Sensitization and individual differences to IP amphetamine, cocaine, or caffeine following repeated intracranial amphetamine infusions

Rats that have a high locomotor response to novelty (HR) sensitize more readily to IP-administered amphetamine than rats with a low locomotor response (LR) to novelty. This experiment compared sensitization in HR and LR rats following amphetamine (3.0 micrograms/side for 5 days) infused bilaterally into either the nucleus accumbens (NACC), ventral tegmental area (VTA), or the medial frontal cortex (MFC). The subsequent locomotor response to IP-administered d-amphetamine sulfate (1 mg/kg), cocaine HCl (15 mg/kg), and caffeine benzoate (20 mg/kg) was also examined. No differences were observed between HR and LR rats following amphetamine infusion into either the MFC, NACC, or VTA. However, HR rats showed greater locomotor activity compared to LR rats following either IP amphetamine, cocaine, or caffeine for subjects cannulated in the NACC, MFC, or the VTA. Repeated infusions of amphetamine into the VTA increased the locomotor response to both IP amphetamine and cocaine, but not to IP caffeine, while repeated infusions of amphetamine into the NACC or MFC had no effect on locomotor response to any drug subsequently administered IP. The results support previous findings that changes induced by intra-VTA infusions, but not intra-NACC or MFC infusions, of amphetamine induce sensitization to IP-administered amphetamine and cocaine. Findings from the present experiment indicate the ability of the dopamine cell body region, but not the dopamine terminal fields, to produce locomotor sensitization to amphetamine and cocaine. The results from the present experiment also indicate the lack of localization to one of studied regions of individual differences.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of mesocortical, mesolimbic, and mesostriatal dopamine depletion on spontaneous, conditioned, and drug-induced locomotor activity

Groups of rats with 6-hydroxydopamine (6-OHDA) lesions of either the medial prefrontal cortex (PFC), nucleus accumbens (NAC), or caudate putamen (CPu) were given daily tests for locomotor activity in photocell cages while food deprived. Two separate groups of NAC-lesioned rats were prepared with either large [NACT (90% NAC dopamine depletion)] or partial [NACP (67% NAC dopamine depletion)] lesions. NACT rats were spontaneously hypoactive whereas NACP rats were hyperactive compared with sham-operated controls. PFC-lesioned rats were also hyperactive compared to their respective controls. Spontaneous locomotor activity in CPu-lesioned rats did not differ from shams. When daily food supplements were paired with the photocell cages, all subjects developed a conditioned locomotor response. During the first few days of conditioning, the response to this conditioning procedure was markedly greater in the NACP group whereas the response in the NACT group was unaffected initially and actually enhanced during the latter days of testing. The locomotor response to the conditioning procedure was unaffected in either the PFC- or CPu-lesioned groups. Both the NACT and NACP lesions attenuated the locomotor response to 1.5 mg/kg d-amphetamine sulphate IP, and the NACT group showed a supersensitive response to 0.1 mg/kg apomorphine HCl SC. PFC or CPu 6-OHDA lesions did not alter the response to either drug. These results differentiate the role of PFC, NAC, and CPu dopamine in spontaneous, conditioned, and drug-induced locomotor activity and further implicate dopaminergic mechanisms of the NAC in the magnitude of the behavioural response to incentive stimuli.

Dopaminergic and serotonergic function following isolation rearing in rats: study of behavioural responses and postmortem and in vivo neurochemistry

