Homeostatic response to sleep/rest deprivation by constant water flow in larval zebrafish in both dark and light conditions.

Sleep-or sleep-like states-have been reported in adult and larval zebrafish using behavioural criteria. These reversible quiescent periods, displaying circadian rhythmicity, have been used in pharmacological, genetic and neuroanatomical studies of sleep-wake regulation. However, one of the important criteria for sleep, namely sleep homeostasis, has not been demonstrated unequivocally. To study rest homeostasis in zebrafish larvae, we rest-deprived 1-week-old larvae with a novel, ecologically relevant method: flow of water. Stereotyped startle responses to sensory stimuli were recorded after the rest deprivation to study arousal threshold using a high-speed camera, providing an appropriate time resolution to detect species-specific behavioural responses occurring in a millisecond time-scale. Rest-deprived larvae exhibited fewer startle responses than control larvae during the remaining dark phase and the beginning of the light phase, which can be interpreted as a sign of rest homeostasis-often used as equivalent of sleep homeostasis. To address sleep homeostasis further, we probed the adenosinergic system, which in mammals regulates sleep homeostasis. The adenosine A1 receptor agonist, cyclohexyladenosine, administered during the light period, decreased startle responses and increased immobility bouts, while the adenosine antagonist, caffeine, administered during the dark period, decreased immobility bouts. These results suggest that the regulation of sleep homeostasis in zebrafish larvae consists of the same elements as that of other species.

Trans-canal laser irradiation reduces tinnitus perception of salicylate treated rat.

The aim of this study was to find out the effect of low-level laser therapy (LLLT) on salicylate-induced tinnitus in the rat model. Fourteen Sprague-Dawley rats (8 weeks; 240-280 gm) were divided into 2 groups (study group, control group). Rats of both groups were treated with 400 mg/kg/day of sodium salicylate for 8 consecutive days. Tinnitus was monitored using GPIAS (Gap Prepulse Inhibition of Acoustic Startle) 2 h after first salicylate treatment, and every 24 h during 9 days of treatment. Rats in laser group were irradiated to each ear with wavelength of 830 nm diode laser (165 mW/cm(2)) for 30 min daily for 8 days. During salicylate treatment, rats of study group irradiated with low level laser showed significantly higher GPIAS values throughout the experiment. Therapeutic effect of LLLT is demonstrated in animal tinnitus model by means of GPIAS. Further experimental studies are needed to find possible mechanisms and better methods to improve LLLT efficacy.

A common genetic predisposition to stress sensitivity and stress-induced nicotine craving.

BACKGROUND: Clinical studies have shown that stress is one of the main causes for relapse in abstinent smokers. In this article, we have asked whether animals with a genetic predisposition to high or low stress responsivity differ in behaviors relevant to nicotine addiction, in particular stress-induced reinstatement of drug addiction. METHODS: First, we selected animals with high, low, and average stress sensitivity from the F2 generation from an intercross of high (C57BL/6J) and low (C3H/J) emotional mouse strains. Next, these animals were trained to self-administer nicotine through a chronic intravenous catheter. After extinction of the operant behavior replacing nicotine with saline, mice were stressed with a foot shock and the reinstatement of drug-seeking behaviors was evaluated. RESULTS: Mice with different stress reactivity showed no difference in the acquisition, extinction, or level of nicotine self-administration. We found an immediate reinstatement of drug-seeking behavior in high stress reactive mice, in contrast to low or average stress reactive animals, which showed no significantly increased activity at the active (nicotine-associated) sensor. CONCLUSIONS: We conclude that a genetic predisposition to high stress sensitivity contributes to relapse vulnerability but not to the initiation or maintenance of nicotine consumption.

Spontaneous nicotine withdrawal potentiates the effects of stress in rats.

