Adverse effects of childhood lead poisoning: the clinical neuropsychological perspective

Elevated blood lead levels in children can result in brain injury and, as a consequence, have negative effects on cognitive functioning and behavior. Risk assessment studies have focused on psychological measures, especially IQ, and also school achievement and behavioral adjustment as endpoints. Such studies, like epidemiological work in other areas, by necessity examine effects in large groups rather than in individuals. Since the peer-reviewed literature primarily describes those adverse effects noted in epidemiological studies, little or no attention has been directed to what is observed in the individual. The present review describes the presentation of individual lead-poisoned children from the perspective of the clinical neuropsychologist. The sequelae of lead poisoning typically observed in evaluation of individuals provide information in addition to that gained from risk assessment studies and has implications for the mechanisms and treatment of this disease. In addition, attention to certain aspects of individual case presentation does provide information relevant to issues of public health.

Inhibition of progenitor cell proliferation in the dentate gyrus of rats following post-weaning lead exposure

Although lead is a potent developmental neurotoxin, the effects of postnatal lead exposure on progenitor cell proliferation in the hippocampus has not been examined. Postnatal day 25 rats were fed a lead containing diet (1500 ppm lead acetate) for 30-35 days and administered bromodeoxyuridine (BrdU, 50 mg/kg, i.p.) during the last 5 days of lead exposure. Animals were killed 24 h after the last BrdU injection. Proliferation of new cells in the subgranular zone and dentate gyrus was significantly decreased in lead-exposed rats compared to control animals that ate a similar diet devoid of lead. These results suggest that postnatal lead exposure can have significant deleterious effects on progenitor cell proliferation and thus the structure and function of the hippocampus.

Enriched environment during development is protective against lead-induced neurotoxicity

It is known that children of lower socioeconomic status have a disproportionately higher risk of being exposed to lead and have a more negative outcome from that exposure than children who are raised under more fortunate circumstances. Yet, little is known about how environmental factors may influence the injurious effects on the brain of a neurotoxin such as lead. The present study used an animal model of lead poisoning to examine the extent to which different environmental milieus may modify the effects of lead on the developing brain. Young rats were raised in either enriched or impoverished environments and drank either distilled water or water with lead. Lead-exposed rats raised in the impoverished environment had spatial learning deficits and significantly decreased neurotrophic factor gene expression in the hippocampus. In contrast, the animals raised in the enriched environment were significantly protected against the behavioral and neurochemical toxicity of lead. These results demonstrate that impoverished environment may accentuate while enriched environment may ameliorate neurobehavioral and neurochemical toxicity from developmental lead exposure.

Persisting insomnia following traumatic brain injury

Persisting insomnia secondary to traumatic brain injury, rarely reported and documented, is described in an adult male following head injury. The neuronal mechanisms underlying this sleep disorder as well as the neuropsychological concomitants and therapeutic approaches are discussed.

Behavioural context and a distributed system: metabolic mapping studies of the basal ganglia

Behavioural context is known to affect neural activity in the striatum. Responses of single cells increase to rewarding stimuli, or drop out as a bar press or saccade is learned. Networks that can accomplish a unique response to changing contexts are of particular interest to systems neuroscience and were a part of Hebb's interest in perception and learning. An overall map of the striatum that localizes changes related to this remarkable phenomenon of contextual responses contributes to our understanding of anatomical substrates of neural systems that integrate information, and may lead us to new striatal regions to study synaptic mechanisms of learning.

Persistent cognitive and motor deficits following acute hydrogen sulphide poisoning

This case study describes the long-term after-effects of hydrogen sulphide exposure in a previously health 27-year-old male. Upon hospital admission the patient had a Glasgow Coma Score (CGS) of 3; with emergency treatment including hyperbaric oxygen treatments, he progressed to a GCS of 15 on day 7. Although both CT and MRI scans were unremarkable, PET using F-18 deoxyglucose administered 3 years after the accident showed abnormally decreased metabolism bilaterally in the temporal and inferior parietal lobes as well as the left thalamus. Uptake in the striatum was heterogeneous and abnormal. A cerebral perfusion study using SPECT performed 3.5 years after the accident revealed bilaterally decreased flow in the putamen but no cortical abnormalities. Neuropsychological and neurofunctional testing revealed the following impairments: microsmia, psychomotor slowing, extrapyramidal signs and deficits in memory and executive/planning functioning. These findings are discussed in the context of hydrogen sulphide's known mechanisms of toxicity and the functions of the basal ganglia.

