Bovine intramuscular, subcutaneous, and perirenal stromal-vascular cells express similar glucocorticoid receptor isoforms, but exhibit different adipogenic capacity.

Understanding preadipocyte differentiation in economically important adipose depots will facilitate efforts to selectively increase intramuscular (i.m.) lipid accretion in cattle. The objectives of this study were to determine if glucocorticoid receptor (GR) expression differs among bovine stromal-vascular (S-V) cells derived from i.m., subcutaneous (s.c.), and peri-renal (p.r.) adipose tissue, and to evaluate the effects of dexamethasone (DEX) on adipogenesis of these cell populations. Stromal-vascular cells isolated from i.m., s.c., and p.r. adipose tissues of 2 steers were propagated in culture and exposed to 0 or 250 nM DEX for 48 h. Cell lysates were subjected to GR immunoblot analysis, and immunoreactive protein bands of approximately 97, approximately 62, and approximately 48 kDa were detected and expressed relative to beta-actin immunoreactivity. The abundance of each GR immunoreactive protein was similar among S-V cell populations (P > 0.50). Dexamethasone exposure decreased the abundance of the approximately 97 and approximately 62 kDa GR immunoreactive bands in S-V cells from the 3 depots (P < 0.001), but did not affect the expression of the approximately 48 kDa band (P = 0.96). Stromal-vascular cells isolated from 3 steers were grown in culture, and upon confluence, were exposed to 0, 25, or 2,500 nM DEX for 48 h. After an additional 10 d in differentiation media, differentiation was determined by glycerol-3-phosphate dehydrogenase (GPDH) specific activity and oil red O staining. The extent of differentiation differed by depot (p.r. > s.c. > i.m.; P < 0.05). Compared with control, 2,500 nM DEX increased GPDH activity in S-V cells from all depots (P < 0.05), and no interaction between depot and DEX concentration was observed (P = 0.99). We observed an adipose tissue depot by DEX concentration interaction (P = 0.03) for S-V cells with large (> or = 10 microm-diameter) lipid droplets. The percentage of p.r. S-V cells with large lipid droplets increased in response to DEX in a linear manner (P < 0.02), but only increased greater than control in s.c. cells exposed to 2,500 nM DEX (P = 0.002). Dexamethasone did not significantly increase the percentage of i.m. S-V cells with large lipid droplets (P > 0.27). Collectively, these data demonstrate differences in adipogenic activity among bovine i.m., s.c., and p.r. S-V cells, but indicate no relationship between adipogenic activity and glucocorticoid receptor abundance or function.

Differentiation of bovine intramuscular and subcutaneous stromal-vascular cells exposed to dexamethasone and troglitazone.

The objectives of these experiments were to compare differentiation of bovine stromal-vascular (S-V) cells isolated from i.m. and s.c. adipose tissues in response to a glucocorticoid and a peroxisome proliferator-activated receptor gamma agonist. Stromal-vascular cells were isolated from i.m. and s.c. fat depots of 3 Angus steers and propagated in culture. Cells were exposed to differentiation media containing 0.25 microM dexamethasone (DEX), a glucocorticoid analog, and 40 microM troglitazone (TRO), a peroxisome proliferator-activated receptor gamma agonist, or both. Cells treated with DEX and TRO had greater (P < 0.02) glycerol-3-phosphate dehydrogenase activity than control cells. No interactions between DEX, TRO, and depot (P > 0.59) or depot differences (P = 0.41) in glycerol-3-phosphate dehydrogenase activity were found. Morphological assessment of adipogenic colonies showed that DEX induced a 1.8-fold increase in the percentage of adipogenic colonies (P = 0.03), whereas TRO increased the proportion of adipogenic colonies by 1.9-fold (P = 0.02) compared with those not treated with DEX or TRO, respectively. Depots had a similar percentage of adipogenic colonies (P = 0.18); however, the percentage of differentiated cells within adipogenic colonies was found to be 6.4-fold greater in s.c. isolates compared with i.m. (P < 0.001). Addition of TRO increased the proportion of differentiated cells within colonies by 10-fold compared with those of nontreated colonies (P < 0.001), whereas the percentage of differentiated cells within adipogenic colonies only tended to be increased by DEX (P = 0.10). These data indicate that bovine i.m. and s.c. S-V cells are capable of enhanced differentiation in response to DEX and TRO, and these effects were additive. Most importantly, inherent differences in the capacity to differentiate exist between adipogenic bovine i.m. and s.c. S-V cells.