Anxiety is a common symptom of nicotine withdrawal in humans, and may predict an inability to abstain from cigarette smoking. It is not clear if self-reports of anxiety during abstinence reflect increased baseline anxiety and/or increased responses to exogenous stressors. We hypothesized that nicotine withdrawal selectively exacerbates reactivity to aversive stimuli in rodents. Here, we investigated the effect of withdrawal from chronic nicotine administration (3.16 mg/kg per day base, delivered via subcutaneous osmotic minipumps) in the light-enhanced startle (LES) test in Wistar rats. In this procedure, baseline startle responding in the dark is compared to startle responding when the chamber is brightly lit. Bright illumination is aversive for rats and potentiates the startle response. Hence, this procedure allows comparisons of withdrawal effects on startle reactivity between relatively neutral and stressful contexts. We found that spontaneous nicotine withdrawal (24 h post-pump removal) did not influence baseline startle responding, but produced a selective increase in LES. Precipitated nicotine withdrawal through injections of one of two nicotinic acetylcholine receptor (nAChR) antagonists, dihydro-beta-erythroidine hydrobromide (DHbetaE: 0, 1.5, 3, or 6 mg/kg) or mecamylamine (0, 1, 2, or 4 mg/kg), did not influence baseline startle responding or LES. These results suggest that spontaneous nicotine withdrawal selectively potentiates responses to anxiogenic stimuli, but does not by itself produce a strong anxiogenic effect. These findings support the hypothesis that nicotine withdrawal exacerbates stress responding, and indicate LES may be a useful model to examine withdrawal effects on anxiety.

Evaluation of the effect of implanted depleted uranium (DU) on adult rat behavior and toxicological endpoints.

In 2002, the Naval Health Research Center Toxicology Detachment began a study to determine the effects of surgically implanted depleted uranium (DU) pellets on adult rat (e.g., P1 generation) health and reproduction. In this report, the effect of implanted DU on adult rat behavior and health is described. Adult Sprague-Dawley (SD) rats, 8 wk of age, were surgically implanted with 0, 4, 8, 12, or 20 DU pellets (1 x 2 mm); 20 DU pellets of size 1 x 2 mm approximates to 0.22 kg (0.5 lb) of DU in a 70-kg (154 lb) person. Control animals were implanted with 12 or 20 tantallum (Ta) pellets. The animals were then housed for up to 150 d postimplantation or 20% of an assumed 2-yr life span for rats. The concentration of uranium in urine directly correlated with the number of implanted DU pellets, indicating that DU was migrating into the body from the implanted pellets. Three male and 4 female animals died during the 150-d period of causes apparently not related to DU implantation. Behavioral testing found no definitive evidence of neurobehavioral perturbations associated with DU implantation. Uranium translocated to tissues known to sequester uranium (bone, teeth, and kidneys), but uranium concentrations varied considerably within each dose group and did not follow a dose-response pattern as anticipated. Serum chemistry values were within normal ranges for the SD rat. However, alanine aminotransferase measurements were significantly lower for rats implanted with 20 DU pellets as compared to sham surgery controls but not when compared to animals implanted with Ta pellets only. Phosphate measurements were significantly lower for female rats implanted with 20 DU pellets as compared to both sham surgery controls and animals implanted with Ta pellets only. Monocyte ratios were higher in adult rats implanted with 20 DU pellets as compared to sham surgery controls but not when compared to animals implanted with 20 Ta pellets. Mean platelet volume was found to be significantly lower for rats implanted with 20 DU pellets as compared to sham surgery controls but not when compared to animals implanted with 20 Ta pellets. Gross necropsy found no obvious tissue abnormalities in implanted rats, and the weights of major tissues did not differ between Ta- and DU-implanted animals. Histopathologic analysis of major tissues from animals implanted with 0 pellets, 20 Ta pellets, or 20 DU pellets found no differences between treatment groups. The findings of this study indicate that implantation of up to 20 DU pellets in adult rats did not have a significant negative impact on their general health and neurobehavioral capacities when assessed after 150 d of pellet implantation. However, the growing body of data on the potential health effects associated with DU exposure warrants further studies involving higher embedded DU body burdens in conjunction with longer surveillance periods postimplantation.

Inhibitory gating of single unit activity in amygdala: effects of ketamine, haloperidol, or nicotine.

BACKGROUND: Inhibitory gating is thought to be a basic process for filtering incoming stimuli to the brain. Little information is currently available concerning local neural networks of inhibitory gating or the intrinsic neurochemical substrates involved in the process. METHODS: The goal of the present study was to examine the pharmacological aspects of inhibitory gating from single units in the amygdala. We tested the effects of ketamine (80 mg/kg) and haloperidol (1 mg/kg) on inhibitory gating. Additionally, we examined the effect of nicotine (1.2 mg/kg) on single unit gating in this same brain structure. RESULTS: We found that in one subset of neurons, ketamine administration significantly reduced tone responsiveness with a subsequent loss of inhibitory gating, whereas the other subset persisted in both auditory responding and gating albeit at a weaker level. Haloperidol and nicotine had very similar effects, exemplified by a dramatic increase in the response to the initial "conditioning" tone with a subsequent improvement in inhibitory gating. CONCLUSIONS: Tone responsiveness and inhibitory gating persists in a subset of neurons after glutamate N-methyl-D-aspartate receptor blockade. Dopamine and nicotine modulate gating in these normal animals and have similar effects of enhancing responsiveness to auditory stimulation at the single unit and evoked potential level.

