Spontaneous eye-blink rates and dopaminergic systems

A series of studies demonstrated a possible relationship between eye-blink rate and central dopamine activity. First, apomorphine and other dopamine agonists acutely increased blink rate in monkeys, an effect blocked by sulpiride. Secondly, parkinsonian patients with levodopa-induced dyskinesia exhibited twice the mean blink rate (21 blinks/min) of other parkinsonians (11 blinks/min, P less than 0.002) whereas the more symptomatic of the nondyskinetic patients had a very slow rate (3 blinks/min, P less than 0.01). Thirdly, schizophrenic patients had an elevated mean blink (31 vs 23 blinks/min for normals, P less than 0.05) which was normalized by neuroleptic treatment. Thus, the correlation with central dopamine activity may also prove clinically useful in selected neuropsychiatric disorders.

Blinking is controlled primarily by ocular surface conditions

PURPOSE

To investigate the relation between blinking and ocular surface conditions and to introduce and examine a new index, the maximum blink interval.

METHODS

In a prospective study, the blink rate of subjects under relaxed conditions was determined from a video recording taken by a hidden observer. The maximum blink interval was defined as the longest time subjects can avoid blinking without feeling uncomfortable.

RESULTS

Significant changes in the blink rate and maximum blink interval were induced by factors that directly or indirectly affect the ocular surface: topical anesthesia, changing exposed ocular surface area, and wind. Moreover, the blink rate and maximum blink interval were significantly different in dry eye patients compared with healthy volunteers, with the values of the former approaching the values of the latter after use of artificial tears. The maximum blink interval was decreased by the same factors that increased the blink rate, and there was a significant inverse correlation between blink rate and maximum blink interval. Use of video display terminals was associated with decreased maximum blink interval and, hence, the development of dry eye symptoms.

CONCLUSIONS

There was an important association among blink rate, maximum blink interval, and ocular surface conditions. The blink rate and our newly introduced measurement, the maximum blink interval, should prove useful in assessing factors that cause dry eye. This prospective study should contribute to the understanding and treatment of dry eyes.

Counteracting driver sleepiness: effects of napping, caffeine, and placebo

Sleepy drivers should "take a break," but the efficacy of feasible additional countermeasures that can be used during the break is unknown. We examined a shorter than 15 min nap, 150 mg of caffeine in coffee, and a coffee placebo, each given randomly across test sessions to 10 sleepy subjects during a 30-min rest period between two 1-hr monotonous early afternoon drives in a car simulator. Caffeine and nap significantly reduced driving impairments, subjective sleepiness, and electroencephalographic (EEG) activity indicating drowsiness. Blink rate was unaffected. Sleep during naps varied, whereas caffeine produced more consistent effects. Subjects acknowledged sleepiness when the EEG indicated drowsiness, and driving impairments were preceded by self-knowledge of sleepiness. Taking just a break proved ineffective.

Effective neuroleptic medication removes prepulse inhibition deficits in schizophrenia patients

BACKGROUND

The magnitude of the startle eyeblink response is reduced if the startle eliciting stimulus is shortly preceded by another stimulus. There is evidence that schizophrenia patients exhibit impairments in this so-called prepulse inhibition. Our study investigated whether prepulse inhibition is affected by neuroleptic drug treatment as is suggested by animal research.

METHODS

Prepulse inhibition was tested in five unmedicated and 20 medicated inpatients with schizophrenia, and 12 normal controls.

RESULTS

The unmedicated schizophrenia patients showed a strong impairment of sensorimotor gating as indexed by the absence of prepulse inhibition. By contrast, the medicated patients showed a pronounced prepulse inhibition that did not differ from that of the normal controls. There was a substantial covariation between the rated severity of the positive syndrome and the amount of prepulse inhibition--i.e., the patients whose positive symptoms were rated as more severe showed less prepulse inhibition.

CONCLUSIONS

These data suggest that the impaired sensorimotor gating of schizophrenia patients is not a stable vulnerability indicator, but may rather be related to the positive syndrome and may be improved by treatments with neuroleptic medication.

