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PubMed1981

Rapid alterations induced by insulin in hepatocyte ultrastructure and glycogen levels.

The speed with which insulin alters hepatocyte ultrastructure and glycogen levels in insulin-deficient rats has been studied. Insulin deficiency was induced with alloxan, followed by insulin treatment with regular and NPH insulin. Rats were killed at various times after the insulin injection, blood samples were obtained, plasma glucose levels were determined, and liver samples were prepared for electron microscopy and glycogen determinations. Plasma glucose levels in insulin-deficient rats declined to normal values by 4 hours post insulin, returning to insulin-deficient levels by 8 hours post insulin. Hepatic glycogen was considerably reduced in the insulin-deficient rats. By 1 hour post insulin hepatic glycogen increased, reached maximal levels by 8 hours, then declined to insulin-deficient levels by 36 hours. The ultrastructural appearance of both centrilobular and periportal hepatocytes from insulin-deficient rats showed abundant vesicular smooth endoplasmic reticulum (SER), decreased rough endoplasmic reticulum (RER), and enlarged RER intracisternal spaces. One-half hour post insulin, centrilobular hepatocytes were unchanged. In periportal hepatocytes, however, vesicular SER was no longer visible, the RER intracisternal spaces appeared normal, and the amount of RER had increased. By 1 hour post insulin the centrilobular hepatocytes showed similar ultrastructural changes. These changes became more pronounced in the next few hours and remained through 24 hours. By 36 hours both centrilobular and periportal hepatocytes appeared similar to those in the insulin-deficient rat. These results demonstrate the rapid and lobular-specific effects insulin has on the hepatocyte.

Animals↗
PubMed1984

The effects of insulin replacement and withdrawal on hepatic ultrastructure and biochemistry.

This study examines the early hepatic biochemical and ultrastructural responses to insulin replacement in streptozotocin-diabetic rats and insulin withdrawal from insulin-maintained diabetic rats. Insulin administration rapidly lowered plasma glucose and the elevated glucose-6-phosphatase (G-6-Pase) specific activity of the diabetic rats. However, hepatic glycogen did not increase until after 3 hr of insulin treatment. Hepatic ultrastructure responded to insulin replacement after the decline in glucose and G-6-Pase. This was seen in periportal hepatocytes as a reduction in the close association between smooth endoplasmic reticulum (SER) and glycogen particles in the diabetic animals. The treated rats showed hepatic SER restricted to the periphery of glycogen masses, as is characteristic of these cells from normal rats, in many cells by 6 hr and all cells by 18 hr. Insulin withdrawal from insulin-treated diabetic rats elicited nearly a total reversal of the above events. Plasma insulin declined to a value half that of the normal rats by 6 hr after withdrawal; concurrently, plasma glucose rose sharply to hyperglycemic values as hepatic glycogen content dropped. Following the rise in plasma glucose and fall in glycogen content, G-6-Pase specific activity increased and by 16 hr reached the high values characteristic of the diabetic animal. Hepatic ultrastructure was also changed as evidenced by an intrusion of elements of the SER into the dense glycogen masses; the result was dispersed glycogen closely associated with SER as seen in the diabetic animal. It is concluded that the hepatic response to insulin replacement in diabetic animals and diabetic onset in insulin-withdrawn animals is rapid and occurs through defined stages.

Animals↗
PubMed1986

Ultrastructure of the giant cell infiltrate of subcutaneously implanted bone particles in rats and mice.