SCH 23390 in the prefrontal cortex enhances the effect of apomorphine on prepulse inhibition of rats.

The aim of this study was to investigate the role of dopaminergic activity in the prefrontal cortex in the regulation of prepulse inhibition (PPI) of acoustic startle. Rats were instrumented with permanent indwelling cannulas into the prefrontal cortex region and tested at least one week after surgery using a randomized sequence, repeated-measures protocol. Doses of apomorphine (0.1 mg/kg subcutaneously, s.c.) and MK-801 (0.03 mg/kg s.c.) were obtained from preliminary dose-response studies. Intracerebral injection of 0.5 microg/side of the dopamine D1 receptor antagonist, SCH 23390, significantly enhanced the disruptive effect of apomorphine on PPI, but had no effect on its own or on startle amplitude or habituation. Furthermore, the effect of SCH 23390 on PPI was not seen with a lower dose (0.2 microg/side) or in combination with the NMDA receptor antagonist, MK-801. These data confirm and extend previous reports on the importance of dopaminergic innervation of the prefrontal cortex in the regulation of PPI. It is suggested that apomorphine treatment directly or indirectly activates dopamine D1 receptors in the prefrontal cortex to inhibit its own action on PPI elsewhere in the brain, presumably in the nucleus accumbens. Antagonism of this inhibitory component by SCH 23390 therefore leads to a larger disruption of PPI.

Dose-response characteristics of ketamine effect on locomotion, cognitive function and central neuronal activity.

The present dose-response study sought to determine the effects of subanesthetic dosages (4-16 mg/kg) of ketamine on locomotion, sensorimotor gating (PPI), working memory, as well as c-fos expression in various limbic regions implicated in the pathogenesis of schizophrenia. In addition, we examined whether ketamine-induced locomotion was influenced by the dark/light cycle. We found that ketamine increased locomotor activity in a dose dependent manner, but found no influence of the dark-light cycle. Additionally, ketamine dose-dependently interrupted PPI, resulting in prepulse facilitation at doses of 8 and 12 mg/kg. The dose of 12 mg/kg also induced impairments in working memory assessed by the discrete-trial delayed-alternation task. C-fos expression indicated that the dose-dependent behavioral effects of ketamine might be related to changes in the activity of limbic regions, notably hippocampus and amygdala.

Algorithmically designed peptides ameliorate behavioral defects in animal model of ADHD by an allosteric mechanism.

This study exemplifies the use of three ADHD-relevant methodological innovations. (1) The use of novel, patented, computational peptide design techniques to generate peptides targeting the extra-cellular and para-transmembrane amino acid loops of the putatively ADHD-involved, D(2) dopamine receptor, D(2)DAR; (2) experimental evidence that these peptides in L-amino acid/ortho ordered or D-amino acid/reverse ordered (retro-inverso), D(2)DAR, hydrophobic eigenmode matched forms, evoked positive allosteric and indirect agonist influences on in vitro stably receptor transfected CHO and LtK cells and on in vivo, brain mediated activity; (3) a representative 15 residue all-D-amino acid, D(2) mode matched peptide, given parenterally, was found to "repair" a key aberrant ADHD behavioral characteristic in a standard animal model of ADHD, the Spontaneously Hypertensive Rat, SHR, relative to its progenitor species control, the Wistar-Kyoto rat, WKY. The representative, retro-inverso peptide, all-D-LLYKNKPRYPKRNRE, reversed SHR's relative deficiency in sensory motor gating (pre-pulse inhibition, PPI) while leaving SHR's nonselective attention (rearings), impulsive behavior (time in center), and activity level (timed total motor behavior) unchanged. Amphetamine also reversed SHRs sensory gating defect, but with significant increases in nonselective attention, impulsivity and hyperactivity. These preliminary results suggest the possibility of a new, "softer" pharmacological approach to ADHD: hydrophobic mode matched peptide allosteric augmentation of the activity of indigenous dopamine with respect to D(2)DAR mediated function, in place of stimulant drug-induced presynaptic dopamine release or impairment of dopamine uptake.

