Evaluation of multigenerational effects of 2-ethylhexyl 4-hydroxybenzoate in Japanese medaka

The Japanese medaka (Oryzias latipes) extended one-generation reproduction test (MEOGRT) (Test Guideline 890.2200) is a Tier 2 test within the Endocrine Disruptor Screening Program of the US Environmental Protection Agency (US EPA). A modified MEOGRT was used to evaluate multigenerational effects of 2-ethylhexyl 4-hydroxybenzoate (2-EHHB) under flow-through conditions starting with adults (parent generation, F0) through a 3-week reproductive phase of the second generation (F2). Fish were exposed to one of five 2-EHHB test concentrations or a dechlorinated tap water control. Fecundity was affected at the lowest exposure (5.32 μg/L) and greater sensitivity occurred in the F1 and F2 generations. Percent fertility was also diminished from no effect level observed in the F0 generation to 101 and 48.8 μg/L in the F1 and F2 generations, respectively. Growth indices were decreased for F0 adult females and F1 subadults and adults at 48.8 μg/L 2-EHHB. Histopathologic examination of gonads, liver, kidney, and thyroid yielded possible delayed reproductive tract development in F1 subadult males, masculinization of the renal phenotype in F1 adult females (renal tubular eosinophilia) and reduced hepatic energy storage (liver glycogen vacuoles) in F1 (11.3 and 48.8 μg/L) and F2 (48.8 and 101 μg/L) males and females, respectively. Endocrine-related findings included a decrease in anal fin papillae in F2 adult males at 101 μg/L. Results of this study demonstrate effects on growth, development, and reproduction that may be mediated by endocrine (weak estrogenic) and nonendocrine mechanisms. Duration of the MEOGRT should not be routinely extended beyond the OCSPP 890 guideline study design.

Quality of Life in Parkinson's Disease: Movement Disorders Clinic vs General Medical Clinic - A Comparative Study

Objectives: to determine the effect of attending a movement disorders (MD) clinic on quality of life (QOL) outcomes for patients with Parkinson's disease (PD). Methods: Postal questionnaire study of forty-two patients with Parkinson's disease attending either a movement disorders clinic or more conventional general medical clinic were selected consecutively to complete the Parkinson's Disease Quality of Life Questionnaire (PDQL). All patients were diagnosed by a consultant physician with an interest in Parkinson's disease (S.B.R.) and had attended either the movement disorders clinic or the general medical clinic on at least three occasions. Questionnaires were completed independently of the examiners and returned by post. Results: Mean PDQL score was 124.1 [5.16] in the movement disorders clinic and 95.9 [5.86] in the general medical clinic. Analysis of covariance revealed that those subjects attending the MD clinic reported a significantly higher QOL than those subjects in general medical care (F(1,39)= 161.98, P<0.001). Conclusion: These data indicate that the quality of life of respondents attending the movement disorders clinic is significantly higher than those attending the general medical clinic.

The effect of excitotoxic lesions of the pedunculopontine tegmental nucleus on performance of a progressive ratio schedule of reinforcement

The pedunculopontine tegmental nucleus has connections with sites in both dorsal and ventral striatum, and a number of studies have suggested that it has a role in reward-related behaviour. The present experiment aimed to investigate the perception of reward in pedunculopontine tegmental nucleus-lesioned rats responding for food under a progressive ratio schedule, which measures willingness to work for a given reward. Rats were trained on a progressive ratio-5 schedule for food reward, then given ibotenic acid or sham lesions of the pedunculopontine tegmental nucleus. Their performance under this schedule was examined again following recovery from surgery. Compared with sham-lesioned rats, those with lesions of the pedunculopontine tegmental nucleus showed significantly reduced breaking points and significantly longer post-reinforcement pauses. However, there was no difference between the groups in their latency to collect food pellets once earned, suggesting that pedunculopontine tegmental nucleus excitotoxin and sham-lesioned rats were equally motivated by the presence of food. Excitotoxin-lesioned rats made significantly more responses on the control lever and more entries to the food hopper as progressive ratio increment increased, but did not differ from controls when the schedule requirement was low. These results are interpreted as indicating no global loss of motivation, since lesioned rats performed normally at low schedule requirements, and were as fast as controls to collect pellets. But as the schedule requirement increased, excitotoxin-lesioned rats showed reductions in responding on the active lever (that is, a reduction in breaking point) and an increase in inappropriate responses towards the food hopper and the control lever.We consider these data to indicate that the behavioural deficits in pedunculopontine-lesioned rats arise not from a sensory or hedonic change, but from alteration in the control of motor output.

