RESUMEN
INTRODUCTION: The intra-hepatic vascular anatomy in rodents, its variations and corresponding supplying and draining territories in respect to the lobar structure of the liver have not been described. We performed a detailed anatomical imaging study in rats and mice to allow for further refinement of experimental surgical approaches. METHODS: LEWIS-Rats and C57Bl/6N-Mice were subjected to ex-vivo imaging using µCT. The image data were used for semi-automated segmentation to extract the hepatic vascular tree as prerequisite for 3D visualization. The underlying vascular anatomy was reconstructed, analysed and used for determining hepatic vascular territories. RESULTS: The four major liver lobes have their own lobar portal supply and hepatic drainage territories. In contrast, the paracaval liver is supplied by various small branches from right and caudate portal veins and drains directly into the vena cava. Variations in hepatic vascular anatomy were observed in terms of branching pattern and distance of branches to each other. The portal vein anatomy is more variable than the hepatic vein anatomy. Surgically relevant variations were primarily observed in portal venous supply. CONCLUSIONS: For the first time the key variations of intrahepatic vascular anatomy in mice and rats and their surgical implications were described. We showed that lobar borders of the liver do not always match vascular territorial borders. These findings are of importance for the design of new surgical procedures and for understanding eventual complications following hepatic surgery.
Asunto(s)
Hígado/irrigación sanguínea , Ratones Endogámicos C57BL/anatomía & histología , Ratas Endogámicas Lew/anatomía & histología , Animales , Arteria Hepática/anatomía & histología , Arteria Hepática/cirugía , Venas Hepáticas/anatomía & histología , Venas Hepáticas/cirugía , Hígado/anatomía & histología , Hígado/cirugía , Ratones , Ratones Endogámicos C57BL/cirugía , Microvasos/anatomía & histología , Microvasos/cirugía , Ratas , Ratas Endogámicas Lew/cirugíaRESUMEN
Variations among inbred rats in terms of anatomy and routine laboratory values can potentially blur surgical experimental results. Therefore, a retrospective analysis aiming at investigating hepatic and perihepatic anatomical variations, liver weight, body weight, liver weight/body weight ratio (LBWR), variations in routine laboratory values, and the influence of shipment and repeated sampling was performed. In our study, liver weight of rats seemed to be strain-specific. LBWR was weakly and negatively correlated with body weight in rats. A statistically significant difference in routine blood tests was found among normal rats grouped by different body weight or shipment. Weekly repeated sampling from the same rats revealed a statistically significant difference in a blood test. In conclusion, the fact that variation among rats or their environment can blur the results of a surgical experimental study should be kept in mind.
Asunto(s)
Variación Anatómica , Hígado/anatomía & histología , Ratas Endogámicas Lew/anatomía & histología , Animales , Recuento de Células Sanguíneas , Hígado/irrigación sanguínea , Trasplante de Hígado , Masculino , Tamaño de los Órganos , Ratas , Ratas Endogámicas Lew/sangre , Ratas Endogámicas Lew/cirugía , Valores de Referencia , Estudios RetrospectivosRESUMEN
The sciatic nerve in the rat is the site most often used for peripheral nerve regeneration studies. The length of sciatic nerve available for research, however, depends on the point at which the sciatic nerve divides into the peroneal and tibial nerves. In the present study, the hind limbs of 150 adult male rats of five different strains (Sprague-Dawley, Fischer 344, Wistar-Han, Lewis and Nude) were analysed with regard to femur length, the point at which the sciatic nerve divides into the tibial and peroneal nerves, and where these are surrounded by the same epineurium, and the point at which they are encased in individual epineurial sheaths. The results indicate that the lengths of sciatic nerve are fairly constant in all strains of rats. In absolute terms, they amount to about one-third of the length of the femur for stretches of undivided sciatic nerve, and up to nearly half of the femur length for stretches where the tibial and peroneal nerves are already present, but are still enclosed by the same epineurium. In 61.7% of the hind limbs examined in Fischer rats, however, no sciatic nerve could be seen as such, but only in the form of its successors surrounded by the separate epineuria. This makes it highly advisable not to use male adult Fischer rats in peripheral nerve regeneration studies with the sciatic nerve as the point of focus.