This series of experiments compared isolation-reared and socially reared rats for their locomotor activity, behavioural stereotypy, and monoamine function both postmortem and in vivo using intracerebral dialysis. In Experiment 1, isolates showed an altered time course of locomotor activity following d-amphetamine sulphate (AMPH) administration (0.5, 2.0, 3.0, or 5.0 mg/kg, SC). Isolation-reared rats also showed increased sensitivity to the sedative effects of a low dose of apomorphine hydrochloride (0.1 mg/kg) but did not differ from social controls following higher doses of the drug (0.5, 1.5, or 3.0 mg/kg, SC). Isolates showed a decrease in the intensity of apomorphine-induced stereotyped behaviours but no change in stereotypy induced by AMPH. In Experiment 2, isolates had higher postmortem dopamine (DA) concentrations and an altered asymmetry in DA function in the medial prefrontal cortex (PFC) but not in the nucleus accumbens (NAC) or caudate putamen (CPu). Isolated rats also had a lower 5-hydroxyindoleacetic acid (5-HIAA)/5-hydroxytryptamine (5-HT) ratio in the NAC (but not in the PFC or CPu) compared to controls. Experiment 3 used intracerebral dialysis to examine monoamine function in vivo following isolation rearing. Isolates showed greater increases in extracellular DA and greater decreases in DOPAC in response to 2 mg/kg AMPH SC in both the NAC and CPu. There were no apparent differences in the perfusate concentrations of either dopamine (DA), dihydroxyphenylacetic acid (DOPAC), or homovanillic acid (HVA) prior to drug administration. However, consistent with the results of Experiment 2, isolates had a reduced basal perfusate concentration of 5-HIAA from the NAC but not from the CPu. Experiment 4 measured postsynaptic DA function in CPu tissue slices following isolation. Isolation rearing did not affect cAMP accumulation in response to stimulation of D1 DA receptors by DA (0, 2.7, 9, or 30 microM). In addition, isolation rearing did not affect the coupling between D1 and D2 receptors, as measured by the increase in cAMP accumulation with 1 microM 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1 H-3-benzazepin (SK&F 38393) and its reduction by 10 microM quinperole hydrochloride (LY 171555). These results are discussed in terms of the possible relationship between these neurochemical findings and the behavioural disturbances following isolation rearing of rats.

6-Hydroxydopamine lesions of the medial prefrontal cortex fail to influence cocaine-induced place conditioning

This study investigated the involvement of medial prefrontal cortex (mPFC) dopamine in cocaine place conditioning using a totally balanced place conditioning design. Presynaptic dopamine terminals of the mPFC were lesioned by bilaterally infusing the selective neurotoxin 6-hydroxydopamine (6-OHDA). These lesions significantly depleted dopamine (-83%) and norepinephrine (-70%) in the mPFC but there were no significant reductions in either the nucleus accumbens or in the caudate-putamen compared with sham-operated controls. Furthermore, serotonin levels were not affected in any of the brain regions investigated. These lesions failed to attenuate place conditioning induced by the intraperitoneal (i.p. 10 mg/kg) administration of cocaine when compared to sham lesioned controls. In addition, there were no significant differences in spontaneous locomotor activity between the two groups during the preconditioning phase or the test phase. These results suggest that 6-OHDA lesions which produced profound depletions of dopamine and norepinephrine in the mPFC did not alter the rewarding efficacy of cocaine as measured by the place conditioning paradigm.

Social isolation increases the density of [125I]omega-conotoxin GVIA binding sites in the rat frontal cortex and caudate nucleus

Rats were reared from weaning either in isolation or in social groups for 12 weeks. Potential isolation-related changes in L- and N-type voltage-sensitive calcium channels (VSCCs) were assessed by the in vitro binding of [3H]isradipine (100 pM) and [125I]omega-conotoxin GVIA (4 pM) to membranes prepared from three discrete central nervous system regions: frontal cortex, caudate nucleus and hippocampus. The [3H]isradipine binding was generally not affected by isolation. However, [125I]omega-conotoxin GVIA binding was significantly higher in frontal cortex (52%) and caudate nucleus (75%) of isolated rats when compared with socially reared controls. The increased [125I]omega-conotoxin GVIA binding reflected an elevated density of binding sites without an alteration of receptor affinity. The possible contribution of an increased density of neuronal N-VSCCs (as labeled with [125I]omega-conotoxin GVIA) to the behavioral and neurochemical changes observed in 'isolation syndrome' is discussed.

Individual differences in amphetamine sensitization: dose-dependent effects

Rats were screened for locomotor activity in a novel environment and divided into high (HR) or low (LR) responders based on whether their locomotor score for the first hour was above or below the median. In the first experiment, HR and LR rats were compared for their locomotor response following repeated administration of either 0.0, 0.5, 1.0, or 1.5 mg/kg d-amphetamine sulfate (AMPH). Injections of either 0.5 or 1.0 mg/kg AMPH produced higher locomotor activity in HR rats than in LR rats. Furthermore, there was a correlation between the locomotor response to novelty and the response to either 0.5 or 1.0 mg/kg AMPH. In addition, whereas both groups of rats developed the same degree of sensitization to 0.5 mg/kg AMPH, only the HR rats developed pronounced sensitization to repeated administration of 1.0 mg/kg AMPH. When both HR and LR were considered, there was a significant correlation between response to novelty and the extent of sensitization to the locomotor-stimulating properties of 1.0 mg/kg AMPH. There were no differences in locomotor activity or sensitization between HR and LR rats following the highest dose of AMPH (1.5 mg/kg). In a separate experiment, HR and LR rats were compared for locomotor activity following a series of intracranial infusions of AMPH. There were no overall differences in locomotor activity between the HR and LR groups following AMPH infusions into either the nucleus accumbens (NACC) or the anterior dorsal striatum (ADS). However, the locomotor activity scores in the novel environment significantly correlated with the locomotor response to 3.0 micrograms AMPH infused into either the NACC or ADS.(ABSTRACT TRUNCATED AT 250 WORDS)