HZE radiation and dopaminergic modification of startle and prepulse inhibition in mice.

C57BL/6 mice were exposed to 5 Gy (28)Si or (56)Fe particle radiation in order to explore the immediate or short-latency effect of exposure to high energy (HZE) particle radiation on dopaminergic modification of acoustic startle and prepulse inhibition. The radiation is representative of the type which would be encountered as galactic cosmic rays during long-duration space flight. The acoustic startle response was elicited with 120 dB white noise and prepulse inhibition of the startle response was produced with 79 dB and 86 dB stimuli presented with a 125 ms onset asynchrony. Startle reactivity was inhibited by (56)Fe radiation but not by (28)Si particles. Apomorphine (3 mg/kg) produced a general inhibition of startle reactivity while haloperidol (1 mg/kg) facilitated it. Apomorphine disrupted prepulse inhibition, but only in animals which were not exposed to radiation. Both (56)Fe and (28)Si radiation exposure attenuated the disruption of prepulse inhibition induced by apomorphine. In contrast, the facilitation of prepulse inhibition induced by haloperidol was not modified by radiation. These data are consistent with a short-latency disruption of dopaminergic systems by HZE particle radiation. We speculate that this disruption may occur as a restriction in the capacity of the dopaminergic system.

Antidepressant-like effects of cranial stimulation within a low-energy magnetic field in rats.

BACKGROUND: Evidence suggests that a novel type of magnetic resonance imaging (MRI) scan called echo planar magnetic resonance spectroscopic imaging (EP-MRSI) has mood-elevating actions in humans during the depressive phases of bipolar disorder. We examined whether a low-energy component of EP-MRSI (low-field magnetic stimulation [LFMS]) has antidepressant-like, locomotor-stimulating, or amnestic effects in rats. METHODS: We examined the effects of LFMS on immobility in the forced swim test (FST) and activity within an open field in separate groups of rats. After exposure to forced swimming, rats received LFMS (three 20-min sessions at 1.5 G/cm and .75 V/m) before behavioral testing. We also examined the effects of LFMS on fear conditioning (FC), a learning paradigm that also involves exposure to stressful conditions. RESULTS: Low-field magnetic stimulation reduced immobility in the FST, an antidepressant-like effect qualitatively similar to that of standard antidepressants. Low-field magnetic stimulation did not alter locomotor activity or FC. CONCLUSIONS: Low-field magnetic stimulation has antidepressant-like effects in rats that seem unrelated to locomotor-activating or amnestic effects. These findings raise the possibility that electromagnetic fields can affect the brain biology and might have physiologic consequences that offer novel approaches to therapy for psychiatric disorders. These same consequences might render MRI-based scans more invasive than previously appreciated.

The acoustic startle reflex in Sprague-Dawley rats is altered by permanent middle cerebral artery occlusion.

The startle reflex is an unconditioned, quantifiable behavior used to study sensory modalities. We examined whether the acoustic startle reflex (ASR) was sensitive to lesions induced by focal cerebral ischemia. Sprague-Dawley rats were pre-screened for startle reflex responses 3-6 days prior to surgery and there were no differences in mean startle amplitude across groups. Animals were subjected to permanent middle cerebral artery occlusion (pMCAo) or a sham surgical procedure. Twenty-four hours later rats were evaluated for ASR prior to sacrifice. Infarct volumes were subsequently determined by quantitative image analysis of 2,3,5-triphenyltetrazolium chloride-stained brain sections. Infarct volumes of rats undergoing pMCAO ranged from 0 to 48%. Data were divided into three groups based upon percent infarction: mild (0-20%), moderate (21-35%), and severe (>35%). A within-subject analysis revealed a significant decrease in mean startle amplitude of only severely infarcted rats relative to their pre-surgery startle responses. Furthermore, the lesioned brain areas observed in these animals provide an anatomical basis for these results. Our findings demonstrate that ASR is affected in a model of stroke. Further work is needed to characterize this behavioral test and to determine whether it may have application as a surrogate endpoint for clinical stroke studies.

Light-potentiation of acoustic startle response (ASR) and monoamine efflux related to fearfulness in Fyn-deficient mice.