Asunto(s)
Miembro Posterior/inervación , Ratas Endogámicas/anatomía & histología , Nervio Ciático/anatomía & histología , Animales , Miembro Posterior/anatomía & histología , Masculino , Ratas , Ratas Endogámicas F344/anatomía & histología , Ratas Endogámicas Lew/anatomía & histología , Ratas Desnudas/anatomía & histología , Ratas Sprague-Dawley/anatomía & histología , Ratas Wistar/anatomía & histología , Especificidad de la EspecieRESUMEN
Previous studies have suggested that cannabis-like drugs produce mainly aversive and anxiogenic effects in Wistar strain rats, but rewarding effects in Lewis strain rats. In the present study we compared Fos expression, body temperature effects and behavioral effects elicited by the cannabinoid CB(1) receptor agonist CP 55,940 in Lewis and Wistar rats. Both a moderate (50 microg/kg) and a high (250 microg/kg) dose level were used. The 250 microg/kg dose caused locomotor suppression, hypothermia and catalepsy in both strains, but with a significantly greater effect in Wistar rats. The 50 microg/kg dose provoked moderate hypothermia and locomotor suppression but in Wistar rats only. CP 55,940 caused significant Fos immunoreactivity in 24 out of 33 brain regions examined. The most dense expression was seen in the paraventricular nucleus of the hypothalamus, the islands of Calleja, the lateral septum (ventral), the central nucleus of the amygdala, the bed nucleus of the stria terminalis (lateral division) and the ventrolateral periaqueductal gray. Despite having a similar distribution of CP 55,940-induced Fos expression, Lewis rats showed less overall Fos expression than Wistars in nearly every brain region counted. This held equally true for anxiety-related brain structures (e.g. central nucleus of the amygdala, periaqueductal gray and the paraventricular nucleus of the hypothalamus) and reward-related sites (nucleus accumbens and pedunculopontine tegmental nucleus). In a further experiment, Wistar rats and Lewis rats did not differ in the amount of Fos immunoreactivity produced by cocaine (15 mg/kg). These results indicate that Lewis rats are less sensitive to the behavioral, physiological and neural effects of cannabinoids. The exact mechanism underlying this subsensitivity requires further investigation.
Asunto(s)
Encéfalo/efectos de los fármacos , Cannabinoides/farmacología , Neuronas/efectos de los fármacos , Proteínas Proto-Oncogénicas c-fos/metabolismo , Ratas Endogámicas Lew/metabolismo , Ratas Wistar/metabolismo , Receptores de Droga/efectos de los fármacos , Analgésicos/farmacología , Animales , Conducta Animal/efectos de los fármacos , Conducta Animal/fisiología , Temperatura Corporal/efectos de los fármacos , Temperatura Corporal/fisiología , Encéfalo/metabolismo , Catalepsia/inducido químicamente , Catalepsia/metabolismo , Catalepsia/fisiopatología , Recuento de Células , Ciclohexanoles/farmacología , Relación Dosis-Respuesta a Droga , Inmunohistoquímica , Abuso de Marihuana/metabolismo , Abuso de Marihuana/fisiopatología , Actividad Motora/efectos de los fármacos , Actividad Motora/fisiología , Neuronas/metabolismo , Ratas , Ratas Endogámicas Lew/anatomía & histología , Ratas Wistar/anatomía & histología , Receptores de Cannabinoides , Receptores de Droga/metabolismoRESUMEN
The responsiveness of hypothalamic CRF to various stressors is reduced in the young female Lewis relative to the histocompatible Fischer rat. Whether such a difference impacts the brain-gut response to water avoidance stress was investigated by monitoring Fos immunoreactivity in the brain and sacral spinal cord and fecal pellet output. Exposure for 60 min to water avoidance stress increased the number of Fos positive cells in the paraventricular nucleus of the hypothalamus (PVN), nucleus tractus solitarius (NTS), and the parasympathetic nucleus of the lumbo-sacral spinal cord (L6-S1) in both Lewis and Fischer rats compared with non stress groups. The Fos response was lower by 32.0% in the PVN, and 63% in sacral parasympathetic nucleus in Lewis compared with Fischer rats while similar Fos expression was observed in the NTS. Stress-induced defecation was reduced by 52% in Lewis compared with Fischer rats while colonic motor response to CRF injected intracisternally resulted in a similar pattern and magnitude of defecation in both strains. The CRF receptor antagonist [D-Phe12,Nle(21,38)C(a)MeLeu(37)]-CRF(12-41) injected intracisternally antagonized partly the defecation response in Lewis and Fischer rats. These data indicate that a lower activation of PVN and sacral parasympathetic nuclei in Lewis compared with Fisher rats may contribute to the differential colonic motor response and that the blunted CRF hypothalamic response to stress, unlike responsiveness to central CRF plays a role.
