平滑肌活性对兔肠系膜上静脉环箍应力应变关系的影响

将１４只家兔的肠系膜上静脉（ＳＭＶ）随机分为两组：Ⅰ（正常组）和Ⅱ（平滑肌失活组）。通过充压试验结果表明：兔ＳＭＶ环箍应力应变关系为指数函数关系，平滑肌活性对兔ＳＭＶ材料常数Ｘ２有明显影响，材料常数Ｘ２组间比较有显著性差异（Ｐ＜０－０５），材料常数Ｘ１组间比较差异无显著性。认为Ｘ２是平滑肌活性参数。     

Serial reconstruction of Lucifer yellow-labeled supraoptic nucleus neurons in perfused rat hypothalamic explants

Intracellular recordings from supraoptic nucleus neurons in perfused explants of rat hypothalamus were followed by intracellular injections of the fluorescent dye, Lucifer yellow. Following fixation, 40 microns sections were processed for whole cell light-microscopic reconstruction in the horizontal or coronal plane. The somata of most supraoptic neurons were elongated (mean 25 X 13 microns) with 1-3 sparsely branched dendrites (length 30-725 microns) that displayed numerous spines. Most (95%) dendrites turned in the ventral direction to end in the glial lamina along the base of the nucleus. Each neuron had one axon: in 60% of cells, the axon arose from a dendritic profile and immediately assumed a varicose appearance; in the other 40% of cells, the axon appeared to arise directly from the soma and demonstrated in its initial 80-200 microns numerous spines and few varicosities, i.e. the morphological features of a dendrite. All axons coursed in a dorsomedial direction over the optic tract. At this point, most axons revealed smaller secondary processes 2-15 microns in length. Axons then turned ventrally towards the basal hypothalamus; some could be followed for up to 2100 microns from the cell somata. This approach to the light microscope morphology of supraoptic neurons provides a surprising array of detail on soma, dendrite and axon characteristics, while retaining the overall relationship between individual neurons and neighboring structures, including the boundaries of the nucleus itself.     

Optimization of pulse train duration for the electrical stimulation of a skeletal muscle ventricle in the dog

The optimal means of electrically stimulating a skeletal muscle to contract around a fluid-filled pouch (i.e., a skeletal muscle ventricle [SMV]) has not been determined. A SMV was made from the latissimus dorsi muscle in five dogs and the rectus abdominis muscle in five dogs, and each SMV was electrically stimulated via the motor nerve(s) to contract around a fluid-filled pouch, which was connected to a mock circulatory system. The pulse train duration (PTD) was varied from 100 ms to 800 ms in 100 ms increments to determine the effect of this variable upon SMV output. The pulse width of the electrical stimulus was kept constant at 100 μs and the pulse frequency was maintained at 50s⁻¹. For SMV contraction rates of 20, 30, and 40 min⁻¹, the optimal PTD was 400 ms for both muscles. The peak output was 710 ml min⁻¹ for the rectus SMV and 556 ml min⁻¹ for the latissimus SMV. For an SMV contraction rate of 10min⁻¹, the optimal PTD was 800 ms for the rectus SMV and 600 ms for the latissimus SMV. Use of less than an optimal PTD caused reductions in SMV output of 25–50%. Although SMVs made from rectus abdominis and latissimus dorsi had similar values for the optimal PTD, the maximum SMV output was usually greater with the rectus abdominis in this acute study with untrained muscles. We conclude that PTD is an important variable to control, which can markedly affect results when studying the potential use of skeletal muscle power for cardiac assistance.     