The giant cells of soft tissues and those of mineralized tissues (osteoclasts) have distinctly different cell surface receptors and ultrastructural characteristics. Recently, the removal of dead bone particles in a subcutaneous environment has been described as a prototype of bone resorption, and a major issue is whether the giant cells that surround these ectopic bone implants and the processes involved in the disruption of bone surfaces are the same as those in the skeleton. We have compared the cytology and ultrastructure of giant cells recruited to subcutaneously implanted isogeneic bone particles with similar features of osteoclasts in metaphyseal bone of young normal rats and mice. Giant cells on surfaces of bone particles 2, 3, and 4 weeks after implantation were multinucleated, had a homogeneous, nonvacuolated cytoplasm, and had a bone surface interface unremarkable by light microscopy. In a few cells randomly distributed, small cytoplasmic vacuoles were present and large vacuoles were noted next to the bone surface at high magnification. By transmission electron microscopy, folded membrane configurations forming extensive interdigitations with adjacent cells were prominent features on most surfaces of giant cells. In instances where these interdigitations abutted bone surfaces, configuration resembling a ruffled border were noted, but these regions were always part of two different cells when examined at lower magnification or in serial sections. Breakdown of bone particles appeared to be by phagocytosis of small pieces and subsequent intracellular digestion in electron-dense cytoplasmic vacuoles. Osteoclasts from these same young animals were smaller with fewer nuclei, had cytoplasmic vacuoles concentrated next to bone surfaces, and had characteristic ruffled borders and clear zones. These results confirm those of others that native osteoclasts and multinucleated giant cells on dead bone particles are distinctly different with respect to both ultrastructure and mechanism of disruption of bone surfaces.

Animals↗
PubMed1989

Ultrastructural epithelial zonation of the primate endometrium (rhesus monkey).

The uterine endometrium of menstruating primates (rhesus monkey, human) consists of a germinal basalis that regenerates a transient functionalis during each menstrual cycle. The endometrium is further subdivided into 4 zones that differ histologically and in epithelial mitotic rate along the longitudinal axes of the uterine glands and microvasculature (Bartelmez et al: Contrib. Embryol. Carnegie Inst., 34:99-146, 1951; Bartelmez: Am. J. Obstet. Gynecol., 74:931-955, 1957; Padykula et al.: Biol. Reprod., 32:1103-1118, 1118, 1984; Biol. Reprod., in press, 1988). The zones are defined as follows: functionalis I, luminal epithelium; functionalis II (upper straight gland segments); basalis III (middle gland segments), and basalis IV (bottoms of the glands). The surrounding stroma and microvasculature also differ zonally. Ultrastructural epithelial differences are evident among the 4 zones during 3 distinct functional states during natural menstrual cycles and after ovariectomy: 1) basal level after ovariectomy and 2) estrogen dominance and 3) progesterone dominance. Zonal structural differences persist at a minimal level of differentiation after ovariectomy and thus zonation is an inherent property. During estrogen dominance, distinctive ultrastructural differences are evident among the 4 zones, such as epithelial cell heterogeneity in functionalis I and homogeneity in functionalis II. Also a distinctive glandular cell type occurs in basalis III and IV that is recognized by a highly irregular cisternal rough endoplasmic reticulum that permeates the cytoplasm. During progesterone dominance, ultrastructural differences exist among the 4 zones except for similarity between the epithelial cells of functionalis II and basalis III. Postovulatory epithelial cells of functionalis I and II and basalis III become postmitotic via progesterone inhibition but intracellular differentiation continues progressively. Postovulatory epithelial mitotic activity in basalis IV escapes progesterone inhibition as the [3H]thymidine labeling index continues to increase from 1 to 12% during the menstrual cycle (Padykula et al.: Reprod., 30(Suppl.1):92 (Abstr. 123), 1984). This post-ovulatory proliferation coupled with progressive differentiation in basalis IV may represent a stem-progenitor set of cells for postmenstrual endometrial regeneration or alternatively for creation of the maternal placenta.

Animals↗
PubMed1984

Classic and generalized variants of Pick's disease: a clinicopathological, ultrastructural, and immunocytochemical comparative study.

