Application Of Potassium Chloride Research Articles

Magnetic resonance imaging assessment of cerebral hemodynamics during spreading depression in rats.

High-speed magnetic resonance imaging was used to perform simultaneous measurements of relative cerebral blood volume (rCBV) and water diffusion changes during spreading depression (SD) induced by cortical potassium chloride application. Rats were fitted epidurally with a rubber chamber. Potassium chloride was perfused through the chamber until SD was indicated by a negative direct current (DC) potential shift. Magnetic resonance imaging scans used echo planar diffusion and T2-weighted images. Iron dextran was injected as a blood pool contrast agent to make subsequent changes in T2 (or T2*) directly proportional to changes in CBV. Multislice maps of apparent diffusion coefficient (ADC) and rCBV were generated with 6- to 16-second time resolution, which revealed transient ADC and rCBV changes propagating over the cortex after potassium chloride application. Transient ADC declines appeared simultaneously with the DC shift, whereas rCBV increase followed with a delay of 16.4+/-14.9 seconds. Prolonged rCBV decrease was observed after the initial increase during the SD in half of the animals. The delayed rCBV response after the ADC change supports the observation of increased energy demand because of repolarization. Simultaneous DC potential recording and ADC measurements in corresponding sites of the cortex indicate that transient ADC decreases during SD reflect water shifts associated with cell depolarization.

Cerebral cortex does not modulate "regulated" decrease in core temperature during hypoxemia in rats.

In newborns and adults of a number of species including humans, exposure to acute hypoxemia produces a "regulated" decrease in core temperature, the mechanism of which is unknown. Considering that various cortical areas participate in autonomic regulation including thermoregulation, the present experiments were carried out to test the hypothesis that the cerebral cortex plays a role in modulating the regulated decrease in core temperature during acute hypoxemia. This hypothesis was tested by determining the core temperature response to acute hypoxemia in chronically instrumented adult Sprague-Dawley rats before and after cortical spreading depression (i.e., functional decortication) was produced by the local application of potassium chloride to the dura overlying the cerebral hemispheres. There was no effect of cortical spreading depression on baseline core temperature. Core temperature decreased during acute hypoxemia in a similar fashion when the cerebral cortex was intact as well as during functional decortication. Thus our data do not support the hypothesis that the cerebral cortex modulates the regulated decrease in core temperature that occurs in adult rats during acute hypoxemia.

Analysis of c-Fos and glial fibrillary acidic protein (GFAP) expression following topical application of potassium chloride (KCl) to the brain surface

Application of high K + concentrations to a limited area of the brain surface is known to trigger spreading depression. We used this model to observe the response of cortical areas, distant to the exposed site, at the cellular level. Immunostaining of glial fibrillary acidic protein (GFAP) and of the proto-oncogene c-Fos was analyzed in brain sections at different times after K + application. Piriform and parietal cortices, as observed in coronal sections located 3 mm rostrally from the center of the stimulated area and ipsilateral to it, showed a dramatic increase in immunostaining for both markers. However, the time course for such increments was different. c-Fos protein(s) expression was high at 1.5 h and decreased at 24 h after K + exposure and c- fos mRNA expression correlated with the immunohistochemical results. At these initial times GFAP immunoreactivity was still low but began to rise between 2 and 7 days after treatment in exactly the same areas where c-Fos expression had been up-regulated. No significant effect, for either marker, was evident in the contralateral piriform or parietal cortices. In addition, we studied the effects of the NMDA antagonist MK-801 (4 mg/kg i.p.) on the expression of mRNA for GFAP and c- fos and demonstrated a marked reduction in the upregulation of these genes.

Role of Na(+)-K+ ATPase in cyclic GMP-mediated relaxation of canine pulmonary artery smooth muscle cells.