Response to novelty predicts the locomotor and nucleus accumbens dopamine response to cocaine

The relationship between a rat's locomotor response to a novel environment and its behavioral and dopaminergic responses to cocaine was examined. Subjects were divided into two groups based on their locomotor response to a novel environment. Subjects who had a novelty response above the median were classified as high responders (HR), while those with a novelty response below the median were classified as low responders (LR). Following administration of cocaine-HCl (0, 2.5, 5.0, 10.0, or 15.0 mg/kg), HR rats showed a greater locomotor response than LR rats. Moreover, there was a significant correlation between a subject's locomotor response to the novel environment and the locomotor response to either 10.0 (r = 0.65) or 15.0 (r = 0.92) mg/kg cocaine. In a separate experiment, the extracellular concentration of dopamine in the nucleus accumbens (NACC) was monitored using microdialysis procedures. Following cocaine administration (15.0 mg/kg) HR rats showed a larger NACC dopamine response and greater locomotor activity than LR rats. In addition, there was a threefold greater locomotor activity to dopamine ratio in HR rats than in LR rats. A correlation between a subject's locomotor response to a novel environment and the dopaminergic response to cocaine was also evident. These results suggest that differences in the locomotor response to cocaine can, to some degree, be predicted by a rat's locomotor response to a novel environment, and that variations in dopamine-dependent mechanisms of the NACC may underlie these individual differences.

Head circumference in elderly long-stay patients with schizophrenia

The head circumference of a long-stay population with schizophrenia was compared with that of a population with dementia, matched for sex and year of birth. Schizophrenics had a smaller head circumference, even after correction for height and weight. This confirms earlier but inconclusive and controversial reports, and might be taken as supporting a neurodevelopmental hypothesis of the aetiology of schizophrenia.

P300 and reaction-time measures in senile dementia of the Alzheimer type

Auditory evoked potentials were recorded in a choice reaction-time task. This test paradigm elicited the attention-related P300 component and was used to study cognitive processing. Compared with age-matched controls, 17 patients with dementia of the Alzheimer type were shown to have significantly longer reaction times as well as delayed latencies of several components of the auditory evoked potentials. The fractional increase in the reaction times was much greater than that of the P300 peak latency. The latter is commonly accepted as an index of stimulus-evaluation time. These findings suggest a delay in both response selection and stimulus evaluation.

Sensitization of amphetamine-stereotypy reduces plasma corticosterone: implications for stereotypy as a coping response

The potential coping functions of amphetamine-induced stereotypy were investigated using a physiological index of stress or arousal, plasma corticosterone level. A series of five injections of d-amphetamine was used to enhance stereotyped behavior in control animals as well as in rats with bilateral dopamine-depleting lesions of the caudate-putamen. This regimen of amphetamine injections significantly increased stereotyped behavior and also reduced the normal elevation in corticosterone produced by treatment with d-amphetamine. This effect was apparent in both control and lesioned animals. These results support the hypothesis that amphetamine-induced stereotyped behavior functions to reduce stress or arousal and additionally suggest that this effect is largely independent of underlying dopaminergic mechanisms.

Behavioural rigidity and rule-learning deficits following isolation-rearing in the rat: neurochemical correlates