Quantitative analysis of the EEG posterior-dominant rhythm in healthy adolescents.

OBJECTIVE: Pivotal studies of the normal EEG posterior-dominant rhythm (PDR) typically relied on visual inspection of a few seconds of EEG data from a relatively small number of subjects in each age category. We sought to analyze and characterize the PDR in a large cohort of healthy 15-year-olds, and to determine if PDR characteristics mature over the following year. METHODS: Seventy-nine healthy 15-year-olds free of neurologic and psychiatric disease underwent a resting-awake EEG, which was repeated 1 year later. In each study, PDR frequency was determined with fast Fourier transform analysis of a continuous 2-min EEG segment. t-Tests were used to compare relevant variables. RESULTS: From age 15 to 16 the mean PDR frequency increased from 9.9 to 10.0Hz, a small but statistically significant difference. The PDR frequency range at both ages was 8.9-11.0Hz, similar to values reported in prior studies on healthy young adults. There was no significant difference in PDR frequency between genders or hemispheres. CONCLUSIONS: Maturation of the PDR is nearly complete at age 16. The frequency range of the PDR in healthy adolescents and adults is substantially narrower than the alpha band. SIGNIFICANCE: Based on this and prior studies, a PDR frequency of less than 8.5 or greater than 11.5Hz should be considered abnormal in adolescents and adults.

Optimization of in vitro conditions for bovine subcutaneous and intramuscular preadipocyte differentiation.

The objective of these experiments was to develop an in vitro cell culture system for differentiation of bovine preadipocytes, which will permit examination of differences in differentiation between intramuscular (i.m.) and subcutaneous (s.c.) bovine preadipocytes. Stromal-vascular cells from bovine i.m. and s.c. adipose depots were isolated and cultured. Clonally derived s.c. preadipocytes were used to determine the ability of insulin, bovine serum lipids, octanoate, acetic acid, dexamethasone (DEX), and troglitazone (TRO) to elicit differentiation of these cells when added to serum-free medium. Addition of 10 and 20 microL/mL of a commercially available serum lipids supplement to low-glucose Dulbecco's modified Eagle's medium containing 280 nM insulin increased glycerol-3-phosphate dehydrogenase (GPDH) activity (P < 0.01). Inclusion of 1.25 to 10 microM TRO to medium containing 280 nM insulin and 20 microL/ mL serum lipids supplement also increased GPDH activity (P < 0.001) compared with 0 microM TRO. The combination of 280 nM insulin, 1 mM octanoate, and 10 mM acetic acid, with 48 h exposure to 0.25 microM DEX caused morphological differentiation in a small number of cells but did not stimulate GPDH activity (P = 0.99). When used together, 280 nM insulin, 20 microL/mL of serum lipids supplement, 40 microM TRO, and 0.25 microM DEX stimulated differentiation compared with the aforementioned treatment (P < 0.001). Omission of TRO or insulin from this medium reduced GPDH activity by 68% (P < 0.001), whereas removal of DEX tended to reduce GPDH activity (P = 0.06). Preadipocytes from s.c. (n = 3) and i.m. (n = 2) adipose tissues of 3 steers were used to determine the effects of TRO on differentiation using the established conditions. Forty to sixty microM TRO enhanced differentiation compared with 0 microM TRO (P < 0.02) in both depots. No depot differences in response to TRO were detected (P = 0.32). These data demonstrate that bovine preadipocytes are capable of differentiation in response to combinations of insulin, serum lipids, DEX, and TRO. Although TRO enhanced differentiation of bovine preadipocytes, no differential effects of TRO on the differentiation of s.c. and i.m. cells were detected.

The effect of hyposmotic and isosmotic cell swelling on the intracellular [Ca2+] in lactating rat mammary acinar cells.