Chronic neuroleptic treatment alters expression of glial glutamate transporter GLT-1 mRNA in the striatum

Recent reports have shown that typical neuroleptics may enhance glutamatergic neurotransmission and that these effects might in part underlie motor side effects of chronic neuroleptic treatment. Since glutamate reuptake is the primary mechanism for controlling extracellular glutamate levels, the present study was conducted to examine whether chronic neuroleptic exposure alters gene expression for the glutamate transporter GLT-1 in the striatum. Although both haloperidol and clozapine treatment for 30 days significantly decreased GLT-1 expression from normal, the effects of haloperidol treatment were consistently, and in the dorsal striatum, significantly greater than those of clozapine. These findings suggest that a deficiency in glutamate transport may underlie the pathogenesis of neuroleptic-induced movement disorders.

Antipsychotic drug effects on glutamatergic activity

Previous work from this laboratory indicated that some antipsychotic drugs possess unique action at N-methyl-D-aspartate (NMDA) receptors. A functional neurochemical assay showed that, at concentrations similar to those found in the cerebrospinal fluid (CSF) of schizophrenics, antipsychotic drugs augment NMDA activity while, at higher concentrations, NMDA activity is suppressed. Using similar analysis, the present paper reports that this pattern of response is also shown by the antipsychotic drugs thioridazine and chlorpromazine. In contrast, promazine, which is structurally similar to chlorpromazine but lacking both D2-effects and antipsychotic potency, had no influence on NMDA receptors. In addition, sulpiride and metoclopramide, drugs with high affinity for D2-dopamine receptors but with weak or no antipsychotic efficacy, also lack effects at the NMDA receptor. Thus, the drugs with clinical efficacy that were tested in the present and previous studies all share unique influence on NMDA receptors. Further work with other antipsychotic agents will be necessary to determine if influence on NMDA receptors contributes to antipsychotic effectiveness.

Sensory and cognitive functions of the basal ganglia

Recent studies have found that the basal ganglia are involved in diverse behavioral activities and suggest that they have executive functions. Highlights from the past year include anatomical and clinical studies that have used sophisticated, novel methods to confirm a role for the basal ganglia in somatosensory discrimination, visual perception, spatial working memory and habit learning.

Glutamate agonist activity: implications for antipsychotic drug action and schizophrenia

Antagonist action at dopamine D2 receptors appears to explain many, but not all of the effects of antipsychotic drugs. Because of the interactions of dopamine with glutamate, and the implication of the latter in the etiology of schizophrenia, possible effects of antipsychotic drugs on glutamate receptors were assessed in the present experiments. These studies showed that, at clinically relevant concentrations, the conventional neuroleptic haloperidol and the atypical antipsychotic clozapine had potent augmenting influences on the NMDA receptor. These data suggest that unique action at glutamate receptors may contribute to antipsychotic efficacy and emphasize the potential importance of glutamatergic dysfunction in the etiology of schizophrenia.

Taurine prevents haloperidol-induced changes in striatal neurochemistry and behavior

Repeated daily administration of haloperidol produces changes in striatal neurochemistry (decreased dopamine synthesis, upregulation of D2 receptors) and behavior (increasing catalepsy). Coadministration of taurine greatly attenuated these neuroleptic-induced changes. Possible mechanisms of taurine's mitigating effects are its attenuating influences on glutamatergic transmission and its actions as a GABAA agonist. The possibility was discussed of adding taurine to chronic antipsychotic regimens to block the side-effects typically accompanying such therapy.

Differential recovery of volitional motor function, lateralized cognitive function, dopamine agonist-induced rotation and dopaminergic parameters in monkeys made hemi-parkinsonian by intracarotid MPTP infusion

There is still controversy regarding the frequency and extent of spontaneous functional recovery in primate models of parkinsonism, perhaps in part stemming from the variety of ways in which recovery has been assessed. The present study examined functional recovery in monkeys made unilaterally parkinsonian by intracarotid infusion of MPTP. Monkeys were evaluated prior to lesioning and for at least 1 year after lesioning on a battery of tests including a rating of spontaneous behaviors, a learned reaction time/movement time task, tests of lateralized neglect or inattention (i.e. lateralized reward retrieval task, extinction with double simultaneous stimulation, and response to a target moving from one hemispace to the other), and rotational asymmetry in response to a dopamine agonist. Some animals also received 6-[18F]Fluoro-L-Dopa (F-DOPA) position emission tomography (PET) scans before MPTP, when symptomatic, and when showing signs of functional recovery. These animals were sacrificed for post mortem neurochemical assessment following the last PET scan. Results showed that estimates of functional recovery in hemi-parkinsonian monkeys may depend upon the behavioral assay used. Even in behavioral tasks that were sensitive to recovery effects, the degree of functional recovery shown by an animal on one such task did not predict recovery on another. This may in part be due to the inherent difficulty in designing behavioral tests to assess basal ganglia functioning, when there is no consensus concerning which aspects of behavior the normal basal ganglia actually control.(ABSTRACT TRUNCATED AT 250 WORDS)