Isolation-reared rats were compared to those reared in social groups on the acquisition of a conditional visual discrimination (Expt. I), a simultaneous (simple) light/dark discrimination and serial reversal learning (Expt. II). In Expt. I, rats reared in social isolation made more errors during the acquisition of the conditional discrimination but did reach a level of accurate performance which was comparable with that of socially-reared rats. Discrimination performance in isolates was less disruptable by manipulations of the task requirements. Reducing the number of stimulus lights or the introduction of a distracting stimulus increased the number of errors committed by socially-reared rats but did not significantly affect accuracy in isolates. Performance in isolated rats was also remarkably resistant to changes in motivational variables. Isolates responded more frequently during conditions of extinction and were virtually unaffected by pre-feeding prior to testing. In Expt. II, isolation-reared rats were not impaired in the acquisition of a simultaneous discrimination but unlike socially-reared rats isolates failed to show improvement with successive reversals of this discrimination. Isolates exhibited stronger position habits than socially-reared rats following reversal of the contingencies. These results of these two experiments combined have demonstrated a specific impairment in rule learning in isolates. Isolated rats were not impaired on a simultaneous discrimination in which accurate performance can be achieved simply by approaching the stimulus associated with reinforcement, but performed worse than controls on both the conditional discrimination and on serial reversal learning, another form of conditional task. In both of these latter tasks each stimulus becomes equally associated with reward and therefore performance can be improved by learning a rule. Post-mortem neurochemical measurements made at the completion of Expt. II revealed selective alterations in dopaminergic, serotoninergic and cholinergic markers in isolated rats. Correlational analyses indicated specific relationships between neurochemical and behavioural measurements.

Pleiotropic effects of a relC mutation in Streptomyces antibioticus

Ochi (Agric. Biol. Chem. 51:829-835, 1987) has isolated a relaxed mutant of Streptomyces antibioticus, designated relC49, relC49 accumulates significantly lower levels of ppGpp than the parent stain, IMRU3720. At its maximum, the ppGpp level in relC49 was only one-fourth that observed in strain IMRU3720. Interestingly, a burst of ppGpp synthesis between 18 and 22 h of growth in IMRU3720 coincided with the onset of actinomycin production in that strain. As shown previously, the activity in protein synthesis of ribosomes from strain IMRU3720 decreases with the age of the culture. The decrease in activity was less pronounced in cultures of relC49. relC49 mycelium contains reduced levels of phenoxazinone synthase, a key enzyme involved in actinomycin biosynthesis. The rel mutation prevents the normal increase in the activity of one of the other enzymes required for production of the antibiotic, 3-hydroxyanthanilate-4-methyltransferase, and a third enzyme, actinomycin synthetase I, appears to be completely absent from relC49 mycelium. Levels of phenoxazinone synthease mRNA were examined by RNA dot blotting with the cloned phenoxazinone synthase gene as a probe. mRNA levels for phenoxazinone synthase were dramatically reduced in relC49 compared with strain IMRU3720. These results are discussed in terms of the possible regulation of the onset of actinomycin production by ppGpp.

Individual differences in locomotor activity and sensitization

Male rats were screened for locomotor activity in a novel environment and divided into high (HR) and low (LR) responders based on whether their locomotor activity score for the first hour was above or below the median locomotor activity for the subject sample. Subsequently, the locomotor response to repeated administration of either amphetamine (AMPH; 0.5 mg/kg), cocaine (10 mg/kg), scopolamine (0.5 mg/kg) or saline was monitored in separate groups of HR and LR rats. HR rats had significantly higher overall activity scores than LR rats for all 3 drugs. Both HR and LR rats developed tolerance at the same rate to repeated scopolamine administration. In contrast, only HR rats showed pronounced sensitization to the locomotor stimulating properties of AMPH and a direct correlation was evident between the locomotor response to novelty and the magnitude of sensitization. These results suggest that an individual's response to a novel environment can, to a certain extent, predict drug-induced locomotor activity and that individual differences in the response to novelty and sensitization to AMPH may result from individual variations in a common neural mechanism.

Cortical, hippocampal, and striatal mediation of schedule-induced behaviors

The sequential occurrence of licking, locomotor activity, entries into the food magazine (panel pressing), and nonreenforced lever pressing engendered by a periodic schedule of food presentation were measured in each 60-s interreenforcement interval in normal and brain-damaged rats. The development of these responses was measured over 20 days in different groups of food-deprived rats that had received aspirations of the hippocampus, small lesions of the cortex overlying the hippocampus (hippocampal-operated control group), decortication, or 6-hydroxy-dopamine lesions of the caudate nucleus or nucleus accumbens. All lesions produced distinctive patterns of change in the measured behaviors, and dissociations as well as similarities in their effects were evident. These results are discussed with respect to dissociations in the motor and motivational effects of the various lesions and in terms of contemporary hypotheses of schedule-induced behavior.

