Temperature-dependent changes in visual evoked potentials of rats

Evaluation of VEP parameters in patients before and after cardiopulmonary by-pass surgery

PURPOSE

Coronary bypass surgery is emphasized in aetiology of ischemic optic neuropathy. Our aim in this study was to investigate the pattern visual evoked potentials (PVEP) in patients before and after coronary bypass surgery.

METHODS

Thirty-one patients were included in the study. After a full ophthalmological evaluation, PVEP was assesed in the pre and postoperative periods. Operative times, hematological parameters, blood pressures, number of transfusions, body temperatures, anaesthetic drugs and systemic illnesses were recorded for each patient.

RESULTS

The mean age of the patients were 59 ± 10.4 years. There was 22 men and 9 women in the study. Only 3 of them needed transfusion during the surgery. The mean duration of the surgery was 3.2 ± 0.7 h. None of the patients had a history of visual disturbance or postoperative ischemic optic neuropathy. The mean VEP P100 amplitude was not statistically significantly different but the mean VEP P100 latency showed statistically significant difference between the preoperative and postoperative periods. (p = 0.014) This significance was more appereant in patients with systemic illnesses. (p = 0.023) There was a positive correlation between the age and VEP P100 latency (r = 0.402, p < 0.05).

CONCLUSIONS

Although surgical techniques and equipments are developing each day in the field of cardiopulmonary bypass surgery, the contributing factors such as hypothermia, anemia and diabetes still seem to affect neurophysiological functions even after a noncomplicated surgery.

Methylphenidate and alcohol effects on flash-evoked potentials, body temperature, and behavior in Long-Evans rats

Methylphenidate (MPD) is a psychostimulant used to treat attention deficit hyperactivity disorder (ADHD). Most adult ADHD patients use ethanol in combination with MPD. This research examined the effects of MPD and ethanol on flash-evoked potentials (FEPs; cortical responses frequently used to assess neural activity and sensory processing) recorded from the visual cortex (VC) and superior colliculus (SC; a structure involved in attention and orientation) of chronically implanted male Long-Evans rats, and on body temperature and open field behavior. For one group of rats, either saline or ethanol (2.0 g/kg) was given 5 min prior to either saline or MPD (2.9 mg/kg). FEPs were recorded 10 and 20 min later. In the VC, ethanol decreased amplitudes of several components, but increased P2. MPD increased N3, but decreased P3 and P4. Ethanol increased the latency of several components. In the SC, ethanol decreased all three components, while MPD increased P3. Ethanol increased latency of all components. During FEP testing, ethanol decreased body movement while MPD increased movement. In the open field, line crossings were increased but rearings were decreased by ethanol. Both ethanol and MPD produced hypothermia. A second group of rats was given MPD at 11.6 mg/kg. Ethanol decreased several VC amplitudes, but increased P2. MPD increased N3 amplitude but decreased amplitude for other components. MPD also counteracted the effect of ethanol on the amplitude of P2 and N3. Both ethanol and MPD increased the latency of several components. In the SC, ethanol decreased all component amplitudes, while MPD increased P3 but decreased N4. Ethanol increased all component latencies, while MPD increased latency for two components. During FEP testing, ethanol decreased body movement while MPD increased movement. In the open field, line crossings were increased by ethanol and MPD. Rearings were eliminated by ethanol in the open field but increased by MPD, and MPD counteracted the effect of ethanol on rearings. Both ethanol and MPD produced hypothermia. Some of these results might help explain why users take MPD and ethanol in combination in order to enable consuming larger amounts of alcohol.

Visual Evoked Potential Recording in a Rat Model of Experimental Optic Nerve Demyelination

The visual evoked potential (VEP) recording is widely used in clinical practice to assess the severity of optic neuritis in its acute phase, and to monitor the disease course in the follow-up period. Changes in the VEP parameters closely correlate with pathological damage in the optic nerve. This protocol provides a detailed description about the rodent model of optic nerve microinjection, in which a partial demyelination lesion is produced in the optic nerve. VEP recording techniques are also discussed. Using skull implanted electrodes, we are able to acquire reproducible intra-session and between-session VEP traces. VEPs can be recorded on individual animals over a period of time to assess the functional changes in the optic nerve longitudinally. The optic nerve demyelination model, in conjunction with the VEP recording protocol, provides a tool to investigate the disease processes associated with demyelination and remyelination, and can potentially be employed to evaluate the effects of new remyelinating drugs or neuroprotective therapies.

The developmental effects of extremely low frequency electric fields on visual and somatosensory evoked potentials in adult rats

The purpose of our study was to investigate the developmental effects of extremely low frequency electric fields (ELF-EFs) on visual evoked potentials (VEPs) and somatosensory-evoked potentials (SEPs) and to examine the relationship between lipid peroxidation and changes of these potentials. In this context, thiobarbituric acid reactive substances (TBARS) levels were determined as an indicator of lipid peroxidation. Wistar albino female rats were divided into four groups; Control (C), gestational (prenatal) exposure (Pr), gestational+ postnatal exposure (PP) and postnatal exposure (Po) groups. Pregnant rats of Pr and PP groups were exposed to 50 Hz electric field (EF) (12 kV/m; 1 h/day), while those of C and Po groups were placed in an inactive system during pregnancy. Following parturition, rats of PP and Po groups were exposed to ELF-EFs whereas rats of C and Pr groups were kept under the same experimental conditions without being exposed to any EF during 68 days. On postnatal day 90, rats were prepared for VEP and SEP recordings. The latencies of VEP components in all experimental groups were significantly prolonged versus C group. For SEPs, all components of PP group, P2, N2 components of Pr group and P1, P2, N2 components of Po group were delayed versus C group. As brain TBARS levels were significantly increased in Pr and Po groups, retina TBARS levels were significantly elevated in all experimental groups versus C group. In conclusion, alterations seen in evoked potentials, at least partly, could be explained by lipid peroxidation in the retina and brain.

