Effects of brief stress exposure during early postnatal development in Balb/CByJ mice: II. Altered cortical morphology.

Early life experience can significantly determine later mental health status and cognitive function. Neonatal stress, in particular, has been linked to the etiology of mental health disorders as divergent as mood disorder, schizophrenia, and autism. Our study uses a Balb/CByJ mouse model to test the hypothesis, that neonatal stress will alter development and subsequent environmental modulation of neocortex. Using a split litter design, we generated stressed mice (STR) and within litter controls (LMC) along with age-matched, untreated animals (AMC), to serve as across litter controls. Short, daily exposure to a psychosocial/physical stressor, during the first week of life, resulted by adulthood in significant changes in neocortical thickness and architecture, which were further modulated by exposure to behavioral testing. Surprisingly, cortical size in LMC mice was also affected. These observations were compared to the effects of environmental enrichment in the same mouse strain. Our data indicate that LMC and STR males share with environmentally enriched males, an increase in thickness in infra-granular cortical layers, while STR also display a stress selective decrease in supragranular layers, in response to behavioral training as adults.

Neonatal 5,7-DHT lesions cause sex-specific changes in mouse cortical morphogenesis.

Both monoaminergic and cholinergic afferent projections to the neocortex putatively modulate cortical morphogenesis and plasticity. Previously we showed that neonatal electrolytic lesions of the cholinergic nucleus basalis magnocellularis (nBM) projections to the neocortex result in significant decreases of cortical layer width that correlate with cognitive alterations. Such electrolytic lesions, performed for lack of a selective neurotoxin in mice, may affect mono-aminergic fibers of passage. Here, we investigate the effects of neonatal 5,7 dihydroxytryptamine (5,7-DHT) focal injections into the nBM region on cortical laminar morphology in adult male and female mice. 5,7-DHT lesions on the first postnatal day resulted in significant cortical depletion of both serotonin and norepinephrine that attenuated with age. Generally, cortical layer widths increased in response to the lesion; the effects were layer, region, and sex specific. Previous reports from our laboratories described long-term behavioral alterations after comparable focal, neonatal 5,7-DHT lesions. The studies described here provide an anatomical basis for such behavioral alterations. Our data suggest that monoaminergic and cholinergic projections to the cortex may have opposite effects on the developing cortical neuropil. Jointly, our morphological and behavioral findings may have important implications for a variety of developmental disorders in humans and provide some insights into sex differences in the penetrance of these disorders.

Sexually dimorphic responses to neonatal basal forebrain lesions in mice: II. Cortical morphology.

Previous studies in the mouse have shown that neonatal lesions to the cholinergic basal forebrain (nBM) areas result in transient cholinergic depletion of neocortex and precipitate altered cortical morphogenesis. Lesion-induced morphological alterations in cortex persist into adulthood and are accompanied by behavioral changes, including spatial memory deficits. The current study investigated whether neonatal nBM lesions affect male and female mice differently in adulthood. Quantitative morphometry of cortical layer width was employed to assess alterations in cytoarchitecture in neonatally nBM-lesioned and littermate control mice of both sexes following behavioral testing. Our results showed significant decreases in cortical layer IV and V widths across somato/motor cortex in neonatally nBM lesioned mice of both sexes. Sexually dimorphic responses were observed in cortical layer II/III and total cortical width, limited to the area containing the "barrel cortex" representation of the whisker hairs. In lesioned females, layer II/III and total cortical width were decreased relative to female controls, and in lesioned males, layer II/III was increased relative to controls, whereas total cortical width was unchanged. In male but not female mice we observed significant correlations between decreased widths in layer IV and V and impaired performance on a spatial memory task. The current data further support a role of developing cholinergic cortical afferents in the modulation of cortical morphogenesis and cortical circuits involved in cognitive behaviors. In addition, our observations provide further evidence for sexually dimorphic development and function in cognitive centers of the rodent brain.

Sexually dimorphic responses to neonatal basal forebrain lesions in mice: I. Behavior and neurochemistry.