Effects of dopamine depletion from the caudate-putamen and nucleus accumbens septi on the acquisition and performance of a conditional discrimination task

Three experiments compared the effects of dopamine depletion from the caudate-putamen (CAUD; dorsal striatum) or nucleus accumbens septi (NAS; ventral striatum), or a systemically administered dopamine receptor antagonist (alpha-flupenthixol) on the acquisition and performance of a conditional discrimination task involving temporal frequency. In Expt. 1, rats receiving 6-hydroxydopamine (6-OHDA) lesions of the CAUD were impaired in the acquisition of a visual version of the task, and rats with 6-OHDA lesions of the NAS were not reliably impaired. Even when the rats with CAUD lesions had acquired the discrimination, they were still significantly slower to collect earned food pellets. Both CAUD and NAS lesions reduced a bias to respond to the faster of the two discriminative stimuli. In Expt. 2, rats with 6-OHDA lesions of CAUD were markedly impaired in their accuracy and speed of responding when they had been trained to criterion preoperatively. These effects could not be mimicked in controls by prefeeding (which had only minor effects on performance). Rats with 6-OHDA-induced lesions of the NAS were unimpaired in either visual or auditory discrimination performance, but were slower to extinguish responding than controls. In Expt. 3, alpha-flupenthixol (0.1-0.56 mg/kg, i.p.) produced dose-dependent impairments in both latency to respond and choice accuracy in visual and auditory versions of the task. In conjunction with other results, these data suggest that (1) dopamine receptor blockade and central dopamine depletion can impair discrimination performance under certain conditions (2) dopamine depletion from the ventral and dorsal striatum, respectively, have dissociable effects on behaviour controlled by conditioned reinforcers and discriminative stimuli and (3) the disruption of discrimination performance by dorsal striatal dopamine depletion is probably attributable to several factors.

The effects of excitotoxic lesions of the basal forebrain on the acquisition, retention and serial reversal of visual discriminations in marmosets

The effects of N-methyl-D-aspartate-induced lesions of the basal forebrain (which included the cholinergic cells of the nucleus basalis of Meynert) were studied on three aspects of visual discrimination; learning, retention and reversal performance, in the marmoset. Neurobiological investigations revealed that the lesion produced large reductions in choline acetyltransferase activity within anterior regions of cortex, particularly prefrontal. In Experiment 1 lesioned animals showed impaired retention, one week after surgery, of a visual discrimination learned immediately prior to surgery and subsequently showed impaired performance over a series of reversals. The reversal deficit could be characterized as a tendency to perseverate on the previously correct stimulus on the first reversal and as a failure to show serial reversal learning on subsequent reversals. Acquisition of a novel discrimination was not impaired five weeks after surgery. As time of testing may have been a confounding factor, in Experiment 2 the effects of the same lesion on new learning were examined immediately following surgery and the effects on retention a month later. The lesion was found to disrupt new learning but did not affect retention. From the two experiments it is clear that, whereas disruption of retention and new learning was relatively transient, the impairments in reversal performance were more long lasting. In addition, lesioned animals exhibited behavioural hyperactivity and elevations in consummatory and schedule-controlled licking. The disinhibitory and preservative effects observed following lesions of the basal forebrain in this study are similar to those following lesions of the orbitofrontal cortex while the disruption of serial reversal learning is commonly seen following damage to the amygdala. Therefore, these results are consistent with the hypothesis that the range of behavioural effects of the lesion result from damage to the cholinergic afferents to orbitofrontal cortex and to the amygdala, two structures intimately connected to one another.

Cortical, hippocampal, and striatal mediation of schedule-induced behaviors

The sequential occurrence of licking, locomotor activity, entries into the food magazine (panel pressing), and nonreenforced lever pressing engendered by a periodic schedule of food presentation were measured in each 60-s interreenforcement interval in normal and brain-damaged rats. The development of these responses was measured over 20 days in different groups of food-deprived rats that had received aspirations of the hippocampus, small lesions of the cortex overlying the hippocampus (hippocampal-operated control group), decortication, or 6-hydroxy-dopamine lesions of the caudate nucleus or nucleus accumbens. All lesions produced distinctive patterns of change in the measured behaviors, and dissociations as well as similarities in their effects were evident. These results are discussed with respect to dissociations in the motor and motivational effects of the various lesions and in terms of contemporary hypotheses of schedule-induced behavior.

Comparison of the effects of Alzheimer's disease, normal aging and scopolamine on human transient visual evoked potentials

Transient visual evoked potentials elicited by the onset of a patterned stimulus were recorded in patients suffering from Alzheimer's disease (AD), in healthy elderly controls and in healthy young individual. The latencies and amplitudes of both the components studied were adversely affected by normal aging and one of the components, CI, but not the other, CII, showed further deterioration in AD. These changes occurred over a range of stimulus contrast levels. The changes found in AD, but not those seen in normal aging, could be mimicked by administration of the cholinergic antagonist scopolamine to young volunteers.