The effect of ingested sulfite on visual evoked potentials, lipid peroxidation, and antioxidant status of brain in normal and sulfite oxidase-deficient aged rats

Sulfite, commonly used as a preservative in foods, beverages, and pharmaceuticals, is a very reactive and potentially toxic molecule which is detoxified by sulfite oxidase (SOX). Changes induced by aging may be exacerbated by exogenous chemicals like sulfite. The aim of this study was to investigate the effects of ingested sulfite on visual evoked potentials (VEPs) and brain antioxidant statuses by measuring superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities. Brain lipid oxidation status was also determined via thiobarbituric acid reactive substances (TBARS) in normal- and SOX-deficient aged rats. Rats do not mimic the sulfite responses seen in humans because of their relatively high SOX activity level. Therefore this study used SOX-deficient rats since they are more appropriate models for studying sulfite toxicity. Forty male Wistar rats aged 24 months were randomly assigned to four groups: control (C), sulfite (S), SOX-deficient (D) and SOX-deficient + sulfite (DS). SOX deficiency was established by feeding rats with low molybdenum (Mo) diet and adding 200 ppm tungsten (W) to their drinking water. Sulfite in the form of sodium metabisulfite (25 mg kg(-1) day(-1)) was given by gavage. Treatment continued for 6 weeks. At the end of the experimental period, flash VEPs were recorded. Hepatic SOX activity was measured to confirm SOX deficiency. SOX-deficient rats had an approximately 10-fold decrease in hepatic SOX activity compared with the normal rats. The activity of SOX in deficient rats was thus in the range of humans. There was no significant difference between control and treated groups in either latence or amplitude of VEP components. Brain SOD, CAT, and GPx activities and brain TBARS levels were similar in all experimental groups compared with the control group. Our results indicate that exogenous administration of sulfite does not affect VEP components and the antioxidant/oxidant status of aged rat brains.

Serum lipid peroxidation markers are correlated with those in brain samples in different stress models

OBJECTIVE

Stress can stimulate increased production of oxygen radicals. We investigated the correlations between serum levels of lipid peroxidation markers and those in brain samples in different stress models.

METHODS

Animals (n = 96) were divided equally into eight groups: a control group and groups treated with vitamin E (Vit E); exposed to immobilisation stress; exposed to immobilisation stress and treated with Vit E; exposed to cold stress; exposed to cold stress and treated with Vit E; exposed to both immobilisation and cold stress; and a final group exposed to both immobilisation and cold stress and treated with Vit E. Thiobarbituric acid-reactive substance (TBARS) in brain samples and levels of TBARS, corticosterone, conjugated dienes (CD), lipids, and paraoxonase-1 (PON1) activity in serum were analysed.

RESULTS

Serum corticosterone (p < 0.001), CD (p < 0.05), lipid (p < 0.05) levels, and brain TBARS (p < 0.05) levels were significantly higher in all stress groups than in controls, and the elevated levels were reversed in the Vit E-treated stress groups (p < 0.05). Serum PON1 activity was not different among the groups (p > 0.05). Serum TBARS levels increased significantly in all stress groups (p < 0.05), but this elevation was only reversed in the group exposed to both immobilisation and cold stress and treated with Vit E (p < 0.001).

CONCLUSION

These results suggest that serum levels of lipid peroxidation markers can be determined readily and may be useful as indicators to evaluate the effects of oxidative stress in the brain.

Interactions between mecamylamine and alcohol in Long-Evans rats: flash-evoked potentials, body temperature, behavior, and blood alcohol concentration

Mecamylamine, a noncompetitive antagonist of nicotinic acetylcholine receptors, has many potential clinical applications, including treating alcohol dependency. However, little is known about the combined effects of mecamylamine and alcohol on visual system electrophysiology. We examined the separate and combined effects of mecamylamine (4.0mg/kg, ip) and alcohol (2.0 g/kg, ip) on flash-evoked potentials (FEPs) recorded from the visual cortex (VC) and superior colliculus (SC) of chronically implanted adult male Long-Evans rats. On separate days, either saline or mecamylamine was given 10 min prior to either saline or ethanol. FEPs were recorded 15 and 30 min after the second injection. In the VC, alcohol significantly decreased the amplitudes of components P23, N29, N39, P89, N143, and P237, but increased P46. N63 amplitude was not significantly altered. In contrast, mecamylamine increased the amplitude of P23, P46, and N63, but reduced the amplitude of N29 and P237. The combination of mecamylamine and alcohol resulted in amplitudes very similar to alcohol alone for components P23, N29, N63, P89, N143, and P237. However, mecamylamine pretreatment reduced the effects of alcohol on components N39 and P46. In the SC, FEP component amplitudes were generally decreased by alcohol but not significantly altered by mecamylamine. Mecamylamine pretreatment did not significantly alter the effects of alcohol on SC amplitudes. Latencies of nearly all components in both structures were significantly increased by all drug treatments, with the greatest increase produced by the combination treatment. Hypothermia was also produced by all drug treatments, with the greatest hypothermia (2.25 °C) produced by the combination treatment, most likely accounting for much of the drug-induced increase in latencies. All drug treatments reduced movement during FEP testing, but later in an open field alcohol increased ambulation while mecamylamine reduced movement. Separate groups of experimentally naïve adult male Holtzman albino and Long-Evans hooded rats were given (ip) either alcohol or mecamylamine plus alcohol. Tail vein samples were taken 30 min later. For both rat strains, blood alcohol concentration in the mecamylamine pretreatment group was significantly less at this time interval by about 50-60 mg/dL, suggesting a mechanism whereby mecamylamine can mitigate some of the acute effects of alcohol (e.g., on VC components N39 and P46).

Protective effects of erdosteine on amikacin induced visual evoked potentials and lipid peroxidation alterations

PURPOSE

We aimed at investigating the effect of erdosteine administration on amikacin induced visual evoked potentials (VEPs) alterations in rats.

METHODS

For this purpose, forty male Wistar rats were divided into 4 groups: control, amikacin treated, erdosteine treated, and amikacin + erdosteine treated. Amikacin (600 mg/kg/day) was applied as a single dose of intramuscular injection for 14 days, and 10 mg/kg/day erdosteine was given by gastric gavage for the same period. We recorded all VEP components and measured plasma thiobarbituric acid reactive substance (TBARS) levels in all groups.

RESULTS

Amikacin increased the latencies of all VEP components (P1, N1, P2, N2, and P3) and elevated plasma TBARS levels compared with control and erdosteine treated rats (p < 0,01). However, prolonged latencies of VEP components in amikacin treated rats returned to control levels after erdostein administration. Treatment of amikacin and erdosteine together significantly decreased plasma TBARS levels (0.05 ± 0.018 nmol/g protein) compared with amikacin group (0.12 ± 0.038 nmol/g protein).

CONCLUSIONS

These results show that erdosteine has a protective effect on amikacin induced changes in the visual system.

