Comparison of quisqualic and ibotenic acid nucleus basalis magnocellularis lesions on water-maze and passive avoidance performance

Impairments in negative patterning, but not simple discrimination learning, in rats with 192 IgG-saporin lesions of the nucleus basalis magnocellularis

Rats with 192 IgG-saporin lesions of the nucleus basalis magnocellularis (NBM) and sham-operated rats were trained in either a simple discrimination paradigm assessing simple association learning or a negative patterning paradigm assessing configural association learning. In the simple discrimination task, rats were reinforced for responding to a light but were not reinforced for responding to a tone. In the negative patterning discrimination task, rats were reinforced for responding to either a light or a tone presented alone but were not reinforced for responding to both stimuli presented simultaneously. Simple discrimination learning was not affected, whereas acquisition of negative patterning was impaired by NBM lesions. Impaired configural association learning may reflect a loss in the ability of rats with NBM lesions to attend to multiple sensory stimuli or to cope with conflicting response strategies.

Transverse patterning reveals a dissociation of simple and configural association learning abilities in rats with 192 IgG-saporin lesions of the nucleus basalis magnocellularis

This experiment tests the hypothesis that the cholinergic nucleus basalis magnocellularis (NBM) is necessary for complex or configural association learning, but not elemental or simple association learning. Male Long-Evans rats with bilateral 192 IgG-saporin lesions of the NBM (n = 12) and sham-operated controls (n = 8) were tested in the transverse patterning problem, which provides a test of both simple and configural association learning. Rats were trained in phases to concurrently solve first one, then two, and finally three different visual discriminations; Problem 1 (A+ vs B- sign) and Problem 2 (B+ vs C-) could be solved using simple associations, whereas solving Problem 3 (C+ vs A-) required the ability to form configural associations. Consistent with our hypothesis, the NBM lesion group solved the simple discriminations in Problems 1 and 2 but showed impaired configural association learning in Problem 3. Additionally, when Problem 2 was introduced, previously high levels of performance on Problem 1 suffered more in the NBM lesion group than in the control group; this finding suggests an impairment in the ability of animals with NBM lesions to divide attention among multiple stimuli or to shift between strategies for solving different problems. Results support our argument that the NBM is critically involved in the acquisition of associative problems requiring a configural solution but not in problems that can be solved using only simple associations. The observed impairments in configural association learning and the apparent loss of cognitive flexibility or capacity are interpreted as reflecting specific attentional impairments resulting from NBM damage.

Cognitive effects of neurotoxic lesions of the nucleus basalis magnocellularis in rats: differential roles for corticopetal versus amygdalopetal projections

The cholinergic hypothesis states that cholinergic neurons of the basal forebrain nucleus basalis magnocellularis (nbm) that project to cortical and amygdalar targets play an important role in memory. Biochemical studies have shown that these target areas are differentially sensitive to different excitotoxins (e.g., ibotenate vs. quisqualate). This observation might explain the finding from many behavioural studies of memory that different excitotoxins affect memory differentially even though they produce about the same level of depletion of cholinergic markers in the cortex and similar cortical electrophysiological effects. Thus, the magnitude of mnemonic impairment might be related to the extent of damage to cholinergic projections to the amygdala more than to the extent of damage to corticopetal cholinergic projections. This explanation might similarly apply to the observation that the immunotoxin 192 IgG-saporin produces mild effects on memory when injected into the nbm. This is because it damages cholinergic neurons projecting to the cortex but not those projecting to the amygdala. Studies comparing the effects on memory of ibotenic acid vs. quisqualic acid lesions of the nbm are reviewed as are studies of the mnemonic effects of 192 IgG-saporin. Results support the cholinergic hypothesis and suggest that amygdalopetal cholinergic neurons of the nbm play an important role in the control of memory.