Pharmacological analysis of cerebellar contributions to the timing and expression of conditioned eyelid responses

Contradictory results have been reported regarding the effects of cerebellar cortex lesions on the expression of conditioned eyelid responses--either no effect, partial to complete abolition of responses, or disruption of response timing. This uncertainty is increased by debates regarding the region(s) of cerebellar cortex that are involved, by the likelihood that cortex lesions can inadvertently include damage to the interpositus nucleus or other pathways necessary for response expression, and by potential confounds from the degeneration of climbing fibers produced by cerebellar cortex lesions. We have addressed these issues by reversibly blocking cerebellar cortex output via infusion of the GABA antagonist picrotoxin into the interpositus nucleus. After picrotoxin infusion, conditioned responses are spared but their timing is disrupted and their amplitude diminished. In the same animals, conditioned responses were abolished by infusion of the GABA agonist muscimol and were unaffected by infusion of saline vehicle. These results are consistent with the hypothesis that (i) plasticity in the interpositus nucleus contributes to the expression of conditioned responses, as suggested by the responses seen with the cortex disconnected, and (ii) plasticity in the cerebellar cortex also contributes to conditioned response expression, as suggested by disruption of response timing.

Event-related potentials in alcoholic men: P3 amplitude reflects family history but not alcohol consumption

Multilead event-related potentials (ERPs), elicited by auditory and visual stimuli requiring a button press response and by a startling noise requiring no response, were recorded from male alcoholics and age-matched male controls (26-60 years old). Single-trial analyses of blink responses to the startling stimuli indicated that alcoholics startle less frequently but with equivalent amplitude as the controls. In contrast, single-trial analyses of P3 indicated that alcoholics generate a P3 as often as controls, but that their individual P3s are smaller. Alcoholics who reported a positive family history of problem drinking had larger startle blink amplitudes and smaller auditory and visual P3s than did alcoholics who reported a negative family history. Hierarchical regression analysis was used to demonstrate that smaller P3s in family history positive alcoholics were independent of lifetime alcohol consumption.

Drug-related information generates placebo and nocebo responses that modify the drug response

OBJECTIVE

Administration of the muscle relaxant carisoprodol and placebo was crossed with information that was agonistic or antagonistic to the effect of carisoprodol. It was investigated whether information alone induced physiological and psychological responses, and whether information modified the response to the drug.

METHODS

Half of the subjects received capsules containing 525 mg carisoprodol together with information that the drug acted in a specific way (Groups Relaxant/C, Stimulant/C, and No Information/C). The other half of the subjects received lactose (Groups Relaxant/L, Stimulant/L, and No Information/L). Dependent variables were blink reflexes and skin conductance responses, subjective measures of tension and sleepiness, and serum carisoprodol and meprobamate concentrations. Recordings were made between 15 and 130 minutes after administration of the capsules.

RESULTS

The Stimulant/L group reported more tension compared with the other two groups, and carisoprodol increased tension even more in the Stimulant/C group. The Relaxant/C group displayed higher levels of carisoprodol serum concentration compared with the other groups that received carisoprodol.

CONCLUSIONS

Reported tension was modulated in the direction suggested by the stimulant information. The effect of carisoprodol on tension was also modulated by stimulant information. Increased carisoprodol absorption in the group that received relaxant information could be a mechanism in the placebo response.

Efficacy of Maternal Choline Supplementation During Pregnancy in Mitigating Adverse Effects of Prenatal Alcohol Exposure on Growth and Cognitive Function: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

BACKGROUND

We recently demonstrated the acceptability and feasibility of a randomized, double-blind choline supplementation intervention for heavy drinking women during pregnancy. In this study, we report our results relating to the efficacy of this intervention in mitigating adverse effects of prenatal alcohol exposure (PAE) on infant growth and cognitive function.