Striatal graft-associated recovery of a lesion-induced performance deficit in the rat requires learning to use the transplant

Peformance in a prelearned choice reaction time task was studied 6 months after surgery in rats with ibotenate-induced lesions of the striatum either with or without striatal grafts, and in sham-operated controls. The long postoperative interval allowed full transplant maturation and the establishment of appropriate connections by the transplants. The animals were trained prior to surgery on a visual choice reaction time task which requires that a movement is made away from stimuli signalling reward. The use of multiple measures allowed a thorough analysis of several aspects of the animals' performance. Whilst sham-operated control animals recovered normal (preoperative) performance rapidly, the lesioned animals had a severe performance deficit. Although the transplanted animals were initially at least as deficient in performance as the lesioned group, repeated testing led to an amelioration of the lesion-induced deficit according to two distinct measures of spatial bias and reaction time. On a third measure, latency to complete the lateralized movement, the grafted group were initially worse than the lesioned group but repeated testing resulted in significant recovery. These results suggest that postoperative training may help to optimize the efficacy of graft-induced recovery, and that animals may need to learn to use a transplant in order for it to confer functional benefit in complex prelearned tasks.

Voluntary saccadic eye movements in humans studied with a double-cue paradigm

In the classic double-step paradigm, subjects are required to make a saccade to a visual target that is briefly presented at one location and then shifted to a new location before the subject has responded. The saccades in this situation are "reflexive" in that they are made in response to the appearance of the target itself. In the present experiments we adapted the double-step paradigm to study "voluntary" saccades. For this, several identical targets were always visible and subjects were given a cue to indicate that they should make a saccade to one of them. This cue was then changed to indicate another of the targets before the subject had responded: double-cue (DC) paradigm. The saccadic eye movements in our DC paradigm had many features in common with those in the double-step paradigm and we show that apparent differences can be attributed to the spatio-temporal arrangements of the cues/targets rather than to any intrinsic differences in the programming of these two kinds of eye movements. For example, a feature of our DC paradigm that is not seen in the usual double-step paradigm is that the second cue could cause transient delays of the initial saccade, and these delays still occurred when the second cue was reflexive--provided that it was at the fovea (as in our DC paradigm) and not in the periphery (as in the usual double-step paradigm). Thus, the critical factor for the delay was the retinal (foveal) location of the second cue/target--not whether it was cognitive or reflexive--and we argue that the second cue/target is here acting as a distractor. We conclude that the DC paradigm can be used to study the programming of voluntary saccades in the same way that the double-step paradigm can be used to study reflexive saccades.

Thalamic reticular nucleus activation reflects attentional gating during classical conditioning

All senses, except olfaction, are routed through the thalamus to cerebral cortex. Thus, the thalamus is often referred to as the sensory gateway to cortex. Located between thalamus and cortex is a thin lamina of neurons called the thalamic reticular nucleus, which may function as an attentional gate. The phenomenon of blocking in classical conditioning provides an opportunity to test whether an attended stimulus activates the thalamic reticular nucleus more than an unattended stimulus: when a second stimulus is presented together with a previously conditioned stimulus, conditioned responding to the second stimulus is inhibited. Different groups of rats were given conditioning sessions with a single stimulus, a light or a tone, and then given conditioning sessions with compound (light and tone) stimuli. Blocking was confirmed using probe trials of single stimulus presentations. After a final test session of compound stimulus presentations, the brains were processed for the presence of Fos protein. Here we show that Fos-positive neurons were more numerous in the sector of the thalamic reticular nucleus associated with the attended conditioned stimulus than in the sector associated with the unattended stimulus. Thus, we provide evidence for an involvement of the thalamic reticular nucleus in selective attention.

Brown's response: difficulties with "the balkans"

Respon to Csaba Varga' comments. Environ Health Perspect 108:494-494 (2000).

Medial frontal cortex mediates perceptual attentional set shifting in the rat

If rodents do not display the behavioral complexity that is subserved in primates by prefrontal cortex, then evolution of prefrontal cortex in the rat should be doubted. Primate prefrontal cortex has been shown to mediate shifts in attention between perceptual dimensions of complex stimuli. This study examined the possibility that medial frontal cortex of the rat is involved in the shifting of perceptual attentional set. We trained rats to perform an attentional set-shifting task that is formally the same as a task used in monkeys and humans. Rats were trained to dig in bowls for a food reward. The bowls were presented in pairs, only one of which was baited. The rat had to select the bowl in which to dig by its odor, the medium that filled the bowl, or the texture that covered its surface. In a single session, rats performed a series of discriminations, including reversals, an intradimensional shift, and an extradimensional shift. Bilateral lesions by injection of ibotenic acid in medial frontal cortex resulted in impairment in neither initial acquisition nor reversal learning. We report here the same selective impairment in shifting of attentional set in the rat as seen in primates with lesions of prefrontal cortex. We conclude that medial frontal cortex of the rat has functional similarity to primate lateral prefrontal cortex.

Cholinergic neurotransmission influences covert orientation of visuospatial attention in the rat

RATIONALE

Both monkey and human studies have suggested that attentional orienting may be mediated by the cholinergic neurotransmitter system.

OBJECTIVES

The purpose of the present study was to examine whether the cholinergic agonist (nicotine) and/or antagonist (scopolamine) influence covert orientation in the rat.