Asunto(s)
Reacción de Prevención/fisiología , Colon/fisiología , Defecación/fisiología , Sistema Nervioso Parasimpático/metabolismo , Núcleo Hipotalámico Paraventricular/metabolismo , Médula Espinal/metabolismo , Estrés Fisiológico/metabolismo , Factores de Edad , Animales , Recuento de Células , Colon/efectos de los fármacos , Colon/inervación , Hormona Liberadora de Corticotropina/antagonistas & inhibidores , Hormona Liberadora de Corticotropina/metabolismo , Defecación/efectos de los fármacos , Femenino , Vías Nerviosas/citología , Vías Nerviosas/efectos de los fármacos , Vías Nerviosas/metabolismo , Neuronas/citología , Neuronas/efectos de los fármacos , Neuronas/metabolismo , Sistema Nervioso Parasimpático/citología , Sistema Nervioso Parasimpático/efectos de los fármacos , Núcleo Hipotalámico Paraventricular/citología , Núcleo Hipotalámico Paraventricular/efectos de los fármacos , Proteínas Proto-Oncogénicas c-fos/efectos de los fármacos , Proteínas Proto-Oncogénicas c-fos/metabolismo , Ratas , Ratas Endogámicas F344/anatomía & histología , Ratas Endogámicas F344/metabolismo , Ratas Endogámicas Lew/anatomía & histología , Ratas Endogámicas Lew/metabolismo , Reflejo/efectos de los fármacos , Reflejo/fisiología , Sacro , Factores Sexuales , Núcleo Solitario/citología , Núcleo Solitario/efectos de los fármacos , Núcleo Solitario/metabolismo , Médula Espinal/citología , Médula Espinal/efectos de los fármacos , Estrés Fisiológico/patología , Estrés Fisiológico/fisiopatologíaRESUMEN
The microanatomical structure of human and rat splenic white pulp is compared, with special emphasis on the localization of the marginal zone occupied by immunoglobulin M (IgM)+ IgD-/dull B lymphocytes and its specialized macrophages. Our study reveals that in contrast to rats, the marginal zone of humans primarily exists in the vicinity of primary and secondary splenic follicles and that it is almost absent around the periarteriolar T-cell zones. We demonstrate that in humans there is an additional compartment, the perifollicular zone, located between the marginal zone and the red pulp. The perifollicular zone is a dynamic region of variable cellular and phenotypic composition, which can be regarded either as a part of the red pulp or of the follicles. In most cases the perifollicular zone appears as a compartment of the red pulp containing erythrocyte-filled spaces which differ from the typical red pulp sinusoids. Similar to the splenic cords, the perifollicular zone mostly harbours scattered B and T lymphocytes. However, sometimes B lymphocytes clearly predominate in the perifollicular area. In addition, strongly sialoadhesin-positive macrophages form sheaths around capillaries in the perifollicular zone. Such capillary sheaths are not observed in rats. In humans weakly sialoadhesin-positive macrophages are also present in the perifollicular zone and in the red pulp. In some specimens sialoadhesin is, however, strongly expressed by a large number of dispersed perifollicular macrophages. Interestingly, in striking contrast to rats, the human marginal zone does not contain sialoadhesin-positive macrophages and marginal metallophilic macrophages are also absent in humans. Thus, sialoadhesin-positive macrophages and IgM+ IgD- memory B lymphocytes both share the marginal zone as a common compartment in rats, while they occupy different compartments in humans. We show that the human splenic marginal zone does not contain a marginal sinus and assume that in humans the perifollicular region is the compartment where antigen and recirculating lymphocytes enter the organ.