METHODS

Sixty-nine Cape Coloured (mixed ancestry) heavy drinkers in Cape Town, South Africa, recruited in mid-pregnancy, were randomly assigned to receive a daily oral dose of either 2 g of choline or placebo from time of enrollment until delivery. Each dose consisted of an individually wrapped packet of powder that, when mixed with water, produced a sweet tasting grape-flavored drink. The primary outcome, eyeblink conditioning (EBC), was assessed at 6.5 months. Somatic growth was measured at birth, 6.5, and 12 months, recognition memory and processing speed on the Fagan Test of Infant Intelligence, at 6.5 and 12 months.

RESULTS

Infants born to choline-treated mothers were more likely to meet criterion for conditioning on EBC than the placebo group. Moreover, within the choline arm, degree of maternal adherence to the supplementation protocol strongly predicted EBC performance. Both groups were small at birth, but choline-treated infants showed considerable catch-up growth in weight and head circumference at 6.5 and 12 months. At 12 months, the infants in the choline treatment arm had higher novelty preference scores, indicating better visual recognition memory.

CONCLUSIONS

This exploratory study is the first to provide evidence that a high dose of choline administered early in pregnancy can mitigate adverse effects of heavy PAE on EBC, postnatal growth, and cognition in human infants. These findings are consistent with studies of alcohol-exposed animals that have demonstrated beneficial effects of choline supplementation on classical conditioning, learning, and memory.

Normal motor learning during pharmacological prevention of Purkinje cell long-term depression

Systemic delivery of (1R-1-benzo thiophen-5-yl-2[2-diethylamino)-ethoxy] ethanol hydrochloride (T-588) prevented long-term depression (LTD) of the parallel fiber (PF)-Purkinje cell (PC) synapse induced by conjunctive climbing fiber and PF stimulation in vivo. However, similar concentrations of T-588 in the brains of behaving mice and rats affected neither motor learning in the rotorod test nor the learning of motor timing during classical conditioning of the eyeblink reflex. Rats given doses of T-588 that prevented PF-PC LTD were as proficient as controls in learning to adapt the timing of their conditioned eyeblink response to a 150- or 350-ms change in the timing of the paradigm. The experiment indicates that PF-PC LTD under control of the climbing fibers is not required for general motor adaptation or the learning of response timing in two common models of motor learning for which the cerebellum has been implicated. Alternative mechanisms for motor timing and possible functions for LTD in protection from excitotoxicity are discussed.

The influence of eye solutions on blinking and ocular comfort at rest and during work at video display terminals

The aim of this work was to study blink frequency changes and levels of ocular discomfort during work at a video display terminal, and the effects on these parameters of augmented or reduced humidification of the ocular surface. Blink rate was measured from recordings of the electrical signal evoked by the contraction of the orbicularis oculi muscle. Blink rate and interblink intervals were analyzed at rest and during performance of a task with a computer (playing a card game) for 10 or 30 min in steady environmental conditions and during application of a continuous stream of air to the face. In two separate sessions, the effect of pretreatment with humidifying ocular solutions of different elastoviscosity (balanced salt solution or elastoviscous 0.1% Hylan A solution) was assayed. At the end of each experimental period, the subjects marked the level of ocular discomfort experienced on a 0-10 cm visual analogue scale. The blink frequency at rest (12.4+/-1.2 blinks min-1) was reduced significantly (to 10.3+/-1.1 blinks min-1) by pretreatment with elastoviscous eyedrops both with and without air applied to the face. This effect was not obtained with balanced salt solution. During performance of the visual task for 10 or 30 min, basal blink rate decreased significantly, to about 40% of the control value. Neither application of an air jet on the face nor application of eye solutions of different viscosity modified this reduced blink rate.A low degree of ocular discomfort developed after performance of the visual task that was enhanced by air application to the face. This discomfort was reduced by pretreatment with ocular solutions, the elastoviscous eye solution being more efficient than the balanced salt solution. Interblink interval duration was also more regular after treatment with the elastoviscous solution. These data suggest that blink rate at rest is maintained in part by activation of sensory receptors of the cornea and conjunctiva, which are stimulated by desiccation of the ocular surface. Reduction of eye blink frequency elicited by the performance of a visual task with a computer appears to depend on central neural mechanisms that are quite independent of peripheral sensory inputs. The reduction of blink frequency consecutive to computer use was associated with a sensation of discomfort that was attenuated more effectively by elastoviscous eyedrops than by regular balanced salt solution.

