Cholinergic Projections Research Articles

Cholinergic denervation attenuates phencyclidine-induced c-fos responses in rat cortical neurons

The cortical cholinergic innervation, which is important for memory and cognition, has been implicated in schizophrenia. To experimentally analyze such a possible role of the cholinergic system, we have used the dissociative drug phencyclidine (PCP), known to produce schizophrenia-like psychosis in humans, to model aspects of schizophrenia in rats. We previously showed that induced cortical cholinergic hypofunction leads to enhanced PCP-induced locomotor activity and attenuated social interaction. After PCP, rats lacking cortical cholinergic innervation also show impaired declarative memory. To directly study the role of the basalo-cortical cholinergic projections for PCP-induced neural activation in different cortical areas, we have now monitored the rapid (30 and 60min) effects of low doses of PCP (2 and 3mg/kg) on neural activation as reflected by transcriptional activation of c-fos in cortical areas, using quantitative in situ hybridization. We find an almost pan-cortical neural induction of c-fos mRNA with doses of PCP low enough not to alter levels of either BDNF or Nogo receptor mRNA levels. Specific unilateral lesioning of the uncrossed cholinergic projections to the cortical mantle by 192-IgG-saporin immunotoxin delivery to nc basalis (NBM) caused a striking ipsilateral decrease of the PCP-induced cortical c-fos mRNA induction, restricted to areas which had become effectively denervated. Because PCP at low doses is unlikely to directly influence cortical neurons, we suggest that it acts by activation of the cholinergic input, which in turn leads to cortical c-fos mRNA increases. Our results are compatible with a role for the cholinergic system in symptoms of schizophrenia, by showing that the basalo-cortical cholinergic projections are needed in order for PCP to have full activating effects on cortical neurons.

?7 Nicotinic Acetylcholine Receptors in Alzheimer's Disease: Neuroprotective, Neurotrophic or Both?

One of the early signs of Alzheimer's disease is the impairment in hippocampus-based episodic memory function, which is improved through the enhancement of cholinergic transmission. Several studies suggest that α7 nicotinic receptor (nAChR) activation represents a useful therapeutic strategy for the cognitive impairments associated with early Alzheimer's disease as the α7 subtype of nicotinic acetylcholine receptors are expressed by basal forebrain cholinergic projection neurons as well as by their targets in the hippocampus. The current model for the cholinergic deficit in Alzheimer's disease posits that inappropriate accumulation of misfolded oligomeric aggregates of β-amyloid peptide leads to the dysfunction of the signaling mechanisms that support the cholinergic phenotype; this is manifested as an altered function of nicotinic acetylcholine receptors and the nerve-growth factor trophic support system that results in the loss of cholinergic markers and eventually cholinergic neurons from the basal forebrain cholinergic system. A view was confounded by the fact that α7 nAChRs and β-amyloid peptides have been shown to interact in vitro and in vivo, including human post-mortem AD brain. This review will begin with a brief overview of the basal forebrain cholinergic system, followed by a discussion of the current knowledge of the cholinergic deficit in Alzheimer's disease, then a summary of the cholinergic phenotype observed in transgenic Alzheimer's disease mouse models. We will also present our recent findings that support our hypothesis that the α7 nicotinic acetylcholine receptor performs both the neurotrophic and neuroprotective roles in the maintenance of the cholinergic phenotype and discusses potential mechanisms and implications for Alzheimer's disease therapy.

M2 muscarinic acetylcholine receptors regulate long-term potentiation at hippocampal CA3 pyramidal cell synapses in an input-specific fashion