Asunto(s)
Macrófagos/metabolismo , Glicoproteínas de Membrana/metabolismo , Ratas Endogámicas Lew/inmunología , Receptores Inmunológicos/metabolismo , Bazo/inmunología , Animales , Subgrupos de Linfocitos B/inmunología , Moléculas de Adhesión Celular/metabolismo , Femenino , Humanos , Técnicas para Inmunoenzimas , Inmunoglobulina M/análisis , Macrófagos/citología , Macrófagos/inmunología , Masculino , Ratas , Ratas Endogámicas Lew/anatomía & histología , Ratas Endogámicas Lew/metabolismo , Lectina 1 Similar a Ig de Unión al Ácido Siálico , Ácidos Siálicos/metabolismo , Especificidad de la Especie , Bazo/citología , Bazo/metabolismoRESUMEN
Differences in sleep-wake patterns in response to light-dark stimulation have been observed between albino Lewis and pigmented Brown Norway strains of rats, which may be associated with albinism. Since several anatomical differences have been demonstrated in the visual pathways of albino and pigmented mammals, the present study was undertaken to determine whether additional differences in visual pathways of these rat strains exist that might account for their behavioral differences. Using anterograde tracing techniques and image analysis, we have investigated the retinal projections of Lewis and Brown Norway rats. Our results demonstrate that the distribution of retinal terminals in the hypothalamic suprachiasmatic nucleus extends over a greater area in Lewis compared to Brown Norway rats. This zone of termination corresponds to a cytoarchitectonically definable ventrolateral subdivision of the suprachiasmatic nucleus (SCN), which is also greater in Lewis than in Brown Norway rats. These results may have implications for behaviors related to the SCN.
Asunto(s)
Albinismo/patología , Hipotálamo/patología , Pigmentación , Ratas Endogámicas Lew/anatomía & histología , Ratas/anatomía & histología , Retina/patología , Animales , Retina/fisiopatología , Núcleo Supraquiasmático/patología , Transmisión Sináptica , Vías Visuales/patologíaAsunto(s)
Células Dendríticas/citología , Ratones/anatomía & histología , Adenohipófisis/citología , Ratas/anatomía & histología , Animales , Anticuerpos Monoclonales/inmunología , Antígenos CD/análisis , Biomarcadores/análisis , Femenino , Antígenos de Histocompatibilidad Clase II/análisis , Humanos , Inmunofenotipificación , Masculino , Ratones Endogámicos BALB C/anatomía & histología , Ratas Endogámicas BB/anatomía & histología , Ratas Endogámicas Lew/anatomía & histología , Ratas Wistar/anatomía & histología , Proteínas S100/análisis , Especificidad de la EspecieRESUMEN
By means of serial sectioning of the head and neck a paired, rod shaped, parachoanic lymphoid organ was identified in Lewis rats. Histological, ultrastructural studies and FACS analysis showed this organ to be a lympho-epithelial organ with high endothelial venules (HEV) and a preponderance of B over T and T helper over T suppressor cells. Consequently this organ resembles the pharyngeal tonsil of man, and it is called the Waldeyer ring equivalent (WRE). The lymphatic drainage of this organ occurs predominantly to the deep, and to a lesser extent to the superficial cervical lymph nodes. Migration studies with 51Cr labeled cells show that the WRE lymphoid cells migrate into the lymphoid organs with HEV (peripheral lymph nodes. Peyer patches and WRE). In this respect they resemble peripheral lymph node cells more than cells from the Peyer patches. Thus the WRE lymphoid tissue in the rat is undoubtedly involved in local oronasopharyngeal immune surveillance and may also contribute to mucosal and systemic immune responses.
Asunto(s)
Linfocitos/fisiología , Tejido Linfoide/citología , Tonsila Palatina/inmunología , Ratas Endogámicas Lew/anatomía & histología , Animales , Movimiento Celular/fisiología , Separación Celular , Citometría de Flujo , Ganglios Linfáticos/inmunología , Sistema Linfático/inmunología , Sistema Linfático/ultraestructura , Tejido Linfoide/inmunología , Masculino , Modelos Biológicos , Tonsila Palatina/ultraestructura , Ganglios Linfáticos Agregados/inmunología , Ratas , Ratas Endogámicas Lew/inmunologíaRESUMEN
On the basis of functional questions, graphic three-dimensional reconstructions of the tympanic bulla of the rat were made to gain insight into the spatial organisation of the contents of the bulla and especially of the tympanic membrane--ossicular chain--middle ear muscle complex. For this purpose drawings of microscopical sections of complete bullae were fed into the computer to make three-dimensional graphic reconstructions with hidden line removal. From these reconstructions plastic representations were made by the medical artist. The topographical anatomy of the tympanic bulla is discussed in detail and compared to the anatomy of the middle ear in man. It is postulated that, despite differences in spatial organisation of the middle ear of the rat compared to that of man, the middle ear muscles influence the ossicular chain in a comparable way. On the basis of the topographical anatomy it is feasible that the muscles in the rat act synergistically in increasing the stiffness of the ossicular chain.