Reevaluation of the mesolimbic hypothesis of antipsychotic drug action

Conventional neuroleptic drugs are thought to derive their antipsychotic efficacy through influences on the mesolimbic dopamine (DA) system. In contrast, motor side effects of these drugs are suggested to follow from influences on the nigrostriatal DA system. This conceptualization is based on the assumption that behaviors mediated by the mesolimbic DA system are involved in schizophrenia while behaviors controlled by the nigrostriatal system are not. In this article, it is argued that although assumptions about mesolimbic activities may indeed be correct, those concerning the nigrostriatal system certainly are not. This being the case, drugs with mesolimbic-specific activity may not have significant antipsychotic potency and probably will not be free of motor side effects. The current thrust of neuropharmacology, which emphasizes development of drugs with pharmacological specificity rather than anatomical selectivity, is more likely to generate new antipsychotic agents with a reduced risk of motor side effects.

Effects of experience on striatal sensory responses

It has been well documented that striatal neurons encode and process sensory information. It was the aim of the present experiment to determine the extent to which behavioral experience influenced striatal sensory responses. Single units were recorded in the striatum of awake restrained cats as they were adapted to the recording situation. To facilitate recording, cats were rewarded with milk for remaining quiet and motionless. As animals evidenced familiarity with the testing environment, striatal neurons showed heightened sensory receptivity. These results indicate the important influence of behavioral determinants of striatal sensory responses. The nature of the behavioral experience may determine the way in which sensory information is processed in this part of the basal ganglia.

Anti-glutamatergic effects of clozapine

Clozapine (Cz) is unique in its efficacy with treatment refractory patients and its freedom from motor side effects. The present work shows that Cz, even after dopamine depletion, suppresses responses evoked via the monosynaptic glutamatergic corticostriatal pathway. In addition, Cz is effective in displacing [3H]MK-801 from striatal homogenates. These data indicate that Cz is a glutamate antagonist. It is unclear, however, if this pharmacological action could explain Cz's lack of motor effects and it's antipsychotic potency.

Acute administration of haloperidol enhances dopaminergic transmission

It has been demonstrated that haloperidol, by blocking presynaptic D2 receptors, enhances dopamine release. However, it is generally assumed that augmentation of dopaminergic transmission is precluded by haloperidol's postsynaptic actions. This assumption was assessed in the present experiment by testing the effects of acute haloperidol administration on the activity of the striatum. Somatosensory stimulation was used to evoke striatal field potentials in rats anesthetized with either urethane or sodium pentobarbital. Haloperidol suppressed striatal responses in a dose-dependent fashion. Enhanced dopaminergic activity, caused by i.v. cocaine or substantia nigra stimulation, similarly suppressed striatal responses. Rather than blocking the effects of cocaine in the striatum, coadministration of haloperidol was additive, causing increased suppression. Substantia nigra lesions that depleted striatal dopamine blocked the suppressive effects of haloperidol. Administration of R-(+)-8-chloro-2,3,4,5-tetrahydro-3- methyl-5-phenyl-1H-3-benzazepine-7-ol to prevent postsynaptic actions of dopamine mediated by D1 receptors did not attenuate haloperidol-induced suppression. The present data suggest that acute administration of haloperidol actually augments dopaminergic activity due to relatively strong presynaptic actions and relatively weak postsynaptic blocking effects. It is plausible that this initial increase in dopaminergic transmission may participate in producing the neural changes evoked by chronic haloperidol administration that allow this drug to have antipsychotic potency.

