Memory related role of the posterior cholinergic system

Functional disconnection of the substantia nigra pars compacta from the pedunculopontine nucleus impairs learning of a conditioned avoidance task

The pedunculopontine tegmental nucleus (PPTg) targets nuclei in the basal ganglia, including the substantia nigra pars compacta (SNc), in which neuronal loss occurs in Parkinson's disease, a condition in which patients show cognitive as well as motor disturbances. Partial loss and functional abnormalities of neurons in the PPTg are also associated with Parkinson's disease. We hypothesized that the interaction of PPTg and SNc might be important for cognitive impairments and so investigated whether disrupting the connections between the PPTg and SNc impaired learning of a conditioned avoidance response (CAR) by male Wistar rats. The following groups were tested: PPTg unilateral; SNc unilateral; PPTg-SNc ipsilateral (ipsilateral lesions in PPTg and SNc); PPTg-SNc contralateral (contralateral lesions in PPTg and SNc); sham lesions (of each type). SNc lesions were made with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine HCl (MPTP, 0.6micromol); PPTg lesions with ibotenate (24nmol). After recovery, all rats underwent 50-trial sessions of 2-way active avoidance conditioning for 3 consecutive days. Rats with unilateral lesions in PPTg or SNc learnt this, however rats with contralateral (but not ipsilateral) combined lesions in both structures presented no sign of learning. This effect was not likely to be due to sensorimotor impairment because lesions did not affect reaction time to the tone or footshock during conditioning. However, an increased number of non-responses were observed in the rats with contralateral lesions. The results support the hypothesis that a functional interaction between PPTg and SNc is needed for CAR learning and performance.

Effects of pre-training pedunculopontine tegmental nucleus lesions on delayed matching- and non-matching-to-position in a T-maze in rats

Lesions of the pedunculopontine tegmental nucleus (PPTg) can impair spatial learning tasks, but it is not clear whether those detrimental effects depend on the specific training conditions (for example, number of response choices available) or are secondary to enhanced anxiety. In the present work, rats with either bilateral excitotoxic (ibotenate) lesions of the PPTg (lesion group) or with vehicle infusions (control group) were tested in an elevated plus-maze, in order to measure anxiety-like behaviours and spontaneous locomotion. Subsequently, they were trained in a delayed matching-to-position (DMTP) task in a T-maze (a two-response choice task). After reaching a predefined learning criterion, or after a maximum of 30 training sessions, the animals were trained in a delayed non-matching-to-position (DNMTP) task. Lesioned animals made less grooming episodes, stretch-attend postures and closed arm entries than controls in the elevated plus-maze, suggesting slightly lower anxiety levels. None of the lesioned rats reached the learning criterion for the DMTP, and overall accuracy levels were significantly lower in those rats, compared to controls. In the DNMTP task, lesioned animals showed lower accuracy levels and higher side bias than controls in some of the sessions, but there were no significant differences between the two groups in the proportion of animals reaching the learning criterion. It is concluded that spatial learning deficits induced by damage to the PPTg are not secondary to enhanced anxiety. Instead, those deficits seem to be influenced by several conditions that modify task demands, the number of response choices being only one of such conditions.

Parafascicular electrical stimulation attenuates nucleus basalis magnocellularis lesion-induced active avoidance retention deficit

Previous experiments from our laboratory showed that retention of two-way active avoidance learning is improved by post-training intracranial electrical stimulation (ICS) of the parafascicular nucleus (PF) and impaired by pre-training electrolytic lesions of the nucleus basalis magnocellularis (NBM). The question investigated here was whether post-training PF ICS is able to attenuate the active avoidance retention deficit observed in rats lesioned pre-training in the NBM. To this goal, the following experimental design was used: rats bilaterally lesioned in the NBM and stimulated in the PF, rats lesioned in the NBM, rats stimulated in the PF, control rats implanted in the PF, and sham-operated rats were first trained in a shuttle-box for a single 30-trial session and tested again following two successive retention intervals (24 h and 11 days). The results showed that: (1) NBM lesions impaired the 11-day performance without affecting either the acquisition or the 24-h retention of the avoidance learning; (2) PF ICS treatment in unlesioned rats improved performance in both retention sessions only when the stimulation was applied in the posterior region of the nucleus; and (3) stimulation of the posterior PF compensated the 11-day retention impairment induced by NBM lesions. These results are discussed in relation to the interaction of arousal systems in the modulation of cognitive processes.