Papillary morphology of the tongue of the American chameleon: Anolis carolinensis

Based on regional differences in surface morphology, the dorsum of the tongue of Anolis carolinensis can be subdivided into four distinct zones. The first quarter of the tongue is relatively smooth, whereas the second and fourth quarters are festooned with closely packed cylindriform papillae, which are covered by typical parakeratotic stratified squamous epithelium. The third quarter of the tongue is covered by papillae of novel morphology that we have named "plumose papillae." These are composed of a slender connective tissue core covered by stratified squamous epithelium from whose surface numerous elongated cells radiate. These "plume cells" are about 30-40 microns long and have an extremely irregular nucleus in their expanded terminus. Their stalks are affixed by desmosomes to the deeper cells of the epithelium, and their free surfaces are covered by intricately patterned microplications. Their cytosol contains a dense web of 100-A cytofilaments that may be involved in maintaining the peculiar morphology of the cells. Regardless of type, all lingual papillae of A. carolinensis contain a single longitudinally oriented skeletal muscle fiber that originates from the underlying lingual muscles, raising the possibility that the papillae can be moved at will. The plumose papillae and their retinue of plume cells are unique morphological structures that may be important in mastication and deglutition of food.     

A quantitative study of satellite cells and myonuclei in stretched avian slow tonic muscle.

Satellite cell frequency was assessed in control and stretched anterior latissimus dorsi (ALD) muscles of adult quail. A weight equal to 10% of body mass was attached to one wing for time intervals ranging from 1-30 days. The contralateral ALD served as the intra-animal control. Satellite cell frequency, expressed as a percentage of total myofiber nuclei within the basal lamina, was determined in eight control and stretched ALD muscles, that had been weighted for 5, 7, or 10 days. Satellite cell frequency was determined in 584 control and 473 stretched fibers and was not different in the control or stretched ALD muscles (15.6 +/- 2.3%, 16.7 +/- 6.1%, respectively). The number of myofiber nuclei (myonuclei and satellite cell nuclei) was examined in whole fiber segments from control and stretched ALD muscles of 27 adult quail. Nuclear frequency was determined in 500 control and 1,200 stretched fiber segments. Fiber volume was calculated from fiber length and diameter measurements. Nuclear number normalized to 10,000 microns 3 fiber volume was correlated to fiber cross-sectional area (P less than 0.0001). Fibers with cross-sectional areas less than 500 microns 2 had a greater nuclear to fiber volume ratio compared to fibers with areas greater than 500 microns 2. The nuclear-to-cytoplasmic ratio was not constant in smaller fibers. Nuclear density decreased as fiber cross-sectional area increased up to 500 microns 2. Fibers with cross-sectional areas greater than 500 microns 2 demonstrated a constant nuclear-to-cytoplasmic ratio. The results demonstrate that absolute nuclear number increased to maintain a constant nuclear-to-cytoplasmic ratio in the stretched hypertrophied fibers. Daughter cells originating from activated satellite cells may have contributed to the myonuclear population to maintain a constant nuclear-to-cytoplasmic ratio in the hypertrophied fibers of the adult quail.     

Direct and indirect actions of acetylcholine and histamine on intrapulmonary artery and vein muscles of the rat

The effects of ACh and histamine on electrical and mechanical properties of intrapulmonary artery and vein muscles were studied in rats. In the artery, ACh and histamine indirectly relaxed the precontracted muscles in high-[K]o solution via the release of endothelium-derived relaxing factor (EDRF) from the endothelial cells, and also produced contractions by acting directly to the muscles. ACh and histamine elicited a transient hyperpolarization of the arterial smooth muscle membrane mainly due to an increase in K permeability, only in the presence of endothelial cells. In the absence of endothelial cells, histamine and ACh depolarized the arterial smooth muscles. The intrapulmonary vein consisted of the invaded cardiac muscles; and ACh, but not histamine, hyperpolarized the membrane of these muscles by an increase in K permeability, with no relationship to the endothelial cells. It is concluded that in the rat intrapulmonary artery, ACh and histamine elicit excitatory and inhibitory responses in these vascular muscles in direct and indirect manners. The indirect actions involve relaxing and hyperpolarizing factors released from the arterial endothelial cells. ACh but not histamine elicited inhibitory responses to the intrapulmonary vein muscles in a direct manner.     