Clozapine's mechanisms of action: non-dopaminergic activity rather than anatomical selectivity

The mechanisms of clozapine's unusual actions were investigated in anesthetized rats. Sensory field potentials were recorded in the nucleus accumbens, striatum and somatosensory cortex. Both haloperidol and clozapine suppressed responses in the striatum and accumbens. Clozapine's but not haloperidol's subcortical actions were unaffected by dopamine depletion. In addition, the cortical effects of the two drugs differed. These data indicate that clozapine has non-dopaminergic activity but no particular specificity for limbic basal ganglia structures. While it is known that clozapine acts as a serotonergic and cholinergic antagonist, several considerations suggest that action on still another transmitter system, possibly glutamate, needs to be investigated.

Nerve conduction studies in chickens given phenyl saligenin phosphate and corticosterone

Clinical signs of delayed neuropathy were induced in adult white leghorn chickens given the organophosphorus ester phenyl saligenin phosphate (PSP, 2.5 mg/kg im) 22-24 d before assessment of nerve conduction parameters. Damage to the myelinated sensory portion of the sciatic nerve was indicated by abnormal compound action potentials in treated chickens. In particular, the amplitude of the A beta response was markedly reduced. In addition, the A beta fibers did not respond normally to increasing stimulation intensity. These parameters were more like controls in chickens that had been given PSP and 30 ppm corticosterone for 11 d, beginning 1 d before PSP administration. These studies indicated that nerve conduction parameters could distinguish peripheral nerve damage in chickens given PSP and improvement could be noted in chickens treated with corticosterone.

The effects of movements on caudate sensory responses

The aim of this experiment was to assess the effects of movement on somatosensory processing in the caudate nucleus. Units were recorded extracellularly in the caudate of awake partially restrained cats. Unit responses were evoked by either natural stimuli (brushing and skin indentation) or transcutaneous electrical stimulation. Response patterns evoked by stimuli presented when the cat was at rest were compared to responses evoked by similar stimuli presented when the cat was either making buccolingual movements or turning its head. In the majority of cases, movement suppressed caudate somatosensory responses. However, impressive augmentation of responses was seen in some cells with either type of movement.

Striatal influences on paravermal cerebellar activity

Units were recorded extracellularly in paravermal cortex (lobule VI) of the cerebellum of chloralose anesthetized cats. Electrical stimulation of the striatum evoked excitation followed by inhibition in these neurons. In addition, the somatosensory properties of these cells were also affected by the striatum. A conditioning-test paradigm (C-T) was used in which conditioning stimulation was applied to the striatum. Test responses were evoked in cerebellar neurons by facial stimulation. As a function of the C-T interval, striatal stimulation could either enhance or suppress the test facial responses. In another procedure, a moveable electrode was used to map the thresholds for affecting the cerebellum from different points in the striatum. The lowest mean threshold was in the putamen followed respectively by the internal capsule and caudate nucleus. Control experiments suggested that striatal effects on the cerebellum were due neither to extra-striatal current spread nor antidromic activation of corticostriatal fibers. These data were discussed with regard to models of striatal motor functioning that indicate a role in postural control and sensory gating.

Peripheral neuropathy of dietary riboflavin deficiency in chickens

A strain of rapidly growing meat-type chickens was fed a diet deficient in riboflavin from 1-40 days of age. Diminished growth rate, progressive gait abnormality and reluctance to move were noted beginning on day 8. Neurologic abnormalities were related to peripheral neuropathy characterized by Schwann cell hypertrophy and degeneration with cytoplasmic lipid droplets' and segmental demyelination. Lesions were initially detected on day 10, and in concert with clinical signs became more profound between days 14 and 21. Sequestration of myelin debris within Schwann cells was common. Other features of the neuropathy included the presence of endoneurial edema and axonal degeneration involving small numbers of fibers. Remyelination of peripheral nerve fibers in birds on the deficient diet was occasionally seen on day 10, became progressively more prominent, and was marked by day 37. There was an associated, variable but incomplete, clinical improvement evident in later stages of the study. Liver concentrations of riboflavin in deficient birds were significantly reduced on day 13 but not on day 26. This neuropathy may be related to diminished tissue levels of the riboflavin-based coenzymes flavin-adenine dinucleotide (FAD) and flavin mononucleotide (FMN) leading to reduced cellular energy levels and profoundly affecting Schwann cells at some critical point in growth.

Influences of the basal ganglia on the medullary reticular formation

Units were recorded extracellularly in the medullary reticular formation of chloralose-anesthetized cats during electrical stimulation of the basal ganglia (BG). Stimulating portions of the BG (caudate nucleus, entopeduncular nucleus, substantia nigra) evoked unit responses in a considerable proportion of these neurons. The majority of reticular cells that were affected by the BG were also receptive to somatic sensory inputs from the face. These units' sensory properties were influenced by BG stimulation. Cells exclusively responsive to either BG or facial inputs were uncommon. The areas of the reticular formation affected by the BG give rise to portions of the reticulospinal tracts and thereby afford the BG access to the final common path.