Effects of pedunculopontine tegmental nucleus lesions on emotional reactivity and locomotion in rats

Bilateral damage to the pedunculopontine tegmental nucleus (PPTg) has been found to impair several learning tasks; however, it is not clear whether this effect could be at least partially attributable to changes in the rat emotional reactivity and/or spontaneous locomotion. Therefore, the present work has tested the effects of bilateral electrolytic lesions of the PPTg on the behaviour of rats in the elevated plus-maze and the open field test. Because the behaviour of rats in learning and emotional tasks can be sensitive to routine experimental manipulations, we also have tested the effects of brief pre-surgical handling procedures on anxiety-like behaviours and locomotion in both lesioned and control rats. Lesions of the pedunculopontine tegmental nucleus (1). did not have any effects on spontaneous locomotor activity and (2). did not increase emotional reactivity. In fact, there was a slight bias towards a reduction in anxiety-like behaviours in lesioned rats, as evidenced by a significant increase in the number of open arm entries. Pre-surgical handling induced a slight decrease of emotional reactivity and a slight increase of exploratory activity. We conclude that damage to the pedunculopontine tegmental nucleus is not accompanied by either an enhancement of emotional reactivity or by an altered spontaneous locomotion.

An examination of the effects of bilateral excitotoxic lesions of the pedunculopontine tegmental nucleus on responding to sucrose reward

The effects of bilateral excitotoxic lesions of the pedunculopontine tegmental nucleus (PPTg) on sucrose intake were examined in three experiments. First, in tests of conditioned place preference using 20% sucrose as the reinforcer, it was shown that lesioned rats, regardless of whether they were food deprived or non-deprived, formed normal place preferences and showed normal amounts of locomotion. However, consumption of 20% sucrose in the pairing trials was increased in the deprived PPTg lesioned rats compared to their matched controls. A second experiment showed that sucrose consumption in the home cage was increased in both deprived and non-deprived PPTg lesioned rats, but only when the concentration of sucrose was greater than 12%: below this there were no differences in intake between the lesioned and control rats. In a third home cage experiment, it was again shown that non-deprived PPTg lesioned rats increased their consumption of 20% sucrose compared to controls. PPTg lesioned rats concomitantly reduced their intake of lab chow such that overall energy intake remained the same as that of control rats. These data are taken to suggest (i) that bilateral excitotoxic lesions of the PPTg increase consumption of sucrose selectively in conditions of high motivational excitement; (ii) that the perception of the rewarding value of 20% sucrose, as judged by place preference, is not affected by these lesions; and (iii) that PPTg lesioned rats are able to adjust their energy intake to accommodate increased sucrose loads. These data are consistent with the hypothesis that bilateral excitotoxic lesions of the PPTg do not affect energy balance regulation or judgment of the hedonic value of sucrose, but that they do affect the control of responding in the face of high levels of motivational excitement.

Impairment of two-way active avoidance after pedunculopontine tegmental nucleus lesions: effects of conditioned stimulus duration

It was investigated whether the disruptive effects of bilateral lesions of the pedunculopontine tegmental nucleus on two-way active avoidance might vary depending on variations of task demand. The animals were either subjected to bilateral electrolytic lesions of the pedunculopontine tegmental nucleus (Lesion groups) or were sham-operated (Control groups). All the rats were subjected to two 30-trial sessions of two-way active avoidance (separated by ten days), using either a 10-s conditioned stimulus (low task demand) or a 3-s conditioned stimulus (high task demand). The lesions induced a significant disruption of two-way active avoidance in the two conditions tested, but, in both lesioned and control rats, the number of avoidance responses was higher when the 10-s conditioned stimulus was used. In lesioned animals, the condition of high task demand was associated with a significant increase of escape failures. Lesions did not affect locomotor activity during the period of adaptation to the conditioning apparatus, but induced training-specific motor deficits (a decrease of intertrial crossings and an enhancement of escape latencies) regardless of the specific training conditions used. The results are discussed in terms of the influences of the pedunculopontine tegmental nucleus in thalamocortical and striatal systems.