Muscarinic receptors have long been known as crucial players in hippocampus-dependent learning and memory, but our understanding of the cellular underpinnings and the receptor subtypes involved lags well behind. This holds in particular for the hippocampal CA3 region, where the mechanisms of synaptic plasticity depend on the type of afferent input. Williams and Johnston (Williams S, Johnston D. Science 242: 84-87, 1988; Williams S, Johnston D. J Neurophysiol 64: 1089-1097, 1990) demonstrated muscarinic depression of mossy fiber (MF) long-term potentiation (LTP) through a presynaptic site of action and Maeda et al. (Maeda T, Kaneko S, Satoh M. Brain Res 619: 324-330, 1993) proposed a bidirectional modulation of MF LTP by muscarinic receptor subtypes. Since then, this issue, as well as muscarinic regulation of plasticity at associational/commissural (A/C) fiber-CA3 synapses has remained largely neglected, not least because of the lack of highly selective ligands for the different muscarinic receptor subtypes. In the present study, we performed field potential and whole cell recordings from the hippocampal CA3 region of M(2) receptor knockout mice to determine the role of M(2) receptors in short-term and long-term plasticity at A/C and MF inputs to CA3 pyramidal cells. At the A/C synapse, M(2) receptors promoted short-term facilitation and LTP. Unexpectedly, M(2) receptors mediated the opposite effect on LTP at the MF synapse, which was significantly reduced, most likely involving a depressant effect of M(2) receptors on adenylyl cyclase activity in MF terminals. Our data demonstrate that cholinergic projections recruit M(2) receptors to redistribute the gain of LTP in CA3 pyramidal cells in an input-specific manner.

Cholinergic modulation of food and drug satiety and withdrawal

Although they comprise only a small portion of the neurons in the region, cholinergic interneurons in the dorsal striatum appear to play an important role in the regulation of various appetitive behaviors, in part, through their interactions with mesolimbic dopamine (DA) systems. In this review, we describe studies that suggest that the activity of cholinergic interneurons in the nucleus accumbens (NAc) and cholinergic projections to the ventral tegmental area (VTA) affect feeding behavior. In vivo microdialysis studies in rats have revealed that the cessation of a meal is associated with a rise in acetylcholine (ACh) levels in the NAc. ACh activation will suppress feeding, and this is also associated with an increase in synaptic accumulation of ACh. Further, we discuss how, in addition to their role in the ending of a meal, cholinergic interneurons in the NAc play an integral role in the cessation of drug use. Another cholinergic system involved in different aspects of appetitive behavior is the projection from the pedunculpontine nuclei directly to the VTA. Activation of this system enhances behaviors through activation of the mesolimbic DA system, and antagonism of ACh receptors in the VTA can reduce drug self-administration. Finally, we discuss the role of accumbens ACh in both drug and palatable food withdrawal. Studies reveal that accumbens ACh is increased during withdrawal from several different drugs of abuse (including cocaine, nicotine and morphine). This rise in extracellular levels of ACh, coupled with a decrease in extracellular levels of DA, is believed to contribute to an aversive state, which can manifest as behaviors associated with drug withdrawal. This theory has also been applied to studies of overeating and/or “food addiction,” and the findings suggest a similar imbalance in DA/ACh levels, which is associated with behavioral indications of drug-like withdrawal. In summary, cholinergic neurons play an important role in the modulation of both food and drug intake, as well as the aversive aspects of food- and drug-related addictive behaviors.

Scopolamine induced memory impairment; possible involvement of NMDA receptor mechanisms of dorsal hippocampus and/or septum

Background and aimThe anatomical connections of septum and hippocampus and the influence of cholinergic and glutamatergic projections in these sites have been reported. In the present study, the effect of pre-training intra-dorsal hippocampal (CA1) and intra-medial septal (MS) administration of scopolamine, a nonselective muscarinic acetylcholine antagonist, and NMDA receptor agents and their interactions, on acquisition of memory have been investigated. MethodsThe animals were bilaterally implanted with chronic cannulae in the CA1 regions and in the medial septum. Animals were trained in a step-through type inhibitory avoidance task, and tested 24h after training to measure step-through latency as memory retrieval. ResultsIntra-CA1 or intra-MS injections of scopolamine (0.5, 1 and 2μg/rat) and D-AP7 (a competitive NMDA receptor antagonist; 0.025, 0.05 and 0.1μg/rat) reduced, while NMDA (0.125 and 0.25μg/rat) increased memory. Intra-MS injection of a subthreshold dose of NMDA reduced scopolamine induced amnesia in the MS. However, similar injection of NMDA into CA1 did not alter scopolamine response when injected into CA1. Moreover, intra-MS or -CA1 injection of a subthreshold dose of NMDA did not alter scopolamine response in the CA1 or MS respectively. On the other hand, co-administration subthreshold doses of D-AP7 and scopolamine into CA1 and/or MS induced amnesia. ConclusionsThe cholinergic system between septum and CA1 are modulating memory acquisition processes induced by glutamatergic system in the CA1 or septum and co-activation of these systems in these sites can influence learning and memory.