Present imperfect: a critical review of animal models of the mnemonic impairments in Alzheimer's disease

This paper reviews the current literature on animal models of the memory impairments of Alzheimer's disease (AD). The authors suggest that modeling of the mnemonic deficits in AD be limited to the amnesia observed early in the course of the disease, to eliminate the influence of impairments in non-mnemonic processes. Tasks should be chosen for their specificity and selectivity to the behavioral phenomena observed in early-stage AD and not for their relevance to hypothetical mnemonic processes. Tasks that manipulate the delay between learning and remembering are better able to differentiate Alzheimer patients from persons with other disorders, and better able to differentiate effects of manipulations in animals. The most commonly used manipulations that attempt to model the amnesia of AD are reviewed within these constraints. The authors conclude that of the models examined, lesions of the medial septal nucleus produce behavioral deficits that are most similar to the mnemonic impairments in the earliest stage of AD. However, the parallel is not definitive and more work is needed to clarify the relationship between neurobiology and behavior in AD.

Simple and configural association learning in rats with bilateral quisqualic acid lesions of the nucleus basalis magnocellularis

We hypothesized that bilateral quisqualic acid lesions of the nucleus basalis magnocellularis (NBM) in rats would impair configural but not simple association learning. In experiment 1, rats were tested in a negative patterning operant discrimination where they were food-reinforced for responding to a light or a tone (L+, T+) but not for responding to the configural stimulus consisting of the light and tone presented simultaneously (LT-). Consistent with our hypothesis, NBM-lesioned rats showed a transient but significant impairment, responding normally to L+ and T+ but responding more often to LT-, in addition to responding more often during the inter-trial interval (ITI) than controls. In experiment 2, rats were tested in a simple operant discrimination where rats were food-reinforced for responding to a light (L+) but not for responding to a tone (T-). Although NBM-lesioned rats again responded normally to L+ as predicted, NBM-lesioned rats were transiently impaired, making more T- responses and more ITI responses than controls. Together, these results suggest that the NBM is involved in both configural and simple association learning but that this involvement is limited to learning to withhold responding to non-reinforced contextual or discrete stimuli. Finally, rats from experiment 2 underwent extinction trials, where results showed no difference between NBM-lesioned and control groups, suggesting that the NBM is not involved in the extinction of conditioned responding to previously reinforced stimuli.

Experimental immune-mediated damage of septal cholinergic neurons

Degeneration of cholinergic neurons in the medial septum and the diagonal band of Broca is a frequent neuropathological feature of Alzheimer's disease. To determine whether an immune process can injure these basal forebrain cholinergic neurons, we serially immunized guinea pigs with septal cholinergic hybrid cells (SN-56). Following immunization, a relatively selective damage of septal cholinergic neurons, reduction in septal choline acetyltransferase (ChAT) activity and decrease in acetylcholine release in hippocampus were detected. Serum IgG from guinea pigs immunized with SN-56 cells and stereotactically injected into the medial septal region of rats produced a loss of ChAT activity in the medial septum, frontal cortex and hippocampus, together with impairment of learning and long term spatial memory. These data suggest that relatively selective damage to septal cholinergic neurons can be caused by an immune-mediated process in experimental animals.

The nucleus basalis magnocellularis cholinergic system: one hundred years of progress