The effect of hyposmotic and isosmotic cell swelling on the free intracellular calcium concentration ([Ca2+]i) in rat mammary acinar cells has been examined using the fura-2 dye technique. Ahyposmotic shock (40% reduction) increased the [Ca2+]i in rat mammary acinar cells in a fashion which was transient; the [Ca2+]i returned to a value similar to that found under isomotic conditions within 180 sec. The increase in the [Ca2+]i was dependent upon the extent of the osmotic shock. The hyposmotically-activated increase in the [Ca2+]i could not be attributed to a reduction in extracellular Na+ or a change in the ionic strength of the incubation medium. Thapsigargin (1 microM) enhanced the hyposmotically-activated increase in the [Ca2+]i. Isosmotic swelling of rat mammary acinar cells, using urea, had no significant effect on the [Ca2+]i. Similarly, a hyperosmotic shock did not affect the [Ca2+]i in rat mammary acinar cells. It appears that the effect of cell swelling on the [Ca2+]i in rat mammary acinar cells depends on how the cells are swollen (hyposmotic vs. isosmotic). This finding may have important physiological implications given that it is predicted that mammary cell volume will change in vivo under isomotic conditions.

Volume-sensitive amino acid efflux from a pancreatic beta-cell line.

Cell swelling, induced by a hyposmotic shock, increased the fractional release of taurine from INS-1 cells. Volume-sensitive taurine release was (a) dependent upon the extent of cell swelling; (b) fully reversible; and (c) temperature dependent. Volume-sensitive taurine efflux was independent from the trans-membrane Na(+)-gradient. DIDS markedly inhibited volume-activated taurine efflux but not basal taurine release suggesting that the volume-sensitive pathway is quiescent under isosmotic conditions. Volume-activated taurine release inactivated in the continued presence of a hyposmotic shock. Cell-swelling also increased the fractional release of D-aspartate from INS-1 cells. Volume-activated D-aspartate efflux was inhibited by DIDS, albeit to a lesser extent than volume-sensitive taurine release. It is predicted that volume-sensitive amino acid efflux acts in parallel with other volume-activated transport mechanisms to regulate the volume of insulin-secreting cells.

A prospective study of handcuff neuropathies.

Prior reports of handcuff-related neuropathies have been retrospective or small series of cases selected for their unusual electrophysiological or historical features. We conducted a prospective 27-month study at a large, urban, teaching hospital of all patients with a complaint of hand numbness, weakness, or paresthesias attributed to overtightened handcuffs. Forty-one patients were evaluated clinically, and electrodiagnostic testing was performed on 18. In the group with electrodiagnostic testing, neuropathies due to overtightened handcuffs were detected in 22 superficial radial, 12 median, and 9 ulnar nerves. The correlation between clinical and electrodiagnostic findings was best for superficial radial neuropathies, some of which were severe. Median and ulnar nerve injuries were generally mild. Similar clinical findings were obtained in the group without electrodiagnostic testing. Handcuff-related injury to the most commonly affected nerve, the superficial radial, can be severe and permanent.

Regulation of protein synthesis in lactating rat mammary tissue by cell volume.

The effect of changing cell volume on rat mammary protein synthesis has been examined. Cell swelling, induced by a hyposmotic challenge, markedly increased the incorporation of radiolabelled amino acids (leucine and methionine) into trichloroacetic acid (TCA)-precipitable material: reducing the osmolality by 47% increased leucine and methionine incorporation into mammary protein by 147 and 126% respectively. Conversely, cell shrinking, induced by a hyperosmotic shock, almost abolished the incorporation of radiolabelled amino acids into mammary protein: increasing the osmolality by 70% reduced leucine and methionine incorporation into mammary protein by 86 and 93% respectively. The effects of cell swelling and shrinking were fully reversible. Volume-sensitive mammary tissue protein synthesis was dependent upon the extent of the osmotic challenge. Isosmotic swelling of mammary tissue, using a buffer containing urea (160 mM), increased the incorporation of radiolabelled leucine into TCA-precipitable material by 106%. Swelling-induced mammary protein synthesis was dependent upon calcium: removing extracellular calcium together with the addition of EGTA markedly reduced volume-activated protein synthesis. Cell swelling-induced protein synthesis was inhibited by the Ca(2+) ATPase blocker thapsigargin suggesting that volume-sensitive protein synthesis is dependent upon luminal calcium.

Tactile perception in blind Braille readers: a psychophysical study of acuity and hyperacuity using gratings and dot patterns.

It is not clear whether the blind are generally superior to the sighted on measures of tactile sensitivity or whether they excel only on certain tests owing to the specifics of their tactile experience. We compared the discrimination performance of blind Braille readers and age-matched sighted subjects on three tactile tasks using precisely specified stimuli. Initially, the blind significantly outperformed the sighted at a hyperacuity task using Braille-like dot patterns, although, with practice, both groups performed equally well. On two other tasks, hyperacute discrimination of gratings that differed in ridge width and spatial-acuity-dependent discrimination of grating orientation, the performance of the blind did not differ significantly from that of sighted subjects. These results probably reflect the specificity of perceptual learning due to Braille-reading experience.