METHODS

Rats carried out a visual reaction time task to measure covert orienting of attention following systemic administration of nicotine or scopolamine.

RESULTS

Nicotine reduced reaction times, abolishing the validity effect by differentially speeding the reaction times for invalidly cued targets. Conversely, scopolamine increased the validity effect by disproportionately lengthening reaction times to invalidly cued targets.

CONCLUSIONS

Taken together, these data indicate that cholinergic transmission represents an important neurochemical substrate of visuospatial attention, specifically influencing disengagement or movement of attention.

Anticipatory errors after unilateral lesions of the subthalamic nucleus in the rat: evidence for a failure of response inhibition

The nature of anticipatory responding in rats with unilateral subthalamic nucleus lesions was examined. Rats were trained to respond toward visual targets that were preceded by 1 of 4 different cues. For normal rats, a cue invokes an involuntary attentional orienting that enhances processing of the target at the location of attention. The cue is also a salient stimulus to which a response must be suppressed. Therefore, this task was used to investigate possible attentional impairments, as well as the ability of a lesioned rat to suppress competing motor programs. Responding under target control was not affected by the lesion. There was an increase in anticipatory responses before target onset, which could be accounted for by a failure to inhibit contralateral responses.

Anticipatory errors after unilateral lesions of the subthalamic nucleus in the rat: evidence for a failure of response inhibition

The nature of anticipatory responding in rats with unilateral subthalamic nucleus lesions was examined. Rats were trained to respond toward visual targets that were preceded by 1 of 4 different cues. For normal rats, a cue invokes an involuntary attentional orienting that enhances processing of the target at the location of attention. The cue is also a salient stimulus to which a response must be suppressed. Therefore, this task was used to investigate possible attentional impairments, as well as the ability of a lesioned rat to suppress competing motor programs. Responding under target control was not affected by the lesion. There was an increase in anticipatory responses before target onset, which could be accounted for by a failure to inhibit contralateral responses.

Attentional orienting is impaired by unilateral lesions of the thalamic reticular nucleus in the rat

The thalamic reticular nucleus (TRN) has been implicated in attentional processes based on its anatomical, electrophysiological, and neurochemical relationships with the sensory nuclei of the thalamus and corresponding sensory areas of cortex. This study examined the possibility that the TRN is involved in covert orienting of attention. Attention can be summoned to a spatial location in the absence of an overt orienting response. The reaction time to a visual target is faster when attention has been drawn to the location of the target by a preceding cue in that location (valid cue) compared with when the cue misdirects attention (invalid cue) away from the location of the subsequent target. This reaction time difference is referred to as the "validity effect." Rats were trained to perform such a reaction time task with visual cues and targets presented in poke holes to either side of the rat's head, which had to be maintained centrally and still. If the rat made an overt orienting response to the cue, the trial was aborted. Unilateral lesions were made by injection of ibotenic acid in the TRN. After surgery, there was no bias apparent in their responding; they were as likely to initiate responses and were equally accurate to either side. There was, however, a complete abolition of the validity effect for responses to contralateral targets. The data are discussed in terms of a role for the TRN in attentional processing.

Mechanisms underlying attentional set-shifting in Parkinson's disease

Patients with Parkinson's disease (PD) show impairments on tasks that require them to switch attention between two perceptual dimensions (extradimensional (ED) shifting). It has been suggested that ED shifting deficits can be caused by two separate mechanisms, 'learned irrelevance' and 'perseveration'. This study set out to test the hypothesis that enhanced learned irrelevance is present in medicated patients with PD. An enhancement of learned irrelevance in PD patients should result in increased errors on a 'deficit' shift relative to controls and decreased errors on an 'improvement' shift. A similar pair of deficit and improvement shifts were used to detect possible enhanced perseveration in patients. Instead of showing the predicted patterns of deficit and improvement, patients displayed a consistent deficit on those shifts that required that they switch their attention to a different dimension (ED shifts). In contrast, patients were not impaired on shifts that required no such shift of attention (intradimensional shifts). Although there was an increase in errors at the learned irrelevance deficit shift, a similar increase at the learned irrelevance improvement shift shows that enhanced learned irrelevance is not responsible for either of these results. Patients were no more distractible than controls, but displayed increased 'loss of set' as measured by errors generated after a rule was learned. These results point to the existence of exaggerated, rigid selective attention in patients with PD rather than a breakdown in the ability to selectively attend. There was no evidence for the existence of enhanced learned irrelevance in the patients.