Asunto(s)
Oído Medio/anatomía & histología , Músculos/anatomía & histología , Ratas Endogámicas Lew/anatomía & histología , Animales , Osículos del Oído/anatomía & histología , Masculino , Ratas , Estapedio/anatomía & histología , Tensor del Tímpano/anatomía & histología , Membrana Timpánica/anatomía & histologíaRESUMEN
The innervation of the tensor tympani muscle and the stapedius muscle in the rat was studied. This was done by acetylcholinesterase in toto staining of the tympanic bullae and of muscles dissected separately, acetylcholinesterase staining of serial cross-sections of the muscles, silver impregnation of serial sections of complete tympanic bullae, serial semithin sections stained according to Laczko & Levai and electron microscopy of both muscles. The gross innervation of the muscles and the relation to other nerves in the bulla are described. It is shown that both muscles are innervated by very thin nerve fibres which form a well-organised elaborate network in the muscles, with very short branches that connect with motor endplates. Electron microscopically there are indications that the endplates in the stapedius muscle seem to enable faster activation of the muscle fibres than those of tensor tympani muscle. No morphological evidence for any sensory innervation of the muscles could be detected in the muscles themselves, in the connective tissue related to the muscles, or in the contents of the bulla tympanica. It is postulated that the afferent input of the acoustic middle ear muscle reflex is sound alone and that sensory information from the muscles themselves or from other structures in the tympanic bulla do not contribute to the reflex.
Asunto(s)
Estapedio/inervación , Tensor del Tímpano/inervación , Animales , Masculino , Microscopía Electrónica , Placa Motora/ultraestructura , Fibras Nerviosas/ultraestructura , Neuronas Aferentes/ultraestructura , Ratas , Ratas Endogámicas Lew/anatomía & histología , Estapedio/ultraestructura , Tensor del Tímpano/ultraestructuraRESUMEN
Four groups of inbred male LEW rats were examined: A, germfree athymic; B, specified pathogen free (SPF) athymic; C, germfree euthymic; D, SPF euthymic. All animals were killed at 18 weeks and compared with respect to body weight, histological appearance and cell density of the lymphoid organs, haematological values and differential counts of bone marrow, peripheral blood and lymph. Athymic rats had a lower body weight, less densely populated lymphoid organs, and fewer lymphocytes in the blood and lymph compared with euthymic animals. No difference was seen between athymic rats under germfree and SPF conditions, and in general the differences between athymic and euthymic animals were less pronounced under germfree conditions.
Asunto(s)
Células de la Médula Ósea , Vida Libre de Gérmenes , Linfa/citología , Tejido Linfoide/anatomía & histología , Ratas Endogámicas Lew/anatomía & histología , Ratas Endogámicas/anatomía & histología , Ratas Mutantes/anatomía & histología , Ratas Desnudas/anatomía & histología , Animales , Peso Corporal , Recuento de Leucocitos , Ganglios Linfáticos/anatomía & histología , Ganglios Linfáticos/citología , Linfocitos , Tejido Linfoide/citología , Masculino , Tamaño de los Órganos , Ratas , Ratas Endogámicas Lew/sangre , Ratas Desnudas/sangre , Organismos Libres de Patógenos Específicos , Bazo/anatomía & histología , Bazo/citología , Timo/anatomía & histología , Timo/citologíaRESUMEN
The occurrence of alterations in testicular weight and morphology after vasectomy and vasectomy reversal by vasovasostomy was studied in Lewis rats. Animals were studied 3, 4, and 7 months after bilateral vasectomy or a vasectomy followed 3 months later by vasovasostomy. Other rats served as sham-operated controls. The weights of the testes in vasectomy and vasovasostomy animals fell into two groups-small testes weighing less than 0.88 g and normal-sized testes of 1.2 g or more. When the extent of testicular alterations was estimated in sections for light microscopy by use of a semiquantitative testicular biopsy score count (TBSC), the morphology of the testes corresponded closely to the testis weight (r = .94), small testes having correspondingly low TBSC scores. In severely altered small testes, the seminiferous tubules were narrower than in sham-operated rats, and numbers of germ cells were greatly depleted. Many tubules contained only Sertoli cells and spermatogonia, although spermatocytes were present in a minority of tubules. A few seminiferous