Fyn tyrosine kinase deficient mice are known to show increased fearfulness. We investigated the fear response of these mice using the light-potentiation of the acoustic startle response (ASR) and examined its neurochemical correlates using in vivo microdialysis. Female homozygous Fyn-deficient mice showed an enhancement of the startle amplitude under a bright light while heterozygotes and wild-types did not show such a change. Along with these behavioral findings, the homozygous Fyn-deficient mice showed an increase in extracellular serotonin (5-HT) and dopamine (DA) in the prefrontal cortex and 5-HT in the hippocampus when they were exposed to bright light, while heterozygous and wild-type mice did not show such changes. These results suggest that the increased fearfulness of Fyn-deficient mice is related to enhanced serotonergic and dopaminergic activity in the prefrontal cortex and limbic system.

Behavioral consequences of radiation exposure to simulated space radiation in the C57BL/6 mouse: open field, rotorod, and acoustic startle.

Two experiments were carried out to investigate the consequences of exposure to proton radiation, such as might occur for astronauts during space flight. C57BL/6 mice were exposed, either with or without 15-g/cm2 aluminum shielding, to 0-, 3-, or 4-Gy proton irradiation mimicking features of a solar particle event. Irradiation produced transient direct deficits in open-field exploratory behavior and acoustic startle habituation. Rotorod performance at 18 rpm was impaired by exposure to proton radiation and was impaired at 26 rpm, but only for mice irradiated with shielding and at the 4-Gy dose. Long-term (>2 weeks) indirect deficits in open-field activity appeared as a result of impaired experiential encoding immediately following exposure. A 2-week recovery prior to testing decreased most of the direct effects of exposure, with only rotorod performance at 26 rpm being impaired. These results suggest that the performance deficits may have been mediated by radiation damage to hippocampal, cerebellar, and possibly, forebrain dopaminergic function.

Some behavioral effects of short-term exposure of rats to 2.45 GHz microwave radiation.

Rats were tested for neurobehavioral alterations immediately after exposure to 2.45-GHz (CW) microwave radiation at 10 mW/cm2 for 7 h. Behavioral tests used were locomotor activity, startle to an acoustic stimulus and acquisition and retention of a shock-motivated passive avoidance task. Both horizontal and vertical components of locomotor activity were assessed in 5-min epochs for a period of 30 min using photoelectric detectors. Microwave-exposed animals exhibited less activity than sham-exposed animals. This was most evident during the last 10-15 min of the 30-min test session. Twenty identical acoustical stimuli (8 KHz, 110 dB) were delivered to each rat at 40-s intervals. The microwave-exposed animals were less responsive to the stimuli than sham-exposed animals. Microwave exposure had no effect on the retention of a passive avoidance procedure when tested at 1 week after training. Both the locomotor activity and acoustic startle data demonstrate that, under the conditions of this experiment, microwave exposure may alter responsiveness of rats to novel environmental conditions or stimuli.

Influence of pre- and postnatal exposure of rats to 2.45-GHz microwave radiation on neurobehavioral function.

Rats exposed to microwaves prenatally (2,450 MHz, 10 mW/cm2, 3 h/day, days 5-20 of gestation) or perinatally (same as above plus days 2-20 postnatally) were examined by a neurobehavioral test battery on postnatal days 30 and 100. Body mass, locomotor activity, startle to acoustic and air-puff stimuli, fore- and hindlimb grip strength, negative geotaxis, reaction to thermal stimulation, and swimming endurance were assessed. The prenatally and the perinatally exposed rats (male and female) weighted more than sham-exposed rats at 30, but not at 100, days of age. In addition, the perinatally exposed animals had less swimming endurance at 30, but not at 100, days of age relative to sham-exposed rats. For the other measures, only the air-puff startle response was altered and was limited to the prenatally exposed female pups; ie, at postnatal day 30, the startle response was increased in magnitude, and at postnatal day 100, the response was decreased. No other reliable effects were observed. In a second experiment, rats treated as described above were examined for alterations in body mass, locomotor activity, reaction to air-puff stimuli, reaction to thermal stimulation, and swimming endurance at postnatal days 30-36. Again, perinatally exposed rats were larger in body mass and had less swimming endurance compared with sham-exposed rats. The latency to the air-puff startle response was longer in female pups exposed prenatally. These data indicate that altered endurance and gross motor activity result from perinatal exposure to microwave irradiation.