The nucleus basalis magnocellularis (NBM) contains a population of large cholinergic (Ch) neurons that send their axons to the entire cortical mantle, the olfactory bulbs, and the amygdala. This is the centennial anniversary of the first exact description of this nucleus by Von Kölliker, who named it in honor of its discoverer. This review will focus upon recent attempts to understand the role of the NBM Ch neurons in higher cognitive function by the use of selective lesion analyses and electrophysiological recording techniques. Behavioral deficits associated with NBM lesions produced by injections of excitatory amino acid agonists have been demonstrated in a variety of tasks. Performance decrements produced by these lesions were initially interpreted as being the result of impairments in learning and memory abilities. However, the precise role of the Ch NBM neurons in these performance deficits could not be more thoroughly investigated until it became possible to produce selective and discrete lesions by injection of the immunotoxin, IgG-192 saporin. The results of investigations using this immunotoxin supported a role for NBM Ch neurons in the performance of tasks that require selected attentional abilities rather than learning and memory per se. These lesion analysis studies suggested that the corticopetal NBM Ch system may be involved in the control of shifting attention to potentially relevant, and brief, sensory stimuli that predict a biologically relevant event, such as a food reward. Electrophysiological evidence has implicated NBM Ch cells in the control of attentional processes, as well as a role in the control and maintenance of arousal and sleep states. Electrophysiological studies also suggest that NBM Ch neurons might influence cortical EEG activity in two ways, by its direct excitatory inputs and by an indirect inhibitory projection to the thalamic reticular nucleus. Taken together with the results of histological and anatomical studies of the basal forebrain, NBM Ch cells appear to be ideally located within the basal forebrain for evaluating sensory stimuli for their level of significance, via inputs from the midbrain and limbic system, and also to modulate intrinsic cortical responsiveness appropriately in order to attend to brief, highly salient sensory stimuli.

Effects of chronic infusion of nerve growth factor (NGF) in rats with nucleus basalis magnocellularis lesion

We attempted to evaluate the effects of bilateral injection of ibotenic acid (IA) into the nucleus basalis magnocellularis (nbm) of rats as well as the potential recovery mediated by the infusion of nerve growth factor (NGF). The lesion caused an impairment of learning and memory processes. Also, a severe depletion of choline acetyl transferase activity was detected in cortical areas. After the NGF administration, a significant reversion of these functional changes was observed. Thus, IA-lesioned rats might serve as a model for the evaluation of neurotrophic factors actions on basal forebrain damaged neurons.

Chronic nicotine treatment prevents neuronal loss in neocortex resulting from nucleus basalis lesions in young adult and aged rats

In both young adult and aged rats, we tested the ability of chronically administered nicotine to rescue neocortical neurons from transneuronal degeneration resulting 5 mo after ibotenic acid (IBO) lesioning of the nucleus basalis magnocellularis (NBM). Young adult (2-3 mo-old) and aged (20-22-mo-old) rats were given unilateral infusions of IBO (5 mu g/1 mu L) at two sites within the NBM. Following surgery, animals began receiving either daily ip injections of nicotine (0.2 mg/kg) or saline vehicle. Treatment continued for 5 mo, at which time all animals were sacrificed and their brains processed histologically. For each brain, computer-assisted image analysis was then used to analyze the unlesioned (left) and lesioned (right) side of five non-consecutive brain sections from parietal cortex Layers II-IV and V. NBM lesioning in both young adult and aged vehicle-treated rats resulted in a significant 16-21% neuronal loss ipsilateral to NBM lesioning in neocortical Layers II-IV. Aged NBM-lesioned rats also exhibited a significant 12% neuronal loss in neocortical Layer V ipsilaterally. By contrast, those NBM-lesioned young adult and aged rats that received daily nicotine treatment postsurgery did not show any ipsilateral neuronal loss in the same parietal cortex areas, indicating that chronic nicotine treatment prevented the transneuronal degeneration of neocortical neurons resulting 5 mo afer NBM lesioning.

Scopolamine differentially affects memory of 8- and 16-month-old rats in the double Y-maze

The present study investigated the effects of scopolamine on working and reference memory in the same rats at 8 and 16 months of age. Rats were trained in the double Y-maze until a criterion of > or = 88% correct was reached on both memory components. Doses of scopolamine (0.1, 0.4, 0.8 mg/kg for rats at 8 months; 0.05, 0.1, 0.4 mg/kg for rats at 16 months) were administered in a counterbalanced order 30 min before test sessions which also included delays of 0, 5, or 30 s prior to both memory components. Results showed that at both ages the 0.1 mg/kg scopolamine dose selectively impaired working memory, whereas higher doses impaired both working and reference memory. Delays selectively decreased working memory choice accuracy and enhanced the effect of scopolamine. Rats at 16 months performed less well on both reference and working memory and showed greater impairments with scopolamine and delays. The present findings support the hypothesis that a decrease in cholinergic neurotransmission contributes to age-related memory deficits.

