A continuing signal maintains NGF receptor expression in hypoglossal motor neurons after crush injury

Inhibition of axonal transport by vincristine applied to hypoglossal nerves 7 days after crush injury turns off the usual injured-induced expression of low affinity nerve growth factor receptor (p75NGFr). Vincristine applied proximal but not distal to the crush prevents p75NGFr induction. These results indicate that a continuing signal is axonally transported from the crush site that induces and maintains p75NGFr expression by injured motor neurons.

Induction of nerve growth factor receptor (p75NGFr) mRNA within hypoglossal motoneurons following axonal injury

The hypoglossal nerve is a useful model system for analysis of gene expression in injured motoneurons. In particular, we sought to determine whether the increased appearance of the low affinity nerve growth factor receptor (p75NGFr) observed immunocytochemically following nerve injury can be directly correlated to increased levels of the p75NGFr mRNA. The present study also examined the relative effects of nerve crush versus nerve transection on the expression of p75NGFr mRNA. In sham-operated or intact animals, p75NGFr mRNA is detected rarely and then only at levels slightly higher than background. Following unilateral transection or crush of the rat hypoglossal nerve, the levels of p75NGFr mRNA increase in a time dependent fashion that parallels the appearance of the protein as reported previously. Moreover, this increase in p75NGFr mRNA following transection is dependent on a signal from the injured site, since blockage of axonal transport with vincristine also blocks the increased p75NGFr mRNA levels. When comparing the effect of nerve crush to nerve transection, we observed that the intensity of the response was greater in the crush paradigm versus that observed following transection. The duration of the response following nerve crush was shorter than that observed following transection of the nerve. The increase in p75NGFr mRNA after crush was most robust 4 days postlesion and appeared more robust primarily due to a 90-150% increased number of motoneurons expressing p75NGFr mRNA when compared to nerve transection. These data suggest that nerve crush is more effective than nerve transection in eliciting increased p75NGFr mRNA levels.

Distribution of neurotensin immunoreactivity within the human amygdaloid complex: a comparison with acetylcholinesterase- and Nissl-stained tissue sections

In a previous study, we reported marked depletion of neurotensin-immunoreactivity (NT-IR) within selected regions of the amygdala of patients with Alzheimer's disease. The significance of these observations was partly obscured largely because we lacked a thorough understanding of the innervation pattern of neurotensin in the normal human amygdala. Accordingly, in the present study, we used a polyclonal antibody against neurotensin to characterize the distribution and morphology of neurotensin-immunoreactive neuronal elements within the human amygdaloid complex. NT-IR occurred in a topographic manner that respected the cytoarchitectural boundaries of the amygdaloid subregions as defined by Nissl staining and acetylcholinesterase histochemistry. Most NT-IR in the amygdala was contained within beaded fibers and dot-like puncta. Within the subnuclei of the amygdala, immunoreactive neuritic elements were most dense within the central nucleus followed by the medial nucleus and intercalated nuclei. The anterior amygdaloid area, basal complex, paralaminar nucleus, cortical nucleus, cortical-amygdaloid transition area, and amygdalohippocampal area contained moderate densities of immunoreactivity. The accessory basal and lateral nuclei exhibited scant NT-IR. Immunoreactive neurons were found only within the anterior amygdaloid area and the central, medial, intercalated, and lateral capsular nuclei. The distribution of NT-immunoreactive processes and cell bodies within selected regions of the amygdala provides an anatomical substrate that may explain, in part, the neuromodulatory actions of neurotensin upon autonomic, endocrine, and memory systems.

Development of the basal forebrain cholinergic system: phenotype expression prior to target innervation

We measured choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities in the rat to determine the time course of development, maturity, and senescence of ChAT activity. Tissue was obtained from Sprague-Dawley rats ranging in age from embryonic day 14 through 23 months. Seven regions were examined, including the magnocellular preoptic/substantia innominata region, frontal cortex, medial septal region, hippocampus, diagnoal band, and medial and lateral striatum. ChAT and AChE activities were first detected as early as E18 in the medial septum, diagonal band and magnocellular preoptic area, all regions of cholinergic cell bodies. Enzyme activity subsequently developed in terminal fields of these cholinergic perikarya (hippocampus and frontal cortex) as well as in the striatum. For all regions, enzyme activity rose during the first four postnatal weeks. This increase in enzyme activity was transient and, in most instances, decreases were observed between postnatal days 30 and 60. Most dramatic were the decreases in enzyme activity in the magnocellular preoptic/substantia innominata and diagonal band regions. Age-related declines also occurred in the frontal cortex, hippocampus, magnocellular preoptic/substantia innominata region, and the striatum. Cholinergic systems undergo dynamic changes especially during development and adulthood.