Morphology of motoneurons in a mixed motor pool of the cat facial nucleus that innervate orbicularis oculis and quadratus labii superioris, stained intracellularly with horseradish peroxidase

Retrograde tracing with horseradish peroxidase showed that motoneurons to two distinct muscles, the orbicularis oculis and quadratus labii superioris, are intermixed within the dorsolateral subnucleus of the cat facial nucleus. Intracellular electrodes were used to identify and fill the motoneurons of the dorsolateral subnucleus with horseradish peroxidase. Soma diameters averaged 55 micron. The average number of primary dendrites was 11.6. The area covered by the dendritic trees varied in shape according to the position of the soma within the subnucleus. Axon hillocks were seen arising in many orientations, bearing no apparent relation to subsequent axonal path, cell position within the nucleus or somatic geometry. Motoneurons to the two muscles appeared to be indistinguishable on the basis of morphology, even though they appear to be functionally independent. Their functional differences are not reflected in any measure of somadendritic shape studied here. Of further interest is the variability in shape associated with the neurons's position within the subnucleus. We conclude that many details of dendritic shape do not reflect specific physiological function.     

Plasma and lymph dopamine-beta-hydroxylase and norepinephrine during carotid occlusion.

Dopamine-beta-hydroxylase (DBH) and norepinephrine (NE) levels in superior mesenteric venous (SMV) and arterial blood and in intestinal lymph were determined sequentially before and during carotid artery occlusion (CAO) in anesthetized rabbits. During the first 15 min of CAO, SMV plasma NE increased 77% but SMV plasma DBH increased only 11%. During the second 15 min of CAO, SMV NE declined to 36% above control but SMV DBH rose further and peaked to 29% above control after CAO was released; arterial DBH and NE showed small insignificant changes. Lymph DBH and NE increased simultaneously throughout the period of CAO. Increases in mean arterial pressure during CAO correlated with superior mesenteric venous NE (r = 0.58, P less than 0.01). In additional experiments, hepatic vein plasma NE was 74% lower than portal vein NE. Thus, during acute sympathetic activation, DBH and NE increase in mesenteric venous plasma and intestinal lymph but the peak response of plasma DBH lags behind that of NE. The degree of NE change in the general circulation is minimized due to hepatic clearance of NE.     

A morphometric study of myocytes of normal and hypertrophic human atria

Morphometric study of myocytes of normal and hypertrophic human atria was performed in semithin and paraffin sections. The hypertrophy is followed by the increase of size of both the myocytes and their nuclei: the average nuclei diameter increases from 5.9 to 7.5 microns, the average length from 13.7 to 20.2 microns. The same parameters of the cell change from 13.5 to 18.5 microns and from 121.6 to 143.9 microns. The increase of the nuclei length correlates with the increase of its ploidy. The ratio nucleus cytoplasm remains unchanged as well as the ratio between muscles and connective tissue. The number of binucleated cells in the hypertrophied atrium increases by factor of 3 or 4. The number of myocytes in the atrium was calculated and was equal to 1790.10(6) +/- 241.10(6) under normal conditions and 1890.10(6) +/- 336.10(6) in case of hypertrophy. The mechanisms of the heart weight increase is discussed.     

A comparison of the wear and debris generation of GUR 1120 (compression moulded) and GUR 4150HP (ram extruded) ultra high molecular weight polyethylene.