Neuroprotection and selective vulnerability of neurons within the nucleus basalis magnocellularis

Neurons within the nucleus basalis may die due to their selective vulnerability to endogenous excitatory amino acid neurotransmitters, nitric oxide and free radicals. The factors influencing the selective vulnerability of neurons within the nucleus basalis depend upon many different factors related to the presence of these agents and the neuron's ability to defend itself against the consequences of exposure. Many different mechanisms have been investigated to provide neuroprotection for neurons within the nucleus basalis and throughout the central nervous system. This review summarizes the results of studies that have investigated our current capability to either attenuate the neurotoxicity of endogenous excitatory amino acids, such as glutamate, or to provide effective neuroprotection during circumstances of neurotoxin exposure.

Effects of scopolamine infusions into the anterior and posterior cingulate on passive avoidance and water maze navigation

We examined the role of anterior and posterior cingulate cortical muscarinic receptors in water maze spatial learning and passive avoidance. Pretraining and posttraining trial scopolamine (a mixed a muscarinic acetylcholine antagonist) infusions into the anterior cingulate cortex dose dependently (3 no effect; 10 and 30 micrograms impaired) impaired passive avoidance performance. Pretesting infusion into the anterior cingulate had no effect on passive avoidance. Scopolamine infusion into the anterior cingulate did not impair spatial navigation. On the contrary, scopolamine (3 micrograms no effect, 10 and 30 micrograms impaired) infusions into the posterior cingulate before daily training trials impaired water maze navigation to a hidden platform, but did not affect navigation to a visible escape platform or passive avoidance. Posttraining and pretesting infusion into the posterior cingulate did not impair WM spatial navigation. The present results indicate that muscarinic acetylcholine receptor antagonist may modulate passive avoidance performance via cholinergic receptors located in anterior cingulate cortex and the ability to develop a spatial navigation strategy via muscarinic receptors located in posterior cingulate.

Behavioural, histochemical and biochemical consequences of selective immunolesions in discrete regions of the basal forebrain cholinergic system

The effectiveness of a recently developed immunotoxin, 192 IgG-saporin, was evaluated for making selective lesions of subgroups of basal forebrain cholinergic neurons. Following a pilot series of injections into the nucleus basalis magnocellularis to establish the effective dose for intraparenchymal lesions, separate groups of rats received injections of the immunotoxin into the septum, into the diagonal band of Broca or into the nucleus basalis magnocellularis. The lesions produced extensive and effective loss of cholinergic neurons in the discrete areas of the basal forebrain, as identified by loss of cells staining for acetylcholinesterase and p75NGFr, with a parallel loss of acetylcholinesterase staining and choline acetyltransferase activity in the target areas associated with each injection site in the dorsolateral neocortex, cingulate cortex and hippocampus. The selectivity of the lesion for cholinergic neurons was supported by the lack of gliosis and sparing of small to medium-sized cells at the site of injection of the toxin, including the glutamate decarboxylase immunoreactive cells that contribute to the septohippocampal projection. In spite of the extensive disturbance in the cholinergic innervation of the neocortex and hippocampus, immunotoxin lesions produced no detectable deficit in the Morris water maze task in any of the lesion sites within the basal forebrain. By contrast small but significant deficits were seen on tests of nocturnal activity (septal and nucleus basalis magnocellularis lesions), open field activity (septal and diagonal band lesions), passive avoidance (nucleus basalis magnocellularis lesions) and delayed non-matching to position (septal lesions). The results indicate that the 192 IgG-saporin provides a powerful tool for making effective lesions of the basal forebrain cholinergic neurons, and that the behavioural sequelae of such lesions warrant further detailed investigation.