Separate signals mediate hypoglossal motor neuron response to axonal injury

Nerve transection causes decreased choline acetyltransferase (ChAT) expression and appearance of nerve growth factor receptor (NGFr) in hypoglossal motor neurons. Topical application of vincristine to the hypoglossal nerve blocks axonal transport of WGA for more than one week and causes loss of ChAT but no appearance of NGFr. These results indicate that loss of ChAT is related to interruption of axonal transport, but another signal induces de novo expression of NGFr.

Glutamate receptor subtypes mediate excitatory synaptic currents of dopamine neurons in midbrain slices

Although dopamine (DA)-containing neurons participate in a number of important cerebral functions, the physiology of their synaptic connections is poorly understood. By using whole-cell patch-clamp recording in thin slices of rat mesencephalon, we have investigated the biophysical properties of synaptic events and the nature of neurotransmitter(s) and receptors involved in the synaptic input to DA neurons in substantia nigra. The histological and electrophysiological characteristics of these cells were consistent with those described by recent in vivo and in vitro studies, thus allowing their unequivocal identification. Under appropriate experimental conditions, intranigral stimulation produced excitatory synaptic inputs in DA neurons. By voltage-clamp analysis, most of these excitatory postsynaptic currents (EPSCs) had a rise time of about 1.0 msec and a decay phase that could be fit by the sum of two exponential curves so that a fast and a slow component could be distinguished. The slow component was enhanced by glycine, by removing Mg2+ from the bath medium, or by membrane depolarization. Moreover, the slow component was consistently decreased by selective antagonists of NMDA receptors, whereas an antagonist for the non-NMDA receptors abolished the fast component slightly affecting the slow component and reduced peak EPSC amplitude. The results indicate that both NMDA-sensitive and non-NMDA-sensitive glutamate receptors contribute to EPSCs of DA neurons. Therefore, it is suggested that these receptors may play a critical role in the physiology (control of excitability, pacemaker firing, and dendritic DA release) as well as pathology (neuronal death in Parkinson's disease, psychosis, and mechanism of action of drugs of abuse, such as ethanol) related to DA neurons.

Strategic considerations in developing a delivery model

Nurse executives must challenge basic assumptions about their organizations and help create visions that are feasible and applicable to the institutions' realities. Evaluative criteria and the relationship of the nurse executive to a reality-based model of care are vital to this goal.

Expression of choline acetyltransferase and nerve growth factor receptor within hypoglossal motoneurons following nerve injury

In the present study we employed light microscopic immunocytochemical techniques in order to investigate the temporal response of choline acetyltransferase (ChAT) and nerve growth factor receptor (NGFr) within hypoglossal motoneurons following unilateral transection or crushing of the XII nerve or after intraneural injections of ricin into the nerve. In control rats (i.e., sham operated) virtually all the motoneurons of the XII nucleus displayed intense immunolabeling for ChAT and were devoid of NGFr immunoreactivity. As early as 3 days post-operative the intensity and the number of ChAT-labeled neurons were reduced on the axotomized side compared to the non-lesioned side. This decrease was maximal approximately two weeks post-operative when virtually no ChAT-labeled cells were present on the lesioned side. In contrast, no loss of hypoglossal neurons was found using Nissl stains. This absence of ChAT immunolabeling persisted for several days, yet by 30 days many of the motoneurons had begun to re-express the enzyme. In contrast to the decrease in ChAT immunoreactivity, transection of the XII nerve also resulted in the expression of NGFr immunoreactivity within the lesioned motoneurons. This response was detected as early as one day post-operatively and continued throughout all time points thus far examined including times after many of the motoneurons had begun to re-express ChAT. Crushing of the XII nerve effected the expression of ChAT and NGFr in a manner comparable to, yet less intense than, that observed following transection. Ricin injected directly into the XII nerve resulted in the loss of hypoglossal motoneurons as demonstrated both in immunohistochemical and Nissl-stained tissue preparations. The cell loss was readily apparent 3 days post-operatively, and ChAT immunoreactivity permanently disappeared. NGFr immunolabeling was seen only in scattered surviving neurons but not in ricin poisoned cells. The possible mechanisms underlying the differential expression of ChAT and NGFr are discussed.