Reaction time performance following unilateral striatal dopamine depletion and lesions of the subthalamic nucleus in the rat

The akinesia resulting from Parkinson's disease or striatal dopamine depletion in experimental animals can be ameliorated or reversed by inactivation of the subthalamic nucleus. This inactivation might be effective by restoring balance to the basal ganglia motor circuits. Alternatively, new movement-related deficits might be introduced which mask the original impairments (e.g. hyperkinesia might replace hypokinesia). In the present study, striatal dopamine depletion was effected unilaterally, in order to dissociate generalized effects, e.g. hyperkinesia, from response-specific initiation effects. Rats were trained in a lateralized visual reaction time task and then assigned to one of four groups: striatal dopamine depletion; cell body lesion of the subthalamic nucleus; combined striatal dopamine depletion and subthalamic nucleus lesion; or control. As expected, rats with striatal dopamine depletion exhibited slower reaction time and a bias to respond to the ipsilateral side. The subthalamic nucleus lesion resulted in no reaction time change (in particular, there was no evidence of faster reaction times), but there was an increase in anticipatory responding. The group with the combined striatal dopamine depletion and subthalamic nucleus lesion had no reaction time impairment. This group showed an increase in anticipatory errors and a contralateral response bias. These data demonstrate that lesions of the subthalamic nucleus do not merely cancel the akinesia which follows striatal dopamine depletion by the addition of a hyperkinetic impairment. Rather, there appears to be a change in the balance of the motor system.

Simple and choice reaction-time performance following occlusion of the anterior cerebral arteries in the rat

Focal cerebral ischemia in the rat has traditionally been studied by examining the consequences of middle-cerebral artery occlusion. However, the anteriorcerebral arteries of the rat may now also be bilaterally occluded by stereotaxic injection of the vasoconstrictor endothelin-1, resulting in ischemic damage to medial prefrontal cortex and the anteromedial basal forebrain. The behavioural consequences of anterior-cerebral artery occlusion (ACAo) were studied in two experiments using simple and choice reaction-time tasks designed to dissociate response impairments from dysfunction of motivation and attention, respectively. Following ACAo, reaction-time increased post-surgery in the choice, but not simple reaction-time task. There was also an increase in incorrect choices in the choice reaction-time task. However, the impairments were independent of motivational or attentional function, which remained intact. Although the ACAo-induced ischemic damage did not disrupt motivation or attention, the results suggest that the lesion results in an executive impairment in selecting and initiating responses.

Effects of excitotoxic lesions of the rat ventral striatum on the perception of reward cost

This study examined the possibility that lesions of the nucleus accumbens in rats impair the perception of the "cost of reward", as defined by the number of operant responses needed to obtain a food pellet. In a first experiment, visual cues indicated the cost of reward under a multiple-ratio schedule of reinforcement. In a second experiment, the number of lever presses required for each reward incremented with each trial in a progressive-ratio schedule of reinforcement. Lesions of the nucleus accumbens altered the behavioral response to the increasing cost of reward when there was an absence of external cues. There was no change in the ability of the lesioned rats to respond to visual cues that indicated reward availability. The results are considered in terms of the traditional idea of the nucleus accumbens as a limbic-motor interface: it is suggested that, if the nucleus accumbens serves such a function, it is limited to only some contexts.

Reaction time deficits and Parkinson's disease

Controversy surrounds the existence and nature of reaction time deficits in Parkinson's disease. Three areas of research are reviewed: the use of precues to speed movement (motor preprogramming), the effects of medication on reaction time, and simple reaction times. No evidence is found for a motor preprogramming deficit, and the presence of a parkinsonian reaction time deficit after medication withdrawal is found to be dependent upon experimental design and the withdrawal method used. Parkinson's disease is found to cause a consistent deficit in simple reaction time. A quantitative analysis of past studies reveals that a parkinsonian reaction time deficit is more likely to be present in tasks that controls can perform with a fast reaction time. This relationship between deficit and control group reaction time applies to choice, but not simple, reaction time tasks. Many studies compare patient and control choice reaction times across experimental conditions that cause control reaction time to vary. The authors of these studies should consider whether their results can be explained in terms of the simple relationship between patient reaction time deficit and control reaction time before drawing more complex conclusions from their data.

Excitotoxic lesions of the subthalamic nucleus ameliorate asymmetry induced by striatal dopamine depletion in the rat

We investigated the effect of unilateral dorsal striatal dopamine depletion (by intrastriatal infusion of 6-OHDA), ibotenic acid lesions of the subthalamic nucleus (STN) and combined dopamine depletion and STN lesions on sensorimotor asymmetry using a test of somatosensory asymmetry [T. Schallert et al., Pharmacol. Biochem. Behav. 16 (1982) 455-462]. The unilateral striatal dopamine depletion resulted in a somatosensory asymmetry. This asymmetry was ameliorated in the rats with combined dopamine depletion and STN lesion. indicating the potential beneficial nature of STN inactivation in rats with striatal dopamine depletion.