1. Sodium-potassium adenosine triphosphate (Na(+)-K+ ATPase) plays a role in the regulation of vascular tone, but contribution of this enzyme to intravasodilator-induced pulmonary vasodilation remains uncertain. We thus studied the interaction between guanosine 3':5'-cyclic monophosphate (cyclic GMP) and Na(+)-K+ ATPase in smooth muscle cells isolated from canine pulmonary artery. 2. To assess the contractile properties, changes in smooth muscle cell length were determined microscopically. Application of potassium chloride (KCl) shortened the cell length, an effect which was reduced by sodium nitroprusside and 8-bromo-cyclic GMP in a concentration-dependent manner. Pretreatment of cells with the cyclic GMP-dependent kinase inhibitor KT 5823 (2 microM) abolished the effects of sodium nitroprusside and 8-bromo-cyclic GMP. 3. Ouabain (0.3 microM) did not alter the KCl-induced muscle shortening, but inhibited the relevant responses to sodium nitroprusside and 8-bromo-cyclic GMP. 4. Incubation of smooth muscle cells with sodium nitroprusside concentration-dependently increased intracellular cyclic GMP levels and ouabain-sensitive 86Rb uptake, and these values were significantly correlated. In the presence of KT 5823, sodium nitroprusside increased cyclic GMP levels but did not alter ouabain-sensitive 86Rb uptake. 5. These results suggest that there is a link between accumulation of intracellular cyclic AMP and activation of sarcolemmal Na(+)-K+ ATPase in pulmonary artery smooth muscle cells and that this link may be involved in the sodium nitroprusside-induced pulmonary vasodilatation.

Cortical application of potassium chloride induces the low-molecular weight heat shock protein (Hsp27) in astrocytes.

Spreading depression induces tolerance to ischemic injury, and ischemic tolerance has been associated with expression of heat shock proteins (Hsp). Here we examine Hsp27 expression after KCl-induced spreading depression. Twenty-minute cortical KCl application induced Hsp27 immunoreactivity in glial fibrillary acidic protein-positive astrocytes of the ipsilateral neocortex. Systemic administration of MK-801 (3 mg/kg) suppressed KCl-induced Hsp27 expression in the parietal cortex. Astrocytes in the posterior cingulate and retrosplenial cortex did not express Hsp27 after KCl application but did express Hsp27 after systemic administration of high dose MK-801 (9 mg/kg). Whereas Hsp27 was usually observed in all layers of the parietal cortex after 5-minute application of KCl, in 2 of 6 rats, Hsp27 was seen in clusters of astrocytes or in astrocytes in the superficial layers I to III of the parietal cortex. We conclude that (1) cortical application of KCl triggered Hsp27 astrocytic expression; (2) astrocytes in the cingulate and retrosplenial cortex responded differently compared with astrocytes of the parietal cortex; (3) Hsp27 expression progressed from small clusters of astrocytes throughout superficial layers of the cortex that joined and recruited astrocytes in deeper layers; (4) several mechanisms induced Hsp27 astrocytic expression. We propose that Hsp27 is involved in spreading depression-induced ischemic tolerance through protection of astrocyte function.

Evidence for slowly conducting afferent fibres innervating both tooth pulp and periodontal ligament in the cat

The presence of afferent nerve fibres branching to innervate both the dental pulp and periodontal ligament was studied in pentobarbitone-anaesthetised cats. Extracellular single nerve-fibre recordings were made from fine filaments split from the proximally cut end of the inferior alveolar nerve. Nerve fibres were identified by bipolar constant-current stimulus pulses applied to the periodontal space via platinum wire electrodes. In each case activation of the nerve fibres was also attempted by monopolar electrical stimulation of the dental pulp via a platinum wire electrode inserted into the dentine. Eleven of 142 C fibres and 4 of 97 A δ fibres identified by electrical stimulation of the periodontal ligament also could be activated by electrical stimulation of the dental pulp. Fourteen of the 142 C fibres identified by electrical stimulation of the periodontal ligament exhibited discrete latency jumps at different suprathreshold stimulus strengths. Eight of them also could be activated by electrical stimulation of the dental pulp. Eight of the 15 fine branching afferent fibres were tested with non-electrical stimuli of both periodontal ligament and dental pulp by application of heat, cold and potassium chloride. Three of the 4 C fibres could be activated with at least one of these stimuli applied to both tissues. In one case receptove fields were located in both periodontal ligament and dental pulp. The remaining 5 slowly conducting fibres were activated only from one type of tissue. The results suggest that a small percentage (6%) of the slowly conducting nerve fibres in the inferior alveolar nerve innervate both the periodontal ligament and the dental pulp. According to their response behaviour they might be involved in nociception.

The role of spreading depression in focal ischemia evaluated by diffusion mapping.