Effects of mecamylamine on flash-evoked potentials, body temperature, and behavior in Long-Evans rats

This experiment examined the effects of mecamylamine, a nicotinic acetylcholine receptor antagonist, on flash-evoked potentials (FEPs) recorded from the visual cortex (VC) and superior colliculus (SC) of chronically implanted male Long-Evans rats, and on body temperature and open field behavior. FEPs were recorded at 20 and 35 min following intraperitoneal injections of saline, and of 0.3, 3.0, and 10.0 mg/kg mecamylamine on separate days. The 0.3 mg/kg dose did not produce significant effects. The amplitude of VC components N₃₀, P₄₈, and P₈₇ increased, N₁₅₀ and P₂₃₁ decreased, and P₂₃, N₄₀, N₅₈, and N₆₈ were unchanged following administration of the 10.0 mg/kg dose. In the SC, component P₂₈ was unaffected, P₃₉ was reduced, and N₄₉ was augmented by the 10.0 mg/kg dose. All component peak latencies were increased by the 3.0 and 10.0 mg/kg doses. Significant hypothermia was also produced by the 3.0 and 10.0 mg/kg doses, suggesting that this was the basis for the increased latencies. The 10.0 mg/kg dose produced a significant decrease in movement during the recording sessions. In subsequent open field observations, both line crossings and rearings were reduced by the 3.0 and 10.0 mg/kg doses. The results suggest that endogenous acetylcholine acting on nicotinic acetylcholine receptors plays at most a modest role in producing FEPs recorded from the VC and SC.

CHANGES IN VISUAL EVOKED POTENTIALS, LIPID PEROXIDATION AND ANTIOXIDANT ENZYMES IN RATS EXPOSED TO RESTRAINT STRESS: EFFECT OF L-CARNITINE

The purpose of our study was to investigate the effects of L-carnitine on lipid peroxidation, Visual Evoked Potentials (VEPs) and antioxidant enzyme activities such as superoxide dismutase and catalase in rats exposed to chronic restraint stress. Forty male Wistar rats, aged three months were used. They were equally divided into four groups: control (C), the group exposed to restraint stress (R), the group treated with L-carnitine(L) and the group exposed to stress and treated with L-carnitine (RL). Chronic restraint stress was applied for 21 days (1 h/day) and L-carnitine (50 mg/kg/day) was given by gavage to the L and RL groups for the same period. Brain and retina levels of thiobarbituric acid reactive substances (TBARS) were significantly increased in the R group and were not altered in the L group compared to the C group. Brain and retina TBARS levels were lower in the RL group than in the R group. Brain and retina superoxide dismutase and catalase activities were significantly decreased in the L and R groups compared to the C group. L-carnitine pretreatment had no significant effect on superoxide dismutase and catalase activity in the RL group. All latencies of VEP components were prolonged in the R and L groups with respect to the C group. L-carnitine increased the latencies of all VEP components in the L group whereas shortened them in the RL group compared to their control groups. L-carnitine may be a promising agent for the prevention of VEP and TBARS alterations caused by stress.

Baclofen does not counteract the acute effects of ethanol on flash-evoked potentials in Long-Evans rats

This experiment examined the separate and combined effects of baclofen (5.0 mg/kg, i.p.), a GABA B receptor agonist, and ethanol (2.0 g/kg, i.p.) on flash-evoked potentials (FEPs) recorded from both the visual cortex and superior colliculus (SC) of chronically implanted male Long-Evans rats. In the visual cortex, ethanol significantly decreased the amplitude of positive component P87, but increased P37 and P47. Other component amplitudes were not significantly altered. In contrast, baclofen reduced the amplitude of negative component N31 to such an extent that it became positive. Although P47 was also reduced by baclofen, the amplitude of most other components was increased. Only P24 and P87 were unchanged by baclofen. The combination of baclofen and ethanol resulted in amplitudes very similar to ethanol alone for secondary components P47, N62, and P87, but very similar to baclofen alone for primary component N31 and late components N147 and P230. In the SC, component amplitudes were generally decreased by ethanol, baclofen, and the combination treatment. Latencies of most components in both structures were increased by the drug treatments. Each drug treatment produced significant hypothermia. Locomotor behavior was also altered. These results demonstrate: (1) pharmacological differences between the primary and late components versus the secondary components of the cortical FEP, (2) that baclofen does not counteract significant effects of ethanol on cortical or collicular component amplitudes, and (3) that baclofen enhances N147-P230 amplitude, suggesting reduced cortical arousal.

Exercise improves visual deficits tested by visual evoked potentials in streptozotocin-induced diabetic rats

Visual evoked potentials (VEP) can be used as an objective non-invasive method to study the electrical activity of the visual system. Latency and amplitude measurements of VEP demonstrated that diabetes mellitus has been associated with increases in the latencies whereas the amplitude measurements revealed contradictory results. Although physical exercise has been reported to reduce the complications of diabetes mellitus, the effect of exercise on the visual system remains unknown. We investigated the effects of long-term moderate physical exercise on VEP in streptozotocin (STZ)-diabetic rats. We also measured brain thiobarbituric acid-reactive substances (TBARS) to explore the possible contribution of lipid peroxidation on the visual system. Animals were divided into four groups: control (C), control exercise (CE), diabetic (D) and diabetic exercise (DE) groups. Diabetes was induced by a single intraperitoneal injection of STZ (60 mg/kg). Three days after the confirmation of diabetes, DE and CE groups were trained by running on a motor-driven treadmill with a progressive eight-week programme. The animals began running at 10 m/min, 0 degrees slope, 10 min/day and reached a level of 28 m/min, 6 degrees slope, 60 min/day by week 8. TBARS were elevated and VEP latencies were delayed in diabetic rats, indicating diabetes-induced defects in the optic pathway. These prolonged latencies were restored by exercise training. VEP amplitudes of the DE group were found unaltered with the exception of a decrement in P(2)N(2) which represents an early component of VEP, suggesting that exercise improves visual system defects in diabetic animals at different levels of the optic pathway.