Deficits in response initiation, but not attention, following excitotoxic lesions of posterior parietal cortex in the rat

Damage to posterior parietal cortex in humans is known to cause hemineglect, and specifically difficulty in disengaging attention in tests of covert orienting. Aspirative lesions of a region of cortex in rats which is thought to be homologous to primate posterior parietal cortex has also been reported to cause what appears to be multimodal neglect. In order to make an assessment of the nature of this disorder, a variety of tests were employed: (1) a test of somatosensory neglect after Schallert et al. (Pharmacol. Biochem. Behav., 16 (1982) 455-462); (2) a skilled paw-reaching test after Whishaw et al. (Brain 109 (1986) 805-843); (3) a visual reaction time task with peripheral cues analogous to Posner's test of covert orienting (Q. J. Exp. Psychol. 32 (1980) 3-25). Following the posterior parietal lesion there was a global increase in reaction time of responses made contralateral to the lesion in the reaction time task, but there was no evidence of a deficit in covert orienting. There was also no evidence of somatosensory neglect. There was a decrease in the number of attempted reaches which the contralateral paw and a tendency to spend a smaller proportion of time in the contralateral half of the reaching cage.

On the relationships between the striatum and the pedunculopontine tegmental nucleus

In this essay we consider the role of the pedunculopontine tegmental nucleus as a striatal output station. We review the relevant anatomical, electrophysiological, behavioral, and pathological studies and conclude that the pedunculopontine tegmental nucleus occupies an important position in striatal outflow, receiving motor output from the dorsal striatum and information from the ventral striatum relating to limbic processes of motivation and reinforcement. The hypothesis we present is that the pedunculopontine tegmental nucleus is at the very least an integral component of the limbic-motor interface, although in discussing this concept we also assess the likelihood that the limbic-motor interface is in fact a distributed system-that is, that limbic-motor interfacing is not all done by a single structure in the central nervous system but that different aspects of it are served by different systems. We present the hypothesis that the pedunculopontine tegmental nucleus is one critical site through which limbic information concerned with motivation, reinforcement, and the construction of novel associations can gain access to a stream of motor outflow coming from the caudate-putamen and directed toward pontomedullary systems without reference back to the cerebral cortex. This hypothesis is important because it highlights striatal outflow, which is not processed through the cortical re-entry systems, and also emphasizes the importance of pontine systems in cognitive processing.

Assessment of sensorimotor neglect after occlusion of the middle cerebral artery in the rat

Evaluating the efficacy of neuroprotective drugs in rat models of focal cerebral ischemia has involved histological and behavioral batteries to examine treatment outcome. However, the behavioral tests used to date provide little insight into the nature of the neurological impairments. To provide an analysis of a possible "neglect" syndrome after occlusion of the middle cerebral artery, M. I. Posner's (1980) visual attentional paradigm was adapted for use in the rat. A paw-reaching task and a test of somatosensory "neglect" also were used to assess forelimb sensorimotor function. The lesion group displayed unilateral deficits; however, there was no evidence of attentional dysfunction. Results are consistent with the conclusion that the behavioral deficits identified arise from a somatosensory deficit rather than hemineglect due to dysfunctional spatial attention.

The effect of systemic d-amphetamine on motor versus motivational processes in the rat

This study examined the effects of systemic amphetamine in rats performing a reaction time task in which motivation and motor readiness were independently varied. Visual cues indicated the number of trials (one, two or three) needed before reinforcement was made available (i.e., reward cost). Lower reward cost was reflected in both a greater proportion of correctly completed trials and faster reaction times. Reaction times were also shorter as a function of increasing time from start of trial to the onset of the imperative stimulus (foreperiod), reflecting motor readiness or temporal probability summation. It was found that increasing dose of amphetamine resulted in faster reaction times, but the manner in which reaction time was speeded more closely resembled that of motor readiness than it did the speeding due to increasing motivation. Furthermore, the effects on performance of amphetamine and motivational condition were found to be entirely independent: there was no evidence to suggest that amphetamine enhanced, or disrupted, the expectation of forthcoming work or the response vigor which this engenders. It is concluded that systemic amphetamine does not act simply to amplify a natural reward signal. By contrast, amphetamine was found to enhance the effect of foreperiod, suggestive of a mechanism for the psychomotor stimulating effects of amphetamine.

Covert orienting of attention in the rat and the role of striatal dopamine

Attention can be directed to a location in the absence of overt signs of orienting, a phenomenon termed "covert orienting." The ability to orient attention covertly has been well documented in humans, but recent progress has been made with the operational definition of the processes involved in covert orienting. Reaction times to visual targets are quickened when attention is drawn to the location of the subsequent target, and processes such as disengagement, maintenance, and movement of attention can be dissociated by using this method. The possible involvement of striatal dopamine in covert orienting is disputed, with conflicting reports of deficits in covert orienting in patients with Parkinson's disease. To examine the significance of dopamine in the striatum in attentional processes, a test of covert orienting, analogous to that used in humans, was devised for the rat. Unilateral dopamine-depleting lesions of the striatum resulted in increases in mean reaction times contralateral to the side of the lesion, but reaction times did not change differentially as a function of the requirements to maintain, disengage, or shift attention. These findings add additional support to the hypothesis that the deficit that appears as hemineglect observed after striatal damage reflects a motor impairment rather than damage in neural systems underlying mechanisms for directing attention.