Enhanced response to repeated d-amphetamine challenge: evidence for behavioral sensitization in humans

Behavioral sensitization is the process whereby intermittent stimulant exposure produces a time-dependent, enduring, and progressively more robust behavioral response. This process serves as an important model of neural plasticity and has also been proposed as a model for a variety of psychiatric syndromes; however, there are no published controlled studies of behavioral sensitization in human subjects. The authors report results from a double-blind, placebo-controlled study of repeated d-amphetamine challenges in a sample of normal human volunteers. Eleven consecutively recruited normal volunteers participated in this 4-day protocol. Each subject received two daily doses of d-amphetamine (0.25 mg/kg) separated by 48 hours that alternated with two daily doses of matched placebo. Symptoms (activity/energy level, mood, rate, and amount of speech) and eye-blink rates were measured hourly for 5 hours following drug administration. All four measures demonstrated significantly enhanced increases following the second amphetamine dose as compared to the first amphetamine dose and both placebo conditions. These findings suggest that behavioral sensitization is measurable in human subjects.

Progressive behavioral response to repeated d-amphetamine challenge: further evidence for sensitization in humans

BACKGROUND

Behavioral sensitization is the process whereby intermittent stimulant exposure produces a time-dependent, enduring, and progressive behavioral response. Although animal models of sensitization are well established, the phenomenon has been relatively little studied in humans. In a previous study, we reported enhanced responses following a second as compared to a first amphetamine dose in eye-blink rate and ratings of increased motor activity/energy, increased speech, and elevated mood in normal human volunteers. This current study extends those findings in a new sample of normal volunteers.

METHODS

Eleven normal human volunteers were administered three single oral doses of d-amphetamine (0.25 mg/kg) at 48-hour intervals, alternating with matched placebo in a randomized, double-blind trial. Hourly behavioral ratings included eye-blink rate, symptoms (elevated mood, increased speech, increased motor activity/energy), and subjective drug effects.

RESULTS

Eye-blink rate and increased motor activity/energy ratings progressively increased following each challenge with the third amphetamine dose response significantly greater than all other conditions 4 hours postadministration. Similar, although less pronounced, responses were observed for elevated mood and subjective drug effect.

CONCLUSIONS

These results provide further evidence for sensitization of some amphetamine-induced behaviors in human subjects.

A fMRI investigation of startle gating deficits in schizophrenia patients treated with typical or atypical antipsychotics

A key feature of schizophrenia is the inability to screen out irrelevant sensory input. Prepulse inhibition (PPI) of the startle response, a cross-species measure of sensorimotor gating, provides a valuable opportunity to study this feature. PPI is reliably impaired in schizophrenia. Animal models of disrupted PPI have proved valuable for the evaluation of antipsychotic substances. The cortico-striato-pallido-thalamic circuitry is primarily responsible for modulation of PPI in animals. We examined PPI and its brain correlates, using functional magnetic resonance imaging (fMRI), in men with schizophrenia treated with typical or atypical antipsychotics. Thirty men with schizophrenia on stable doses of typical antipsychotics (n=10), risperidone (n=10) or olanzapine (n=10; 9 with usable fMRI data) and 12 healthy men underwent psychophysiological testing and fMRI during a tactile PPI paradigm. The results showed reduced PPI of the eye-blink startle response in patients compared with healthy controls. Within the patient group, those on typical antipsychotics showed significantly impaired PPI but risperidone- or olanzapine-treated patients showed a milder (non-significant) deficit. Increased activity in the striatum, thalamus, insula, hippocampal, temporal, inferior frontal and inferior parietal regions occurred in association with PPI in controls. Patients treated with risperidone or olanzapine, but not with typical antipsychotics, showed significant activation in PPI-relevant regions. Our findings provide preliminary evidence that atypical antipsychotics positively influence PPI and partially restore associated brain functions in schizophrenia. Imaging data buttress the validity of PPI as a useful animal model of schizophrenia.