Tactile perception in developmental dyslexia: a psychophysical study using gratings.

Multiple sensory abnormalities have been reported in individuals with developmental dyslexia, especially in the visual and auditory systems. We used gratings of alternating ridges and grooves to investigate tactile perception in this disorder using two tasks: spatial acuity-dependent discrimination of grating orientation and discrimination of gratings varying in ridge width. Compared to age-matched normal subjects, dyslexics were significantly impaired on grating orientation discrimination, with mean thresholds that were nearly twice normal. Unlike normal subjects, their performance on this task was slightly but significantly worse on the dominant hand than on the non-dominant hand. Dyslexics also showed a substantial but non-significant trend for impairment on grating ridge width discrimination. A group of subjects with attention deficit disorder did not differ significantly from normal on any of these measures. These findings expand the range of perceptual deficits reported in developmental dyslexia. Possible explanations for the results, including difficulties with temporal processing, abnormal lateral masking or parietal lobe dysfunction are discussed.

A critical comparison of the dose delivery characteristics of four alternative inhalation devices delivering salbutamol: pressurized metered dose inhaler, Diskus inhaler, Diskhaler inhaler, and Turbuhaler inhaler.

Salbutamol is a short-acting beta 2 agonist which is effective as a rescue therapy in the treatment of asthma. This study uses in vitro test methods to compare the capability of four alternative devices to deliver an accurate and precise dose of salbutamol. It is demonstrated that the conventional metered dose inhaler (MDI) achieves excellent accuracy and precision in dose delivery. Additionally, it is the most efficient inhaler in terms of generating in-vitro a fine particle fraction from the dose. A spacer device has been shown to further enhance the dosing characteristics. When tested over a wide range of inspiratory air flow rates, the Diskus (GlaxoWellcome, Hertfordshire, UK) has comparable accuracy and precision to the MDI tested at 60 L/min, and it offers an advantage over two alternative dry powder inhalers (DPIs), delivering a more consistent dose across the range of flow rates tested and being more efficient at generating a fine particle fraction than either Turbuhaler (Astra, Lund, Sweden) or Diskhaler (GlaxoWellcome) at both 28 and 60 L/min inspiratory flow rates. Diskus, Diskhaler, Ventolin, Volumatic, and Rotadisk are trademarks of the GlaxoWellcome Group of companies. The Accuhaler is the alternative to the Diskus in those countries where the Diskus trademark is not available. Inspiryl and Turbuhaler are trademarks of the Astra Group of companies.

Stroke-associated stuttering.

OBJECTIVE: To present patients with stuttering speech in association with stroke. DESIGN: Case series with follow-up for 5 years, or until the stuttering resolved. SETTING: University and community hospital neurology wards, and ambulatory neurology clinics. PATIENTS: Four patients who developed stuttering speech in association with an acute ischemic stroke. A 68-year-old man acutely developed stuttering with a large left middle cerebral artery distribution stroke. A 59-year-old man who had stuttered as a child began to stutter 2 months after a left temporal lobe infarction, as nonfluent aphasia was improving. Another childhood stutterer, a 59-year-old originally left-handed man developed severe but transient stuttering with a right parietal infarction. A 55-year-old man with a left occipital infarction had a right hemianopia and an acquired stutter, for which he was anosognosic. CONCLUSION: The clinical presentation of stroke-associated stuttering is variable, as are the locations of the implicated infarctions.

A case of acute monocytic ehrlichiosis with prominent neurologic signs.

Human monocytic ehrlichiosis is a recently described tick-borne infection with the rickettsial organism Ehrlichia chaffeensis. We describe a patient with documented E chaffeensis infection and multiple organ system involvement. Prominent neurologic symptoms and signs included severe headache, meningismus, and altered mental status. Additional neurologic findings included unilateral arm weakness and a Bell's palsy. Biopsy of brain and meninges demonstrated an infiltrate of atypical lymphoid cells in the leptomeninges with involvement of blood vessel walls and extension into the Virchow-Robin spaces. Bone marrow biopsy revealed fibrin-ringed granulomas. The patient also developed a nonspecific increase in immunoglobulin production. Host immune response may play a critical role in the pathophysiology of ehrlichiosis.