Memory for the changing cost of a reward is mediated by the sublenticular extended amygdala

The aim of this study was to examine the role of the sublenticular extended amygdala (SEA) in processes of reward and reinforcement. Previous studies have examined the effects of ibotenate lesions in this area on motivation for cocaine reward. In this study, animals were trained to work for sucrose pellets, rather than a drug, on a progressive-ratio schedule of reinforcement. Bilateral intracerebral infusions of ibotenic acid (lesion group) or vehicle (control group) were made into the SEA, following the same procedures as used in previous studies. After recovery from surgery, animals were tested for six sessions on the progressive ratio schedule. The lesion did not result in motivational impairments of the kind that have previously been reported: rather than decreases in breaking point (a measure of motivational strength), the lesion resulted in greater variability of breaking points, with a tendency for lesioned animals to work harder for reward than controls. The SEA-lesioned rats did not show the increase in postreinforcement pause that usually accompanies the increase in perceived work as the number of bar presses for a reward increases. Histological analyses showed that the ibotenate lesions had successfully destroyed the SEA and that damage was also present in adjacent structures. The results are interpreted in terms of a mnemonic, rather than a motivational, deficit.

Discriminative cues indicating reward magnitude continue to determine reaction time of rats following lesions of the nucleus accumbens

The role of the nucleus accumbens in incentive motivation is accepted but poorly understood. In this study, we examined in the rat one aspect of motivated behaviour which might be mediated by the nucleus accumbens, namely the translation of a motivational signal (the expected value of a reward) into motor output (responding for the reward). Rats were trained in a reaction time task in which on each trial they received one, two or three pellets. The number of pellets for each trial was randomly determined in advance and signalled to the rats by cue lights. Rats responded with faster reaction times as the size of the expected reward increased. Following ibotenic acid lesions of the nucleus accumbens, there was no difference in the pattern or the speed of reaction times. Although lesions of the nucleus accumbens did not disconnect the motivational system from the motor system, it is possible that the nucleus accumbens is involved in the learning of the incentive salience of external stimuli. Therefore, after postoperative testing the cue contingencies were reversed. Initially, the cues continued to be interpreted according to their prior significance, but eventually both the lesioned rats and the control group acquired the new relationship and did so in equivalent times. We conclude that the nucleus accumbens is not involved in the acquisition or expression of the processes whereby the expectation of rewards of different value is translated into a motor initiation signal.

Responses of cells in the tail of the caudate nucleus during visual discrimination learning

1. The tail of the caudate nucleus and adjacent ventral putamen (ventrocaudal neostriatum) are major projection sites of the extrastriate visual cortex. Visual information is then relayed, directly or indirectly, to a variety of structures with motor functions. To test for a role of the ventrocaudal neostriatum in stimulus-response association learning, or habit formation, neuronal responses were recorded while monkeys performed a visual discrimination task. Additional data were collected from cells in cortical area TF, which serve as a comparison and control for the caudate data. 2. Two monkeys were trained to perform an asymmetrically reinforced go-no go visual discrimination. The stimuli were complex colored patterns, randomly assigned to be either positive or negative. The monkey was rewarded with juice for releasing a bar when a positive stimulus was presented, whereas a negative stimulus signaled that no reward was available and that the monkey should withhold its response. Neuronal responses were recorded both while the monkey performed the task with previously learned stimuli and while it learned the task with new stimuli. In some cases, responses were recorded during reversal learning. 3. There was no evidence that cells in the ventrocaudal neostriatum were influenced by the reward contingencies of the task. Cells did not fire preferentially to the onset of either positive or negative stimuli; neither did cells fire in response to the reward itself or in association with the motor response of the monkey. Only visual responses were apparent. 4. The visual properties of cells in these structures resembled those of cells in some of the cortical areas projecting to them. Most cells responded selectively to different visual stimuli. The degree of stimulus selectivity was assessed with discriminant analysis and was found to be quantitatively similar to that of inferior temporal cells tested with similar stimuli. Likewise, like inferior temporal cells, many cells in the ventrocaudal neostriatum had large, bilateral receptive fields. Some cells had "doughnut"-shaped receptive fields, with stronger responses in the periphery of both visual fields than at the fovea, similar to the fields of some cells in the superior temporal polysensory area. Although the absence of task-specific responses argues that ventrocaudal neostriatal cells are not themselves the mediators of visual learning in the task employed, their cortical-like visual properties suggest that they might relay visual information important for visuomotor plasticity in other structures. (ABSTRACT TRUNCATED AT 400 WORDS)

Using flowcharts in policy development: reporting abuse and neglect of patients

Reports of abuse, both domestic and institutional, are increasingly common. A myriad of statutes and rules govern when and how incidents of abuse are reported. It is incumbent upon medical centers to establish policies that clearly outline the responsibility of all staff members to identify and report suspected abuse and neglect. This article presents a summary of a comprehensive hospital policy on identifying and responding to all types of suspected or witnessed abuse and neglect of patients. It also illustrates how multidisciplinary teams and flowcharts can be useful in developing and implementing policy in complicated areas that involve many players, rules, and regulations.