Diazepam modifies the effect of pedunculopontine lesions on morphine but not on amphetamine conditioned place preference

We have previously shown that T-maze learning impairments caused by lesions to the pedunculopontine tegmental nucleus (PPTg) can be reversed by the anxiolytic diazepam. We now report that diazepam also reverses the effect of PPTg lesions on conditioned place preference (CPP) to morphine but not to amphetamine. Rats with bilateral sham or N-methyl-D-aspartate lesions (0.1 or 0.05 M) to the PPTg were trained in a unbiased CPP paradigm with 2 mg/kg morphine or 2 mg/kg D-amphetamine associated with one compartment of the apparatus and vehicle injections in the alternative compartment. After three drug/saline-compartment pairings, the preference of the animals was assessed by allowing them to explore the entire apparatus for 20 min. In contrast to sham-lesioned subjects, the rats with PPTg lesions did not show a preference for the compartment paired with morphine or amphetamine. In two experiments the expression of a morphine CPP was restored by injecting the lesioned animals with 1 mg/kg of diazepam 30 min before the test session. Diazepam pre-treatment did not restore the expression of amphetamine CPP.

Pontine tegmentum lesions increase anxiety-like behavior in rats: a comparison with anxiety produced by beta-CCE

Electrolytic lesions of the pedunculopontine tegmental nucleus (PPTg) have been previously reported to increase anxiety-like behavior in rats. The aim of the present study was to compare these behavioral changes with those produced by an anxiogenic compound, the partial inverse agonist at benzodiazepine receptors, beta-CCE. Three groups of rats, sham-lesioned treated with vehicle, sham-lesioned treated with 10 mg/kg of beta-CCE, and PPTg-lesioned rats treated with vehicle, were tested in the elevated plus-maze, the social-interaction test, and for spontaneous locomotion. Histology showed that lesions were concentrated on the caudal half of the PPTg. Measures of both the PPTg-lesioned and beta-CCE-treated rats indicated increased anxiety-like behavior in the elevated plus-maze and in the social-interaction test. Spontaneous locomotion, measured in the open- field arena, did not differ between sham controls and PPTg-lesioned rats, but was decreased in rats treated with beta-CCE. Our results confirmed that electrolytic lesions of the caudal PPTg produce increased anxiety-like behavior. This behavior is quantitatively and qualitatively similar to that produced by 10 mg/kg of beta-CCE.

Learning impairments caused by lesions to the pedunculopontine tegmental nucleus: an artifact of anxiety?

Bilateral N-methyl-d-aspartate lesions of the pedunculopontine tegmental nucleus (PPTg) blocked the acquisition of a delayed non-matching to position task (DNMP) performed in a T-maze. This acquisition impairment, however, was reversed by pre-testing injections of diazepam (1 mg/kg). These results, in addition to the finding that PPTg lesions elevated anxiety as measured by the elevated plus maze, suggest that PPTg is not involved in learning or memory, but in the regulation of anxiety.

Effects of pedunculopontine tegmental nucleus lesions on responding for intravenous heroin under different schedules of reinforcement

The pedunculopontine tegmental nucleus (PPTg) is believed to play important roles in reward and learning. We examined the effect of PPTg lesions (0.5 microl of 0.1 M NMDA injected bilaterally over 10 min) on the learning of an operant response for opiate reward. In 14 adult male Long-Evans rats, bilateral lesions of the PPTg disrupted the acquisition of responding for intravenous heroin (0.1 mg/kg infused at a rate of 0.25 ml/28 sec) on a fixed ratio-1 (FR-1) schedule of reinforcement. The 12 remaining lesioned animals increased their heroin intake over the acquisition sessions but did not reach the response levels of sham-lesioned animals on the 15th and final session. The sham- and PPTg-lesioned animals that learned the FR-1 task exhibited similar patterns of responding during extinction and reacquisition sessions. When tested on a progressive ratio (PR) schedule of reinforcement, however, PPTg-lesioned animals had lower break points than sham-lesioned animals. Asymmetric lesions, which destroyed the majority of the nucleus in one hemisphere only, did not produce any behavioral deficits. Rats that were lesioned after training also did not show deficits in responding under either FR or PR schedules. These findings suggest that PPTg lesions reduce the rewarding effect of opiates but do not disrupt the ability either to learn an operant response or the response requirements of a PR schedule.