This study investigated the role of spontaneous and induced spreading depression (SD) on the evolution of focal ischemia in vivo. We induced focal ischemia in 12 rats using the middle cerebral artery suture occlusion (MCAO) method. Chemical stimulation of nonischemic ipsilateral cortex by potassium chloride application (KCl group; n = 7) and saline (NaCl group; n = 5) was performed at 15, 30, 45, and 60 minutes following MCAO, and SD was detected electrophysiologically. Ischemic lesion volumes assessed over 15-minute intervals, evaluated by continuous apparent diffusion coefficient (ADC) of water mapping, demonstrated that the ischemic region increased significantly during 15-minute time epochs with a single SD episode (36.5 +/- 12.9 mm3, mean +/- SD) or multiple SD episodes (39.8 +/- 22.3) compared with those without SD (13.9 +/- 11.5) (p = 0.0009). Infarct volume at postmortem 24 hours after MCAO was significantly larger in the KCl group, with more total SDs (237.8 +/- 13.8) than the NaCl group (190.5 +/- 12.6) (p = 0.0001). This study demonstrates that ischemia-related and induced SDs increase significantly ischemic lesion volume in vivo, supporting the hypothesis for a causative role of SD in extending focal ischemic injury.

Spreading waves of a reduced diffusion coefficient of water in normal and ischemic rat brain.

Using echo planar diffusion-weighted magnetic resonance imaging, we measured three-dimensional changes in the apparent diffusion coefficient (ADC) of water in eight contiguous coronal slices, encompassing the entire rat brain, before and after local cortical stimulation. We applied chemical (potassium chloride application; n = 6) and mechanical (needle stab; n = 4) stimulations to the right posterior parietal rat cortex. In all animals in which potassium chloride or the needle stab was applied, a region of decreased ADC values to a mean of 0.45 +/- 0.03 x 10(-5)cm2/s occurred. These reduced ADC levels appeared in the posterior parietal cortex within 1 min after cortical stimulation and the change recovered within 1 min. Then a ripple-like movement of similar changes developed across the unilateral cortex. This change was localized to the cortex and no significant ADC changes occurred in subcortical structures. The propagating speed of this movement was 3.4 +/- 0.5 mm/min. These findings are compatible with spreading depression as observed electrophysiologically. Similar ADC changes occurred in areas distinct from the ischemic lesion in 3 of 12 animals subjected to focal cerebral ischemia. This magnetic resonance method could detect spreading ADC decline if it occurred in human diseases including brain ischemia.

The effect of N, P and KCl fertilizers on grain yield and Cd concentration of malting barley

A three-year field study, conducted on two Orthic Black Chernozemic soils, investigated the effects of application of N, P and KCl fertilizers on grain yield and Cd concentration of two cultivars of malting barley (Hordeum vulgare). Soil levels of N and P were good predictors of the likelihood of a yield response to fertilizer applications, while increases in yield with potassium chloride (KCl) application occurred in spite of high levels of soil K. Additions of ammonium nitrate increased Cd concentration in malting barley when soil nitrate levels were low, with increased Cd concentrations in the grain generally being associated with increasing crop yields. Applications of monoammonium phosphate or KCl tended to increase concentrations of Cd in malting barley, with the significance of the effect varying from year to year. Response of Cd concentration in the grain to P and KCl application was not related to levels of these nutrients in the soil. As the N and K fertilizer used in the study did not contain significant quantities of Cd, the increase in Cd concentration in the grain with fertilizer application was not solely a result of Cd addition as a fertilizer contaminant. The fertilizer salts may increase Cd concentration in the soil solution, increasing availability for crop uptake. Increased crop yield associated with N application may also increase Cd accumulation through increased root interception and enhanced mass flow.

A REVIEW OF FERTILISER TRIALS IN TUVALU AND KIRIBATI

A brief introduction is given to a programme of 34 fertiliser trials (possibly the largest programme of fertiliser trials in the world) that have been carried out in Tuvalu and Kiribati. Some of the more striking results that have emerged have been presented, and it is hoped that readers who would find more detailed information for use to them will ask for the relevant reports from the Department of Agriculture of the two countries concerned.
 
 The majority of the trials were conducted within the 1978 and 1993 period, being started by Trewren, and the longer running trials in Kiribati were continued by Edwards and, in most cases to their conclusion, by Barr.
 
 The results obtained have made it possible to formulate with some confidence recommendations on the manuring of coconuts on atolls, from seedlings in the nursery to mature palms in the field, including the rehabilitation of palms suffering from very severe deficiencies of trace elements and potassium. From foliar analysis, much useful information has been obtained on the inter‑relationships between nutrients, and in particular, on the fundamental importance of iron and other trace elements on the assimilation of macro‑nutrients and on the need to maintain a correct balance amongst trace elements.
 