Abnormal Habituation of ‘nociceptive’ Blink Reflex in Migraine-Evidence for Increased Excitability of Trigeminal Nociception

We studied the habituation of the ‘nociceptive’ blink reflex (nBR) in 15 healthy subjects and 17 migraine patients interictally as well as during unilateral migraine headache within six hours of onset and after treatment. In healthy volunteers the mean regression coefficient (MRC) was – 3.9 following right sided and – 4.9 left sided stimulation. This equals an amplitude loss of 19.5% (5 X −3.9) and 24.5% (5 X −4.9), respectively, across five consecutive sweeps. An augmentation of nBR responses was found in migraine patients interictally: MRC = 3.3 following stimulation of the headache side (HA) and MRC = 4.0 of the non-headache side (non-HA). The differences were statistically significant (ANOVA: d.f. = 1, F = 25.8, P < 0.001). During the migraine attack MRCs were negative both before (−5.0, HA and – 4.0, non-HA) and after treatment (−2.6, HA and −1.9 non-HA) and significantly differed from those outside the migraine attack (ANOVA: d.f. = 2, F = 12.4, P < 0.001). The demonstrated lack of habituation of the nBR responses indicates an abnormal trigeminal nociceptive processing in migraine patients outside the migraine attack.

Testosterone-induced acceleration of recovery from facial paralysis following crush axotomy of the facial nerve in male hamsters

In this study, the effects of testosterone propionate (TP) on recovery from facial paralysis following crush axotomy of the facial nerve in male hamsters were examined. In the first experiment, TP (5 mg/ml sesame oil; 0.1 ml) was injected subcutaneously and on alternate days in one-half of the animals subjected to crush axotomies of the facial nerve, with the second half receiving vehicle alone. An accelerative effect of TP on recovery from facial paralysis was observed near the end of the first and beginning of the second week after crush axotomy. When the dosage and frequency were doubled in the next experiment, a greater accelerative effect of TP on recovery from facial paralysis was observed. In the last experiment, castrated animals were used in order to eliminate the endogenous source of the hormone and two different modes of hormone administration, TP implants vs TP injections, were compared. The results of that experiment indicate that continuous exposure to the hormone, in the form of subcutaneous implants of 100% crystalline TP, had the most pronounced effect on acceleration of recovery from facial paralysis. In addition, no differences in the responses of the castrated, axotomized animals and the normal, axotomized animals were found. This suggests that the presence of endogenous hormone contributes little to the acceleration of functional recovery observed with TP. Finally, the time course of the accelerative effect of TP suggests that the hormone is acting primarily at the level of the facial neuron, which contains androgen receptors, and perhaps secondarily at the level of the facial muscles, which are also known to contain androgen receptors.

Botulinum toxin in the treatment of dystonic tics

Botulinum toxin (BTX) injections provide effective treatment for a variety of disorders manifested by inappropriate muscle contractions, but its efficacy in the treatment of tics has not been previously studied. Ten male patients 13-53 years of age who were diagnosed with Tourette's syndrome manifested by disabling focal tics were included in this pilot study. Five patients had frequent blinking and blepharospasm, rendering them "blind," and five patients had severe and painful dystonic tics involving their neck muscles. All 10 patients experienced moderate to marked improvement in the intensity and frequency of tics after BTX injections into the involved muscles. Patients in whom premonitory urges preceded their tics noted marked lessening of these sensory symptoms. The benefit lasted 2-20 weeks after injections. There were no serious complications, except for transient ptosis in two and neck pain, stiffness, or weakness in three patients. BTX injections appear to be safe and effective treatment for patients with focal dystonic tics. The treatment ameliorates not only involuntary movements but also the premonitory sensory component associated with some tics.