Behavioral and adaptive status in an experimental model of Alzheimer's disease in rats

Ten days after bilateral electrolytic lesions of nucleus basalis magnocellularis (NBM) we tested behavioral (spontaneous motor activity, acquisition and performance of two-way active avoidance, fear-response in open field test, foot shock induced aggression, depression-response in learned helplessness test) and adaptive status (body temperature at standard, hot and cold environment as well as cold restraint-induced gastric lesions) in adult male Wistar rats. Compared to intact control and sham-operated rats, the bilateral NBM-lesioned rats showed the significant impairment of learning behavior and reduced fear, aggression and depression as well as altered body temperature at standard and stressed conditions. Namely, it was established that body temperature in NBM-lesioned rats was significantly lower at standard laboratory conditions, but in these rats body temperature significantly was raised after exposing to cold and hot environment. On the other hand, spontaneous motor activity and number and length of cold restraint-induced gastric lesions (erosions and petechiae) in NBM-lesioned rats were similarly to those in both controls. It could be concluded that NBM plays a significant role in cognitive, emotional and adaptive processes in the rats.

Septal lesions impair rats' Morris test performance but facilitate left-right response differentiation

Lesions in the septum impaired performance on the Morris test, a task in which the rat locates a hidden escape platform by use of fixed landmarks, but facilitated a water maze-based left-right response differentiation, a task in which the rat finds a hidden escape ramp by means of its internal sense of direction. These results are interpreted as supporting an allocentric/egocentric dichotomy with respect to navigation, and support the notion that rats approach spatial problems with a hierarchy of potential solutions in which allocentric solutions take precedence over egocentric ones. The septal lesions are inferred to disrupt the allocentric mapping system.

Selective immunolesioning of the basal forebrain cholinergic system disrupts short-term memory in rats

Selective depletion of nerve growth factor receptor-bearing neurons in the basal forebrain cholinergic system nuclei by the immunotoxin 192 IgG-saporin offers a new and highly useful tool for the study of the role of the forebrain cholinergic system in cognitive functions. In the present study, we have tested the effects of 192 IpG-saporin in an operant delayed matching-to-position task which has previously been used to discriminate between delay-dependent learning impairments and delay-independent disturbances of non-mnemonic processes. Rats were first trained to criterion performance and then received intraventricular injections of 5 microg of 192 IgG-saporin 4 weeks prior to a second testing session. Rats with 192 IgG-saporin lesions displayed a significant delay-dependent decline in performance compared to normal controls, indicating a deficit in short-term memory. Administration of the muscarinic blocker scopolamine (0.5 mg/kg, i.p.) produced more pronounced impairment in the performance of the normal control rats across all delays, and induced further impairment also in animals with 192 IgG-saporin lesions. These effects were not observed following control injections of methyl scopolamine, suggesting that the impairment induced by scopolamine was due to the blockade of central muscarinic receptors. No improvement in performance was observed in either group following systemic treatment with the muscarinic cholinergic agonist arecoline (1.00 mg/kg). Biochemical and morphological analyses confirmed the selective and severe (>90-95%) depletion of cholinergic neurons throughout the septal-diagonal band area and the nucleus basalis region by the intraventricular 192 IgG-saporin treatment. Although the immunotoxin was observed to produce additional damage to the cerebellar Purkinje cells, no gross motor abnormalities were observed that could contribute to the effects on accuracy in the task used here. In conclusion, the results show that selective combined lesions of the basal forebrain cholinergic neurons in the septal-diagonal band area and nucleus basalis produce long-lasting impairments in short-term memory, thus providing further support for a role of this system in cognitive functions.

Neuropathology of thiamine deficiency: an update on the comparative analysis of human disorders and experimental models

This paper provides a re-examination of the neuroanatomical consequences of thiamine deficiency in light of more recent studies of human disorders and models of experimental thiamine deficiency. A major goal is to elucidate the relative roles of thiamine deficiency and chronic alcohol consumption in the pathogenesis of Wernicke-Korsakoff syndrome (WKS). Particular emphasis is placed on the role of thiamine deficiency in lesions to basal forebrain, raphe, locus coeruleus, white matter and cortex and their role in the cognitive and memory disturbances of human WKS and experimental models of thiamine deficiency.