Long-term use of the low molecular weight heparin tinzaparin in haemodialysis.

Fifty-two patients with chronic renal failure undergoing hospital haemodialysis were given a single bolus dose of tinzaparin (Innohep, Leo Laboratories, UK) into the arterial side of the dialyser, for up to 43 consecutive dialyses. The mean tinzaparin dose at the beginning was 2,139 IU anti-Xa and at the end 2,186 IU anti-Xa. Overall, tinzaparin proved a satisfactory anticoagulant for 1,370 (96.0%) out of 1,427 dialyses. Significant clot formation was prevented in 1,326 (92.8%) out of 1,429 dialyses. The clinically effective dose was associated with a mean plasma anti-Xa activity 1 h after dosing of 0.4 IU/ml and suppressed fibrinopeptide A formation for up to 4 h. Bleeding, from the skin or mucous membranes, was recorded at 27 (1.9%) of 1,408 dialyses. Prolonged fistula bleeding on completion of dialysis was recorded on only 20 occasions. Other haemorrhagic events included haematemesis, bruising and subconjunctival haemorrhage (each in 1 patient) and epistaxis (2 patients). Three patients died during the study of causes considered unrelated to tinzaparin therapy, myocardial infarction (2 patients) and multiple myeloma. Other adverse events reported included vomiting (3 patients) and hypotension (3 patients). Three patients ceased treatment due to haematemesis, prolonged bleeding from fistula puncture and thrombosis of the arteriovenous access, respectively. A small, but statistically significant, increase within the normal reference range was recorded in the mean values for aspartate aminotransferase and alanine aminotransferase.

Functional properties of regenerated optic axons terminating in the primary olfactory cortex.

When the optic nerve of Rana pipiens is cut and deflected into the telencephalon, the regenerating fibers terminate selectively in the superficial neuropil of the primary olfactory cortex. These redirected fibers and their terminals on the dendrites of the cortical cells appear normal by LM and EM criteria. Electrical recording, done 2-16 months after surgery, shows visually evoked activity in the superficial neuropil (Layer I) of the olfactory cortex, and visually excited responses in the deep cortical cell layer (Layer II). In the normal frog, the electrical activity seen in the neuropil of the olfactory cortex consists of small transients about 2-3 x the noise level of the electrode contact. These occur spontaneously and are also excited by puffs of air to the nose. There is no such excitation by visual stimuli. Larger initially negative spikes cell above noise level are recorded in the cell layer next to the ependymal surface, and these are also spontaneous, or excited by puffs of air to the nose, but not by visual stimuli. In the operated frog, the small transients in the neuropil appear and are excited by the puffs of air and by visual stimuli. Similarly the responses in the cell layer are excited by both sorts of stimuli. But new types of electrical signals appear in the neuropil; they are driven only by visual stimuli presented to the affected eye. These are very large transients of the kind found in the tectal neuropil and have the two characteristic shapes which were classified as B and C types in the tectum. Such large transients are never seen in the neuropil of the olfactory cortex in normal frogs. The receptive fields of the small visually driven transients in the neuropil are not easy to make out because the signal levels are so close to the noise level that different units cannot be reliably distinguished from each other. But the receptive fields of the much larger B and C type unit responses are as easy to classify and plot as they are in tectum, even though on the average they are only about 2/3 as large as in tectum. The single-unit receptive fields belong to one or another of the several types of retinal ganglion cell classes distinguished in optic-nerve recordings. Four of the major classes normally project to the tectum and a fifth projects to the lateral geniculate complex. But all five are present in the ectopic projection to the olfactory cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Circadian sneezing.

Prompted by the observation that a fellow medical student sneezed at about the same time in class every morning, we recorded the time of each of the 118 sneezes she made on 69 days over a 6.5-month period. Analysis of the sneeze times with the goodness-of-fit test revealed a highly nonuniform distribution (p < 0.0001) with a significantly increased probability of sneeze production within a small time interval centered at 8:20 AM. After ruling out the known causes of sneezing, we propose that the subject had a circadian fluctuation in her sneeze threshold independent of any immediate external stimulus. We compare this circadian rhythm to other periodic phenomena such as cyclic esotropia and rapid-cycling bipolar disease as well as to illnesses such as the periodic paralyses in which rapid and reversible changes occur in the neuromuscular system, and we discuss the peculiar circumstances favorable to documenting a circadian sneeze.