Long-term effects of early social isolation in Macaca mulatta: changes in dopamine receptor function following apomorphine challenge

The hypothesis that early social isolation results in long-term alterations in dopamine receptor sensitivity was tested using older adult rhesus monkeys. Isolated and control monkeys were challenged with apomorphine (0.1 and 0.3 mg/kg), and the drug effects on spontaneous blink rate, stereotyped behavior, and self-injurious behavior were quantified using observational measures. Monoamine metabolites were quantified from cisternal CSF by HPLC-EC, prior to pharmacological challenge. Isolated and control monkeys did not differ in CSF concentrations of HVA, 5-HIAA, or MHPG. At the higher dose, apomorphine significantly increased the rate of blinking, the occurrence of whole-body stereotypies, and the intensity of stereotyped behavior (as measured by observer ratings) in isolated monkeys. The frequency of occurrence of self-injurious behavior was too low to allow for meaningful comparisons. These significant differences in response to apomorphine challenge support the hypothesis that long-term or permanent alterations in dopamine receptor sensitivity, as assessed by drug challenge, are a consequence of early social deprivation.

Pharmacodynamic interaction between propofol and alfentanil when given for induction of anesthesia

BACKGROUND

Propofol and alfentanil often are combined during induction of anesthesia. However, the interaction between these agents during induction has not been studied in detail. The influence of alfentanil on the propofol concentration-effect relationships was studied for loss of eyelash reflex, loss of consciousness, and hemodynamic function in 20 unpremedicated ASA physical status 1 patients aged 20-55 yr.

METHODS

Patients were randomly divided into four groups to receive a computer- controlled infusion of alfentanil with target concentrations of 0, 50, 200, or 400 ng/ml (groups A, B, C, and D, respectively). While the target concentration of alfentanil was maintained constant, patients received a computer- controlled infusion of propofol, with an initial target concentration of 0.5-1 microgram/ml, that was increased every 12 min by 0.5-1 microgram/ml. Every 3 min, the eyelash reflex and state of consciousness were tested an an arterial blood sample was taken for blood propofol and plasma alfentanil determination. The propofol-alfentanil concentration-response relationships for loss of eyelash reflex and loss of consciousness were determined by nonlinear regression, and for the percentage of change in systolic blood pressure and heart rate by logistic regression.

RESULTS

The patient characteristics did not differ significantly among the four groups. The patients in groups A and B continued to breathe adequately, whereas all patients in groups C and D required assisted ventilation. End-tidal carbon dioxide partial pressure remained less than 46 mmHg in all patients. With plasma alfentanil concentrations increasing from 0 to 500 ng/ml, the EC(50) of propofol decreased from 2.07 to 0.83 microgram/ml for loss of eyelash reflex and from 3.62 to 1.55 microgram/ml for loss of consciousness. With plasma alfentanil concentrations increasing from 0 to 500 ng/ml, the blood propofol concentrations associated with a 10% decrease in systolic blood pressure and heart rate decreased from 1.68 to 0.17 microgram/ml and from 2.36 to 0.04 microgram/ml, respectively.

CONCLUSIONS

Alfentanil significantly reduces blood propofol concentrations required for loss of eyelash reflex and loss of consciousness. In addition, alfentanil enhances the depressant effects of propofol on systolic blood pressure and heart rate. Hemodynamic stability, therefore, does not increase in patients receiving propofol in combination with alfentanil compared to those receiving propofol as the sole agent for induction of anesthesia.

Comparative effects of electroacupuncture and transcutaneous nerve stimulation on the human blink reflex

The effects of low frequency (2 Hz) high intensity (10-12 mA) (electroacupuncture, EA) and of high frequency (100 Hz) low intensity (2 mA) (transcutaneous nerve stimulation, TNS) conditioning stimuli were studied on the nociceptive component (R2) of the blink reflex in normal volunteers. EA induced a progressive and moderate partially naloxone-reversible depression in the R2 response. In contrast, TNS induced a rapid and major depression in this reflex. In this latter case, naloxone failed to produce any reversal effect. These two patterns of data are discussed and further electrophysiological studies provide some evidence for two different mechanisms in the depressive effects of EA and TNS upon the nociceptive component of the blink reflex in man.