Determination of xanomeline (LY246708 tartrate), an investigational agent for the treatment of Alzheimer's disease, in rat and monkey plasma by capillary gas chromatography with nitrogen-phosphorus detection

A GC method is described for the determination of xanomeline (LY246708 tartrate) and selected metabolites in rat and monkey plasma. The analytes, including an internal standard, were extracted from plasma at basic pH with hexane. The organic extract was evaporated to dryness and the residue was reconstituted in hexane. The analytes were separated from metabolites and endogenous substances using a DB1701 capillary column. The analytes were detected using nitrogen-phosphorus detection (NPD). The limit of quantitation was determined to be 8 ng/ml, and the response was linear from 8 to 800 ng/ml. The method has been successfully applied to rat and monkey samples pursuant to the development of xanomeline as an agent for the symptomatic treatment of Alzheimer's disease.

The pedunculopontine tegmental nucleus: a role in cognitive processes?

The cholinergic pedunculopontine tegmental nucleus, located in the brainstem and part of the reticular formation, has been traditionally linked to motor function, arousal and sleep. Its anatomical connections, however, raise the possibility that the pedunculopontine tegmental nucleus is also involved in other aspects of behaviour such as motivation, attention and mnemonic processes. This is of obvious importance, since the pedunculopontine tegmental nucleus undergoes degeneration in human neurodegenerative disorders also characterized by attentional and/or mnemonic deficits. Moreover, recent behavioural animal work suggests that cognitive processes may be represented in the pedunculopontine tegmental nucleus. The difficulty that faces research in this area, however is the possible influence of cognition by other processes, such as arousal state, motivation and motor function. Nevertheless, by reviewing the literature, the pedunculopontine tegmental nucleus seems to be involved in attentional and possibly also in learning processes. These processes could be mediated by influencing cortical function via the thalamus, basal forebrain and basal ganglia. The involvement of the pedunculopontine tegmental nucleus in mechanisms of memory, however, seems to be rather unlikely.

Lesions of the pedunculopontine tegmental nucleus do not alter delayed non-matching to position accuracy

The cholinergic pedunculopontine tegmental nucleus, located in the brainstem, and part of the reticular formation, has traditionally been linked to motor function, sleep and arousal, but has recently been implicated in cognition. To investigate this possibility, rats with radiofrequency lesions were tested on a delayed non-matching to position task, a test for spatial recognition memory abilities. Data were analysed according to the methods of signal detection theory. Lesions of the pedunculopontine nucleus did not produce marked deficits in accuracy, although there was some evidence to suggest that motivational processes could have been affected.

Differential effect of functional ablation of thalamic reticular nucleus on the acquisition of passive and active avoidance

The possible contribution of inadvertent damage of the thalamic reticular nucleus to memory impairment caused by lesion of nucleus basalis magnocellularis (NBM) was examined. Rats carrying chronically implanted cannulae received unilateral injection of 3 ng tetrodotoxin (TTX) into the reticular nucleus either 60 min before (PRE) or 2 min after (POST) acquisition of a combined passive avoidance (PAR)--active avoidance (AAR) task. Three days later retrieval was tested during unilateral TTX blockade of the reticular nucleus in the same (IPSI) or in the opposite (CONTRA) hemisphere. Unilateral inactivation of the reticular nucleus affected neither acquisition nor retrieval of PAR, but interfered with AAR acquisition under the PRE conditions. AAR reacquisition was impaired in the PRE-CONTRA but not in the other groups. The effects of reticular nucleus blockade (AAR disruption without PAR impairment) contrast with AAR facilitation and PAR disruption after NBM lesions. It is concluded that the consequences of NBM damage are not enhanced by unintentional thalamic encroachment.

Hippocampal long-term potentiation in nucleus basalis magnocellularis-lesioned rats

The probability of hippocampal long-term potentiation induction in the mossy fiber CA3 and commissural/associational CA3 responses and the cortical levels of choline acetyltransferase (ChAT) activity were compared in right nucleus basalis magnocellularis (NBM)-lesioned rats. A 50% reduction in the right cortical ChAT activity was demonstrated 4 weeks after an ibotenic acid lesion of the NBM. No significative differences were found in the probability of LTP induction of right hippocampal slices in sham-operated rats from 10 to 40 days after the injection into the right NBM. On the contrary, a progressive and significative increase in the probability of LTP induction was shown in right hippocampal slices of NBM-lesioned rats from 10 to 40 days after the injection of ibotenic acid into the right NBM. The results demonstrated the appearance of a paradoxical increase of hippocampal synaptic plasticity when the cortical cholinergic biochemical alterations are still present. This finding might be responsible for a behavioural recovery, in NBM-lesioned rats.