Effect of aminoguanidine on visual evoked potentials (VEPs), antioxidant status and lipid peroxidation in rats exposed to chronic restraint stress

The purpose of the study was to investigate the effect of aminoguanidine (AG) on visual evoked potentials (VEPs), thiobarbituric acid reactive substances (TBARS), the activities of Cu, Zn superoxide dismutase (Cu,Zn-SOD), glutathione peroxidase (GSH-Px) and catalase (CAT), and nitrite/nitrate levels. Forty healthy male Wistar rats, aged 3 months, were divided into four equal groups: Control (C), the group treated with aminoguanidine (A), the group exposed to restraint stress (S), the group exposed to restraint stress and treated with aminoguanidine (AS). Chronic restraint stress was applied for 21 days (1 h/day) and aminoguanidine (50 mg/kg/day) was injected intraperitoneally to the A and AS groups for the same period. Aminoguanidine treatment significantly decreased retina and brain TBARS levels in rats exposed to restraint stress compared to rats exposed to restraint stress alone. Aminoguanidine treatment produced a significant decrease in brain and retina nitrite and nitrate levels with respect to the control groups. Aminoguanidine increased all antioxidant enzyme activities in both brain and retina in rats exposed to restraint stress compared to rats exposed to restraint stress alone. All VEP components were significantly decreased in AG treated rats exposed to restraint stress compared to rats exposed to restraint stress alone. Our study clearly showed that AG has the potential to prevent changes caused by stress.

Baclofen alters flash-evoked potentials in Long–Evans rats

This experiment examined the effects of the GABA-B agonist baclofen on flash-evoked potentials (FEPs) recorded from both the visual cortex (VC) and superior colliculus (SC) of chronically implanted male Long-Evans rats. FEPs were recorded at 5, 25, 45, and 65 min following intraperitoneal injections of saline, and of 1.25, 2.5, 5.0, and 10.0 mg/kg baclofen on separate days. In the VC, the amplitude of components P(23), P(37), N(55), N(150), and P(242) increased, while the amplitude of components N(31) and P(48) decreased following baclofen administration. P(88) was unchanged. In the SC, components P(28), N(49), N(55), and N(59) were reduced in amplitude, while P(39) was unaffected by baclofen. These effects on amplitudes were dose- and time-dependent. Many peak latencies in the VC and SC were altered by baclofen, although there was no obvious pattern of change, with some decreasing, a few increasing, and others unchanged. Body temperature was recorded in a separate group of animals, with both the 5.0 and 10.0 mg/kg doses of baclofen producing significant hypothermia. The 10.0 mg/kg dose of baclofen resulted in a significant decrease in movement during the recording sessions, but not in subsequent open field observations. The results show the involvement of GABA-B receptors in the production/modulation of the various components of FEPs.

The role of docosahexaenoic acid on visual evoked potentials in one kidney-one clip hypertension

PURPOSE

To investigate the effects of polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA) on visual evoked potentials (VEPs) in a one kidney-one clip (1K-1C) hypertension model in rats.

METHODS

Five experimental groups were formed: a control group, a sham group, a group supplemented with DHA, a 1K-1C group, and a 1K-1C + DHA group. The DHA groups were treated for 60 days. In the 1K-1C groups, the right kidney was removed and a silver clip with a 0.2-mm gap was placed on the left renal artery.

RESULTS

The DHA-supplemented rats had lower blood pressure than their respective controls (p < 0.01). The increased brain and retina thiobarbituric acid reactive substances (TBARS) levels in hypertensive rats were abolished by DHA administration. The brain nitrite levels were lower in the DHA, 1K-1C and 1K-1C + DHA groups compared with the control group (p < 0.01), and the retina nitrite level was higher in the 1K-1C + DHA group compared with the DHA and 1K-1C groups (p < 0.01). There was an improvement of P(2), N(2) and P(3) components following DHA supplementation in 1K-1C hypertensive rats compared with the 1K-1C group.

CONCLUSION

The present study suggests that DHA supplementation has the potential to prevent VEP changes caused by an experimental model of hypertension. This state might be related to the lipid peroxidation lowering effect of DHA.

Nicotine-ethanol interactions in flash-evoked potentials and behavior of Long-Evans rats

Although nicotine and ethanol are often used together, little is known about their combined effects on visual system electrophysiology. This experiment examined the separate and combined effects of nicotine and ethanol on flash-evoked potentials (FEPs) recorded from both the visual cortex (VC) and superior colliculus (SC) of chronically implanted male Long-Evans rats. There were four treatment conditions administered on separate days: either saline or ethanol (2.0 g/kg, i.p.) was given 10 min before either saline or nicotine (1.0 mg/kg, s.c.). FEPs were recorded at 5, 20, and 40 min following the second injection. In the VC, ethanol significantly decreased the amplitude of most components, but increased P46. Peaks P22 and N53 were unchanged. Nicotine enhanced most component amplitudes, but decreased N29 and P234, while P22 and N139 were unchanged. In the SC, ethanol depressed the amplitude of all components studied. In contrast, nicotine significantly depressed only P27 and N48. Latencies of most components in both structures were increased by ethanol, nicotine, and the combination treatment, although a nicotine-induced enhancement of the effects of ethanol on latencies was not typically observed. Each drug treatment also produced significant hypothermia, with the combination treatment resulting in the greatest hypothermia. Ethanol, either alone or in combination with nicotine, significantly reduced body movements during the FEP recording sessions. In subsequent open-field observations, ethanol, but not nicotine, significantly increased the number of squares crossed, while the combination treatment produced the greatest increase in movement. Nicotine significantly increased rearing behavior, but both ethanol and the combination treatment eliminated rearings. Overall, data suggesting that nicotine can counteract some of the effects of ethanol was demonstrated in varying degrees in the amplitude of VC components N39, P46, N53, N65, and P88, the latency of VC component N53, the amplitude of SC component N59, and the latency of SC components N48 and N54. In contrast, a nicotine-induced enhancement of the effects of ethanol was found for only the latency of VC components N39, P88, and P234, body temperature, and open-field ambulation.

The effect of chronic restraint stress and sulfite on visual evoked potentials (VEPs): Relation to lipid peroxidation

Stress and sulfite can stimulate numerous pathways leading to an increased production of free radicals which generate a peroxidation cascade producing lipid peroxidation, protein oxidation, DNA damage and cell death, and contribute to the occurrence of pathologic conditions. The purpose of our study was to investigate the effects of stress and sulfite on visual evoked potentials (VEPs) and to examine the relationship between lipid peroxidation and VEP changes. Forty male wistar rats, aged three months were used. They were equally divided into four groups: control (C), the group exposed to restraint stress (R), the group treated with sulfite (S) and the group exposed to stress and treated with sulfite (RS). Chronic restraint stress was applied for 21 days (1h/day) and sodium metabisulfite (520 mg/kg/day) was given by gavage for the same period. All latencies of VEP components were prolonged in the R, S and RS groups with respect to the C group. Brain and retina TBARS levels were found to be increased in those groups compared to the C group. Our results strongly suggest that the latency prolongations of all VEP components may have resulted from the enhancement of lipid peroxidation. Correlation analysis between brain and retina TBARS levels and VEP latencies also support this conclusion. Our data in regard to latency prolongations of all VEP components in the stress group exposed to sulfite, reflected an additive effect of sulfite toxicity on VEP components. Therefore it could be suggested that chronic exposure to stress and sulfite together is associated with a considerable health risk.