The wear debris generated from UHMWPE (ultra high molecular weight polyethylene) has been recognised as one of the major causes of failure in THR (total hip replacement). GUR 1120 (compression moulded) and GUR 4150HP (ram extruded) which are currently the most frequently used materials in THR were studied in pin-on-plate wear test. The wear particles generated from this test were observed by scanning electron micrograph and analysed by image analysis. The results from this study showed that GUR 4150HP had superior wear resistance than GUR 1120 under relatively high wear factor conditions. These results also highlighted the importance of multidirectional motion and its effect on the wear rates of UHMWPE. The multidirectional motion tended to show a higher wear factor than previous studies using unidirectional motion conducted under otherwise similar conditions. The wear debris analysis conducted with the wear particles collected from unidirectional (relatively rough) pin-on-plate wear tests (GUR 1120 and GUR 4150HP) showed that the greatest number of particles had a size range of 0.1-0.5 micron followed by 0.5-1.0 micron, 1.0-5.0 microns and 5.0-10.0 microns, in both GUR 1120 and GUR 4150HP. However, comparing the masses of the wear particles, the bigger size range of greater than 10 microns, had the highest percent mass followed by 1.0-5.0 microns, 0.5-1.0 micron, 0.1-0.5 micron and 5.0-10.0 microns.     

Ploidy of smooth muscle tumours: retrospective image analysis study of formalin fixed, paraffin wax embedded tissue.

The feasibility of using an image analyser, the CAS 100, to assess the ploidy of smooth muscle tumours on formalin fixed paraffin wax embedded tissue was assessed. Various different methods of assessment were compared. A paraffin wax block of 15 leiomyomata and 13 leiomyosarcomata yielded serial sections of 3 microns, 5 microns, and 7 microns and a cytospin preparation (from a 50 micron section). Sections and cytospin preparations were stained with Feulgen and quantified using the CAS 100. The suitability of lymphocytes, previously suggested to be unsuitable as control cells in tissue sections due to the compact nature of their DNA, was assessed in sections and cytospin preparations and compared with endothelial cells, the standard alternative, on the same slide. Despite having a mean nuclear area of only 18.5 microns 2 in sections lymphocytes had a similar diploid peak--that is, 4.1 pg--to endothelial cells (mean nuclear area 39 microns 2). A comparison of 3 microns, 5 microns, and 7 microns sections showed 5 microns to be the optimal thickness. Cytospin preparations yielded histograms of superior quality than those from tissue sections. All 15 leiomyomata had a 5C exceeding rate of less than 0.3%. Ten of 11 histologically malignant tumours had a 5C exceeding rate of more than 5% (mean 14%) in sections and cytospins. Two leiomyosarcomata that had arisen in the lower gastrointestinal tract had a mitotic rate of less than or equal to 1/10 per high power fields and yielded histograms similar to those of the leiomyomata. It is concluded that formalin fixed, paraffin wax embedded tissue can be used for DNA quantification by image analysis; that tissue sections yield poorer results than cytospin preparations; that lymphocytes are reliable control cells in cytospin preparations; and that a population of cell greater than 5C is seen in 90% of leiomyosarcomata.     

The organization and hypothalamic projections of the tuberomammillary nucleus in the rat: an immunohistochemical study of adenosine deaminase-positive neurons and fibers

The intense immunohistochemical reaction for the enzyme adenosine deaminase displayed by neurons in the tuberomammillary nucleus in the rat was used to study the distribution and morphology of cells comprising this nucleus, their fiber fields within the posterior hypothalamus and their projection pathways from the hypothalamus. Neurons immunoreactive for adenosine deaminase were found along ventricular and basal aspects of the hypothalamus from the level of the dorsomedial nucleus to the caudal pole of the mammillary body. Approximately 4500 neurons were seen on each side of the brain. Positive neurons showed a complex distribution, largely avoiding nuclear boundaries within the posterior basal hypothalamus and mammillary body. This distribution is mapped in detail and a nomenclature based on topography is introduced so that different regions of the cell distribution may be discussed more easily. Reactive neurons showed a Golgi-like staining which allowed careful study of their morphology. In general, neurons were large, with major axes of from 22 to 30 micron, and bipolar in shape. A second, smaller cell type, 14-16 micron in diameter was also seen and, although often less intensely stained, it was considered a constituent of tuberomammillary nucleus of the hypothalamus as well. Stained dendritic arbours extended considerable distances from the parent cell bodies and branched regularly. Dendrites showed very sparse spines and had an apparently scalloped surface. Features suggestive of varicose segments of dendrites were also noted. The long, smooth dendrites of positive neurons were often seen to aggregate into bundles which avoided nuclear boundaries and tended to collect adjacent to basal and ventricular surfaces of the posterior hypothalamus. Varicose fibers immunoreactive for adenosine deaminase formed a dense network within the hypothalamus. These fibers were considered to derive from the positive neurons in the tuberomammillary nucleus and were similar to adenosine deaminase-immunoreactive fibers seen throughout much of the rest of the brain. The density of this type of positive fiber was, however, much greater within the hypothalamus. The region of the posterior basal hypothalamus also contained relatively sparse populations of adenosine deaminase-positive fibers, apparently distinct from this network. These consisted of a field of fine fibers in the median division of the medial mammillary nucleus and a few large varicosities in the dorsolateral part of the median eminence.(ABSTRACT TRUNCATED AT 400 WORDS)     