Thalamic cholinergic innervation is spared in Alzheimer disease compared to parkinsonian disorders

There are two major sources of cholinergic projections in the brain. The nucleus basalis of Meynert provides the principal cholinergic input of the cortical mantle and the pedunculopontine nucleus–laterodorsal tegmental complex (PPN–LDTC; hereafter referred to as PPN) provides the major cholinergic input to the thalamus. Cortical cholinergic denervation has previously been shown to be part of Alzheimer and parkinsonian dementia but there is less information about subcortical thalamic cholinergic denervation. We investigated thalamic cholinergic afferent integrity by measuring PPN–Thalamic (PPN–Thal) acetylcholinesterase (AChE) activity via PET imaging in Alzheimer (AD), Parkinson disease without dementia (PD), Parkinson disease with dementia (PDD) and dementia with Lewy bodies (DLB). AD (n=13; mean age 75.4±5.5), PD (n=11; age 71.4±6.4), PDD (n=6; age 70.8±4.7), DLB (n=6; age 68.0±8.6) and normal controls (NC; n=14; age 69.0±7.5) subjects underwent AChE [11C]-methyl-4-piperidinyl propionate (PMP) PET imaging. PPN–Thal PET data were analyzed using the Nagatsuka method. There were no significant differences in mean age between the groups (F=1.86, p=0.134). Kruskal–Wallis testing demonstrated a significant group effect for PPN–Thal AChE hydrolysis rates (F=9.62, p<0.0001). Compared to NC, reduced thalamic k3 hydrolysis rate was noted in subjects with PDD (−19.8%; AChE k3 hydrolysis rates 0.1072±0.0143min−1), DLB (−17.4%; 0.1103±0.0112min−1) and PD (−12.8%; 0.1165±0.0114min−1). Each of these 3 subgroups was statistically different from AD subjects (−0.7%; 0.1326±0.0095min−1) who showed relatively spared thalamic k3 hydrolysis rates which were comparable to NC (0.1336±0.0142min−1). Thalamic cholinergic denervation is present in PD, PDD, and DLB but not in AD. Neurodegenerative involvement of thalamic cholinergic afferent projections may contribute to disease-specific motor and cognitive abnormalities.

Behavioural state differentially engages septohippocampal cholinergic and GABAergic neurons in R6/1 Huntington’s disease mice

Huntington’s disease (HD) is a neurodegenerative condition characterised by progressive motor, psychological and cognitive decline. R6/1 HD transgenic mice model the clinical hippocampal-dependent cognitive deficits observed in patients. Cholinergic and GABAergic septohippocampal projections play important roles in hippocampal-dependent cognition. The current study examined neuronal activity of cholinergic and GABAergic septohippocampal projections in response to arousal elicited during differing behavioural states. The different behavioural states examined were; home cage (controls), acute exploration of a novel enriched environment and either spontaneous wakefulness (dark phase) or spontaneous sleep (light phase). We employed triple-label immunohistochemistry using c-Fos as an indirect marker of neuron activation and parvalbumin and choline acetyltransferase (ChAT) to label GABAergic and cholinergic neurons in the basal forebrain, respectively. The Y-maze was used to assess short-term hippocampal-dependent memory independently during either the dark or light phase and revealed a memory deficit in R6/1 HD mice compared to wildtypes that was particularly prominent during the dark phase. Three-way ANOVA of basal forebrain cholinergic and GABAergic activity through co-expression of c-Fos revealed overt responses to differing behavioural states. Both genotypes increased cholinergic neuron activity in response to exploring a novel enriched environment and also an increase during the dark phase compared to the light phase. Novel enriched environment exploration caused a larger response of GABAergic neuron activity in R6/1 HD mice, which also failed to increase the activity of GABAergic neurons during the dark phase compared to the light phase as observed for wildtype mice. Basal levels of c-Fos-positive cells were greatly increased in the hippocampal granule cell layer of R6/1 HD mice during both circadian phases. The differential activation of septohippocampal cholinergic and GABAergic neurons in R6/1 HD mice in response to differing behavioural states may be associated with impaired hippocampal-dependent short-term memory.