Striatal glutamic acid decarboxylase immunoreactivity is increased after dopaminergic deafferentation: densitometric analysis

Several lines of evidence suggest that dopamine exerts a chronic inhibitory action on GABAergic cells in the striatum, and striatal glutamic acid decarboxylase (GAD) mRNA levels are increased after ipsilateral dopaminergic denervation. In the present study we have used GAD immunocytochemistry to assess whether dopaminergic denervation results in an increase in GAD protein synthesis. In three 6-hydroxydopamine-lesioned animals, there was a perceptible increase in the density of GAD-immunoreactive (ir)staining on the side ipsilateral to the lesion. Computer-assisted densitometric analysis showed a significant increase in GAD-ir staining in the ipsilateral striatum compared to the contralateral (control) side. These data suggest that removal of striatal dopaminergic innervation results in an increase in the amount of immunoreactive GAD, the rate limiting enzyme in the synthesis of GABA.

Mapping the development of the rat brain by GAP-43 immunocytochemistry

Growth-associated protein-43 (GAP-43) is a phosphoprotein of the nerve terminal membrane which has been linked to the development and restructuring of axonal connections. Using a monospecific antibody prepared in sheep against purified GAP-43, we examined the temporal and spatial changes in the distribution of this protein from embryonic stage day 13 (E13) to adulthood. At stages in which neurons are still dividing and migrating, levels of GAP-43 are extremely low, as is seen in the cortical plate throughout the embryonic period. With the onset of process outgrowth, intense GAP-43 immunoreactivity appears along the length of axons: by E13, such staining is already strong in the brainstem, where it continues up through the first postnatal week and then disappears. In the neocortex, intense fiber staining first appears several days later but ends at the same time as in the brainstem. At the end of the period of intense axonal staining there is a brief interval in which high levels of GAP-43 immunostaining are seen in the neuropil. In regions of the brain in which specific developmental events have been characterized anatomically and physiologically, the period of dense neuropil staining coincides with the formation of axonal end-arbors, the beginning of synaptogenesis, and the time at which synaptic organization can be modified by the impingent pattern of activity (i.e. the critical period). Over the next few days, staining in neuropil declines sharply in most regions except for certain structures in the rostral neuraxis which may be sites of ongoing synaptic remodeling.

Reduction of neurotensin immunoreactivity in the amygdala in Alzheimer's disease

The density of neurotensin immunoreactivity (NT-IR) was dramatically decreased in 6 of 12 amygdaloid nuclear subregions in patients with Alzheimer's disease (AD) compared to age-matched normals. Diminution of NT-IR was most pronounced in amygdaloid regions containing the greatest number of senile plaques. This contrasts to our previous findings of little, if any, loss of substance P or somatostatin immunoreactivity within these same regions. The present findings corroborate biochemical reports of a decrease in NT-IR in the AD amygdala and suggest that this peptide may be selectively affected relative to other neuropeptides.

Locomotion-related variations in excitability of spino-olivocerebellar paths to cat cerebellar cortical c2 zone