Vascular anatomy for right colon lymphadenectomy

Since the superior mesenteric artery (SMA) mostly originates on the left side of the superior mesenteric vein (SMV), the ileocolic artery (ICA) and the right colic artery (RCA) cross the SMV. Understanding the three-dimensional relation of these vessels is important for dissecting these arteries to their origin. Hence, we conducted a study of the vascular anatomy of the right colon in 27 cadavers. The RCA was separate from the SMA in eight cases (30%). The RCA passed the SMV either anteriorly (5 cases, 63%) or posteriorly (3 cases, 38%). In seven (88%) of these eight cases, the ICA was posterior to the SMV. The ICA was identified in all 27 cases, and passed the SMV anteriorly in nine cases (33%) and posteriorly in 18 cases (67%). Thus, the ICA and the RCA may pass on either side of the SMV. The surgeon must dissect the arteries with the SMV, being aware of both possibilities.     

Control of number and distribution of synapses during ectopic synapse formation in adult rat soleus muscles

Changes in the number and distribution of synaptic inputs and acetylcholine receptor clusters were studied during the formation of ectopic nerve-muscle junctions between the transplanted fibular nerve and the denervated soleus muscle of adult rats. The tibial nerve was cut 3 weeks after implanting the fibular nerve. New sites of transmission were first detected 3 days after the cut. These sites were located electrophysiologically, marked by dye and found to coincide with clusters of acetylcholine receptors. There were no ectopic clusters away from fibular nerve sprouts and no clusters on muscles which had not been denervated. Three days after cutting the tibial nerve, the acetylcholine receptor clusters, and probably also the sites of transmission, were randomly distributed along individual muscle fibres. Six days after the cut, the clusters continued to be randomly distributed whereas the synaptic inputs were either close together (within 300 microns) or more than 600 microns apart. Two weeks later the spatial distributions of both clusters and inputs were similar with peaks around 100-300 microns, 1200-1400 microns and 2000-2600 microns. No ectopic clusters were closer than 0.5 mm to the original endplate. We conclude that nerve-muscle contacts and associated acetylcholine receptor clusters initially form at random. One or a few of these contacts develop further and, as a result, the surrounding regions undergo changes that prevent the contacts initially formed there from being maintained. Apparently, in this preparation, approximately 1.5 mm length of fibre is needed to support the maturation and maintenance of each ectopic endplate (mean length 111 micron).     

Distributions of adipocyte, blood vessel, and muscle fiber in human lateral petrygoid muscle during ageing.

The composition of adipocyte, blood vessel, and muscle fiber during ageing from 30 to 90 years of age was examined by a computer analyzing system in human lateral petrygoid muscle. The human lateral petrygoid muscle, the intramuscular connective tissue with adipocyte and blood vessel, displayed a specific change in morphology during ageing. Numerous adipocyte appeared around the blood vessel in the perimysium of the human petrygoid muscle from 60 years of age. The percentage and size of adipocyte and vein per 10,000 micron 2 of the cross sectional area in the muscle increased as well. However, the cross sectional area of muscle fiber was almost constant. The increase of adipocyte was related with changes of blood vessel and connective tissue in the perimysium.     