Evidence for Broad Versus Segregated Projections from Cholinergic and Noradrenergic Nuclei to Functionally and Anatomically Discrete Subregions of Prefrontal Cortex

The prefrontal cortex (PFC) is implicated in a variety of cognitive and executive operations. However, this region is not a single functional unit; rather, it is composed of several functionally and anatomically distinct networks, including anterior cingulate cortex (ACC), medial prefrontal cortex (mPFC), and orbitofrontal cortex (OFC). These prefrontal subregions serve dissociable behavioral functions, and are unique in their afferent and efferent connections. Each of these subregions is innervated by ascending cholinergic and noradrenergic systems, each of which likewise has a distinct role in cognitive function; yet the distribution and projection patterns of cells in the source nuclei for these pathways have not been examined in great detail. In this study, fluorescent retrograde tracers were injected into ACC, mPFC, and OFC, and labeled cells were identified in the cholinergic nucleus basalis of Meynert (NBM) and noradrenergic nucleus locus coeruleus (LC). Injections into all three cortical regions consistently labeled cells primarily ipsilateral to the injection site with a minimal contralateral component. In NBM, retrogradely labeled neurons were scattered throughout the rostral half of the nucleus, whereas those in LC tended to cluster in the core of the nucleus, and were rarely localized within the rostral or caudal poles. In NBM, more than half of all retrogradely labeled cells possessed axon collaterals projecting two or more PFC subregions. In LC, however, only 4.3% of retrogradely labeled neurons possessed collaterals targeting any two prefrontal subregions simultaneously, and no cells were identified that projected to all three regions. Of all labeled LC neurons, 49.3% projected only to mPFC, 28.5% projected only to OFC, and 18.0% projected only to ACC. These findings suggest that subsets of LC neurons may be capable of modulating neuronal activity in individual prefrontal subregions independently, whereas assemblies of NBM cells may exert a more unified influence on the three areas, simultaneously. This work emphasizes unique aspects of the cholinergic and noradrenergic projections to functionally and anatomically distinct subregions of PFC and provides insights regarding global versus segregated regulation of prefrontal operations by these neuromodulatory pathways.

Sex Differences in Counting and Timing

Sex Differences in Counting and Timing

Cholinergic Control in Developing Prefrontal–Hippocampal Networks

The cholinergic drive enhances input processing in attentional and mnemonic context by interacting with the activity of prefrontal-hippocampal networks. During development, acetylcholine modulates neuronal proliferation, differentiation, and synaptic plasticity, yet its contribution to the maturation of cognitive processing resulting from early entrainment of neuronal networks in oscillatory rhythms remains widely unknown. Here we show that cholinergic projections growing into the rat prefrontal cortex (PFC) toward the end of the first postnatal week boost the generation of nested gamma oscillations superimposed on discontinuous spindle bursts by acting on functional muscarinic but not nicotinic receptors. Although electrical stimulation of cholinergic nuclei increased the occurrence of nested gamma spindle bursts by 41%, diminishment of the cholinergic input by either blockade of the receptors or chronic immunotoxic lesion had the opposite effect. This activation of locally generated gamma episodes by direct cholinergic projections to the PFC was accompanied by indirect modulation of underlying spindle bursts via cholinergic control of hippocampal theta activity. With ongoing maturation and switch of network activity from discontinuous bursts to continuous theta-gamma rhythms, accumulating cholinergic projections acting on both muscarinic and nicotinic receptors mediated the transition from high-amplitude slow to low-amplitude fast rhythms in the PFC. By exerting multiple actions on the oscillatory entrainment of developing prefrontal-hippocampal networks, the cholinergic input may refine them for later gating processing in executive and mnemonic tasks.