The nucleus basalis magnocellularis (nBM) provides the primary source of cholinergic input to the cortex. Neonatal lesions of the nBM produce transient reductions in cholinergic markers, persistent abnormalities in cortical morphology, and spatial navigation impairments in adult mice. The present study examined sex differences in the effects of an electrolytic nBM lesion on postnatal day 1 (PND 1) in mice on behavior and neurochemistry in adulthood. Mice were lesioned on PND 1 and tested at 8 weeks of age on a battery of behavioral tests including passive avoidance, cued and spatial tasks in the Morris water maze, simple and delayed nonmatch to sample versions of an odor discrimination task, and locomotor activity measurements. Following behavioral testing, mice were sacrificed for either morphological assessment or neurochemical analysis of a cholinergic marker or catecholamines. There were no lesion or sex differences in acquisition or retention of passive avoidance, performance of the odor discrimination tasks, or activity levels. Control mice showed a robust sex difference in performance of the spatial water maze task. The lesion produced a slight cued but more dramatic spatial navigation deficit in the water maze which affected only the male mice. Neurochemical analyses revealed no lesion-induced changes in either choline acetyltransferase activity or levels of norepinephrine or serotonin at the time of testing. The subsequent report shows a sex difference in lesion-induced changes in cortical morphology which suggests that sexually dimorphic cholinergic influences on cortical development are responsible for the behavioral deficits seen in this study.

Cholinergic regulation of cortical development and plasticity. New twists to an old story.

Cholinergic afferents innervate cerebral cortex during the most dynamic period of neuronal differentiation and synapse formation, suggesting they play a possible regulatory role in these events. A number of in vivo studies have shown over the last decade that alterations in cholinergic innervation during early postnatal development can change various features of cortical ontogeny. In particular, neonatal lesions to basal forebrain cholinergic afferents result in delayed cortical neuronal development and permanently altered cortical cytoarchitecture and cognitive behaviors. Likewise, cholinergic manipulations affect morphological plasticity in cat visual cortex as well as in the somatosensory cortex of rodents. Furthermore, augmentation of cholinergic function by means of perinatal choline treatment enhances cognitive performance in a sex specific manner. Additional indications for a sexual dimorphism in cortical cholinergic innervation and resulting function are gathered from a variety of paradigms. Recent information about effects of NGF, BDNF and NTB-4/5 on cortical morphogenesis and plasticity reveals complex interactions between the cholinergic basal forebrain afferents and this neurotrophin family. Detailed studies on the expression of cholinergic receptor proteins in cortical development and their associated signal transduction pathways strongly point towards a morphogenetic function of muscarinic receptors, in particular. Transient receptor localization in thalamocortical terminal fields and on a variety of other non-cholinergic fiber bundles suggest a cholinergic role in target finding and/or synapse formation for cortical afferents and efferents. We propose a hypothesis regarding the mechanisms for cholinergic regulation of neuronal differentiation and synapse formation on the level of the individual growth cone and discuss possibilities for cholinergic interactions with differential gene expression. We conclude that understanding the precise role of the cholinergic system in cortical morphogenesis and its relationship to neurotrophin function will be of clinical relevance for a number of developmental brain disorders, including Down Syndrome and Rett Syndrome.

Effects of neonatal cholinergic basal forebrain lesions on excitatory amino acid receptors in neocortex.

The role of cholinergic basal forebrain projections in the modulation of cortical plasticity and associated functional changes is currently the subject of renewed attention. Excitatory amino acid receptors have been identified as mediators of cortical topographic efferent and afferent information. In addition some of these receptors, notably the NMDA and metabotropic [mGluR] type, participate in cortical plasticity. Growing evidence suggests that interactions between cholinergic and glutamatergic systems contribute to cognitive cortical functions and their anatomical and physiological substrates. Though cholinergic and glutamatergic mechanisms have both been shown to be involved in cortical morphogenesis, few studies have attempted to study their interactions in development. The present study investigates the effect of neonatal lesions to the cholinergic basal forebrain on NMDA, AMPA and mGluR receptors in BALB/CByJ mice, at two different developmental ages. We demonstrated previously that nBM lesions at birth result in transient cholinergic depletion for the first two postnatal weeks, substantial morphogenetic alterations in neocortex and cognitive deficits by adulthood. We show here that unilateral neonatal lesions result in decreases in NMDA and AMPA receptors but increases in mGluRs during the second postnatal week (PND 14). At 30 days postnatal, lesion mediated changes were attenuated, compared with PND 14, but significant sex differences in control and nBM lesioned mice were apparent. These data support the notion that cholinergic/glutamatergic interactions are important during early cortical morphogenesis. Moreover, our results highlight the fact that cholinergic as well glutamatergic developmental mechanisms are sexually dimorphic.