1. Cutaneous nerve stimulation was used to study the excitability of the spino-olivocerebellar pathways (SOCPs) to the c2 zone of the paravermal cerebellar cortex in the cat. Non-noxious single-shock stimulation of the right and left superficial radial (SR) nerves via implanted cuff electrodes was used to evoke field potentials in the cerebellar cortex via the SOCPs. 2. The evoked potentials were recorded extracellularly either in lobule V of the anterior lobe (three cats) or within the paramedian lobule of the posterior lobe (one cat) with glass-coated tungsten microelectrodes. Measurement of the amplitudes of the responses was used to monitor transmission in the SOCPs in cats at rest and during walking. 3. A total of eleven c2 recording sites were investigated in detail. At seven of these sites, responses were recorded both during locomotion and at rest. For all seven sites responses during locomotion were smaller, more variable in amplitude and less securely evoked (average reduction 59%). 4. At five out of the eleven recording sites (45%) the mean amplitude of responses elicited during different tenths of the step cycle fluctuated sufficiently that the largest response was more than twice the smallest. In the majority of these cases (4/5) the responses were largest in either mid-stance or late swing. These fluctuations in response size occurred without parallel fluctuation in the amplitude of the peripheral nerve volley. At the remaining sites fluctuation of the cerebellar field size was less and in some cases practically absent. 5. At six recording sites it was possible to record the climbing fibre potentials evoked by stimulation of both the ipsilateral and contralateral superficial radial nerves. In all six cases the fluctuations in size of the response during locomotion occurred in phase, despite the fact that the two limbs move out of phase. 6. The probability that an individual stimulus would evoke any cerebellar response also varied between the different tenths of the step cycle and such variations occurred in parallel with the fluctuations in response size. This shows that the SOCP regulatory mechanism(s) must, at least in part, operate at a precerebellar level.

Topographical organisation within the cerebellar nucleocortical projection to the paravermal cortex of lobule Vb/c in the cat

The projection from the intracerebellar nuclei to the paravermal (intermediate) cerebellar cortex of lobule Vb/c has been investigated in the cat using a combined electrophysiological and neuroanatomical technique. A small (10-30 nl) injection of WGA-HRP was made into one of the three paravermal zones (c1, c2 or c3) after the mediolateral boundaries of the zones had been delimited on the cerebellar surface by recording climbing fibre field potentials evoked in response to percutaneous stimulation of one or more paws. The distribution of retrogradely labelled cell bodies within the intracerebellar nuclei was compared with the distribution of terminal labelling arising from anterograde transport by cerebellar Purkinje cells. The three paravermal zones displayed marked heterogeneity in their receipt of a projection from the intracerebellar nuclei. The c1 and c3 zones received virtually no such input, although injections in either zone resulted in significant terminal labeling (which was largely restricted to nucleus interpositus anterior). By contrast, the intervening c2 zone received a much heavier nucleocortical input which arose almost exclusively from nucleus interpositus posterior (to which the zone also projected). A sparse contralateral nucleocortical input to the c2 zone was also demonstrated. This arose primarily from nucleus fastigius. It is concluded that the nucleocortical projection to the paravermal cortex of lobule Vb/c displays marked topographical specificity and some functional implications of this are discussed.

Co-localization of choline acetyltransferase and tyrosine hydroxylase within neurons of the dorsal motor nucleus of the vagus

In the present study, we employed a dual-immunofluorescent labeling procedure to determine if the biosynthetic enzymes tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT) are co-localized within neurons in the dorsal medulla of rat. Within this region TH-labeled neurons are distributed within the nuclei of the solitary tracts and medial aspect of the dorsal motor nucleus of the vagus. The absence of dopamine-beta-hydroxylase immunoreactivity within TH-labeled cells in the medial portion of the dorsal motor nucleus of the vagus suggests that these neurons are dopaminergic. Cholinergic perikarya also are present in the dorsal medulla and are distributed throughout the dorsal motor nucleus of the vagus and hypoglossal nucleus. Of these ChAT-positive perikarya, a small percentage limited to the medial aspect of the dorsal motor nucleus of the vagus (i.e., corresponding to the location of dopamine neurons) also contain TH. The existence of TH within ChAT-positive neurons in the dorsal motor nucleus of the vagus provides an anatomical substrate with which to suggest that catecholaminergic and cholinergic fibers contribute to the vagus nerve and may serve to explain some of the cardiac and gastric effects resulting from systemic administration of catecholamine agents.