The potential for muscarinic receptor subtype-specific pharmacotherapy for Alzheimer's disease

In several neurodegenerative disorders, including Alzheimer's disease, a loss of the cholinergic projections of the basal forebrain to the cerebral cortex and hippocampus occurs. Studies of the anatomic and physiologic characteristics of these ascending cholinergic systems suggest that they are important in processing information and in memory function. Muscarinic receptors are situated at various critical control points in these pathways. Activation of postsynaptic muscarinic receptors often increases the excitability of neurons; thus, the signal-to-noise ratio for sensory processing is enhanced. In addition, muscarinic receptors negatively control cholinergic tone at presynaptic sites. Molecular biologic methods have disclosed the existence of five muscarinic receptors, which are coupled to different second messenger systems. The evidence reviewed suggests that at least four of the five muscarinic receptor genes are expressed as functional receptor proteins in the neocortex and hippocampal formation. On the basis of the current information about their pharmacologic properties and coupling mechanisms in nervous tissue, drugs that selectively affect subtypes of muscarinic receptors could enhance cortical cholinergic function and thereby ameliorate certain cognitive impairments in Alzheimer's disease.

The role of cholinergic projections from the nucleus basalis in memory

The behavioral effects of lesions of the nucleus basalis magnocellularis (NBM) are reviewed, focusing on the anatomical extent of the lesion, the involvement of neurotransmitter systems and the alterations in memory processes. Most behavioral deficits after NBM lesions can be attributed to damage to the NBM itself, although during spontaneous or pharmacologically induced recovery, other brain structures might play a role. The neurochemical deficit underlying the behavioral impairments is most likely the decrease in cholinergic functioning, since, for example, enhancement of cholinergic functioning is sufficient for behavioral improvement. However, since the lesions are not specific for cholinergic neurons, the extent to which noncholinergic damage causes behavioral deficits is still unclear. Finally, lesions of the NBM impair memory, but affect also other behavioral processes, such as discrimination and habituation. A common process underlying these various impairments could be that of insufficiently focused processing of stimuli.

Learning disturbances following excitotoxic lesion of cholinergic pedunculo-pontine nucleus in the rat

Compared to brain anterior cholinergic systems such as the septo-hippocampal and nucleus basalis-cortical pathways, posterior cholinergic groups have received little attention with respect to their involvement in learning and memory. In this study, the effect of lesion of the cholinergic pedunculo-pontine cell bodies (PPN) by the excitotoxin quisqualic acid was investigated on spontaneous locomotor activity and learning in rats. Behavioral tasks designed to test both reference memory (cross maze and water maze) or working memory (radial maze) were used. PPN lesion had no effect on initial nor on nocturnal locomotor activity in a circular corridor. The lesion disrupted learning in the water and radial mazes, but was without influence on acquisition in the cross maze. The difference in results obtained in the two tasks designed to test reference memory (cross maze and water maze) indicated that the disturbance depended on task difficulty rather than on a particular memory component. It is suggested that the PPN is involved in the sustained attention required to perform correctly in water and radial mazes. The PPN cannot therefore be considered as a uniquely extrapyramidal structure. In addition to its descending outputs, the PPN has ascending connections to the neocortex, either directly or indirectly via the thalamus, and so pathological changes in this region may be partly responsible for the cognitive disorders of aging or those observed in various neurodegenerative conditions.

Memory deficits following nucleus basalis magnocellularis lesions may be mediated through limbic, but not neocortical, targets

In order to test the contribution of the target areas of the nucleus basalis magnocellularis to the mediation of item and order recognition memory for spatial locations, one set of rats received lesions of the dorsolateral frontal cortex, parietal cortex, or basolateral amygdala after training in an order recognition memory task, whereas another set of animals received lesions of the nucleus basalis magnocellularis or basolateral amygdala in an item recognition memory task. Animals with basolateral amygdala lesions displayed a deficit for order recognition memory, but no deficit for item recognition memory, a pattern equivalent to that found for animals with nucleus basalis magnocellularis lesions. In contrast, animals with dorsolateral frontal cortex displayed no deficit, and animals with parietal cortex lesions displayed only a partial deficit for order recognition memory, results that differ from those found for animals with nucleus basalis magnocellularis lesions. It appears that the nucleus basalis magnocellularis influences item and order recognition memory for lists of spatial locations primarily through projections to limbic but not neocortical targets.