Neonatal monoaminergic depletion in mice (Mus musculus) improves performance of a novel odor discrimination task.

This experiment examined behavior and neurochemistry in adult mice (Mus musculus) after neonatal depletion of monoaminergic fibers projecting to the neocortex and hippocampus. Lesions were made on Postnatal Day 1; mice developed to adulthood and were assessed on simple odor discrimination (SOD) and odor delayed nonmatch-to-sample (DNMS) tasks, passive avoidance (PA), and locomotor activity. On SOD, lesioned mice performed faster than controls but with similar accuracy. On the DNMS task, the lesioned mice performed faster and more accurately than controls. On PA, the lesioned mice exhibited a retention deficit relative to controls. Locomotor activity was similar in the 2 groups. Postmortem analyses revealed that the lesions reduced significantly norepinephrine and serotonin levels in both the neocortex and hippocampus. The data suggest that cortically projecting monoaminergic fibers play an important role in normal cognitive development.

Behavioral consequences of abnormal cortical development: insights into developmental disabilities.

Cerebral cortical development occurs in precisely-timed stages that can be divided into neurogenesis, neuronal migration and neuronal differentiation. These events occur during discrete time windows that span the late prenatal and early postnatal periods in both rodents and primates, including humans. Insults at particular developmental stages can lead to distinctive cortical abnormalities including cortical hypoplasia (reduced cell number), cortical ectopias (abnormalities in migration) and cortical dysplasias (abnormalities in the shapes or numbers of dendrites). In this review, we examine some of the most extensively-studied animal models of disrupted stages of cortical development and we compare long-term anatomical, neurochemical, and behavior abnormalities in these models. The behavioral abnormalities in these models range from alterations in simple motor behaviors to food hoarding and maternal behaviors as well as cognitive behaviors. Although we examine concisely animal models of cortical hypoplasia and cortical ectopias, we focus here on developmental manipulations that affect cortical differentiation, particularly, those that interrupt the normal ontogeny of the neurotransmitter-defined cortical afferent systems: norepinephrine, serotonin, dopamine and acetylcholine. All of these afferents presumably play a critical role in the maturation of their cortical targets; the timing of the afferents' entry into the cortex and their effects on their cortical targets, however, are different. We, therefore, compare the specific anatomical, neurochemical and behavioral effects of manipulations of the different cortical afferents. Because of the considerable evidence that cortical development proceeds differently in the two sexes, when data are available, we address whether perinatal insults differentially affect the sexes. Finally, we discuss how these developmental studies provide insights into cellular and neurochemical correlates of behavioral functional abnormalities and the relevance of these data to understanding developmental disabilities in humans.

Abnormalities in neuronal maturation in Rett syndrome neocortex: preliminary molecular correlates.

In correspondence with the severe cognitive impairment and autistic features of Rett syndrome (RS), multiple anomalies of the cerebral cortex that include generalized reductions in dendritic arborizations and in cholinergic markers have been found. Considering the potential role of neurotransmitters in cortical differentiation, we have studied the relationship between cholinergic deficit and dendritic protein expression in RS and in a relevant animal model. Dendritic development is characterized by the sequential expression of cytoskeletal proteins whose levels remain relatively stable in adult life. Using quantitative immunoblotting, we have determined that in RS there is a reduction in proteins linked to early dendritic development [microtubule-associated protein (MAP)-5, MAP-2]. By contrast, in Down syndrome there is relative generalized increase in dendritic proteins. Mice with basal forebrain lesions at birth, which transiently decrease cholinergic innervation to the cortex, showed in adulthood reductions in MAP-2 that resemble those seen in RS. We conclude that dendritic anomalies in RS represent disturbances in early cortical differentiation and that cholinergic deficit may play a critical role in their pathogenesis as suggested by the animal data.

Development of muscarinic receptor subtypes in the forebrain of the mouse.