Basal forebrain cell loss following fimbria/fornix transection

Following fimbria/fornix transection, cells in the medial septum appear to undergo retrograde degeneration as shown by Nissl and acetylcholine esterase (AChE) staining. Recent studies using immunocytochemical techniques have also demonstrated loss of choline acetyltransferase (ChAT) and nerve growth factor receptor (NGFr) labeling of neurons in this region. Whether the apparent loss of ChAT- and NGFr-positive neurons is the result of the actual death of these neurons, or is instead a loss of ChAT enzyme or NGFr expression below levels detectable by immunocytochemical methods, remains an unresolved issue. In order to address this question, rhodamine-labeled fluorescent latex microspheres were injected into the hippocampus where they retrogradely transported to the cell bodies of the medial septum. Five days later these animals received either unilateral or bilateral fimbria/fornix lesions and were allowed to survive an additional 4 weeks. Compared to unlesioned control animals, unilaterally lesioned animals showed a 91% loss of fluorescently labeled cells and bilaterally lesioned animals showed a 93% loss. The inability to detect the fluorescent microspheres in the medial septum suggests that the majority of medial septal cells die after fimbria/fornix transection. ChAT and NGFr immunohistochemical staining were also performed. Cells stained for ChAT were reduced in number by 92% in animals with unilateral lesions and by 75% in animals with bilateral lesions, while NGFr-stained cells were reduced in number by 75% in animals with unilateral lesions and by 68% in animals with bilateral lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the discharge patterns of motor cortical neurones associated with volitional changes in stepping in the cat

Extracellular recordings have been obtained from motor cortical neurones of cats walking along a horizontal ladder. We present responses obtained when the animal produced defined volitional changes in limb trajectory, and during different conditions of locomotion. Our results show substantial changes in discharge pattern of some cells under these different conditions. Encounters with displaced rungs produce marked changes in discharge pattern including some which precede foot contact and others graded to the magnitude and direction of displacement.

Gene therapy in the CNS: intracerebral grafting of genetically modified cells

Grafting cells to the CNS has been suggested and applied as a potential approach to CNS therapy through the selective replacement of cells lost as a result of disease or damage. Independently, studies aimed at direct genetic therapy in model systems have recently begun to suggest conceptually new approaches to the treatment of several kinds of human genetic disease, especially those caused by single gene enzyme deficiencies. We suggest that a combination of these two approaches, namely the graftment into the CNS of genetically modified cells, may provide a new approach toward the restoration of some functions in the damaged or diseased CNS. We present evidence for the feasibility of this approach, including a description of some current techniques for mammalian cell gene transfer and CNS grafting, and several possible approaches to clinical applications. Specifically, we report that fibroblasts, genetically modified to secrete NGF by infection with a retroviral vector and implanted into the brains of rats with a surgical lesion of the fimbria-fornix, prevented the degeneration of cholinergic neurons that would die without treatment.

NGF-dependent sprouting and regeneration in the hippocampus

While a variety of sprouting and regenerative responses have been investigated in the hippocampus, the cellular and molecular events responsible for these plastic responses have not been determined. One transmitter system, the cholinergic system, shows several distinct responses to damage in the septohippocampal circuit. Present evidence strongly supports a role for nerve growth factor (NGF) in these responses. NGF is not only important for the survival of the adult cholinergic neurons, but can also induce regrowth of the damaged fibers given an appropriate substratum for growth. These reparative effects of NGF can manifest themselves in functional recovery in the aged rat and the young rat with fimbria-fornix lesions. Finally, a role for glia cells is proposed to clarify how NGF availability may be regulated during the degenerative and regenerative events. While all plasticity events certainly cannot be explained by the coincidence of NGF and the cholinergic system, their interaction may provide a template for other transmitter/trophic factor interactions.

Responses of motor cortical neurones in the cat to unexpected perturbations of locomotion

Extracellular recordings have been obtained from individual motor cortical neurones of cats walking along a horizontal ladder. We present responses obtained when selected rungs dropped unexpectedly by a small amount beneath the animal's weight. Our results show that forelimb motor cortex is rapidly and in graded fashion informed of such events, which may produce appreciable changes in impulse activity in the corticospinal tract.