Six sporadic cases of dementia with lobar atrophy and neuronal cytoplasmic inclusions (Pick's disease) could be separated into two groups on the basis of the involvement of subcortical structures, the distribution and the histochemical, immunochemical, and ultrastructural characteristics of the inclusions, and possibly the age at onset. The first group (classic) was characterized by predominantly cortical atrophy and the presence in the hippocampus and neocortex of argyrophilic cytoplasmic inclusion bodies that reacted with a monoclonal antibody against neurofilament proteins and antitubulin antisera. Ultrastructurally the bodies were composed of straight fibrils of variable diameter, averaging 15 nm, and long-period constricted fibrils. The second group (generalized) showed subcortical as well as antibodies against neurofilaments and microtubules. Ultrastructurally the straight fibrils composing the bodies were coated with granular material, presumed to be derived from ribosomes. The generalized cases occurred in younger patients than did the classic cases in this series.

Adult↗
PubMed1990

Immunocytochemical and ultrastructural studies of Pick's disease.

Cerebral cortical changes in 10 cases with Pick's disease were studied immunocytochemically and ultrastructurally. All cases contained Pick's argentophilic bodies and ballooned neurons. The antibodies against phosphorylated tau proteins that intensely stained all Pick bodies recognized numerous neuronal processes around Pick body-bearing cells and focal portions in the perikarya of ballooned neurons. Monoclonal and polyclonal anti-ubiquitin antibodies stained not only some Pick bodies with variable intensity, but also the perikarya of all ballooned neurons. Ultrastructurally, Pick bodies consisted of accumulation of randomly oriented, approximately 15-nm straight filaments and paired twisted profiles with a minimal diameter of 13 nm, maximal diameter of 26 nm, and twist periodicity of 120 nm. These Pick body-type filaments were also observed in the perikarya of ballooned neurons and neuronal processes around Pick body-bearing cells. Our studies demonstrate, for the first time, the characteristic pathological feature of neuropil in Pick's disease. Pick body-bearing cells and ballooned neurons show unique immunocytochemical and ultrastructural properties that may be a clue to the pathogenesis of Pick's disease.

Aged↗
PubMed1981

Ultrastructural evidence indicating reorganization at the neuromuscular junction in the normal rat soleus muscle.

The ultrastructural organization of 40 soleus neuromuscular junctions from ten normal young adult male and female Sprague-Dawley (SD)-derived rats (Charles River Breeders, CD-Crl:COBS (SD)BR) has been studied. A smaller sample of motor endplates from the gastrocnemius, diaphragm, and extensor digitorum longus muscles of these rats as well as from the soleus muscles of two adult Wistar (W) rats (Crl:COBS(WI)BR) was included. Widespread ultrastructural reorganization was evident at the soleus neuromuscular junction during the growth period from three to five months of age. A major characteristic of reorganization is the presence of junctional folds not associated with axonal terminals; such sites occur within a single endplate adjacent to areas with typical intact synaptic associations. Additional features possibly related to remodelling are: 1) spatial separation of axonal terminals from the myofiber, 2) intervention of Schwann cell cytoplasm between an axon terminal and myofiber, 3) aggregates of satellite cells, and 4) folded or multilayered basal lamina. These features are most pronounced in the soleus muscle but occur to varying degrees in the neuromuscular junctions of other muscles of SD-derived rats. Distinctive characteristics of the rat soleus postjunctional sarcoplasm include the widespread occurrence of myofibrillar components, abundant free and membrane-associated polysomes, and triads oriented in various planes. Away from such discrete sites, myofibers possess the usual highly oriented organization of myofibrils, T tubules, sarcoplasmic reticulum, and mitochondria. The soleus muscle is a postural muscle that responds directly to rising workload imposed by continuous body growth during young adulthood by steady myofiber hypertrophy and conversion of motor units (Kugelberg, '76). This changing structural-functional relationship may be reflected also by ultrastructural remodelling of the neuromuscular junctions reported here.

Aging↗
PubMed1982

Ultrastructural demonstration of chemical modification of melanogenesis in hairless mouse skin.