Cholinergic mechanisms are involved in the regulation of developmental events in the nervous system. Muscarinic cholinergic receptors are thought to be the predominant mediator of cholinergic neurotransmission in the forebrain; however, their developmental role is less well understood. The present study takes advantage of subtype-specific antibodies to muscarinic receptor proteins to investigate the cellular localization of the subtypes in developing mouse forebrain. Receptor protein expression was assessed between postnatal day (PND) 5 and adulthood by immunocytochemical methods with antibodies to m1, m2, and m4 receptors, the most abundant subtypes in rodent brain. We have found dramatic developmental changes in the distribution of all three receptors. In the adult mouse, m1 and m2 receptor immunoreactivity displayed complementary staining patterns in most forebrain areas with m4 sharing similarities in pattern with both m1 and m2. Furthermore, each receptor was expressed transiently in gray matter areas or fiber bundles at various developmental stages. The m4 receptor was also expressed in developing blood vessels. Such transient immunoreactivity was usually associated with times and areas of dynamic morphogenesis, thus suggesting distinct roles for the receptor subtypes in ontogenetic events.

Developmental regulation of adult cortical morphology and behavior: an animal model for mental retardation.

The purpose of this study was to examine the behavioral performance in adult mice which, as neonates, had received lesions to cortically projecting, cholinergic basal forebrain neurons. The nucleus basalis magnocellularis (nBM) provides the primary cholinergic innervation to cerebral cortex. Lesions in the nBM in neonatal mice result in transient cholinergic denervation and persistent abnormalities in cortical morphology and cytoarchitecture. These cortical abnormalities resemble pathologies observed in a number of developmental disabilities in humans, including Down Syndrome. Balb/CByJ mice received lesions to the nBM 12-24 hr after birth; littermates served as controls. Behavioral testing began 8 weeks after the lesion and included assessments of spontaneous motor activity, retention (a passive avoidance task) and cognition (the Morris swim task). Following behavioral testing, a subset of mice was killed for Nissl and acetylcholinesterase (AChE) histology. The cortical morphology in these brains was evaluated and ranked by the experimenter, who was blind to the lesion and behavioral studies. The lesioned mice exhibited increased spontaneous activity as compared to littermate controls. The lesioned mice were also severely impaired in performance of the retention and cognitive task; they showed decreased passive avoidance retention latencies and increased swim maze latencies as compared to controls. The brains of all of the lesioned mice exhibited cortical morphological abnormalities that ranged from slight to severe. Cortical AChE intensity and distribution in the brains of the lesioned mice, however, were comparable to those of controls. In correlation studies of behavioral and morphological data, motor activity did not correlate with either passive avoidance retention or swim maze latencies. Additionally, cortical cytoarchitectural abnormalities did not correlate with motor activity. Cortical cytoarchitectural abnormalities did, however, correlate with both passive avoidance and swim maze latencies, i.e. severely abnormal cortical morphology predicted low passive avoidance retention latencies and high swim maze latencies. These data indicate that cortical cytoarchitectural abnormalities resulting from nBM lesions in neonates correlate with impairments on the cognitive task, but not with the activity measures, in adult mice. Thus, in this lesion model, and by extrapolation in developmental disabilities in humans, structural changes in the cortex which result from transient disruption of cortical cholinergic innervation may lead to persistent cognitive impairments in adulthood.

Brain transplants of cells expressing the carboxyl-terminal fragment of the Alzheimer amyloid protein precursor cause specific neuropathology in vivo.

PC12 cells transfected with retroviral recombinants expressing the carboxyl-terminal 104 amino acids of the Alzheimer amyloid protein precursor (beta APP-C104) or PC12 cells transfected with the retroviral vector (DO) alone were transplanted into the brains of newborn mice. At 20 days after grafting, transplants could be detected in all of the mouse brains examined. At 4 months after transplantation, experimental animals exhibited significant cortical atrophy. Some also revealed immunoreactivity with Alz-50, an antibody that detects an Alzheimer disease-related protein, in the somatodendritic domain of neurons in the cortex surrounding the transplants. In addition, disorganization of the neuropil in the CA2/3 region of the hippocampus ipsilateral to the transplant was revealed by staining with an antibody to the carboxyl-terminal end of the amyloid protein precursor. A decrease in cell body immunoreactivity for this portion of the amyloid protein precursor was also detected with this antibody. Together, these results suggest that the carboxyl-terminal fragment of beta APP may cause specific neuropathology and neurodegeneration in vivo.

Distinct immunoreactivity to 110 kDa laminin-binding protein in adult and lesioned rat forebrain.