Recognition of novel objects and their location in rats with selective cholinergic lesion of the medial septum

The importance of cholinergic neurons projecting from the medial septum (MS) of the basal forebrain to the hippocampus in memory function has been controversial. The aim of this study was to determine whether loss of cholinergic neurons in the MS disrupts object and/or object location recognition in male Sprague-Dawley rats. Animals received intraseptal injections of either vehicle, or the selective cholinergic immunotoxin 192 IgG-saporin (SAP). 14 days later, rats were tested for novel object recognition (NOR). Twenty-four hours later, these same rats were tested for object location recognition (OLR) (recognition of a familiar object moved to a novel location). Intraseptal injections of SAP produced an 86% decrease in choline acetyltransferase (ChAT) activity in the hippocampus, and a 31% decrease in ChAT activity in the frontal cortex. SAP lesion had no significant effect on NOR, but produced a significant impairment in OLR in these same rats. The results support a role for septo-hippocampal cholinergic projections in memory for the location of objects, but not for novel object recognition.

Optogenetic release of ACh induces rhythmic bursts of perisomatic IPSCs in hippocampus.

Acetylcholine (ACh) influences a vast array of phenomena in cortical systems. It alters many ionic conductances and neuronal firing behavior, often by regulating membrane potential oscillations in populations of cells. Synaptic inhibition has crucial roles in many forms of oscillation, and cholinergic mechanisms regulate both oscillations and synaptic inhibition. In vitro investigations using bath-application of cholinergic receptor agonists, or bulk tissue electrical stimulation to release endogenous ACh, have led to insights into cholinergic function, but questions remain because of the relative lack of selectivity of these forms of stimulation. To investigate the effects of selective release of ACh on interneurons and oscillations, we used an optogenetic approach in which the light-sensitive non-selective cation channel, Channelrhodopsin2 (ChR2), was virally delivered to cholinergic projection neurons in the medial septum/diagonal band of Broca (MS/DBB) of adult mice expressing Cre-recombinase under the control of the choline-acetyltransferase (ChAT) promoter. Acute hippocampal slices obtained from these animals weeks later revealed ChR2 expression in cholinergic axons. Brief trains of blue light pulses delivered to untreated slices initiated bursts of ACh-evoked, inhibitory post-synaptic currents (L-IPSCs) in CA1 pyramidal cells that lasted for 10's of seconds after the light stimulation ceased. L-IPSC occurred more reliably in slices treated with eserine and a very low concentration of 4-AP, which were therefore used in most experiments. The rhythmic, L-IPSCs were driven primarily by muscarinic ACh receptors (mAChRs), and could be suppressed by endocannabinoid release from pyramidal cells. Finally, low-frequency oscillations (LFOs) of local field potentials (LFPs) were significantly cross-correlated with the L-IPSCs, and reversal of the LFPs near s. pyramidale confirmed that the LFPs were driven by perisomatic inhibition. This optogenetic approach may be a useful complementary technique in future investigations of endogenous ACh effects.