Hypothalamo-pituitary-adrenal axis in uraemia: evidence for primary adrenal dysfunction?

To study hypothalamo-pituitary-adrenal axis disturbances in chronic renal failure, we administered corticotrophin-releasing hormone to patients undergoing haemodialysis and CAPD and to normal controls. Cortisol, ACTH, and ACTH precursors were measured before and after corticotrophin-releasing hormone using sensitive and specific two-site assays. Baseline ACTH and cortisol were similar in all groups. Peak values occurred at 30 min (ACTH) and between 30 and 60 min (cortisol). The cortisol (but not the ACTH) responses were significantly reduced in patients with renal failure (P < 0.05). ACTH precursors did not change from baseline following corticotrophin-releasing hormone but were significantly elevated in patients with renal failure compared to controls (P < 0.01). The reduced cortisol response to corticotrophin-releasing hormone may reflect a primary defect of adrenal function in renal failure.

Dialysis at home in the west of Scotland: a comparison of hemodialysis and continuous ambulatory peritoneal dialysis in age- and sex-matched controls.

OBJECTIVE: To audit the outcome of patients treated at home by hemodialysis and continuous ambulatory peritoneal dialysis (CAPD). DESIGN: Retrospective comparison of nondiabetic hemodialysis patients with age- and sex-matched nondiabetic patients treated by CAPD. SETTING: Renal Units, Stobhill General Hospital and Western Infirmary, Glasgow, providing the home dialysis service for the West of Scotland. PATIENTS: Between 1982 and 1988, 139 hemodialysis patients starting treatment at home, compared with 139 matched patients starting CAPD over the same time period. MAIN OUTCOME MEASURES: Patient characteristics and cardiovascular risk factors at the start of home treatment. Patient and technique survival with both forms of dialysis. RESULTS: Patients selected for home hemodialysis were less likely to be smokers (p < 0.02) and to have electrocardiographic evidence of ischemia or left ventricular hypertrophy (p < 0.05) than patients treated by CAPD. Patient survival and technique survival (excluding death and renal transplantation) at 3 years were 93.8% versus 86.2% (p < 0.05) and 94.2% versus 80.8% (p < 0.04) for hemodialysis and CAPD, respectively. Cardiovascular events were responsible for the majority of deaths in both groups, but there was a greater proportion of deaths from other causes in patients treated by CAPD. There was no significant difference in the transplantation rate between the two treatment groups. CONCLUSIONS: Home dialysis is an effective method of renal replacement treatment for patients with end-stage renal disease. The results of hemodialysis are superior to CAPD, but this may be partly due to selection bias.

Sources of electrical transients in tectal neuropil of the frog, Rana pipiens.

We have studied the outer neuropil layers in frog tectum where the unmyelinated optic nerve fibers terminate. At any point in the neuropil an extracellular microelectrode records several different visually evoked electrical transients, distinct by size and shape. When classified by shape alone, each transient falls into one of 3 distinct classes. Some of these transients are binocularly driven, as originally described by Finch and Collett. The aggregate of the receptive fields of all the elements recorded at a single point defines a multiunit receptive field (MURF). Each MURF is characteristically oval, and divided into 3 sections along its long axis. Each section represents the aggregate of the receptive fields associated with one class of transient; i.e. transients belonging to only one specific class can be evoked by stimulating that part of the visual field corresponding to the appropriate section of the MURF. All of the MURFs mapped by recording in a single tectum are radially arranged in visual space about a central point, or 'visual pole'. Several conclusions are made. First, the two larger types of transient are generated postsynaptically by electrically active dendritic elements, specifically the beaded dendritic appendages of tectal neurons. The smallest type of transient is of presynaptic origin. Second, these tectal elements have a local and global anatomical order across the tectum, which accounts for both the tripartite structure of the MURFs and their radial arrangement about a visual pole. Third, since the large transients are of postsynaptic origin, genuine recordings of single retinal ganglion cell (RGC) activity can be made only in the optic nerve or retina itself. Fourth, information is conveyed over the unmyelinated optic nerve fibers at pulse rates as high as 80/s and is transsynaptically effective at such rates. Finally, the electrically active tectal dendritic elements, with their highly organized spatial arrangement, are an important component of the frog's visual processing apparatus, instead of being merely relays or repeaters.