 Further research is needed to identify a suitable source of nitrogen. Less important topics for research could be investigations into the optimum quantity of potassium chloride application to nursery seedlings and the optimum frequency of application of potassium chloride in the field.

Spreading waves of decreased diffusion coefficient after cortical stimulation in the rat brain.

A method is demonstrated for the noninvasive detection and study of spreading cortical depression. Spreading depression (SD) was elicited in rats by topical application of potassium chloride to the exposed cortex. The apparent diffusion coefficient (Dapp) of water in a region of the cortex, measured using a PFG-NMR spin echo sequence with an observation time of 40 ms, declines 35% within 30 s and recovers to the normal value within the next 30 s. The region of decreased Dapp was shown to be 2 mm in size and to move in the cortex, away from the point of application, with a uniform velocity of 3.3 +/- 0.5 mm/min. The behavior of the affected region is consistent with other reports of the behavior of SD as monitored by electrophysiological means. The technique can be implemented on currently available MRI equipment and makes possible the noninvasive study of SD in animal models of neurological disorders, their therapeutic intervention, and possibly the study of SD in humans.

Interaction between Plant Nutrients: IV. Interaction between Calcium and Phosphate

Abstract The interaction between calcium and phosphate is complex because these ions both support and counteract each other. The supporting effect is due to a simultaneous uptake and translocation of calcium and phosphate. The counteracting effect is caused by precipitation of less soluble calcium phosphates at the vicinity of nutrient-absorbing roots. At high activity ratios between potassium and calcium the risk of calcium deficiency is obvious. The capability of plants to absorb calcium ions is then increased by application of soluble phosphate fertilizers. In a field experiment, application of potassium chloride decreased the uptake of phosphorus and crop yield. Application of ammonium phosphate increased the content of water-soluble phosphate in a soil extract and the early uptake of phosphorus and calcium. Application of ordinary superphosphate had less effect than ammonium phosphate on the solubility of phosphate in the soil, whereas the calcium ion activity and crop yield increased considerably. E...

Spreading depression induces c- fos-like immunoreactivity and NGF mRNA in the rat cerebral cortex

Application of potassium chloride (KCl) to the brain surface elicits spreading depression which leads to a marked induction of the proto-oncogene c- fos in the treated cerebral cortex at the earliest time examined (90 min). High levels of c- fos immunoreactivity are observed up to 6 h after KCl treatment. The areas affected include the cingulate, entorhinal and frontoparietal cortex throughout the treated hemisphere. The c- fos expression preceded an increase in both NGFmRNA and NGF-like protein(s). A maximal increase in c- fos was detected within 3 h, whereas NGFmRNA peaked at 12 h and NGF-like protein(s) reached their maximum level 24 h after KCl application. The most prominent increase in NGFmRNA was measured in the entorhinal cortex (50-fold), but other cortical areas also showed a moderate increase of 2–3-fold. In conclusion, our results provide that increases in c- fos and NGF expression are early adaptive responses following brain injury.

Fertiliser requirements of luceme cut for hay in northern Southland

Three field trials were laid down, on established luceme (Medicago sativa L.) stands and continued for 2,3 or 4 years. On two sites fertilisers applied were potassium chloride (0 and 200 kg/ha) and single superphosphate (0,200.400 and 800 kg/ha), while on the third site potassium chloride (0, 100 and 200 kg/ha), sulphur (0,25,50 and 100 kg S/ha as gypsum) and phosphorus (0,18,36 and 72 kg P/ ha as monocalcium phosphate) were applied. Lucerne was harvested at the hay stage with 2 or 3 cuts per year. Consistent annual yield responses to 200 kg/ ha of potassium chloride application occurred at all sites. At the site where 100 kg/ha was applied it produced about 95% of maximum yield but nil K gave 8594% of maximum yield. Responses to superphosphate treatments were recorded at two sites with the major response considered to be due to phosphorus. 200 - 400 kg/ha of superphosphate was sufficient for near maximum response. Response to both phosphorus and sulphur occurred at site 3 with 18 kg/ha phosphorus and 25 kg/ha sulphur being sufficient for near maximum response. Results indicate that a soil P test of 13 and K test of 6 should support approximately 95% of maximum yield. Herbage P and S concentrations associated with near maximum yields were slightly higher than indicated in current standards for plant analysis interpretations, but K concentrations agreed with current standards. Maintenance fertiliser requirements derived from this trial series are similar to those predicted from AgResearch's fertiliser recommendation models. Keywords Medicago sativa, potassium, phosphorus, soil test, plant analyses, sulphur, fertiliser