Investigations of neurotoxicity and neuroprotection within the nucleus basalis of the rat

The present study investigated the specific ways by which cytotoxicity due to glutamate receptor stimulation could be attenuated by the administration of agonists and antagonists of the ionotropic and metabotropic glutamate receptors within the nucleus basalis magnocellularis (NBM) of rats as measured by cortical choline acetyltransferase activity. The results of these studies suggest that (1) the cytotoxicity of ibotenate to NBM cholinergic cells is not dependent upon stimulation of metabotropic glutamate receptors, but results from activation of N-methyl-D-aspartate (NMDA) receptors, (2) the cytotoxicity of quisqualate to cholinergic cells within the NBM is not dependent upon stimulation of NMDA or metabotropic receptors, and (3) the cytotoxicity of NMDA was prevented by administration (i.p.) of the un-competitive NMDA antagonist memantine (30 mg/kg), resulting in plasma levels of 2.5 micrograms/ml, a concentration known to block efficiently NMDA receptors in vitro. Finally, performance of a food-motivated, delayed-alternation task on a T-maze was impaired by injections of NMDA into the NBM, but was prevented by co-administration of NMDA with memantine.

Quisqualic acid-induced seizures during development: a behavioral and EEG study

Quisqualic acid (QA) is an excitatory amino acid analogue that binds to the glutamate ionotropic receptor subclass AMPA (alpha-amino-3 hydroxy-5 methyl-4 isoxazol propionic acid) and metabotropic receptor phospholipase C. To study its epileptogenic properties, we administered QA through an intraventricular cannula to 23-, 41-, and 60-day-old rats with recording electrodes implanted in amygdala, hippocampus, and neocortex. The frequency power spectra of the recorded EEG was computed by fast fourier transform (FFT), and coherence between anatomic sites was computed. Seizures occurred in all animals receiving QA. The behavioral manifestations of the seizures varied as a function of age, with younger rats demonstrating rigidity and immobility followed by circling activity and intermittent forelimb clonus and 60-day-old animals exhibiting severe, wild running followed by generalized clonus. Ictal electrical discharges occurred in all animals. Neocortical ictal discharges occurred more prominently in the younger animals, and amygdala ictal discharges were more prominent in the older animals. Marked increases in spectral power occurred during the seizures in all anatomic structures and at all frequencies. Our results demonstrate that the clinical manifestations of QA seizures vary during development; results of the neurophysiologic studies suggested that neocortex may play an important role in genesis of QA seizures in immature brain.

Comparison of intracranial infusions of colchicine and ibotenic acid as models of neurodegeneration in the basal forebrain

Colchicine and ibotenic acid were compared for their ability to produce neurodegeneration and cognitive deficit after bilateral infusions into the nucleus basalis magnocellularis of male Long-Evans rats. Four weeks post-lesion, there was no difference in locomotor activity following infusion of either neurotoxicant or vehicle. In a passive avoidance task, both treated groups had significantly shorter step-through latencies compared with vehicle. Five weeks post-lesion, rats were killed for neurochemistry or histochemistry. Choline acetyltransferase (ChAT) activity in both the frontal and parietal cortex was significantly decreased (25-35%) in the colchicine- and ibotenic acid-infused rats when compared to control. There was no effect of either neurotoxicant on ChAT activity in the hippocampus or striatum. Both neurotoxicants produced damage in the general area of the ventromedial pallidum, although ibotenic acid infusion consistently produced a larger area of damage as assessed in Nissl-stained sections. Analysis of the number of ChAT-immunoreactive cells in the nucleus basalis magnocellularis (NBM) showed an average 60% cell loss following colchicine infusion and a 75% cell loss after ibotenic acid infusion. Area of glutamic acid decarboxylase (GAD) staining was significantly decreased in several regions surrounding the NBM for ibotenic acid (51% average decrease), and showed non-significant decreases (28%) following colchicine infusion. Colchicine infusion decreased dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) in the striatum; ibotenic acid had no effect on brain catechol of indoleamine levels. The results indicate that although similar cholinergic hypofunction and behavioral deficits were achieved, several non-cholinergic differences between the neurotoxicants were detected.