Cholinergic systems in the rat brain: IV. Descending projections of the pontomesencephalic tegmentum

Descending projections from cholinergic neurons in the pedunculopontine and laterodorsal tegmental nuclei, collectively referred to as the pontomesencephalotegmental (PMT) cholinergic complex, were studied by use of the fluorescent retrograde tracers fluorogold, true blue, or Evans Blue in combination with choline acetyltransferase (ChAT) immunohistochemistry of acetylcholinesterase (AChE) pharmacohistochemistry. Pedunculopontine somata positive for ChAT or staining intensely for AChE were retrogradely labeled with fluorescent tracers following infusions into the motor nuclei of cranial nerves 5, 7, and 12. ChAT-positive cells in both the pedunculopontine and laterodorsal tegmental nuclei demonstrated projections to the vestibular nuclei, the spinal nucleus of the 5th cranial nerve, deep cerebellar nuclei, pontine nuclei, locus ceruleus, raphe magnus nucleus, dorsal raphe nucleus, median raphe nucleus, the medullary reticular nuclei, and the oral and caudal pontine reticular nuclei. Fluorescent tracers used in combination with AChE pharmacohistochemistry corroborated these projections and, in addition, provided evidence for cholinergic pontomesencephalic projections to the lateral reticular nucleus and inferior olive. The majority of retrogradely labeled neurons demonstrating ChAT-like immunoreactivity were found ipsilateral to the injection site, but, in all cases, tracer-containing cholinergic cells contralateral to the infused side of the brain were detected also. More retrogradely labeled cells containing ChAT were observed in the pedunculopontine tegmental than in the laterodorsal tegmental nucleus following tracer injections at all sites with the exceptions of the locus ceruleus and dorsal raphe nucleus where the converse profile was observed. None of the pedunculopontine or laterodorsal tegmental cells immunopositive for ChAT or stained intensely for AChE contained retrogradely transported tracers following dye infusions into the cerebellar cortex or cervical spinal cord. Triple-label experiments using two tracers infused into different sites in the same animal revealed that individual ChAT-immunoreactive cells in the PMT cholinergic complex projected to more than one hindbrain site in some cases and had ascending projections as well. Certain ChAT-positive somata in the pedunculopontine and laterodorsal tegmental nuclei were found in close association with several fiber tracts, including the superior cerebellar peduncle, lateral lemniscus, dorsal tegmental tract, and medial longitudinal fasciculus.

Nucleus basalis magnocellularis lesions facilitate two-way active avoidance

Bilateral ibotenic acid lesions of the nucleus basalis magnocellularis (NBM), which resulted in 30% depletion of cortical choline acetyltransferase, facilitated acquisition of shuttlebox two-way active avoidance learning in rats. These results contrast with a report of impaired two-way active avoidance after bilateral electrolytic lesions of the NBM, but support findings of facilitation after ibotenic acid lesions. The data suggest that electrolytic lesions impair shuttlebox learning by damaging fibers of passage in the vicinity of the NBM.

Nootropic drugs and brain cholinergic mechanisms

1. This review has two aims: first, to marshal and discuss evidences demonstrating an interaction between nootropic drugs and brain cholinergic mechanisms; second, to define the relationship between the effects on cholinergic mechanisms and the cognitive process. 2. Direct or indirect evidences indicating an activation of cholinergic mechanisms exist for pyrrolidinone derivatives including piracetam, oxiracetam, aniracetam, pyroglutamic acid, tenilsetam and pramiracetam and for miscellaneous chemical structures such as vinpocetine, naloxone, ebiratide and phosphatidylserine. All these drugs prevent or revert scopolamine-induced disruption of several learning and memory paradigms in animal and man. 3. Some of the pyrrolidinone derivatives also prevent amnesia associated with inhibition of acetylcholine synthesis brought about by hemicholinium. Oxiracetam prevents the decrease in brain acetylcholine and amnesia caused by electroconvulsive shock. Oxiracetam, aniracetam and pyroglutamic acid prevent brain acetylcholine decrease and amnesia induced by scopolamine. Comparable bell-shaped dose-effect relationships result for both actions. Phosphatidylserine restores acetylcholine synthesis and conditioned responses in aging rats. 4. The mechanisms through which the action on cholinergic systems might take place, including stimulation of the high affinity choline uptake, are discussed. The information available are not yet sufficient to define at which steps of the cognitive process the action on cholinergic system plays a role and which are the influences of the changes in cholinergic function on other neurochemical mechanisms of learning and memory.