Two models for the leaching of a non‐reactive solute to a mole drain

SUMMARYTwo models of solute leaching to a mole‐pipe drainage system are described. The first model is research‐oriented. It simplifies two‐dimensional water and solute flow to a mole drain by dividing the soil between the mid‐mole plane and the mole into notional compartments. Solute movement between compartments is assumed to occur by convection andmechanical dispersion. Within each compartment a mobile and immobile solute phase is defined, with diffusion occurring between them. Rainfall intensity (over approximately hourly intervals) and basic soil hydraulic data are needed as inputs. An explicit finite‐difference solution to the water and solute mass‐balance and flux equations is used.The second simpler model is management‐oriented. It uses daily time steps, and assumes the soil solution behaves as if it were well‐mixed system. It requires only daily rainfall and evaporation data, the drainage coefficient of the mole‐pipe system, and the soil macroporosity as inputs. In both models a source/sink term accounts for additions of solute in rainfall and fertilizer, and extraction by plant uptake.The models were used to simulate leaching losses of chloride to a mole‐pipe drainage system in a silt loam under pasture, following the application of potassium chloride to the soil surface. The first model simulated leaching better immediately after ertilizer application, and during bypass flow induced by heavy rain. However, both models were able to simulate the measured losses over a 2‐year period equally well.

Application of potassium chloride to the brain surface induces the c-fos proto-oncogene: reversal by MK-801

The proto-oncogene c-fos is activated in the brain by a variety of stimuli including brain injury. In unilateral brain injury, c-fos immunoreactivity is confined to the damaged hemisphere, an effect reminiscent of spreading depression. Here we show that topical application of KCl (3 M) to the brain surface (which induces spreading depression) is accompanied by ipsilateral increase in c-fos immunolabeling. The activation of c-fos, like spreading depression, is markedly reduced by the non-competitive NMDA antagonist MK-801 (3 mg/kg i.p.).

EFFECT OF POTASSIUM CHLORIDE, IMAZALIL, AND METHOD C IMAZALIL APPLICATION ON BARLEY INFECTED WITH COMMON ROO ROT

Two experiments were conducted at six locations in North Dakota in 1986 using Morex barley (Hordeum vulgare L.) as the test crop. The first consisted of a factorial combination of 3 KCl fertilizer rates (0, 50, and 200 kg ha−1 of KCl) by two rates of imazalil impregnated on the seed (0 and 0.1 g a.i. kg−1 seed). Potassium chloride application reduced plant nitrate concentrations at all sites, while imazalil had little effect. Imazalil reduced common root rot (CRR, incited primarily by Cochliobolus sativus) at four sites and KCl fertilization reduced CRR at two sites. At these latter two sites differing KCl × imazalil interactions were observed. At one site, KCl reduced CRR in the absence of imazalil but not in the presence of imazalil. Imazalil was quite effective in controlling CRR at this site, however. At the second site, both KCl and imazalil reduced CRR and their effects were complementary. Imazalil seed treatment substantially increased yield at one site where there was infection with take-all (Gaeumannomyces graminis) as well as CRR. Imazalil application significantly reduced yields at another site. Potassium chloride fertilization significantly increased yield at one site, but this yield increase could not be attributed to control of CRR. The second experiment compared seed impregnation with imazalil to impregnation of monoammonium phosphate fertilizer drilled with the seed. Fertilizer impregnation with imazalil eliminated all seedling toxicity associated with the fungicide, but imazalil-impregnated fertilizer was totally ineffective in controlling CRR.Key words: Chloride fertilization, fertilizer-fungicide interaction, fertilizer-pesticide mixtures, take-all, Cochliobolus sativus, Gaeumannomyces graminis, Hordeum vulgare

Potassium-induced release of endothelium-derived relaxing factor from canine femoral arteries.