Covert orienting of attention in macaques. I. Effects of behavioral context

1. A task was used by Posner (1980) to measure shifts of attention that occurred covertly, in the absence of an eye movement or other orienting response. This paradigm was used here to assess the nature of covert attentional orienting in monkeys to develop an animal model for neurophysiological studies. Shifts of attention were measurable in monkeys and were consistent across a variety of experimental conditions. 2. The paradigm required that monkeys fixate and release a bar at the appearance of a target, which was preceded by a cue. Reaction times to targets that followed peripheral cues at the same location (validly cued) were significantly faster than those that followed cues in the opposite visual field (invalidly cued). This difference was defined as the validity effect, which as in humans, is used as the measure of a covert attentional shift. 3. When the proportion of validly to invalidly cued targets was decreased, no change was seen in the validity effect of the monkeys. This is in contrast to humans, for whom the ratio of validly to invalidly cued targets affected the magnitude of the validity effect. When 80% of the targets were preceded by cues at the same location, the validity effect was greatest. The effect was reversed when the proportions were reversed. From this result, it is concluded that cognitive processes can affect covert orienting to peripheral cues in humans, whereas in trained monkeys, performance was automatic. 4. To test whether cognitive influences on attention could be demonstrated in the monkey, an animal was taught to use symbolic, foveal signals to covertly direct attention. The magnitude of this validity effect was greater than that obtained with peripheral cues. 5. The effects of motivational and perceptual processes were tested. Although overall reaction times could be modified, the facilitating effects of the cues persisted. This constancy across motivational and perceptual levels supports the notion that the monkeys were performing the task in an automatic way, under the exogenous control of peripheral cues. 6. Most visual cuing has been tested with visual landmarks at the locations of cues and targets. These monkeys were trained with such landmarks, and when tested without them, the attentional effect of the cues was nearly abolished. These data suggest that local visual features can be important for covert orienting. 7. To determine the spatial extent of the effect of the cue, monkeys and humans were tested with four cue-target distances (0-60 degrees).(ABSTRACT TRUNCATED AT 400 WORDS)

Dopamine dependent reaction time deficits in patients with Parkinson's disease are task specific

This study tested the hypothesis that patients with Parkinson's disease are impaired when they must rely on internal information to generate a response. Choice reaction times of control subjects and patients with Parkinson's disease, on and off their medication, were measured in tasks in which the motor demands were constant but which varied in the degree to which the stimuli held intrinsic information about the required response. A dopaminergic deficit was observed only in the tasks which employed stimuli compatible with the response and not in a task employing stimuli arbitrarily associated with the response. The data do not support the hypothesis that patients are differentially impaired in using internalized stimulus-response relationships.

Is calcium oxalate an adequate explanation for nonvisualization of breast specimen calcifications?

This study was initiated to determine whether the apparent calcium loss during histologic breast specimen processing could be explained by the presence of birefringent, transparent calcium oxalate crystals (type I). In previous investigations, the authors had noted a possible loss of 26.2% of calcium during the processing and sectioning of breast specimens. Two hundred thirteen histologic slides prepared from blocks demonstrating calcium radiographically but not histologically were reviewed with polarized light. An additional 506 slides from 19 malignancies appearing as microcalcifications were also reviewed with polarized light. Only one slide from each group (0.2% and 0.5% from the malignant and benign groups, respectively) demonstrated birefringent calcium oxalate (type I). Thus, the presence of calcium oxalate does not sufficiently explain the non-visualization of calcium, which is due instead to processing of breast specimens.

Breast specimen microcalcifications: radiographic validation and pathologic-radiologic correlation

A prospective analysis of specimens from location and biopsy of mammographically suspect microcalcifications in 108 patients was carried out to determine if microcalcifications were lost during histopathologic processing and the clinical relevance of such loss. Nine hundred sixty-eight paraffin blocks were prepared from 425 gross tissue slices containing calcifications identified at radiography of the specimens. Calcium was apparently lost both during preparation of the blocks (13.6%) and after slide preparation (12.6%), for a total possible loss of 26.2%. All specimens demonstrated calcification histologically. One pathology report was amended because of information obtained after recuts, but all cancers were detected on original slides whether or not calcifications were identified initially. The results indicate that, by following the suggestions offered to ensure adequate histopathologic sampling of calcification seen at mammography, most if not all of the calcification present can be detected on the original slide.

Response-related deficits following unilateral lesions of the medial agranular cortex of the rat

Rats with lesions of the medial agranular frontal cortex (AGm) were tested for sensorimotor function. Spatial response bias and reaction time to lateralized visual targets were recorded in an automated test of visual reaction time. The same rats were also tested for somatosensory capacity and on a skilled reaching task. In all tasks, there was an ipsilateral response bias but no evidence of sensory neglect. In the visual reaction time task, initiation time was lengthened bilaterally. These deficits may parallel the effects on motor function after unilateral frontal cortical lesioning in primates. The results support the hypothesis that rat AGm contains a homologue of primate secondary motor cortex.

