sections under the light microscope at a magnification of 1250 x. The raw value of cell counts were corrected according to the method of Hendry (21) in order to avoid the overestimation due to splitting of the nucleus during sectioning. The latero-lateral extent of the cerebellar cortex, obtained by multiplying the thickness of the section by the number of sections in which Purkinje cells were counted, was not statistically different (mean +/- standard deviation): 12.8 +/- 1.16 mm (n = 6) for the control rats and 12.0 +/- 1.02 mm for the old animals (n = 8) (Student's t-test, p = 0.18). The corrected number of the Purkinje cells (mean +/- standard deviation) was 330,350 +/- 35,448 cells (n = 6) for the control animals and 299,019 +/- 50,223 (n = 8) cells for the old rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

(R)-alpha-lipoic acid reverses the age-associated increase in susceptibility of hepatocytes to tert-butylhydroperoxide both in vitro and in vivo

Hepatocytes were isolated from young (3-5 months) and old (24-28 months) rats and incubated with various concentrations of tert-butylhydroperoxide (t-BuOOH). The t-BuOOH concentration that killed 50% of cells (LC50) in 2 hr declined nearly two-fold from 721 +/- 32 microM in cells from young rats to 391 +/- 31 microM in cells from old rats. This increased sensitivity of hepatocytes from old rats may be due, in part, to changes in glutathione (GSH) levels, because total cellular and mitochondrial GSH were 37.7% and 58.3% lower, respectively, compared to cells from young rats. Cells from old animals were incubated with either (R)- or (S)-lipoic acid (100 microM) for 30 min prior to the addition of 300 microM t-BuOOH. The physiologically relevant (R)-form, a coenzyme in mitochondria, as opposed to the (S)-form significantly protected hepatocytes against t-BuOOH toxicity. Dietary supplementation of (R)-lipoic acid [0.5% (wt/wt)] for 2 weeks also completely reversed the age-related decline in hepatocellular GSH levels and the increased vulnerability to t-BuOOH as well. An identical supplemental diet fed to young rats did not enhance the resistance to t-BuOOH, indicating that antioxidant protection was already optimal in young rats. Thus, this study shows that cells from old animals are more susceptible to oxidant insult and (R)-lipoic acid, after reduction to an antioxidant in the mitochondria, effectively reverses this age-related increase in oxidant vulnerability.     

Long-term effects of gustatory neurectomy on fungiform papillae in the young rat

Recent evidence from mature hamster fungiform papillae indicates that following denervation taste buds are present from 21 to 330 days in the absence of discernible intragemmal nerve fibers. In contrast, most prior taste bud degeneration studies focused on shorter survival times. The present inquiry in young rats examined the issue of postneurectomy buds, in which regeneration of the resected chorda tympani or facial nerves was prevented and anterior tongue tissue examined over a range of relatively long survival times (30-90 days). Conditions for observing potential taste buds used three histologic stains and a definition of the taste bud not necessarily requiring pore identification. In each case, serial section examination of the anterior-most 2-3 mm of lingual epithelium revealed 29-56 bud-containing fungiform papillae on the unoperated side. In contrast, ipsilateral to the neurectomy, only zero-7 medially-placed, mature-looking buds were observed per case, as well as zero-3 more laterally situated fungiform papillae containing small clusters of cells in basal epithelium that lacked the vertical organization and cytoplasmic staining intensity of mature taste buds. These cell aggregates were distributed evenly across survival time and stain used. Therefore, in young rats following gustatory neurectomy, longer survival times, per se, would not appear to be a prerequisite for sustaining fungiform taste buds. The appearance of "midline" buds postsurgery may be attributed to either normal contralateral or a net bilateral innervation, and/or ipsilateral denervation and bud loss inducing neural sprouting from the contralateral side.