Neurotoxicity of carbonyl sulfide in F344 rats following inhalation exposure for up to 12 weeks

Carbonyl sulfide (COS), a high-priority Clean Air Act chemical, was evaluated for neurotoxicity in short-term studies. F344 rats were exposed to 75-600 ppm COS 6 h per day, 5 days per week for up to 12 weeks. In rats exposed to 500 or 600 ppm for up to 4 days, malacia and microgliosis were detected in numerous neuroanatomical regions of the brain by conventional optical microscopy and magnetic resonance microscopy (MRM). After a 2-week exposure to 400 ppm, rats were evaluated using a functional observational battery. Slight gait abnormality was detected in 50% of the rats and hypotonia was present in all rats exposed to COS. Decreases in motor activity, and forelimb and hindlimb grip strength were also detected. In rats exposed to 400 ppm for 12 weeks, predominant lesions were in the parietal cortex area 1 (necrosis) and posterior colliculus (neuronal loss, microgliosis, hemorrhage), and occasional necrosis was present in the putamen, thalamus, and anterior olivary nucleus. Carbonyl sulfide specifically targeted the auditory system including the olivary nucleus, nucleus of the lateral lemniscus, and posterior colliculus. Consistent with these findings were alterations in the amplitude of the brainstem auditory evoked responses (BAER) for peaks N3, P4, N4, and N5 that represented changes in auditory transmission between the anterior olivary nucleus to the medial geniculate nucleus in animals after exposure for 2 weeks to 400 ppm COS. A concentration-related decrease in cytochrome oxidase activity was detected in the posterior colliculus and parietal cortex of exposed rats as early as 3 weeks. Cytochrome oxidase activity was significantly decreased at COS concentrations that did not cause detectable lesions, suggesting that disruption of the mitochondrial respiratory chain may precede these brain lesions. Our studies demonstrate that this environmental air contaminant has the potential to cause a wide spectrum of brain lesions that are dependent on the degree and duration of exposure.

Effects of N-nitro l-arginine methyl ester (l-NAME), a potent nitric oxide synthase inhibitor, on visual evoked potentials of rats exposed to different experimental stress models

AIM

The aim of our study was to investigate the effects of the nitric oxide synthase inhibitor, N-nitro l-arginine methyl ester (l-NAME, 10 mg kg-1 day-1 i.p.), on visual evoked potentials (VEPs) and lipid peroxidation expected to occur during chronic stress (15 days).

METHODS

Eight experimental groups, each consisting of 10 rats, were formed: control group (C), the group injected with l-NAME (L), groups exposed to cold stress (CS), immobilization stress (IS), and both cold and immobilization stress (CIS), groups exposed to stress and injected with l-NAME (CSL, ISL, CISL).

RESULTS

l-NAME decreased brain and retina nitrite levels in all experimental groups compared with their corresponding control groups. l-NAME decreased glutathione peroxidase (GSH-Px) activity in the brain and retina in the L group, but increased it in the CSL and CISL groups compared with the C group. Lipid peroxidation was increased in the brain and retina tissues of all stress groups with respect to the C group. l-NAME markedly increased brain thiobarbituric acid reactive substances (TBARS) levels in the L group, while significantly decreasing brain and retina TBARS levels in all stress groups in comparison with their respective control groups. l-NAME caused a significant delay in all components of VEPs in the L group compared with the C group. However, l-NAME significantly decreased latencies of P1, N1, P2 and P3 components in the CSL group and all components in the ISL and CISL groups with respect to their corresponding control groups.

CONCLUSION

This study clearly indicated that lipid peroxidation may be one possible factor affecting VEP components.

Nicotine alters flash-evoked potentials in Long–Evans rats

This experiment examined the effects of nicotine on flash-evoked potentials (FEPs) recorded from both the visual cortex (VC) and the superior colliculus (SC) of chronically implanted male Long-Evans rats. FEPs were recorded at 5, 20, 40, and 60 min following subcutaneous injections of saline, and of 0.4, 0.7, and 1.0 mg/kg nicotine on separate days. In the VC, the amplitude of components N(39), N(53), N(67), and P(88) increased, while the amplitude of components N(30) and P(235) decreased following nicotine administration. P(22), P(47), and N(153) were unchanged. In the SC, components P(27), N(48), and N(53) were reduced in amplitude, while P(37) and N(57) were unaffected by nicotine. Many peak latencies in the VC and SC were increased by nicotine, often at all three doses. However, effects of nicotine on FEPs were both dose- and time-dependent. When body temperature was recorded 65 min after drug administration, significant hypothermia was found with both the 0.7- and 1.0-mg/kg nicotine doses. The 1.0-mg/kg dose of nicotine resulted in a significant increase in movement during the recording sessions, but not in subsequent open-field observations. The results demonstrate that nicotinic acetylcholine receptors (nAChRs) play a differential role in the production/modulation of the various components of FEPs.