Increased sensitivity to amphetamine and reward-related stimuli following social isolation in rats: possible disruption of dopamine-dependent mechanisms of the nucleus accumbens

These experiments compared isolation-reared and socially-reared rats in two complementary paradigms for measuring responding to signals of reward, both undrugged and following either systemic or intraaccumbens d-amphetamine (AMPH). In experiment 1, locomotor activity conditioned to food presentation was measured in rats exposed to a restricted feeding schedule. The interaction between this conditioned activity, AMPH administration (0.5, 2.0, 3.5, 5.0 mg/kg IP) and motivational state was measured. In experiment 2, hungry rats were trained to associate a compound light/noise stimulus with sucrose reward and were then implanted with guide cannulae in the nucleus accumbens. In the test phase, responding on one of two novel levers produced the compound stimulus (conditioned reinforcer; CR). Responses on the other lever had no effect. Each rat received four counterbalanced intra-accumbens infusions of AMPH (0, 3, 10, 20 micrograms). In both experiments, isolated rats responded more with stimuli associated with reward and this differential rearing effect was further exaggerated by AMPH. The isolation-induced sensitivity to these stimuli and to AMPH was critically dependent on motivational variables. Thus, in experiment 1 there were no differences between the groups when sated or during extinction and in experiment 2 the increased responding was restricted to the lever providing CR. Measurements of the locomotor response to intra-accumbens AMPH (0, 3, 10 micrograms) also revealed that isolated rats were more sensitive to a low dose of the drug when tested food-deprived in a relatively novel environment. These results suggest that the experience of isolation-rearing interacts either directly or indirectly with dopamine-dependent mechanisms of the nucleus accumbens to enhance the effects of reward-related stimuli.

Molecular cloning and in vitro expression of a silent phenoxazinone synthase gene from Streptomyces lividans

Phenoxazinone synthase (PHS) catalyzes a step in actinomycin D biosynthesis in Streptomyces antibioticus. Two sequences from Streptomyces lividans that hybridize to the phs gene of S. antibioticus have been cloned in Escherichia coli K-12 using the plasmid pBR322. Although there was some similarity in the restriction maps of the two cloned fragments, neither insert appeared to be a direct subset of the other nor of the S. antibioticus phs gene. In vitro expression studies, in a streptomycete coupled transcription-translation system, showed that a 3.98-kb SphI fragment encoded a PHS-related protein. These observations provide additional support for the existence of silent genes for antibiotic production in streptomycetes.

Comparative effects of ibotenic acid- and quisqualic acid-induced lesions of the substantia innominata on attentional function in the rat: further implications for the role of the cholinergic neurons of the nucleus basalis in cognitive processes

Two experiments examined the effects of excitotoxic lesions of the substantia innominata on cholinergic activity in the neocortex and on performance in a paradigm measuring selective attention in the rat. In Expt. 1, ibotenate-induced lesions produced approximately 30% reductions in cortical choline acetyltransferase (ChAT) activity, and damage to wide regions of the substantia innominata and ventral pallidum. The rats were impaired in their ability to localize brief visual targets in a serial reaction time task, as measured by reduced choice accuracy. This impairment was particularly evident at short stimulus durations, but the lesioned rats did not exhibit evidence of primary visual sensory dysfunction and exhibited only minor deficits when the stimuli were presented unpredictably. The deficit was exacerbated when distracting white noise was interpolated into the task. The rats with lesions were also slower to respond correctly, probably resulting partly from the adoption of a speed/error trade-off strategy, and were slower to collect earned food pellets, although they made no more errors of omission than controls. In Expt. 2, quisqualate-induced lesions produced fewer signs of non-specific damage and 50% reductions in cortical ChAT activity. This lesion produced generally qualitatively similar, but weaker effects to those of ibotenate-induced lesions. It was notable that many of the deficits following either ibotenate- or quisqualate-induced lesions lasted for several months after surgery. The results are discussed in terms of the cholinergic hypothesis of cognitive dysfunction. It is argued that lesions of the substantia innominata, including the magnocellular cholinergic neurons of the nucleus basalis of Meynert, produce deficits in attentional processing, which may not result from damage specifically to cholinergic cells. However, the longevity of the effects makes these preparations suitable for further exploration of the restorative effects of cholinergic treatments.