Simple and choice reaction time performance following unilateral striatal dopamine depletion in the rat. Impaired motor readiness but preserved response preparation

Rats were trained to perform a visual spatial discrimination, where stimulus luminance provided information regarding the required direction of response. The visual stimuli were presented either in advance of a temporally unpredictable auditory imperative stimulus (simple reaction time condition) or simultaneously with the imperative stimulus (choice reaction time condition). Following unilateral striatal dopamine depletion, produced by intracerebral infusion of 6-hydroxydopamine, there was not only a marked spatial response bias towards the side of the dopamine depletion but also an abolition of the delay-dependent speeding of reaction time that reflects motor readiness, on the side contralateral to the lesion. Nevertheless, the rats continued to show a benefit in performance of the simple reaction time condition compared with the choice reaction time condition, indicating that they were able to use advance information to select and prepare responses. The results are discussed in the context of differential deficits shown by patients with Parkinson's disease in simple versus choice reaction time performance, and of the functions of parallel corticostriatal loops subserving the normal control of action.

Response-related deficits following unilateral lesions of the medial agranular cortex of the rat

Rats with lesions of the medial agranular frontal cortex (AGm) were tested for sensorimotor function. Spatial response bias and reaction time to lateralized visual targets were recorded in an automated test of visual reaction time. The same rats were also tested for somatosensory capacity and on a skilled reaching task. In all tasks, there was an ipsilateral response bias but no evidence of sensory neglect. In the visual reaction time task, initiation time was lengthened bilaterally. These deficits may parallel the effects on motor function after unilateral frontal cortical lesioning in primates. The results support the hypothesis that rat AGm contains a homologue of primate secondary motor cortex.

Elementary processes of response selection mediated by distinct regions of the striatum

The relative contributions of the medial and lateral caudate putamen to performance of a visual reaction time task were compared by examining the effects of unilateral ibotenate-induced lesions to these regions in the rat. Different groups of rats were trained to respond either towards (Discrimination 1) or away from (Discrimination 2) unpredictable, brief visual stimuli presented to either side of the head. Lateral striatal lesions produced a strong spatial bias towards the side of the lesion but left the latency for the initiation of responses to the visual cues unchanged. By contrast, the medial striatal lesions resulted in a smaller degree of spatial response bias but a significant slowing of initiation latency to the side contralateral to the lesion. These effects were irrespective of the side of the stimulus presentation and thus represent response-related impairments. The lesions were further dissociated in their effects on responding inappropriately to task requirements. These results demonstrate a double dissociation of behavioral effects of lateral and medial striatal damage that can be used to infer the operation of distinct elementary processes of response output within a single task. They are important not only in demonstrating functional effects of hypothetical segregated parallel corticostriatal loops but also in showing that these loops must interact to produce integrated performance.

Comparison of adrenal and foetal nigral grafts on drug-induced rotation in rats with 6-OHDA lesions

Separate groups of rats with unilateral 6-OHDA lesions of the nigrostriatal pathway received intrastriatal foetal (E14) substantia nigra suspension grafts, intrastriatal postnatal (P22-25) adrenal medulla suspension grafts using either collagenase- or trypsin-based dissociation procedures, intraventricular adrenal medulla grafts, or remained with lesions alone. Rats with nigral or adrenal suspension grafts, but not rats with adrenal solid grafts, showed reduced apomorphine-induced rotation in comparison with lesion rats. The nigral graft group alone showed substantial reduction of amphetamine-induced rotation, and this was the only group manifesting good long-term graft survival. These results indicate that nigral and adrenal grafts do not have comparable mechanisms of functional action, and suggest that adrenal grafts can ameliorate apomorphine-induced rotation by a non-specific mechanism.

Deficits in response space following unilateral striatal dopamine depletion in the rat

Hungry rats were trained to report the occurrence and location of brief, unpredictable visual stimuli presented to the left of their heads in 1 of 2 response locations. After training, they received unilateral infusions of 6-hydroxydopamine, depleting dopamine throughout the head of the caudate putamen, either on the left or the right side, that is, either ipsilateral or contralateral to the side on which they were required to respond. Following an ipsilateral lesion there were no impairments in localization of the visual discriminanda and there was no lengthening of reaction time. The contralaterally lesioned rats, however, showed considerably lengthened reaction times to both stimuli and a profound bias to the nearer of the 2 response locations. Evidence from probe trials in which the visual stimuli were presented separately or simultaneously showed that the impairment was not due to a failure to localize the stimuli in contralateral space but, rather, resulted from a deficit in directing responses in contralateral space. It is suggested that this may be due to a distortion in the representation of response space.