Acquisition, consolidation, reconsolidation, and extinction of eyelid conditioning responses require de novo protein synthesis

Memory, as measured by changes in an animal's behavior some time after learning, is a reflection of many processes. Here, using a trace paradigm, in mice we show that de novo protein synthesis is required for acquisition, consolidation, reconsolidation, and extinction of classically conditioned eyelid responses. Two critical periods of protein synthesis have been found: the first, during training, the blocking of which impaired acquisition; and the second, lasting the first 4 h after training, the blocking of which impaired consolidation. The process of reconsolidation was sensitive to protein synthesis inhibition if anisomycin was injected before or just after the reactivation session. Furthermore, extinction was also dependent on protein synthesis, following the same temporal course as that followed during acquisition and consolidation. This last fact reinforces the idea that extinction is an active learning process rather than a passive event of forgetting. Together, these findings demonstrate that all of the different stages of memory formation involved in the classical conditioning of eyelid responses are dependent on protein synthesis.

A nicotinic agonist (GTS-21), eyeblink classical conditioning, and nicotinic receptor binding in rabbit brain

The septo-hippocampal cholinergic system is of demonstrated involvement in eyeblink classical conditioning (EBCC). To determine if a nicotinic cholinergic agonist, GTS-21, would facilitate acquisition of EBCC in older rabbits, three doses (0.1, 0.5, 1.0 mg/kg) in sterile saline vehicle and vehicle alone were administered to older rabbits (n = 48; mean age = 29.8 months). A control group of vehicle-treated young rabbits (n = 12; mean age = 3.5 months) was included. Rabbits were conditioned for fifteen 90-trial sessions in the 750 ms delay paradigm with a tone conditioned stimulus and corneal airpuff unconditioned stimulus. Dependent measures of trials to learning criterion, percentage of conditioned responses (CRs) and CR amplitude consistently showed significant improvement in older rabbits treated with 0.5 and 1.0 mg/kg of GTS-21. Acquisition was similar in vehicle-treated young and GTS-treated older rabbits. Vehicle-treated older rabbits conditioned more poorly than vehicle-treated young rabbits. No non-associative learning effects were observed in GTS-21 treated animals. Nicotinic receptor binding was similar in all groups of older rabbits, indicating that GTS-21 administration over a 15-day period did not affect nicotinic receptors. Alzheimer's disease (AD) has been associated with significant loss of nicotinic cholinergic receptors, and patients diagnosed with probable AD are seriously impaired on EBCC. These results demonstrating that the nicotinic agonist, GTS-21, facilitated EBCC in older rabbits suggest that the compound should receive additional investigation for its potential to affect cognition in AD.

The effect on human eye blink frequency of exposure to limonene oxidation products and methacrolein

Oxidation products of terpenes (e.g. limonene) contain unidentified irritants, which may be responsible for a fraction of the reported eye and airway complaints in indoor environments. Here we report exposure to parts per billion (ppb) levels of limonene oxidation products (LOPs) and the terpene oxidation product methacrolein using blink frequency (BF) as a measure of trigeminal stimulation of the human eye. Ten male subjects averaging 43 (standard deviation 10.5) years were exposed for 20 min to LOPs, methacrolein, and clean air, respectively. A baseline BF was measured prior to and following each exposure (8 min and 4 min, respectively). The subjects were exposed locally in the non-dominant eye and single blind at 20% relative humidity (RH), while viewing an educational film. Blinking was video recorded and evaluated for full sessions of 36 min. Mean BF increased significantly during exposure to LOPs and methacrolein compared to the baseline of clean air, and the findings coincided with weak eye irritation symptoms. Lowest observed effect levels were 286 ppb methacrolein and a 10-min-old LOPs mixture of initially 92 ppb limonene and 101 ppb ozone (O3), which increased the BF comparably by 18% (p=0.001) and 17% (p=0.003), respectively. The increase in BF was smaller, although not significantly different, during exposure to LOPs at 50% RH to 20% RH in mixtures prepared from ca. 350 ppb limonene and 300 ppb O3. LOPs may cause trigeminal stimulation and possibly eye irritation at O3 and limonene concentrations, which are close to high-end values measured in indoor settings. The effects may be exacerbated by low RH.