Potassium accumulation in smooth muscle and associated ultrastructural changes

1. The water content, extracellular ((60)CoEDTA) space, ionic composition and ultrastructure of several mammalian smooth muscles were studied after incubation in solutions of varying ionic compositions and osmolarities.2. Substitution of KCl for NaCl resulted in an increase in cell water, K and Cl, accompanied by little change in total wet weight. This was due to a reduction in the extracellular space.3. Changes in extracellular osmolarity produced a wider range of cell volumes in high KCl solutions than in Krebs. The addition of 29-58 mM sucrose to high KCl prevented the swelling.4. Electron microscopy of smooth muscle swollen in high KCl solution revealed light (less electron opaque than normal) fibres of increased diameter, reduction in extracellular space, and nuclear swelling. The normal thick filament lattice was destroyed in swollen, osmium-fixed smooth muscles.5. The ultrastructural changes ascribed to swelling were absent in smooth muscles, (a) depolarized in high K(2)SO(4) solutions, (b) in high KCl solutions with 29-58 mM sucrose, and (c) returned to normal Krebs solution for recovery from swelling.6. Smooth muscles incubated in high KCl (swollen) and high K(2)SO(4) (unswollen) exhibited similar contractile responses, suggesting the filament lattice was intact until fixation, and that the contractile mechanism can operate over a relatively wide range of actin to myosin separations.7. Shrinkage of smooth muscles in high KCl solutions made hypertonic with the addition of 10% sucrose was accompanied by an aggregation of the thick filaments.8. The cell water of fixed taenia coli was reduced (a) by incubation in hypertonic solution followed by fixation in normal glutaraldehyde, or (b) by fixation of normal tissue in hypertonic glutaraldehyde. Osmotic responses during aldehyde fixation may be a source of artifact in the visualization of the normal filament lattice.     

Membrane properties of the smooth-muscle fibres of the guinea-pig portal vein

The membrane activities and the various characteristic constants of the smooth-muscle membrane of the guinea-pig portal vein were investigated with the micro-electrode technique.1. The mean membrane potential was -37 mV. Spontaneous discharges appeared as regular bursts of short trains of spikes alternating with silent periods, as a mixture of single spikes and bursts of spikes appearing continuously, or as regular spikes with low frequency.2. Spontaneous spikes with overshoot were frequently observed. The maximum rate of rise of the spike was 3.7 V/sec. The shapes of the spikes were classified into three different types, i.e. pace-maker type of spike, monophasic spike and spike with a hump during the falling phase.3. Tetrodotoxin (10(-5) g/ml.) did not influence the patterns of the spontaneous train discharges nor the shape of the spike.4. Extracellularly applied outward current elicited spikes which were either monophasic or had a hump on the falling phase. Inward current elicited break excitation of the spike.5. Current-voltage relations, produced by application of inward current pulses to the tissue and measured at various distances from the stimulating partition, were linear.6. The smooth-muscle membrane of portal vein showed cable-like properties. The mean space constant of the membrane was 0.52 mm; the mean time constant of the membrane calculated from the electrotonic potential was 330 msec.7. Conduction velocity of the spike measured by insertion of two micro-electrodes was 0.58 cm/sec.8. The time constant of the foot of the propagated spike was 27 msec. The time constant of the membrane calculated from the time constant of the foot of the spike and the conduction velocity was 310 msec.9. The membrane properties of longitudinal smooth muscle of the portal vein were discussed in comparison with other veins and various visceral smooth muscles.     