Mnemonic deficits in the double Y-maze are related to the effects of nucleus basalis injections of ibotenic and quisqualic acid on choline acetyltransferase in the rat amygdala

Many researchers have reported that the magnitude of decrease in cortical choline acetyltransferase (ChAT) following excitotoxic lesions of the nucleus basalis magnocellularis (nbm) is unrelated to the degree of cognitive impairment. Recently, an explanation has been offered for this lack of correlation: different excitotoxins, when injected into the nbm, differentially affected cholinergic projections to the cortex and amygdala, and those excitotoxins previously reported to produce the greatest mnemonic deficits produced the largest decreases in amygdaloid ChAT. The present study evaluated the role of amygdalofugal cholinergic projections in memory by comparing the effects of intra-nbm ibotenic and quisqualic acid on cortical and amygdaloid ChAT and on mnemonic performance in the double Y-maze. Rats were trained in the double Y-maze until working and reference memory choice accuracy stabilized to a criterion of > or = 78% correct. Rats then were given either bilateral quisqualic acid (60 nmol in 0.5 microliter), bilateral ibotenic acid (50 nmol in 0.5 microliter), or sham (0.9% saline in 0.5 microliter) lesions of the nbm, and again were tested on the maze. Quisqualate produced a selective impairment of working memory, a large (51%) decrease in cortical ChAT and a small (17%) decrease in amygdaloid ChAT; ibotenate, on the other hand, produced a greater impairment of working memory, an impairment of reference memory, a similar (51%) decrease in cortical ChAT, but a greater (30%) decrease in amygdaloid ChAT. These results suggest that the cholinergic projections from the nbm to the cortex and amygdala play an important role in memory. They suggest that excitotoxins producing greater depletions of amygdaloid ChAT produce greater mnemonic deficits.

The behavioral effects of serotonin synthesis inhibition and quisqualic acid induced lesions of the nucleus basalis magnocellularis in rats

1. To investigate the role of the cholinergic and serotonergic systems in the regulation of cognitive functions, the effects of concurrent lesioning of nucleus basalis magnocellularis (NB) with quisqualic acid (quis) and inhibition of brain serotonin synthesis by systemic p-chlorophenylalanine (PCPA) treatment on passive avoidance (PA) retention and water maze (WM) spatial navigation performance were studied in rats. 2. Quis NB lesioning induced a marked reduction (-62%) in frontal cortical choline-acetyltransferase activity, impaired retention of PA, and slightly and transiently impaired acquisition of WM spatial navigation. 3. PCPA (400 mg/kg/day x 3, i.p.) treatment depleted frontal cortical concentrations of both serotonin (82% depletion) and its major metabolite 5-HIAA (90% depletion) and slightly affected the noradrenergic and dopaminergic systems. PCPA treatment alone had no effect on WM or PA behavior, but potentiated the PA retention deficit and slightly aggravated the WM deficit in rats subjected to quis NB lesioning. 4. The present results further support the view that serotonergic and NB neurons interact in the regulation of cognitive functions.

Improvement of ischemic myocardial dysfunction by nisoldipine in relation to its coronary vasodilating action

We examined the cardioprotective effect of nisoldipine against myocardial dysfunction during ischemia and reperfusion in comparison with those of diltiazem and nifedipine in rabbit hearts perfused at constant pressure. These calcium antagonists were administered to the hearts before 60 min of ischemia. They inhibited the increase of end-diastolic pressure during ischemia in a dose-dependent manner. Diltiazem at 1.0 microM, nifedipine at 3.0 microM and nisoldipine at 0.01 microM produced the maximal cardioprotective effect. Nisoldipine had a beneficial effect with less negative inotropic effect than those of diltiazem and nifedipine and it produced a significant increase of coronary flow during reperfusion. When the vascular component was eliminated under constant flow perfusion, nisoldipine also showed the cardioprotective effect. Nisoldipine did not produce any beneficial effect without the inhibition of the increase in end-diastolic pressure during ischemia nor did it do so without the increase of reperfusion flow. Therefore, the nisoldipine-increased coronary flow during reperfusion as well as the inhibition of ischemic contracture by nisoldipine seems to play a crucial role in improving the myocardial dysfunction of ischemic-reperfused hearts.