A phosphorylated, approximately 110 kDa laminin-binding protein (110 kDa LBP) from mouse brain has been previously identified. This protein recognizes a neurite-outgrowth promoting 19-amino acid synthetic peptide (PA 22-2) derived from the laminin A chain. In the present study, an antibody against the 110 kDa LBP was used to localize immunoreactivity in the normal adult rat brain and also following a stab wound and ischemic lesion. Immunoreactive cells were found in layers II/III and V of the cerebral cortex and within apical dendrites of pyramidal neurons. Specific immunoreactivity was also found in the stratum lucidum in the CA3 region of the hippocampus which exhibited densely stained mossy fibers and terminals. Mechanical and ischemic lesions induced intense immunolabeling of reactive glial cells around the lesion site. The distinct and anatomically restricted localization of the immunostain in adult and lesioned rat brain suggests that 110 kDa LBP-like molecules might have an important function in forebrain structures and may be involved in the response to CNS injury.

Efferent and afferent connections of mouse sensory-motor cortex following cholinergic deafferentation at birth.

The present study investigates the effect of cholinergic basal forebrain lesions at birth on cortical connectivity in adulthood. We have previously shown that such neonatal lesions result in extensive cortical cholinergic deafferentation during early postnatal development, which is accompanied by abnormal morphogenesis of cortical cytoarchitecture (Höhmann at al., 1988). Here, we have used WGA-HRP to label anterogradely and retrogradely afferent and efferent projections of dorsal neocortex. Our results show an altered projection pattern from dorsal thalamus to layer IV of sensory-motor cortex following lesions among the cholinergic basal forebrain neurons (nBM), while corticothalamic projections from layer VI appear normal. In addition, corticofugal projections from layer V, labeled by striatal injection, appear to be expanded following the lesion. This indicates that cortical layers undergoing differentiation after the newborn nBM lesion present with long-term abnormalities in connectivity. The present results are compatible with the hypothesis that cholinergic afferents are instrumental in the regulation of cortical morphogenesis. Furthermore, our data show that ontogenetic disturbances can lead to structural abnormalities that persist long after the initial deficiency has abated. We discuss the significance of these results in relationship to human neurological disorders.

Newborn basal forebrain lesions disrupt cortical cytodifferentiation as visualized by rapid Golgi staining.

We have previously shown that neonatal lesions of the basal forebrain cholinergic afferents result in transient cholinergic depletion concomitant with abnormal morphogenesis of cerebral cortex in Balb/CByJ mice (Höhmann et al., 1988). Here, we have utilized the rapid Golgi method to further characterize these previously observed abnormalities. We compared layer V pyramidal neurons in somatomotor cortex ipsi- and contralateral to the lesion at postnatal days (PND) 7 and 14. Quantitative evaluations showed a significant reduction in all aspects of the dendritic tree as well as in cell body size in ipsilateral cortex at PND 7. Differences between ipsi- and contralateral pyramidal cells had attenuated by PND 14, but significant somatic size differences persisted, as did changes in the apical branching pattern. Qualitative differences between ipsilateral and contralateral hemispheres included the relatively more immature appearance of ipsilateral neurons at both ages, in addition to unusual dendritic morphology, particularly at PND 14. A close correlation was apparent between the magnitude of cholinergic depletion in cortex (larger at PND 7 than at PND 14) and the severity of abnormalities in pyramidal cell morphogenesis. We conclude that a normal cholinergic innervation to neocortex is instrumental in the timely differentiation of cortical neurons, because neonatal nBM lesions disrupted the time schedule of differentiation, but did not preclude the pyramidal neurons from further differentiation at a later time.

Lesions of the basal forebrain alter stimulus-evoked metabolic activity in mouse somatosensory cortex.

The role that acetylcholine plays in processing sensory stimuli is beginning to be characterized; however, morphological correlates of cholinergic effects on activity patterns in sensory cortex are not available. To study this problem, unilateral neurotoxic lesions that depleted the necortex of acetylcholine were made in the basal forebrains of mice. The aim of these experiments was to study the effect of cholinergic depletion on stimulus-evoked activity in the barrel field of the mouse somatosensory cortex. One month following the lesion, 2-deoxyglucose (2DG) experiments were conducted on the lesioned and on normal mice while the animal received bilateral stimulation to the C3 whisker. The tissue was processed for acetylcholinesterase and cytochrome oxidase histochemistry and 2DG autoradiography. Evaluation of the column-like 2DG label evoked in the somatosensory cortex revealed that the activity on the lesioned side was significantly reduced in dimension and intensity from that in the normal hemisphere. On the normal side, the activated barrels averaged 641 microns in tangential width, were 76.5% above background in density, and extended from lamina I-V. On the lesioned side, the activated barrels were 485 microns in tangential width, 65.4% above background in density, and extended from lamina II-V. In other cortical regions, outside the stimulus-evoked barrel field, 2DG activity values were similar on the normal and lesioned side. Additionally, both the pattern and intensity of the cytochrome oxidase staining within the barrel field displayed no differences in either hemisphere. These studies suggest that acetylcholine plays a significant role in the processing of somatosensory information. Neurotoxic lesions that diminish cortical cholinergic innervation cause a reduction of stimulus-evoked activity levels, while underlying metabolic activity is either not affected or recovers over time.