We investigated chemical and physical modifications of the genetically determined ultrastructure of melanosomes. The flank skin of hairless mice was treated with ultraviolet energy (UV) shorter than 320 nm or with a combination of a photosensitizer and UV (PUVA treatment). All melanosomes in the induced melanocytes and those in resident melanocytes in the ear skin showed eumelanogenesis, although the degree of melanin deposition differed considerably according to the induction process. Eumelanogenesis was most advanced in the resident melanocytes while PUVA-induced melanocytes showed more immature premelanosomes. We then topically applied 4-tertiary butyl catechol on the skin. The depigmenting agent caused an appearance of pheomelanosomes. The alteration in melanogenesis was seen most distinctly in premelanosomes of the PUVA-induced cells. Altered ultrastructure was also observed in matured melanosomes; this change was most apparent in the resident melanocytes. These findings indicate that cells with eumelanogenesis may undergo pheomelanogenesis. The present study demonstrated effects of chemicals on genetically determined function of melanocytes by quantitative analysis of melanosome ultrastructure.

Animals↗
PubMed1982

Genetic comparisons of eumelanosome ultrastructure.

We recently reported the existence of several new ultrastructural components of the eumelanosome matrix from developing chick pigment epithelium. The material used in the original study was obtained from a random sample of heterogeneous chicken. We have now extended this analysis to four genetically well-characterized chicken types: jungle fowl, blue, dominant white, and recessive wheaten. In these four genotypes there are specific ultrastructural alterations in the eumelanosome matrix. These alterations are different for each of the genotypes studied and are probably reflective of differences in the functional nature of the genes involved. The data thus provide evidence as to which genes are structural and which regulatory in action. Furthermore, since the material analyzed was all derived from pigmented pigment epithelium, it is clear that these melanosomes are affected by genes previously thought to leave them untouched. Finally, data are presented that these new ultrastructural elements are also found in a different class of animals, the C57BL/10 mouse.

Animals↗
PubMed1985

An ultrastructural analysis of dog mastocytoma cells and normal mast cells.

A well-differentiated dog mastocytoma was characterized ultrastructurally using morphometric, histochemical, and biochemical methods. The ultrastructure of cells in the intact tumor was compared to the morphology of cells disaggregated from the tumor and cultured for periods as long as 4 weeks and to normal dog connective tissue mast cells. Most of the tumor cells contained histamine (mean = 5.81 pg/cell), demonstrated chloroacetate esterase activity histochemically, stained metachromatically with toluidine blue, and were similar in ultrastructure to normal dog mast cells. The proportion of mast cells in this tumor averaged 67%; eosinophils, fibroblasts, plasma cells, and macrophages also were present. The mean diameter of mast cells (12.79 micron) and the mean diameter of their cytoplasmic granules (473 nm) were similar to those reported for mast cells and mastocytoma cells from various species. The heterogeneity in appearance of the mastocytoma granules is consistent with a variable degree of granule maturation. After disaggregation or periods of culture ranging from 2 days to 4 weeks, the mean granule diameters were 15% larger than those measured in the intact mastocytoma cells, though other morphological features remained unchanged. Although the cells retained their distinct morphological features for at least 4 weeks, some of their physiological responses were lost after 1 week in culture. Our study showed that dog mastocytomas can be a source of a large, relatively homogeneous population of cells that are useful for elucidating some of the structural and functional properties of mast cells.

Animals↗
PubMed1986

Ultrastructure and cytochemistry of thyroid lysosomes following subtotal thyroidectomy.

Following subtotal thyroidectomy, the amount of circulating thyroid hormone decreases and causes an increase in the secretion of thyrotropin (TSH) by the anterior pituitary gland. Serum levels of circulating TSH remain elevated until thyroid secretion returns to normal. In this study we have analyzed the effects of such chronic stimulation of thyroid cells by TSH, with particular emphasis on ultrastructural and cytochemical changes in the lysosomes. Weanling Sprague-Dawley rats underwent subtotal thyroidectomy and 6 weeks later the residual thyroid tissue was removed and processed for ultrastructural and cytochemical analysis. There were obvious ultrastructural signs of hyperactivity. The cells were hypertrophied and there were colloid droplets in the cells as well as extremely abundant oddly shaped lysosomes. The lysosomes reacted positively for acid phosphatase and for glycoproteins, suggesting that they are secondary lysosomes, ones which have complexed with thyroglobulin prior to release of thyroid hormones from the cells. This tremendous increase in the number of these structures in the cells is similar to that observed under normal conditions during the aging process and suggests a slowdown in the proteolytic degradation of thyroglobulin during long periods of chronic stimulation by TSH.