Cholinergic modulation of slow cortical rhythm in urethane-anesthetized rats

Slow cortical rhythm (SCR) is characterized by rhythmic cycling of active (UP) and silent (DOWN) states in cortical cells. In urethane anesthesia, SCR appears as alternation of almost isoelectrical EEG periods and low-frequency, high-amplitude large shifts with superimposed high-frequency activity in the local field potentials (LFPs). Dense cholinergic projection reaches the cortex from the basal forebrain (BF), and acetylcholine (ACh) has been demonstrated to play a crucial role in the regulation of cortical activity. In the present experiments, cholinergic drugs were administered topically to the cortical surface of urethane-anesthetized rats to examine the direct involvement of ACh and the BF cholinergic system in the SCR. SCR was recorded by a 16-pole vertical electrode array from the hindlimb area of the somatosensory cortex. Multiple unit activity (MUA) was recorded from layer V to VI in close proximity of the recording array. Neither a low dose (10 mM solution) of the muscarinic antagonist atropine or the nicotinic agonist nicotine (1 mM solution) had any effect on SCR. In contrast, the higher dose (100 mM solution) of atropine, the cholinergic agonist carbachol (32 mM solution), and the cholinesterase inhibitor physostigmine (13 mM solution) all decreased the number of UP states, delta power (0-3 Hz) and MUA. These results suggest that cholinergic system may influence SCR through muscarinic mechanisms during urethane anesthesia. Cholinergic activation obstructs the mechanisms responsible for local or global synchronization seen during SCR as this rhythm was disrupted or aborted. Muscarinic antagonism can evoke similar changes when high dose of atropine is applied.

Involvement of hippocampal phosphatidylethanolamine‐binding protein in morphine dependence and withdrawal

Drug addiction is thought to result from an intractable and aberrant learning and memory in response to drug-related stimulation, and cholinergic neurotransmission plays an important role in this process. Phosphatidylethanolamine-binding protein (PEBP) is the precursor of the hippocampal cholinergic neurostimulating peptide (HCNP), an 11 amino acid peptide that enhances the production of choline acetyltransferase (ChAT) and assists in the development of cholinergic projections from the medial septal nuclei to the hippocampus. However, whether PEBP is involved in drug addiction remains unclear. In the present study, PEBP expression in the hippocampus, as detected by proteomics analysis, was found to be dramatically up-regulated after rats received chronic morphine treatment. Western blotting analysis revealed a specific up-regulation of PEBP expression in the hippocampus but not in any other brain regions assessed. A down-regulation of hippocampal PEBP levels induced by antisense oligodeoxynucleotides resulted in aggravated morphine dependence. Together, these findings indicate that PEBP is involved in morphine dependence. Moreover, the time course of PEBP expression changes and ChAT activity was investigated during chronic morphine treatment and withdrawal. The results showed that the hippocampal PEBP levels were up-regulated during chronic morphine treatment and returned to the baseline 3 days after withdrawal, after which PEBP levels were persistently up-regulated for 28 days after withdrawal. The changes in hippocampal ChAT activity followed a pattern that was similar to that of the PEBP levels. Taken together, these results suggest that hippocampal PEBP is involved in morphine dependence and withdrawal, perhaps through modulating cholinergic transmission in the hippocampus.

Excitatory projections from the amygdala to neurons in the nucleus pontis oralis in the rat: an intracellular study

There is a consensus that active (REM) sleep (AS) is controlled by cholinergic projections from the laterodorsal and pedunculopontine tegmental nuclei (LDT/PPT) to neurons in the nucleus pontis oralis (NPO) that generate AS (i.e. AS-Generator neurons). The present study was designed to provide evidence that other projections to the NPO, such as those from the amygdala, are also capable of inducing AS. Accordingly, the responses of neurons, recorded intracellularly in the NPO, were examined following stimulation of the ipsilateral central nucleus of the amygdala (CNA) in urethane-anesthetized rats. Single pulse stimulation in the CNA produced an early, fast depolarizing potential (EPSP) in neurons within the NPO. The mean latency to the onset of these excitatory postsynaptic potentials (EPSPs) was 3.6±0.2 ms. A late, small-amplitude inhibitory synaptic potential (IPSP) was present following EPSPs in a portion of the NPO neurons. Following stimulation of the CNA with a train of 8-10 pulses, NPO neurons exhibited a sustained depolarization (5-10 mV) of their resting membrane potential. When single subthreshold intracellular depolarizing current pulses were delivered to NPO neurons, CNA-induced EPSPs were sufficient to promote the discharge of these cells. Stimulation of the CNA with a short train of stimuli induced potent temporal facilitation of EPSPs in NPO neurons. Two forms of synaptic plasticity were revealed by the patterns of response of NPO neurons following stimulation of the CNA: paired-pulse facilitation (PPF) and post-tetanic potentiation (PTP). Six of recorded NPO neurons were identified morphologically with neurobiotin. They were medium to large, multipolar cells with diameters >20 μM, which resemble AS-on cells in the NPO. The present results demonstrate that amygdalar projections are capable of exerting a powerful excitatory postsynaptic drive that activates NPO neurons. Therefore, we suggest that the amygdala is capable of inducing AS via direct projections to AS-Generator neurons in the NPO.