Neurogenesis of the basal forebrain in euploid and trisomy 16 mice: an animal model for developmental disorders in Down syndrome.

The neurogenesis and early histochemical differentiation of the basal forebrain in trisomy 16 fetal mice and their euploid littermates were examined by combining [3H]thymidine autoradiography with acetylcholinesterase histochemistry. Neurons of the basal forebrain were being born between embryonic day 11 and 15 in both chromosomally normal (euploid) and aneuploid mice. In euploid littermate controls, neurogenesis proceeded along a caudal to rostral gradient with the peak on embryonic day 11 for caudal portions and embryonic day 13 for rostral portions of the basal forebrain. In contrast, in trisomy 16 mice, rostral sections exhibited a peak of neurogenesis on embryonic day 11, 2 days earlier than in their euploid littermate controls. Hypocellularity of the basal forebrain region was noted in trisomy 16 mice; particularly dramatic was the reduction of the population of cells that expressed acetylcholinesterase. This reduction in cell number in the trisomics was not accompanied by a reduction in cell size or by a dramatic change in the distribution of residual neurons when compared to that of euploid littermate controls. Since trisomy 16 mice do not survive the perinatal period, we examined the pattern of acetylcholinesterase expression in normal C57B1/6J mice from embryonic day 16 to postnatal day 5 to determine the postnatal disposition of these neurons. Already at embryonic day 16, fibers staining for acetylcholinesterase penetrated the striatal anlage, in their course towards targets in the cerebral cortices. By postnatal day 5, the previously expansive distribution of basal forebrain neurons had become consolidated in a more ventral and rostral position by the extensive outgrowth of the striatal neurons, a pattern resembling that seen in adult animals.

Expression of cholinergic markers in transplants of immature mouse neocortex into adult mouse parietal cortex.

Cerebral cortex of embryonic and newborn mouse was removed and transplanted into adult mouse neocortex to investigate whether the development of cholinergic markers would proceed normally after transplantation. It is shown that both AChE and muscarinic receptors developed in transplanted mouse neocortex. However, while muscarinic receptor binding increased to adult levels in transplants from both pre- and postnatal donors AChE staining intensity only achieved adult levels in tissue from postnatal donors. These results are in accordance with the normal developmental time course of the two different cholinergic markers, since muscarinic receptors appear prenatally in cortex while AChE becomes histochemically detectable after birth. These data suggest that the prenatal donor tissue, unlike the postnatal transplants, lacks an environmental signal for the appearance of AChE stained elements, that is, presumably host AChE fiber ingrowth. Transplantation of immature donor CNS tissue into adult host thus appears to be a useful paradigm to study the regulation of differentiation processes.

A long-acting cholinesterase inhibitor reverses spatial memory deficits in mice.

The effects of the long-acting acetylcholinesterase (AChE) inhibitor, galanthamine, on spatial memory were investigated in mice. Mice received ibotenic acid or sham lesions to the nucleus basalis magnocellularis (nBM). Groups of nBM-lesioned and control mice were then trained on a modified Morris swim maze task. Each mouse was first placed on a platform and then into quadrants of the swim tank in a random order. Time required to find the hidden platform was measured. In different phases of testing, the animal had to find a platform that either remained in the same quadrant (reference memory component) or was moved daily (working memory component). The nBM-lesioned mice took significantly longer to find the platform as compared to controls on the working, but not on the reference, memory component of the task. Galanthamine (5.0 mg/kg, IP), given 3.5 hours before testing, improved performance on the working memory task in nBM-lesioned mice by 70% and strikingly impaired performance in controls. Galanthamine's ability to reverse cognitive deficits induced by nBM lesions and its comparatively long half-life suggest that it may be effective in treating the central cholinergic deficits in Alzheimer's disease patients.