The effects of ageing and sulfur dioxide inhalation exposure on visual-evoked potentials, antioxidant enzyme systems, and lipid-peroxidation levels of the brain and eye

The effects of ageing and 10 ppm sulfur dioxide (SO(2)) inhalation exposure on visual-evoked potentials (VEPs), thiobarbituric acid reactive substances (TBARS), a product of lipid peroxidation, and the activities of Cu, Zn superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) of brain and eye were investigated in young (3-month), adult (12-month), and mature (24-month) Swiss male albino rats. The experimental groups were placed in an exposure chamber containing a constant level of 10 ppm SO(2), while control groups were placed in an exposure chamber, which was continually pumped with filtered air, for 1 h/day x 7 days/week for 6 weeks. SO(2) inhalation exposure caused increased levels of brain, retina, and lens Cu, Zn SOD activity, and decreased levels of brain and lens GSH-Px activity in all experimental groups with respect to their corresponding control groups, whereas no change was observed in the level of retina GSH-Px activity. No alterations were observed in brain CAT activity. On the other hand, retina CAT activity was slightly decreased in SO(2)-exposed rats, but no change was observed in their lens CAT activity. The brain and lens TBARS levels of all SO(2)-exposed groups were significantly increased in comparison with their respective control groups. The amount of TBARS was only increased in the retina of the SO(2)-exposed 3-month group compared with its control. Of the SO(2)-exposed rats, the mean latencies of the P(1), N(1), P(2), and P(3) components of the 3-month group, P(1), N(1), and N(2) components of the 12-month group, and only P(3) of the 24-month group were significantly prolonged in comparison with those of their control groups. The amplitudes of N(1)P(2) and P(2)N(2) in the 12- and 24-month control groups were significantly decreased compared with those of the 3-month group. On the other hand, no differences were observed among those of SO(2)-exposed groups. These findings suggest that ageing and SO(2) inhalation exposure have the potential to induce antioxidant enzymes in the brain and eye, and VEP alterations, which are the primary target for air pollutants. It could be concluded that lipid peroxidation could play a critical role in the mechanism responsible for VEP alterations with ageing.

The effect of vitamin E on stress-induced changes in visual evoked potentials (VEPs) in rats exposed to different experimental stress models

PURPOSE

The aim of the study was to investigate the effects of vitamin E on stress-induced changes in visual evoked potentials (VEPs) and lipid peroxidation.

METHODS

Eight experimental groups of 10 rats per group were formed. These consisted of the control group (C); the group treated with vitamin E (E); groups exposed to cold stress (CS), immobilization stress (IS) and both cold and immobilization stress (CIS), and groups exposed to equivalent stresses and treated with vitamin E (CSE, ISE, CISE). Vitamin E was injected intramuscularly in a dose of 30 mg/kg/day.

RESULTS

Following chronic stress (15 days), plasma corticosterone concentrations in all experimental groups were significantly increased over those in C group. Vitamin E significantly decreased corticosterone levels in all stress groups compared with their respective control groups. Brain nitrite levels were significantly more elevated in all stress groups than in the C group. Vitamin E reduced retina and brain nitrite levels in all stress and E groups compared with their respective control groups. Vitamin E decreased glutathione peroxidase (GSH-Px) activity in retina and brain tissues in the CSE group, but increased it in the ISE group compared with their respective control groups. Lipid peroxidation was increased in brain and retina tissues in all stress groups as indicated by the significant increase in thiobarbituric acid-reactive substance (TBARS) levels with respect to the C group. Vitamin E produced a significant decrease in brain and retina TBARS levels in all stress groups with respect to their corresponding control groups. The mean latencies of P1, N1, P2, N2 and P3 components were significantly prolonged in all stress groups compared with the C group.

CONCLUSION

Vitamin E returned the VEP latencies in the stress groups to control values. Our findings clearly indicated that vitamin E has the potential to prevent VEP changes caused by stress.

Flash-, somatosensory-, and peripheral nerve-evoked potentials in rats perinatally exposed to Aroclor 1254

Pregnant Long-Evans rats were exposed to 0, 1 or 6 mg/kg/day of Aroclor 1254 (A1254; Lot no. 124-191), a commercial mixture of polychlorinated biphenyls (PCBs), from gestation day (GD) 6 through postnatal day (PND) 21. At 128-140 days of age, male and female offspring were tested for visual-, somatosensory- and peripheral nerve-evoked potentials. The evoked responses increased in amplitude with larger stimulus intensities, and gender differences were detected for some endpoints. In contrast, developmental exposure to A1254 failed to significantly affect the electrophysiological measures. A subset of the animals were tested for low-frequency hearing dysfunction using reflex modification audiometry (RMA). An elevated threshold for a 1-kHz tone was observed, replicating previous findings of A1254-induced auditory deficits [Hear. Res. 144 (2000) 196; Toxicol. Sci. 45(1) (1998) 94; Toxicol. Appl. Pharmacol. 135(1) (1995) 77.]. These findings indicate no statistically significant changes in visual-, somatosensory- or peripheral nerve-evoked potentials following developmental exposure to doses of A1254 that produce behavioral hearing deficits. However, subtle changes in the function of the visual or somatosensory systems cannot be disproved.

Effects of ethanol on flash-evoked potentials of rats: lack of antagonism by naltrexone

The present study examined the effects of ethanol and naltrexone hydrochloride (a nonselective opiate receptor antagonist) on flash-evoked potentials recorded from both the visual cortex (VC) and the superior colliculus (SC) of chronically implanted hooded rats. There were four treatment conditions administered on separate days: Either saline or naltrexone (10 mg/kg; volume of 1.0 ml/kg) was given 10 min before either saline or ethanol (2.0 g/kg; 20% ethanol solution in a volume of 1.26 ml/100 g). Evoked potentials were recorded 15 min after the intraperitoneal injections were completed. Animals were tested at 23.1 degrees C room temperature. In the VC, ethanol significantly decreased the amplitude of components N1, P3, and N3, whereas it increased the amplitude of P2. Components P1 and N2 were unaffected by ethanol treatment. The SC components P3 and N4 were reduced in amplitude by ethanol, but component P1 was not altered. Latencies of all components in both structures were increased by ethanol. Naltrexone alone did not significantly affect the potentials, nor did naltrexone pretreatment significantly alter the effects of ethanol on the potentials. Naltrexone produced a modest hypothermia of about 0.25 degrees C, whereas ethanol resulted in hypothermia of about 1.0 degrees C. Ethanol, either alone or in combination with naltrexone, significantly reduced body movement during the evoked-potential recording sessions. The results indicate that endogenous opioid systems do not play a major role in the acute effects of ethanol on flash-evoked potentials recorded from primary areas of the visual system.