Caudate neuronal activity in cats during head turning: selectivity for sensory-triggered movements

Units were recorded extracellularly from the caudate nucleus (CN) of cats during movement. The majority of CN units fired during sensory-triggered movements rather than movements in general. However, sensory stimulation was a necessary but not a sufficient condition for CN unit responding; stimuli caused unit responses only when movements were evoked. Additionally, only movements triggered by particular stimuli were associated with unit responding. These unit responses were not sensory because neural activity changes were associated with movement onset rather than stimulus presentation. These data are in accord with recent suggestions of a sensory-based motor function for the basal ganglia.

Substantia nigra projection to medullary reticular formation: relevance to oculomotor and related motor functions in the cat

Wheat germ lectin-horseradish peroxidase was injected into the medial medullary reticular formation in 4 cats. Retrogradely labeled cell bodies were observed in the ipsilateral substantia nigra pars reticulata and bilaterally in the superior colliculus, oculomotor nucleus and fastigial nucleus of the cerebellum. The nigral projection to this reticular formation area, which receives diffuse afferents from cortex, cerebellum, oculomotor system and vestibular nucleus and projects to spinal cord, may be of some relevance in understanding the nigral role in postural, head- and eye-movement control.

A consideration of sensory factors involved in motor functions of the basal ganglia

There is a sizeable literature concerning basal ganglia (BG) functioning that is based on data from experiments employing a method of analysis that is traditionally used with other motor areas. A brief review of this literature is presented and the following conclusion is reached: as compared to the success of traditional methodologies in elucidating the workings of other motor systems, their use in BG investigations has proven disappointing. A possible reason for the shortcomings of traditional analyses in BG research is discussed. The remainder of this review concerns an alternative approach to the study of the BG that follows from consideration of a variety of clinical and experimental findings. The literature suggests that sensory aspects of BG functioning must be taken into account to fully appreciate the role of this system in motor control. A review of the literature concerning the latter suggests two points: The BG function as sensory analyzer for motor systems. That is, the BG convert sensory data from a form that is receptor oriented to a form that is relevant for guiding movement. The BG ultimately affect movement by gating sensory inputs into other motor areas rather than by directly affecting these areas. This sensory-based model of BG functioning explains a number of apparent discrepancies in the literature. In addition, seemingly anomalous findings are reconciled with the overwhelming evidence that the BG are a motor system. In particular, the suggestions of a BG role in attention and cognition are viewed as being intrinsic rather than orthogonal to the role of the BG in movement.

Somatosensory properties of globus pallidus neurons in awake cats

The somatosensory properties of globus pallidus (GP) neurons were assessed in awake restrained cats. Forty-two percent of GP units responded to stimulation of the face. Receptive fields were typically bilateral (49%) or contralateral and 75% included perioral tissues. Responsive units showed little ability to encode force. In contrast, cells were sensitive to changes in stimulus location within the receptive zone. The majority of cells so tested showed enhanced responding to stimuli applied within the perioral zone. Many (42%) of the cells which responded to brushing of the guard hairs or vibrissa were directionally sensitive. Of those, 89% showed enhanced responding to stimuli which moved toward the front of the mouth. These data were discussed in relation to a role of the GP in feedback regulated head positioning movements.

A device enabling single unit recordings during head movements in cats

An inexpensive light weight head restraint device enabling horizontal rotational head movements is described. The restrainer provides sufficient stability to allow prolonged single unit recording and is compatible with conventional recording techniques.

Are movement disorders the most serious side effects of maintenance therapy with antipsychotic drugs?

This paper concerns assessment of the full range of risks associated with prolonged use of antipsychotic medication. It is generally accepted that the most common side effects of drug therapy involve motor problems. Movement disorders arise because antipsychotics, in a substantial proportion of patients, disrupt the basal ganglia. The basal ganglia, however, are involved in much more than simply motor control. Specifically, this neural system has been implicated in sensory reactivity, attention, memory, and cognition. It follows from this that antipsychotic drugs, in addition to causing motor problems, might also disrupt complex psychological processes.