tubules contained multinucleate spermatids. Electron microscopy of severely altered tubules revealed closely apposed processes of Sertoli cells, which contained filaments, microtubules, and endoplasmic reticulum. In contrast, testes with normal weight in vasectomy and vasovasostomy groups resembled those of the sham-operated animals. Comparison of distributions of testicular biopsy score counts demonstrated differences between vasectomy and vasovasostomy groups as time after operation increased. At the 3-4-month intervals, approximately one-third of the testes were severely altered in both vasectomy and vasovasostomy groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Ratas Endogámicas Lew/anatomía & histología , Ratas Endogámicas/anatomía & histología , Reversión de la Esterilización , Testículo/anatomía & histología , Vasectomía , Animales , Histocitoquímica , Masculino , Microscopía Electrónica , Tamaño de los Órganos , Ratas , Recuento de Espermatozoides , Testículo/ultraestructuraRESUMEN
Several age groups of nude homozygous rnu/rnu and heterozygous rnu/+ rats of the same genetic background at an early stage of back-crossing (LEW/Mol) were compared as to body and organ weights, histological appearance and cell density of lymphoid organs, haematological values and differential counts of bone marrow and peripheral blood. No thymic tissue was found in the nude animals. 7-week-old nudes were smaller than control animals and had relatively larger non-lymphoid organs and cell-depleted peripheral lymphoid organs. Other age groups showed little difference. Peripheral blood of nude rats showed no signs of lymphopaenia in contrast with the findings in nude mice. The number of thoracic duct lymphocytes was, however, significantly smaller in all age groups of the nude rats, and the bone marrow tended to contain fewer lymphocytes.
Asunto(s)
Homocigoto , Tejido Linfoide/anatomía & histología , Ratas Endogámicas Lew/genética , Ratas Desnudas/genética , Factores de Edad , Animales , Células de la Médula Ósea/citología , Femenino , Heterocigoto , Recuento de Leucocitos/veterinaria , Masculino , Tamaño de los Órganos/genética , Ratas , Ratas Endogámicas Lew/anatomía & histología , Ratas Desnudas/anatomía & histologíaAsunto(s)
Médula Renal/ultraestructura , Porcinos/anatomía & histología , Animales , Membrana Celular/ultraestructura , Cilios/ultraestructura , Epitelio/ultraestructura , Glucógeno/análisis , Aparato de Golgi/ultraestructura , Microscopía Electrónica , Microscopía Electrónica de Rastreo , Microvellosidades/ultraestructura , Ratas , Ratas Endogámicas Lew/anatomía & histologíaRESUMEN
Quantitative methods were used to examine the cerebral cortex of the albino rat. A computer-controlled automatic image analyzer was used to determine by a systematic scanning procedure the grey level index of the 60 X 60 mum measuring fields in Nissl-stained serial sections form three brains. Based upon various selected thresholds or ranges of grey level indices, topographically accurate computer plots were produced, and an areal pattern of the cortex worked out according to quantitative considerations. Maps of the cytoarchitectonic areas of the cortex were reconstructed graphically. The present analysis shows a cortical pattern which differs to a great extent from Krieg's (1946) classical description, but corresponds to the degeneration studies, studies on axonal transport and neurophysiological studies of various cortical areas as described in the literature.
Asunto(s)
Corteza Cerebral/citología , Ratas Endogámicas Lew/anatomía & histología , Ratas Endogámicas/anatomía & histología , Albinismo , Animales , Mapeo Encefálico , Recuento de Células , Computadores , Masculino , RatasRESUMEN
By 3 months after surgery, testicular weights were 12-14% below control values in a large series of vasectomized rats of the inbred Lewis strain. Testicular sperm concentrations in the vasectomized rats were 25-29% below those in the sham-operated animals. Although modest in magnitude, these differences were highly significant (P less than 0.001). Histometric analysis of testes from a smaller series of vasectomized Lewis rats revealed various proportions of abnormal seminiferous tubules. The degenerative changes included reduction in tubule diameter, fusion of spermatids, and depletion of advanced germinal elements. In the most severely affected tubules, leakiness of the blood-testis barrier was indicated by penetration of lanthanum through Sertoli-cell tight junctions.