Temperature dependence and independence of effects of pentobarbital on visual evoked potentials of rats

Visual cortex flash evoked potentials (FEPs), pattern reversal evoked potentials (PREPs), and body temperature were measured in hooded rats following IP injections on separate days of saline, and of 15 and 30 mg pentobarbital/kg body weight. Two experiments were performed, differentiated by standard (23 degrees C) and warm (31 degrees C) room temperatures. The 30 mg/kg dose produced hypothermia of 2.6 degrees C in the standard environment, but not in the warm environment. Early components of FEPs were generally increased in amplitude by the 15 mg/kg dose, and decreased by the 30 mg/kg dose at 23 degrees C. At 31 degrees C, the 30 mg/kg dose did not decrease early component amplitude, suggesting that hypothermia can potentiate some effects of pentobarbital. Amplitudes of late FEP components were depressed at both ambient temperatures. The main PREP components N1P1 and P1N3 were increased in amplitude by the 15 mg/kg dose, but returned to near baseline levels at 30 mg/kg, at both temperatures. PREP component N2P2 was reduced in amplitude by the 30 mg/kg dose only at 23 degrees C. Treatment with 30 mg/kg pentobarbital increased FEP and PREP latencies at both ambient temperatures, but the magnitudes of the increases at 31 degrees C were typically less than half those observed at 23 degrees C. These results indicate that hypothermia contributes to some pentobarbital-induced changes in both FEPs and PREPs, but that pentobarbital also produces effects independent of hypothermia.

Cortical and thalamic visual evoked potentials during sleep-wake states and spike-wave discharges in the rat

Flash visual evoked potentials (VEP) were simultaneously recorded from the primary visual cortex and the dorsal lateral geniculate nucleus in freely-moving WAG/Rij rats, to investigate whether the thalamic VEP shows the same state-dependent alterations as the cortical VEP. VEPs obtained during active and passive wakefulness (AW and PW), slow-wave sleep (SWS), REM sleep and during the occurrence of spike-wave discharges (SWD), a specific trait of the genetically epileptic WAG/Rij rat, were compared. The general architecture of the thalamic VEP resembles the cortical VEP, although its polarity is reversed. This facilitated the interpretation of components in terms of underlying neuronal events. The primary excitation peak is differently modulated in cortex and thalamus. Whereas the thalamic component (P30) is not affected by brain-state, the cortical component (N1) shows a strong increase in latency during SWS and SWD. In contrast, the modulation of later components is highly similar for cortex and thalamus. VEPs obtained during AW and REM resemble each other. During SWS and SWD there is a considerable, and during PW a moderate, enlargement of primarily inhibitory components. After-discharges are enhanced during SWS, SWD and REM. No evidence is found for a major impairment of sensory transmission during SWD.

The effects of cadmium and experimental diabetes on VEP spectral data and lipid peroxidation

Fifty-two healthy swiss male albino rats, aged three months were used in this study. They were divided into four groups: Control (C), diabetic (D), Cadmium (Cd) and diabetic + Cadmium (D + Cd) groups. Diabetic condition was induced in D and D + Cd groups by administration of alloxane (5 mg/100 g). After this treatment, Cd and D + Cd groups were injected with CdCl2 i.p. (2 mg/kg/week). At the end of the two months of experimental period, flash visual evoked potentials (FVEPs) of four groups were recorded and amplitude spectral analysis was computed by transient response-frequency characteristics (TRFC) method. Significant amplitude decrement was found in 2-4 Hz frequency band of D + Cd group in comparison with C group. On the other hand, our data showed that Cd treatment and diabetic condition caused a significant increase of lipid peroxidation in kidney, brain, retina and lens.

The effect of developmental exposure to cadmium (Cd) on visual evoked potentials (VEPs) and lipid peroxidation

Pregnant Swiss albino rats were divided into three groups: control (C), gestational exposure of Cd (G-Cd), and gestational/postnatal exposure of Cd (GP-Cd) groups. Control animals received tap water, and the rats of GP-Cd group received Cd as CdC12 in their drinking water during the experimental period. The G-Cd group was given Cd during pregnancy, but given tap water after birth. Twenty-two days after birth, 15 rats (for each group) were taken from their mothers and continued to be treated with Cd (GP-Cd group) or tap water (C and G-Cd groups) for an additional 38 days. On postnatal day (PND) 60, flash visual evoked potentials (FVEPs) were recorded with disc electrodes attached with collodion 0.5 cm in front of and behind bregma. The mean latencies on N1, P2, and P3 were prolonged in the GP-Cd group compared with controls. The mean latency of P3 was also significantly different between G-Cd and GP-Cd groups. P1-N1 and N1-P2 amplitudes of VEPs were significantly decreased in the GP-Cd group compared with control group. N1-P2 amplitude of the G-Cd group was significantly lower than that of the control group. Thiobarbituric acid reactive substances (TBARS) were determined as an indicator of lipid peroxidation. Our data showed that pre- and postnatal Cd treatment caused a significant increase of lipid peroxidation in the brain.

Possible confounding effects of strobe "clicks" on flash evoked potentials in rats

Flash evoked potentials (FEPs) undergo within- and between-session changes and are modified by auditory white noise (26). We examined whether an auditory potential produced by the "click" associated with the strobe discharge could be recorded, and if alterations in an auditory response could explain the within- and between-session changes in FEPs. We also examined differences between a frontal cortex or a nasal reference electrode location on FEPs and auditory potentials. An auditory potential associated with the strobe discharge could be clearly recorded. This response was eliminated by the presence of 80 dB SPL masking white noise. However, the within- and between-session changes in FEPs could not be explained by modifications of the auditory potential. Animals whose ear drums were ruptured did not exhibit an auditory response, and their FEPs were similar to those of controls tested in the presence of masking white noise. A nasal reference electrode decreased the impact of auditory potentials on FEPs, but allow visual potentials (electroretinogram and optic tract activity) to influence FEPs. The data show that auditory potentials associated with the strobe discharge can be recorded from the visual cortex of rats, and that these auditory responses represent a possible confounding factor in the interpretation of toxicological studies employing FEPs.

Acute effects of ethanol on pattern reversal and flash-evoked potentials in rats and the relationship to body temperature

The effects of acute ethanol treatment on flash and pattern reversal visual evoked potentials (FEPs and PREPs, respectively) were examined in three experiments using Long-Evans rats. The relationships of evoked potential parameters with blood ethanol concentration and body temperature were examined. In Experiment 1, rats were treated i.p. with vehicle or 0.5, 1.0 or 2.0 g ethanol/kg body weight, and tested 30 min later. The 2.0 g/kg group had prolonged latencies of PREP peaks, no changes in PREP peak-to-peak amplitudes, and lower body temperatures than saline-treated controls. The peak latency shifts were significantly correlated with both blood ethanol concentration and body temperature, and were of a magnitude to be expected from similar changes in body temperature alone. Experiment 2 measured both PREPs and paired-flash FEPs in rats 30 min after injection of either 0, 0.5 or 2.0 g/kg ethanol. PREP changes were found following treatment with the high dose which were similar to those of Experiment 1. Some FEP peak latencies were prolonged and peak-to-peak amplitudes were reduced by both doses of ethanol, despite the fact that body temperatures were reduced at only the high dose. At 2.0 g/kg ethanol, the FEP changes in latency, but not amplitude, were in accordance with what would be expected from body temperature changes alone. The third study attempted to investigate the role of reduced body temperature in producing the visual evoked potential changes by testing at room temperatures of 22 or 30 degrees C. Contrary to expectations, the rats receiving 2 g/kg ethanol were approx. 1 degree C cooler than controls at both room temperatures. Evoked potential latencies were greater in ethanol-treated rats than controls at both room temperatures. There were no significant effects of ethanol on FEP amplitudes. Overall, the effects of low doses of ethanol were independent of temperature changes, but the effects of higher doses of ethanol (2.0 g/kg) could not be distinguished from those produced by differences in body temperature alone.