Neural mechanisms of tardive dyskinesia

Tardive dyskinesia is a disabling movement disorder, caused by antipsychotic medications, that occurs frequently and is not responsive to treatment. It is not known how the brain damage underlying tardive dyskinesia produces abnormal movement. We propose that altered sensory flow to motor systems results in this syndrome. Verification of such a mechanism could lead to early detection and improved treatment of tardive dyskinesia.

Jaw movements evoked by substantia nigra stimulation: role of extranigral current spread

Electrical stimulation of the substantia nigra in cats elicits jaw movements. A variety of tests were performed to assess the contribution of current spread to this phenomenon. The results of these tests strongly suggest that stimulation-evoked movements are not due to activation of the substantia nigra but rather are the result of current spread to adjacent structures.

Implications of basal ganglionic dysfunction for schizophrenia

This paper is addressed to presenting evidence that the basal ganglia are involved in mediating schizophrenia. Data from the experimental and clinical literature suggest a basal ganglionic role in higher cognitive processes, affect, and attention. Deficits of these same factors serve to characterize the major symptoms of schizophrenia. Moreover, psychiatric patients tend to have frank motor problems characteristic of basal ganglia lesions and pathological conditions of the basal ganglia manifest psychiatric difficulties as a major symptom. Taken together, these data are in accord with the hypothesis that some dysfunction involving the basal ganglia is a major factor in schizophrenia.

The effects of stimulation of trigeminal sensory afferents upon caudate units in cats

This investigation assessed the influences of trigeminal primary sensory afferents upon caudate neuronal activity in locally anesthetized and chloralose anesthetized cats. Afferents from jaw elevator stretch receptors were stimulated via electrodes in the trigeminal mesencephalic nucleus (Mes 5). Afferents from dental and periodontal receptors were stimulated via electrodes in the inferior dental nerve (IDN). Low intensity electrical stimulation of either locus evoked caudate neuronal responses with Mes 5 being more effective. Higher intensity stimulation of IDN in chloralose anesthetized cats was used to determine if thresholds of trigeminal evoked caudate responses corresponded to thresholds of particular fiber groups in the sensory afferent. In all tested units, neuronal responses were only evoked when stimulation was suprathreshold for both A beta and A delta fibers. These data were discussed in relation to processing of oropharyngeal sensory information within the basal ganglia. Possible implications for bucco-lingual dyskinesias were noted.

Trigeminal influences on entopeduncular units

Because considerable work has implicated the basal ganglia in oral-ingestive behavior, an assessment was made of the effects of trigeminal stimuli upon entopeduncular single units. Units wre recorded extracellularly in awake, paralyzed and locally anesthetized cats. The effects of two types of sensory input were tested. Afferents from periodontal mechano-receptors involved in reflex jaw opening were stimulated via electrodes in the inferior dental nerve. Afferents from stretch receptors involved in reflex jaw closure were stimulated via electrodes in the trigeminal mesencephalic nucleus. A significant proportion of cells responded to both types of stimulation. The data were discussed in the context of a basal ganglionic role in oropharyngeal motor processes and a more general role in movement per se.

Effects of hippocampal stimulation on acquisition, extinction and generalization of conditioned suppression in the rat

Rats implanted with electrodes in the dorsal or ventral hippocampus received posttrial stimulation in training sessions with footshock reinforcement. Afterdischarges without overt seizures were consistently without effect on the rate of acquisition of suppression of licking during an auditory conditioned stimulus (CS), although conditioning was retarded by the delivery of distracting stimuli following footshock. The rate of conditioning remained insensitive to elicitation of dorsal hippocampal afterdischarges (DHAD) despite subsequent alterations of session length, intertrial interval and preexposure to the CS. However, faster extinction of suppression occurred following DHAD, suggesting a limited but essential role of the hippocampus in addressing stored information.

Pallidal and entopeduncular single unit activity in cats during drinking

It has been shown that pallidal units display changes in firing rate during food seeking and consummatory behavior. The purpose of the present work was to determine which properties of the ingested material or ingestive behavior were most potent in altering unit activity. Single unit activity was recorded in the globus pallidus and entopeduncular nucleus of awake restrained cats during introduction of fluid into the mouth. A very high proportion of pallidal and entopeduncular neurons showed changes in firing rate during fluid injection. Two patterns of response were observed. Typically, responses were phasic and time-locked to the occurrence of fluid presentation. Less frequently, a long lasting change in firing occurred which persisted throughout the period of fluid introduction. Additional observations indicated that both of these changes in firing rate seemed to be related to the sensory rather than the motor aspects of ingestion.