Reevaluation of the contribution of the basal forebrain cholinergic system to memory

In this review the relationship between the basal forebrain cholinergic system and memory is explored. It appears that different components of the cholinergic forebrain system [e.g., medial septum (MS) and nucleus basalis magnocellularis (NBM)] have dissociable mnemonic functions in animals, and comparable mnemonic functions in humans are dissociable as well. Furthermore, the cholinergic input from MS to the hippocampus and NBM to basolateral amygdala appear to be of critical importance in mediating mnemonic function. Finally, comparable impairments in memory function are found in basal forebrain-damaged rats and patients with dementia of the Alzheimer's type, suggesting that there might be important homologies between animals and humans in terms of basal forebrain-mediated memory function.

Radial-arm maze deficits produced by colchicine administered into the area of the nucleus basalis are ameliorated by cholinergic agents

Rats were given bilateral injections of colchicine into the area of the nucleus basalis. Colchicine produced dose-dependent alterations in the acquisition of a food-reinforced working-memory task. Colchicine-induced deficits in maze performance were attenuated by cholinergic agents, including physostigmine, RS-86 (2-ethyl-8-methyl-2,8-diazospiro-(4,5)-decan-1,3-dione-hydro bromide) and nicotine. Naloxone and vasopressin did not affect radial-arm maze performance of colchicine-treated rats. Subsequent neurochemical analysis showed that colchicine decreased choline acetyltransferase (ChAT) activity and levels of norepinephrine, dopamine, 3,4-dihydroxyphenylacetic acid, serotonin and 5-hydroxyindoleacetic acid in the neocortex. However, ChAT activity and other neurochemical measures were not altered in the hippocampus or corpus striatum. Histological assessment indicated damage limited to the injection in the area of the nucleus basalis and enlarged cerebrolateral ventricles. These data suggest the possible utility of the colchicine model in the study of cognitive deficits associated with neurodegenerative diseases.

Physostigmine improves water maze performance following nucleus basalis magnocellularis lesions in rats

Bilateral excitotoxic lesions of the nucleus basalis magnocellularis in rats were used along with testing in the water maze task to assess whether inhibition of acetylcholinesterase with physostigmine would reverse the lesion-induced impairment. Rats were lesioned bilaterally in stages using ibotenic acid and then behaviorally tested 3 weeks after surgery. Lesioned animals were administered one of three doses of physostigmine (0.06, 0.19, or 0.32 mg/kg) or vehicle solution 15 min prior to water maze testing. Sham lesioned animals injected with vehicle solution served as an untreated control group. Animals were tested for 5 consecutive days followed by 2 days off and then tested for 5 additional days. The rats were then sacrificed and their frontal cortex was assayed for choline acetyltransferase. The nucleus basalis magnocellularis lesion caused approximately a 27% depletion of choline acetyltransferase in the frontal cortex of these animals. The lesion also impaired the performance of the rats given vehicle solution as compared to untreated controls. Two doses (0.06 and 0.19 mg/kg) of physostigmine improved performance relative to lesioned controls. The lower dose, 0.06 mg/kg, improved performance more than the 0.19 mg/kg dose of physostigmine. The highest dose of physostigmine impaired water maze performance relative to lesioned controls. These data are discussed in relation to the cholinergic hypothesis of Alzheimer's disease and the potential therapeutic use of physostigmine.

Primate learning tasks reveal strong impairments in patients with presenile or senile dementia of the Alzheimer type

Eight subjects with the likely diagnosis of presenile or senile dementia of the Alzheimer type were tested on two frequently used primate learning tasks: a concurrent object discrimination task and a delayed non-match-to-sample task. In addition, various tests for cognitive, mnemonic, perceptual, and language functions were applied. The results suggest a severe decline of the Alzheimer subjects in all measures when compared with 10 control subjects matched for age, gender, and education. The two animal learning tasks revealed strong impairments, thus demonstrating a high sensitivity for the detection and assessment of human amnesic disorders. Implications of these findings for human neuropsychological, and especially comparative neuropsychological, research are discussed.