Medial septal cholinergic neurons are necessary for context‐place memory but not episodic‐like memory

Loss of cholinergic cortical input is associated with diseases in which episodic memory impairment is a prominent feature, but the degree to which this neurochemical lesion can account for memory impairment in humans with neurodegenerative diseases remains unclear. Removal of cholinergic input to hippocampus impairs some of its functions in memory, perhaps by reducing the plasticity of information representation within the hippocampus, but the role of cholinergic hippocampal input in episodic-like memories has not been investigated. To address this question, we tested rats with selective lesions of basal forebrain neurons in the medial septum and vertical limb of the diagonal band (MS/VDB), which contains hippocampal-projecting cholinergic neurons, on a task of integrated memory for objects, places, and contexts ("what-where-which" memory). This task serves as a rodent model of human episodic memory (episodic-like memory) and is sensitive to damage to the hippocampal system. Rats with lesions of cholinergic MS/VDB neurons performed as well on the what-where-which task as controls, but were impaired in a task that simply required them to associate places with contexts ("where-which" memory). Thus, episodic-like memories that rely on the hippocampus do not require cholinergic neuromodulation to be formed. Nevertheless, some more specific aspects of where-which memory, which may be more dependent on the plasticity of hippocampal spatial representations, require acetylcholine. These results suggest that cholinergic projections to hippocampus are not necessary for episodic memory and, furthermore, that hippocampal spatial representations may be to some extent dissociable from episodic memory function.

Impaired social interaction and enhanced sensitivity to phencyclidine-induced deficits in novel object recognition in rats with cortical cholinergic denervation

Dysregulated cholinergic neurotransmission has been implicated in the pathophysiology of schizophrenia, particularly negative symptoms and cognitive deficits. The aim of the present study was to evaluate the role of neocortical cholinergic innervation and of the N-methyl-d-aspartate (NMDA) receptor antagonist phencyclidine (PCP) on social interaction and novel object recognition (NOR), a declarative memory task. The cholinergic corticopetal projection was lesioned by local infusion of the immunotoxin 192 IgG-saporin into nucleus basalis magnocellularis of adult male Lister hooded rats. Behavior was assessed 2.5 weeks later in a social interaction paradigm followed by the NOR task. We found that selective cholinergic denervation of neocortex led to a significant reduction in duration of social interaction, specifically active social interaction. Acute administration of PCP (1.0 mg/kg, s.c.) caused a marked decrease of active social interaction, such that there was no longer a difference between intact and denervated animals. Neither cholinergic denervation alone, nor PCP (1.0 mg/kg, s.c.) alone blocked the ability of rats to recognize a novel object. However, when animals lacking cortical cholinergic innervation were challenged by PCP, they were no longer able to recognize a novel object. This study indicates that rats lacking cholinergic innervation of neocortex have impaired social interaction and specifically that the duration of active contact is shortened. Animals with severe cortical cholinergic hypofunction maintain the ability to perform in a declarative memory test, although the task is carried out less intensively. However, a provocation of psychosis-like behavior by a dose of PCP that does not by itself impair performance in normal animals, will abolish the ability to recognize novel objects in animals lacking cortical cholinergic innervation. The present findings support a possible role for cortical cholinergic hypofunction in the negative and cognitive symptoms of schizophrenia, and the potential for cholinergic augmentation as part of the pharmacological profile of antipsychotic drugs.