Radiologic anatomy of the superior mesenteric vein and branching patterns of the first jejunal trunk: evaluation using multi-detector row CT venography

The purpose of this study was to describe radiologic anatomy of the superior mesenteric vein (SMV) and to evaluate branching patterns of the first jejunal trunk on axial CT images and multi-detector row CT (MDCT) venography in adults. Two hundred and twenty consecutive patients who underwent abdominal CT examinations were enrolled in this study. Appearance of the SMV, branching patterns of the first jejunal trunk, and drainage site of the inferior mesenteric vein (IMV) were assessed on axial CT images and MDCT venography. The SMV and first jejunal trunk were identified in all patients. A single trunk of the SMV was present in 95% (210/220) and absent in 5% (10/220). First jejunal trunk crossed dorsal to the superior mesenteric artery (SMA) towards the left abdomen in 64% (141/220) and first jejunal trunk crossed ventral to the SMA in 19% (41/220). First jejunal trunk crossed dorsal to the SMA and abruptly turned towards the right abdomen in 17% (38/220). Among these 38 patients, biliary-enteric bypass surgery (n = 9) and large hematoma in left abdomen (n = 1) were present. The IMV was identified in 213 patients and was observed to drain into splenic vein in 112 patients (53%), SMV in 67 (31%), splenoportal confluence in 26 (12%), and first jejunal trunk in 8 (4%). In conclusion, the first jejunal trunk, abruptly turning toward the right abdomen, may be an anatomic variant or indirect finding of biliary-enteric anastomosis. The IMV may drain into the first jejunal trunk as well as splenic vein, splenoportal confluence, and SMV.     

Synaptic relationships of a type of GABA-immunoreactive neuron (clutch cell), spiny stellate cells and lateral geniculate nucleus afferents in layer IVC of the monkey striate cortex

The precise stimulus specificity of striate cortical neurons is strongly influenced by processes involving gamma-aminobutyric acid (GABA). In the visual cortex of the monkey most afferents from the lateral geniculate nucleus terminate in layer IVC. We identified a type of smooth dendritic neuron (clutch cell) that was immunoreactive for GABA, and whose Golgi-impregnated dendrites and axon were largely restricted to layer IVC beta. The slightly ovoid somata were 8-12 micron by 12-15 micron and the dendritic field was often elongated, extending 80-200 micron in one dimension. The axonal field was 100-150 micron in diameter and densely packed with large bulbous boutons. Although mainly located in IVC beta both the dendritic and axonal processes entered IVC alpha. Fine structural features of GABA-immunoreactive and-impregnated clutch cells and impregnated spiny stellate cells were compared. Clutch cells had more cytoplasm, more densely packed mitochondria and endoplasmic reticulum, and made type II as opposed to type I synapses. A random sample of 159 elements postsynaptic to three clutch cells showed that they mainly terminated on dendritic shafts (43.8-58.5%) and spines (20.8-46.3%), rather than somata (10-17%). The majority of the postsynaptic targets were characteristic of spiny stellate cells. This was directly demonstrated by studying synaptic contacts between an identified GABA positive clutch cell and the dendrites and soma of an identified spiny stellate cell. The termination of clutch cells mainly on dendrites and spines of spiny stellate cells suggests that they interact with other inputs to the same cells. Following an electrolytic lesion in the ipsilateral lateral geniculate nucleus we examined the distribution of degenerating terminals on three identified spiny stellate neurons in layer IVC beta. Out of eight synapses from the lateral geniculate nucleus one was on a dendritic shaft, the rest on spines. Only a small fraction of all synapses on the cells were from degenerating boutons. A clutch cell within the area of dense terminal degeneration was not contacted by terminals from the lateral geniculate nucleus. The results show that layer IVC in the monkey has a specialized GABAergic neuron that terminates on spiny stellate cells monosynaptically innervated from the lateral geniculate nucleus. Possible functions of clutch cells may include inhibitory gating of geniculate input to cortex; maintenance of the antagonistic subregions in the receptive fields; and the creation from single opponent of double colour opponent receptive fields.