The effects of low-pass filtering on the flash visual evoked potential of the albino rat

Flash visual evoked potentials (FVEPs) were recorded from the rat in order to determine the effects of low-pass filtering on the wave form. The low-frequency (high pass) filter remained fixed at 3.2 Hz while the setting of the high-frequency (low-pass) filter was progressively raised from 32 Hz to 3.2 kHz. The amplitude of the primary cortical potential (P30) steadily increased while its latency decreased until asymptotic values were recorded with a low-pass cut-off of 320 Hz. Thereafter, there was little additional change in wave form. It is concluded that a bandpass of 3.2-320 Hz is optimal to record the primary cortical response of the FVEP, and this is consistent with the theory that the P30 potential is generated by comparatively slow post-synaptic activity. In a second experiment the effects of low-pass filtering were examined on the later and more labile secondary components of the FVEP wave form. These were found to be less responsive to low-pass filtering than the early components and assumed a near optimal configuration when the high-frequency cut-off was raised to 80 Hz. The high-frequency filter setting which is most appropriate to record the primary component of the FVEP therefore appears to be more than adequate also to record the secondary responses. It is also shown that the same principles of low-pass filtering on the FVEP will apply irrespective of whether the subject is awake or anaesthetised.

Thermal influences on nervous system function

The various effects of temperature change are only partially predictable. Temporal measures relevant to membrane activity, action potentials, synaptic transmission, and evoked potentials are all consistently increased with cooling and decreased by warming. However, the various measures of amplitude at different levels, and even within similar preparations, are contradictory: Some laboratories report increased amplitudes with cooling and others report decreased amplitudes under similar conditions. Emphasis is given to identifying factors that may resolve the differences. These include: (a) the rate of temperature change, (b) sites of cooling, stimulation and recording, (c) stimulus characteristics, and (d) fundamental differences in temperature sensitivities of different neural tissue. Other factors that may affect the ability to predict thermal influences on neural function from existing formulations are: relative ion permeabilities, metabolic ion pumps, the resting potential at the onset of cooling, and an animal's acclimated temperature at sacrifice.

Auditory potentials elicited by the grass photic stimulator in the rat

Flash visual evoked potentials were recorded from the rat to determine whether the Grass photic stimulator could generate an auditory component of the waveform. When the click associated with each lamp flash remained unmuffled, the primary response of the visual cortex (P30) was preceded by an earlier positivity with a latency between 6-8 ms. When the photic stimulator lamp was subsequently insulated in order to deaden the sound of the click, the P30 potential remained intact while the earlier response disappeared. It is concluded that the photic stimulator is capable of eliciting a distinct auditory potential of probable collicular origin.

Abnormalities of the electroretinogram and visual-evoked potential in vitamin E deficient rats

Flash electroretinograms, retinal oscillatory and cortical visual-evoked potentials were recorded in 10-month vitamin E deficient rats and in age-matched controls. A significant increase in the latency (P less than 0.0001) and decrease in amplitude (P less than 0.0001) of the electroretinogram a- and b-waves were observed in the vitamin E deficient rats compared with controls. The vitamin E deficient rats also showed a significant delay (P less than 0.002) in early oscillatory potentials. No significant group differences were obtained in the P1 latency or P1-N1 amplitude of the visual-evoked potential; however, the N1 peak was significantly delayed (P = 0.01) in the vitamin E deficient rats. This study shows, for the first time, that the electroretinogram and visual-evoked potential to flash stimulation provide a sensitive index for monitoring the visual effects of vitamin E deficiency in the rat.

Differential impact of hypothermia and pentobarbital on brain-stem auditory evoked responses

Two experiments were conducted to determine the effects of hypothermia and pentobarbital anesthesia, alone and in combination, on the brain-stem auditory evoked responses (BAERs) of rats. In experiment I, unanesthetized rats were cooled to colonic temperatures 0.5 and 1.0 degrees C below normal. In experiment II, 2 groups of rats were cooled and tested at 37.5, 36.0, 34.5 and 31.5 degrees C. One group was anesthetized during testing and the other group was awake. The rat BAER was sensitive to cooling of 1 degree C or less. Peak latencies were prolonged and peak-to-peak amplitudes were increased by hypothermia alone. The effect on amplitude may be related to the time course of temperature change or to stimulus level. Pentobarbital significantly affected both latencies and amplitudes over and above the effects of cooling. The specific effects of pentobarbital differed by BAER peak and by temperature. The findings point up the importance of the potential confound of anesthetic drugs in most of the evoked potential literature on hypothermia and, for the first time, quantify the complex interactions between pentobarbital and temperature which affect the BAER wave form.

P300 and time of day: circadian rhythms, food intake, and body temperature

The P300 or P3 component of the event-related brain potential (ERP) was obtained from five groups of 24 young adult subjects, with each group measured at a different time of day (8 a.m., 11 a.m., 2 p.m., 5 p.m., 8 p.m.). An activity-preference questionnaire was used to ensure that an equitable number of morning- and evening-preferring subjects were obtained for each testing time. P3 measures, physiological (body temperature, heart rate, subjective alertness), and cognitive performance (digit span, prose memory, digit symbol) variables were assessed. P3 amplitude and latency were not affected directly by the time of day. However, P3 amplitude was smaller in subjects who had not eaten within 6 hours of testing relative to subjects who had a recent meal, and P3 latency was correlated negatively with body temperature. The findings suggest that although the P3 ERP is not influenced by circadian rhythms, it is related to recency of food intake and physiological factors which change with time of day.