Enhanced Control of Attention by Stimulating Mesolimbic-Corticopetal Cholinergic Circuitry

Sustaining and recovering attentional performance requires interactions between the brain's motivation and attention systems. The first experiment demonstrated that in rats performing a sustained attention task (SAT), presentation of a distractor (dSAT) augmented performance-associated increases in cholinergic neurotransmission in prefrontal cortex. Because stimulation of NMDA receptors in the shell of the nucleus accumbens activates PFC cholinergic neurotransmission, a second experiment demonstrated that bilateral infusions of NMDA into the NAc shell, but not core, improved dSAT performance to levels observed in the absence of a distractor. A third experiment demonstrated that removal of prefrontal or posterior parietal cholinergic inputs, by intracortical infusions of the cholinotoxin 192 IgG-saporin, attenuated the beneficial effects of NMDA on dSAT performance. Mesolimbic activation of cholinergic projections to the cortex benefits the cognitive control of attentional performance by enhancing the detection of cues and the filtering of distractors.

BMP9 Protects Septal Neurons from Axotomy-Evoked Loss of Cholinergic Phenotype

BackgroundCholinergic projection from the septum to the hippocampus is crucial for normal cognitive function and degeneration of cells and nerve fibers within the septohippocampal pathway contributes to the pathophysiology of Alzheimer's disease. Bone morphogenetic protein (BMP) 9 is a cholinergic differentiating factor during development both in vivo and in vitro.Methodology/Principal FindingsTo determine whether BMP9 could protect the adult cholinergic septohippocampal pathway from axotomy-evoked loss of the cholinergic phenotype, we performed unilateral fimbria-fornix transection in mice and treated them with a continuous intracerebroventricular infusion of BMP9 for six days. The number of choline acetyltransferase (CHAT)-positive cells was reduced by 50% in the medial septal nucleus ipsilateral to the lesion as compared to the intact, contralateral side, and BMP9 infusion prevented this loss in a dose-dependent manner. Moreover, BMP9 prevented most of the decline of hippocampal acetylcholine levels ipsilateral to the lesion, and markedly increased CHAT, choline transporter CHT, NGF receptors p75 (NGFR-p75) and TrkA (NTRK1), and NGF protein content in both the lesioned and unlesioned hippocampi. In addition, BMP9 infusion reduced bilaterally hippocampal levels of basic FGF (FGF2) protein.Conclusions/SignificanceThese data indicate that BMP9 administration can prevent lesion-evoked impairment of the cholinergic septohippocampal neurons in adult mice and, by inducing NGF, establishes a trophic environment for these cells.

Projections from the rat pedunculopontine and laterodorsal tegmental nuclei to the anterior thalamus and ventral tegmental area arise from largely separate populations of neurons

Cholinergic and non-cholinergic neurons in the brainstem pedunculopontine (PPT) and laterodorsal tegmental (LDT) nuclei innervate diverse forebrain structures. The cholinergic neurons within these regions send heavy projections to thalamic nuclei and provide modulatory input as well to midbrain dopamine cells in the ventral tegmental area (VTA). Cholinergic PPT/LDT neurons are known to send collateralized projections to thalamic and non-thalamic targets, and previous studies have shown that many of the afferents to the VTA arise from neurons that also project to midline and intralaminar thalamic nuclei. However, whether cholinergic projections to the VTA and anterior thalamus (AT) are similarly collateralized is unknown. Ultrastructural work from our laboratory has demonstrated that cholinergic axon varicosities in these regions differ both morphologically and with respect to the expression and localization of the high-affinity choline transporter. We therefore hypothesized that the cholinergic innervation to these regions is provided by separate sets of PPT/LDT neurons. Dual retrograde tract-tracing from the AT and VTA indicated that only a small percentage of the total afferent population to either region showed evidence of providing collateralized input to the other target. Cholinergic and non-cholinergic cells displayed a similarly low percentage of collateralization. These results are contrasted to a control case in which retrograde labeling from the midline paratenial thalamic nucleus and the VTA resulted in higher percentages of cholinergic and non-cholinergic dual-tracer labeled cells. Our results indicate that functionally distinct limbic target regions receive primarily segregated signaling from PPT/LDT neurons.