Acid Phosphatase↗
PubMed1993

Ultrastructural characteristics of primordial germ cells in the quail embryo.

An avian species, the quail has become a desirable animal model in experimental embryology and reproductive biology. To understand the ultrastructural characteristics of primordial germ cells (PGC) of this species, we studied PGC in the Japanese quail (Coturnix coturnix japonica) embryo at various developmental stages from their appearance in the germinal crescent through migration to settlement in the gonadal ridges by means of electron microscopy. The results were compared with those of another well-known avian species, the chick. Several ultrastructural characteristics of quail PGC not described previously in chick PGC were observed as follows: 1) No glycogen particles were detected in the cytoplasm at any stage examined. 2) Electron-dense and membrane-bounded granules were found in the PGC cytoplasm during the sexually indifferent gonadal stages. 3) Quail PGC were characterized by a prominent nucleolus associated with condensed chromatin (heterochromatin), and the developmental changes of the nucleus were noted; the nucleolus initially appeared as a compact mass at the germinal crescent stage and became dispersed at later stages during the colonization of the gonadal ridges. These findings suggest several physiological and functional differences in the cell cycle between these two avian species. This is the first report describing detailed ultrastructural characteristics of PGC in the quail embryo.

Animals↗
PubMed1994

Phagocytic defence mechanism in sea bass (Dicentrarchus labrax L.): an ultrastructural study.

BACKGROUND: The ultrastructure of the phagocytic process in fish has not been established in spite of the significant morphofunctional differences detected in the fish immune system with respect to the basic immunological pattern in vertebrates. We report the ultrastructure of the bacterial phagocytic defence mechanism in sea bass (Dicentrarchus labrax L.). METHODS: Head-kidney, blood, and peritoneal exudate leukocytes were challenged with Aeromonas salmonicida and Escherichia coli and processed for transmission electron microscopic study. RESULTS: Macrophages challenged with bacteria showed changes in the cell outline, in the chromatin pattern, and in the ultrastructural features of the cytoplasm as a consequence of an activation process. The phagocytic process consists of the following: 1) Bacteria-macrophage contact. One or more spot contacts between the bacterial wall and the phagocyte membrane are observed. 2) Bacteria engulfment. Slight depressions, membrane invaginations, or cytoplasmic processes are formed at the phagocyte surface. Macrophage processes occasionally surround the bacteria, overlapping and roaming parallel, or a single, long pseudopod encircles a bacterium several times. 3) Endocytic vesicle formation. Macrophages show one or more bacteria inside membrane-bound cytoplasmic vesicles. 4) Phagolysosome formation. Some dense granules (lysosomes) fuse with the endocytic vesicle. 5) Intracellular killing/digestion. Bacteria inside the endocytic vesicles are observed both virtually intact or damaged at different digestion stages. CONCLUSIONS: Sea bass macrophages possess the mechanisms necessary to both engulf and kill bacteria. Cellular and subcellular events in the morphology of phagocytosis and lysosomal dissolution of bacteria fit the general pattern described for mammals.

Aeromonas↗
PubMed1995

Ultrastructure and cytochemical staining characteristics of canine natural killer cells.