Experiments were designed in a bioassay system to analyze the effect of elevated (from 5.9 mM to 7.5-45.9 mM) extracellular K+ concentration on the release of endothelium-derived relaxing factor. Segments of canine femoral artery with endothelium (donor segment) were mounted in an organ bath and perfused with modified Krebs-Ringer bicarbonate solution; the effluent from the donor segment was used to superfuse a canine coronary artery ring without endothelium (bioassay tissue). Elevation of perfusate K+ concentration by 1.6-15 mM by intraluminal infusion of potassium chloride upstream of the donor segment evoked further contractions of bioassay rings contracted with prostaglandin F2 alpha. In contrast, the bioassay rings progressively relaxed when increasing concentrations of potassium chloride (10-40 mM) were added extraluminally to the organ bath where the perfused segment was mounted. Extraluminal application of phenylephrine or prostaglandin F2 alpha did not evoke relaxations in the bioassay ring. Removal of the endothelium from the donor segment or selective exposure of the segment (but not the bioassay ring) to Ca2+-deficient solution prevented the K+-induced relaxations. Treatment of the donor segment and the bioassay ring with inhibitors of known endogenous vasoactive substances (acetylcholine, norepinephrine, adenine nucleotides, and prostanoids) had no significant effect on the relaxation of the bioassay ring evoked by extraluminal application of potassium chloride. Simultaneous measurements of changes in isometric force in the donor segment and bioassay ring revealed that extraluminal elevation of K+ concentration relaxed the segments as well and that the relaxations could not be prevented by simultaneous intraluminal infusion of potassium chloride.(ABSTRACT TRUNCATED AT 250 WORDS)

Estudo do parcelamento da adubação potássica do algodoeiro

Em dez experimentos de campo conduzidos com o algodoeiro no Estado de São Paulo, no período compreendido entre os anos agrícolas de 1975/76 e 1980/81, estudou-se a conveniência de parcelar a aplicação de cloreto de potássio. Foram aplicadas no sulco de semeadura, em posição lateral e em nível inferior ao das sementes, as doses de 0, 60 e 120kg/ha de K2O. Nos demais tratamentos, a dose de 120kg/ha ou parte dela (1/3, 1/2 e 2/3) foi aplicada em cobertura, após o desbaste, em mistura com o adubo nitrogenado, com incorporação na operação de "chegar terra". Na análise individual dos resultados de produção de algodão em caroço, em apenas 10% dos casos houve efeito linear de potássio, quando aplicado tradicionalmente. Com o parcelamento, esse número subiu para 40%. Entretanto, no conjunto dos ensaios, a diferença entre modos de aplicação do nutriente não foi estatisticamente significativa. Os ensaios foram reagrupados em função de resultados dos estudos de correlação entre a produção relativa (PR) da testemunha (PR = 100 x produção sem potássio/produção com potássio) e índices de análise de solo. Estabeleceram-se grupos de respostas esperadas nos estudos de correlação linear entre PR e os índices analíticos mais relacionados com a resposta das plantas à adubação, que foram, em ordem decrescente de importância, (Ca2+ + Mg2+)/K+ e 1/K+. No grupo de alta resposta esperada a potássio [K+ < 0,08 meq e (Ca2+ + Mg2+)/K+ > 43], o parceamento da dose de 120Kg/ha de K2O superou a forma tradicional de aplicação; no grupo de média resposta esperada [0,08 a 0,24 meq para K+ e (Ca2+ + Mg2+)/K+, na faixa de 20-43 ], notou-se clara tendência para maior efeito da aplicação parcelada. Dessa forma, recomenda-se que, em condições de deficiência potássica, a aplicação de cloreto de potássio seja parcelada com cerca de 1/2 a 2/3 da dose no sulco de plantio (ao lado e em nível inferior ao das sementes) e o restante em cobertura, após o desbaste, com o adubo nitrogenado, com incorporação da mistura na operação de "chegar terra".

Early positive component of the tectal evoked potential ofSqualus acanthias during electrical stimulation of the optical nerve

The evoked potential of the tectum opticum during electrical stimulation of the optic nerve was studied in acute experiments on the dogfishSqualus acanthias L. The negative phase of the "classical" negative-positive evoked potential of the contralateral hemisphere of the tectum opticum was shown to be a complex potential, including an early positive component. A similar potential also was recorded from the ipsilateral hemisphere. Enhancement of this positive potential on insertion of the recording electrode deep into the brain, its resistance to functional block on application of potassium chloride to the brain surface, and recording a similar potential from the surface of the floor of the third ventricle after extirpation of the tectum opticum are evidence of the nontectal location of the source of this evoked potential component. On the basis of existence of a focus of maximal activity in the rostral zones of the brain beneath the tectum opticum, and disappearance of the early positive component during functional block and extirpation of this brain region, it is concluded that a leading role in the generation of this component is played by thalamic nuclei.