Scopolamine injected into the rat amygdala impairs working memory in the double Y-maze

Recent neurochemical results suggest the hypothesis that the nucleus basalis magnocellularis (nbm) cholinergic projection to the amygdala may play a role in memory. The present study investigated the effects of intra-amygdaloid injections of the cholinergic antagonist scopolamine on working and reference memory in the double Y-maze. Rats were pretrained until working and reference memory choice accuracy stabilized to a criterion of > or = 86% correct. Bilateral cannulae were then surgically implanted in the basolateral amygdaloid complex. Rats (n = 9) received scopolamine in doses of 8.0, 24.0, and 72.0 micrograms/0.5 microliter and saline (0.5 microliter) in a counterbalanced order with retraining to criterion between injections. Intra-amygdaloid scopolamine produced a dose-dependent and differential impairment of working and reference memory. A dose of 24.0 micrograms impaired working memory without significantly affecting reference memory; doses of 8.0 micrograms and 72.0 micrograms affected neither and both types of memory, respectively. Results implicate amygdaloid acetylcholine in memory.

Muscimol injections into the nucleus basalis magnocellularis of rats: selective impairment of working memory in the double Y-maze

Anatomical and neurochemical results suggest that the cortico- and amygdalopetal cholinergic neurons of the nucleus basalis magnocellularis (NBM) may receive GABAergic inputs. The present experiments were undertaken to evaluate the possible influence of intra-NBM injections of the GABAA agonist, muscimol, on memory. In two experiments, rats were chronically implanted with guide cannulae placed bilaterally into the NBM. Rats were trained to a criterion of at least 83% correct on each component in a double Y-maze task that allowed a dissociation of working and reference memory. The task began with placement into one of the two end arms of the first Y-maze and the reference memory task was to go to the stem for food. Access to the second Y was then given and the working memory task was to go to the goal arm opposite the arm in the first maze from which that trial began. In experiment 1, pre-trained rats (n = 7) received muscimol (0.5 microliter) in doses of 0, 0.01, 0.1 and 1.0 microgram in a counterbalanced order with re-training to criterion between injections. In experiment 2, pre-trained rats (n = 8) received saline, muscimol (0.1 microgram), the GABAA antagonist, bicuculline (0.01 microgram), and muscimol + bicuculline. Results of experiment 1 revealed that intra-NBM muscimol produced a dose-dependent and differential impairment of working and reference memory. A dose of 0.1 microgram impaired working memory without significantly affecting reference memory; doses of 0.01 microgram and 1.0 microgram affected neither and both types of memory, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the effects of acute and chronic ibotenic and quisqualic acid nucleus basalis lesioning

The present study examines the effects of acute (1 month recovery) and chronic (8 month recovery) bilateral quisqualic (quis) and ibotenic (ibo) acid nucleus basalis (NB) lesioning on the activity of cholinergic neurons and on passive avoidance (PA) and water-maze (WM) performance. Our data demonstrate that A: The activity of choline acetyltransferase (ChAT) in cortical tissue and the number of ChAT positive neurons in the NB were decreased 1 and 8 months after quis or ibo NB lesioning. B: Ibo NB lesioning produced a greater nonspecific subcortical cell loss than quis NB lesioning. C: PA retention was impaired by acute and chronic quis and ibo NB lesioning. D: Acute ibo NB lesioning impaired acquisition and reversal learning in WM performance whereas chronic ibo NB lesioning impaired only reversal WM learning. Acute and chronic quis NB lesioning impaired reversal WM learning. The present results suggest that NB cholinergic neurons do not recover spontaneously from excitotoxin-induced damage and that they may be importantly involved in inhibitory avoidance and spatial reversal learning performance.