BACKGROUND: The purpose of this work was to describe the ultrastructure and cytochemical staining characteristics of canine peripheral blood lymphocytes with natural killer (NK) cell activity, with comparison made to non-NK lymphocytes. METHODS: Canine lymphocyte populations evaluated for ultrastructure, cytochemical staining, and NK function (by 51chromium release assay) included: peripheral blood lymphocytes; lymphocytes from band 1 (NK-enriched), band 2, and the pellet of a 45/50% percoll gradient; lymphocytes from the supernatant fluid (non-conjugated lymphocytes) and pellet (lymphocytes conjugated to tumor cell targets) of a 17% percoll gradient; and null (CD4-CD8-) and CD4-CD8+ lymphocytes. RESULTS: NK activity was concentrated in band 1 lymphocytes of the 45/50% percoll gradient with further enhancement of activity occurring in sorted null cells. Canine NK cells were 5.5 to 6.5 microns in diameter with a reniform (kidney bean shape) nucleus, and electron-dense cytoplasmic granules. NK cells (percoll band 1 cells and null cells) had larger cell and nuclear area, and less round nuclei when compared to non-NK lymphocytes. The overall cytochemical staining (chloracetate esterase, peroxidase, sudan black B, naphthyl acetate esterase, naphthyl butyrate esterase periodic acid-Schiff stain, and acid phosphatase with and without tartrate) pattern was similar in all the lymphocyte populations evaluated. CONCLUSIONS: This work confirms the usefulness of a 45/50% percoll gradient in obtaining a NK-enriched fraction of canine lymphocytes, and shows further enhancement of NK activity in sorted CD4- CD8- cells. The ultrastructure of canine NK cells is similar to that reported for human NK cells, but is different from that of other canine peripheral blood lymphocytes. Standard cytochemical staining does not discriminate canine NK cells from other lymphocytes.

Animals↗
PubMed2003

Ultrastructural morphology of adrenal chromaffin cells indicative of a process of piecemeal degranulation.

Chromaffin cells of the mouse adrenal medulla were found by transmission electron microscopy (TEM) to exhibit ultrastructural changes suggestive of piecemeal degranulation (PMD), a unique model of cell secretion characterized by the slow release of granule materials without granules opening to the cell exterior. The expression of PMD was recognized in both adrenaline- and noradrenaline-containing cells. Ultrastructural changes included specific granule and cytoplasmic morphologies. In adrenaline-releasing cells the granule content was loosely packed or condensed, and surrounded by a clear halo. In noradrenaline-storing cells, the granule material appeared asymmetrically arranged and exhibited characteristic "semilunar" electron-dense domains within the granule chambers. Notably, altered granules did not fuse with each other or with the plasma membrane, and were intermingled with normal, resting granules. Large, empty cytoplasmic containers or vacuoles filled with partially dissolved matrices were frequently observed. In addition, both adrenaline- and noradrenaline-storing cells presented a rich supply of membrane-bound, smooth vesicles (50-200 nm diameter) that were either free in the cytoplasm or attached to granules. The finding of ultrastructural features characteristic of PMD in adrenal chromaffin cells suggests that such a secretory model may be an alternative secretory pathway to regulated exocytosis. Moreover, these results support the hypothesis that PMD may be a general degranulation pattern in cells involved in paracrine-endocrine secretion.

Adrenal Medulla↗
PubMed2006

Increased angiogenic response but deficient arteriolization and abnormal microvessel ultrastructure in critical leg ischaemia.

BACKGROUND: Ischaemia is known to induce angiogenesis, but the effects of critical leg ischaemia (CLI) on angiogenesis remain unclear. The aim of this study was to examine the physiological angiogenic response in CLI by investigating the extent of neovascularization, characterizing microvessel subtypes and determining the microvessel ultrastructure. METHODS: Gastrocnemius muscles were biopsied from 12 patients with CLI and 12 without leg ischaemia. Microvessels were evaluated immunohistochemically using three endothelial markers (anti-CD31, anti-CD34 and PAL-E) and anti-alpha smooth muscle actin (SMA) as a mural cell marker to label arterioles. Ki67 was used to demonstrate active cell proliferation. Further microvessel ultrastructural characteristics were determined by transmission electron microscopy. RESULTS: The CLI group had significantly higher microvessel density and microvessel : muscle fibre ratio for all endothelial subtypes examined (P < 0.001). PAL-E staining demonstrated the highest increase: 4.7 times higher in CLI muscle. There was no significant difference in alphaSMA-positive microvessel density (P = 0.118) or microvessel: muscle fibre ratio (P = 0.214). Ki67 staining showed no active cell proliferation. Transmission electron microscopy showed CLI microvessels had abnormal morphology, mainly a thick basement membrane. CONCLUSION: A physiological angiogenic response was found in CLI, but the microvessels had an abnormal ultrastructure. A lack of active cell proliferation suggests that the angiogenic response may have been exhausted.