Contextual-specificity of short-delay extinction in humans: renewal of fear-potentiated startle in a virtual environment

A recent fear-potentiated startle study in rodents suggested that extinction was not context dependent when extinction was conducted after a short delay following acquisition, suggesting that extinction can lead to erasure of fear learning in some circumstances. The main objective of this study was to attempt to replicate these findings in humans by examining the context specificity of short-delay extinction in an ABA renewal procedure using virtual reality environments. A second objective was to examine whether renewal, if any, would be influenced by context conditioning. Subjects underwent differential aversive conditioning in virtual context A, which was immediately followed by extinction in virtual context B. Extinction was followed by tests of renewal in context A and B, with the order counterbalanced across subjects. Results showed that extinction was context dependent. Evidence for renewal was established using fear-potentiated startle as well as skin conductance and fear ratings. In addition, although contextual anxiety was greater in the acquisition context than in the extinction context during renewal, as assessed with startle, context conditioning did not influence the renewal effect. These data do not support the view that extinction conducted shortly after acquisition is context independent. Hence, they do not provide evidence that extinction can lead to erasure of a fear memory established via Pavlovian conditioning.

Nicotine withdrawal in adolescent and adult rats

Previous research with animal models has demonstrated that adolescent rats display heightened sensitivity to the reinforcing and stimulant effects of nicotine relative to adult rats. Little work has focused on the response of adolescent rats to measures of nicotine withdrawal. To test the hypothesis that adolescent rats may be differentially sensitive to withdrawal relative to their adult counterparts, the present study was designed to compare precipitated withdrawal in adolescent and adult rats following chronic nicotine administration. Adult and adolescent rats were prepared with subcutaneous osmotic minipumps that delivered either saline or nicotine (9 mg/kg per day, salt; N =12 per group). All rats were challenged with the nicotinic receptor antagonist mecamylamine (1.5 mg/kg) on day 7 of chronic nicotine treatment. Twenty minutes after the injection, overt somatic signs of withdrawal (i.e., eye blinks, writhes, body shakes, teeth chatter, gasps, and ptosis) were recorded for 10 min. Adult rats were observed on postnatal day 73-77, and adolescent rats were tested on postnatal day 36-40. The results revealed a robust increase in mecamylamine-induced withdrawal signs in adult rats receiving chronic nicotine relative to adult rats receiving saline. In contrast, mecamylamine did not precipitate withdrawal signs in adolescent rats receiving chronic nicotine. These results indicate that there is decreased sensitivity to the somatic aspects of nicotine withdrawal in adolescent rats that may maximize the reinforcing effects of nicotine during adolescence by minimizing the aversive effects of abstinence.

Stable parkinsonian syndrome and uneven loss of striatal dopamine fibres following chronic MPTP administration in baboons

The progressive degeneration of dopamine neurons observed in idiopathic Parkinson's disease was mimicked by injecting low doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to baboons, on a chronic basis. Five Papio papio baboons were treated on two different regimens (chronic intravenous administration at weekly intervals for 20-21 months or, daily MPTP treatment for five days followed five to six months later by chronic weekly injections for 5-21.5 months). All animals were assessed for motor symptoms during and after neurotoxic treatment. Both regimens invariably resulted in the appearance of a progressive and irreversible syndrome characterized by action and resting tremor, cogwheel rigidity, postural impairments, hypokinesia and bradykinesia. In some animals, symptoms of resting tremor and rigidity initially restricted to one side of the body became bilateral within a few months of treatment. Subtle abnormalities that may be found in idiopathic Parkinson's disease such as alterations of the blink reflex response were also noted. Neuropathological examination of caudate nucleus, putamen, substantia nigra and ventral tegmental area in brain sections stained for tyrosine hydroxylase showed a typical uneven striatal dopamine fibre loss and a neuronal depletion in the dopaminergic mesencephalic cell groups that reproduce those observed in idiopathic Parkinson's disease. Immunocytochemical observations and behavioural data show that chronic rather than acute MPTP injection regimens can replicate most of the neuropathological and the clinical features typical of idiopathic Parkinson's disease, possibly by increasing the ability of this neurotoxin to target specific subpopulations of mesencephalic dopaminergic neurons.