Aged↗
PubMed2002

Ultrastructure of afferents from the zona incerta to the posterior and parafascicular thalamic nuclei of rats.

We have examined the general ultrastructure of the posterior thalamic (Po) and parafascicular (Pf) nuclei of the dorsal thalamus, together with the ultrastructure of afferents to these nuclei from the zona incerta (ZI). The ZI of Sprague-Dawley rats was injected with biotinylated dextran (BD) by using stereotaxic coordinates, and the brains were prepared for routine BD histochemistry. The Po and Pf were then dissected free and processed for electron microscopy by using standard methods. A survey of the general ultrastructure of Po and Pf revealed many RS profiles (small with round vesicles) making asymmetric synapses around single, small (distal; 0.5-1.5 microm in diameter) or larger (proximal; 2-4 microm in diameter) dendrites. RL (large with round vesicles) and F type (pleomorphic vesicles) profiles, although sparse, were also observed. Single RLs were seen to envelope proximal dendrites and make asymmetric synapses that usually had a perforated appearance. F type profiles were seen to make symmetric synapses on proximal and sometimes distal dendrites. There were no profiles making synapses on other vesicle-filled profiles seen, reflecting the scarcity of interneurons in the Po and Pf of rats. Finally, BD-labeled terminal profiles from the ZI formed a homogeneous population within both the Po and Pf. They were small (1.1 +/- 0.2 microm in diameter; n = 238), contained round vesicles, and made asymmetric synapses with proximal ( approximately 75%) and, to a lesser extent, distal ( approximately 25%) dendrites; they formed part of the RS population of the Po and Pf. In conclusion, our results indicate that the ZI imparts a presumably excitatory (asymmetric synapses) input of high efficacy (preference for proximal dendrites) to the Po and Pf of the dorsal thalamus.

Animals↗
PubMed2003

Comparison of the ultrastructure of cortical and retinal terminals in the rat dorsal lateral geniculate and lateral posterior nuclei.

We compared the ultrastructure and synaptic targets of terminals of cortical or retinal origin in the rat dorsal lateral geniculate nucleus (LGN) and lateral posterior nucleus (LPN). Following injections of biotinylated dextran amine (BDA) into cortical area 17, two types of corticothalamic terminals were labeled by anterograde transport. Type I terminals, found throughout the LGN and LPN, were small, drumstick-shaped terminals that extended from thin axons. At the ultrastructural level in both the LGN and LPN, labeled type I corticothalamic terminals were observed to be small profiles that contained densely packed round vesicles (RS profiles) and contacted small-caliber dendrites. In tissue stained for gamma amino butyric acid (GABA) using postembedding immunocytochemical techniques, most dendrites postsynaptic to type I corticothalamic terminals did not contain GABA (97%). Type II corticothalamic terminals, found only in the LPN, were large terminals that sometimes formed clusters. At the ultrastructural level, type II terminals were large profiles that contained round vesicles (RL profiles) and contacted large-caliber dendrites, most of which did not contain GABA (98%). Retinogeniculate terminals, identified by their distinctive pale mitochondria, were similar to type II corticothalamic terminals except that 26% of their postsynaptic targets were vesicle-containing profiles that contained GABA (F2 profiles). Our results suggest that type I corticothalamic terminals are very similar across nuclei but that the postsynaptic targets of RL profiles vary. Comparison of the responses to retinal inputs in the LGN and to layer V cortical inputs in the LPN may provide a unique opportunity to determine the function of interneurons in the modulation of retinal signals and, in addition, may provide insight into the signals relayed by cortical layer V.

Animals↗