Nerve growth factor receptor and choline acetyltransferase colocalization in neurons within the rat forebrain: response to fimbria-fornix transection

Although it is well known that magnocellular cholinergic basal forebrain neurons are trophically responsive to nerve growth factor (NGF) and contain NGF receptors (NGFr), the exact distribution of forebrain NGFr-immunoreactive neurons and the degree to which cholinergic neurons are colocalized with them have remained in question. In this study we employed a very sensitive double-labelling method and examined in the same tissue section the distribution and cellular features of NGFr-positive and choline acetyltransferase (ChAT)-immunolabelled neurons within the rat basal forebrain. Throughout this region the majority of magnocellular basal forebrain neurons were immunoreactive for both NGFr and ChAT. However, a small percentage of neurons in the ventral portion of the vertical limb of the diagonal band of Broca were immunoreactive only for NGFr, whereas a larger population of magnocellular neurons in the substantia innominata exhibited only ChAT immunoreactivity. No NGFr-immunoreactive cells were found associated with ChAT-positive neurons in the striatum, neocortex, or hippocampus, and no single-labelled NGFr-immunoreactive neurons were found outside the basal forebrain area, except for a large number of positive-labelled cells along the ventricular walls of the third ventricle. In addition to its function in maintaining the normal integrity of the basal forebrain and cholinergic, peripheral sympathetic, and neural-crest-derived sensory neurons, NGF may also have a role in the growth of these neurons after damage to the nervous system. To examine this postulate the hippocampus was denervated of its septal input and examined 8 weeks later. Two populations of neurons were found to have undergone collateral sprouting--namely, the midline magnocellular cholinergic neurons of the dorsal hippocampus and the sympathetic noradrenergic neurons of the superior cervical ganglion. Both of these neuronal populations also stained strongly for NGFr. In contrast, the small intrinsic cholinergic neurons of the hippocampus exhibited neither sprouting response nor staining for NGFr. In view of these results, we suggest that the differing sprouting responses demonstrated by these three neuronal populations may be due to their responsiveness to NGF, as indicated by the presence or absence of NGF receptors.

A lightweight hybrid microdrive for use with awake unrestrained animals

A hybrid microdrive is described, comprising remote stepper motors connected by a hydraulic link to a slave electrode positioner which is light enough for use with freely walking cats. The system provides 18 mm of electrode movement in 2 or 10 microns steps.

Substance P and somatostatin coexist within neuritic plaques: implications for the pathogenesis of Alzheimer's disease

In recent years the present authors and others have sought to determine the neurochemical composition of the dilated neuronal processes found within neuritic plaques of patients with Alzheimer's disease. To date a number of neurotransmitter and neuropeptide systems have been observed within different plaques, yet at present it is unclear whether individual human plaques contain more than one transmitter substance. In the present study a highly sensitive dual-immunolabeling procedure was employed and it was demonstrated that substance P and somatostatin-immunoreactive profiles coexist within single senile plaques of patients with Alzheimer's disease. Coexistence of somatostatin and substance P immunoreactivity within plaques was observed in the hippocampus and amygdala but not in the neocortex, although the latter region contained plaques within which somatostatin and substance P existed alone. The frequency with which we observed one or more neuropeptide within plaques was relatively low and in fact most plaques contained neither substance P nor somatostatin immunoreactivity. In addition, a large number of swollen peptidergic processes were observed outside of plaques. The significance of these observations with respect to the pathogenesis of Alzheimer's disease is discussed.

Cholinergic neurons from the dorsolateral pons project to the medial pons: a WGA-HRP and choline acetyltransferase immunohistochemical study

In this study we determined that cholinergic neurons from the lateral dorsal tegmental (LDT) and peribrachial pontine region (PPG) innervate the medial pontine reticular formation (medial PRF), a region involved in the generation of REM sleep. Wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) was injected into the medial PRF and the brainstem tissue was processed using a combined retrograde transport/immunocytochemical procedure. Results showed that 10-15% of choline acetyltransferase (ChAT) immunoreactive neurons in the LDT and PPG project to the medial PRF. It is hypothesized that these neurons play an important role in the generation of the REM sleep state.

Nucleus basalis magnocellularis lesions: lack of biochemical and immunocytochemical recovery and effect of cholinesterase inhibitors on passive avoidance

Lesions of the rat nucleus basalis magnocellularis (nBM) result in a marked decrease in cortical choline acetyltransferase (CAT) and in behavioral deficits. After unilateral ibotenic acid (IBO) lesions of the nBM in rats, there was a significant ipsilateral loss of frontal and parietal CAT, which did not recover for 3 months following surgery and was accompanied by a loss of CAT immunoreactivity in the peripallidal region. Bilateral ibotenate nBM lesions resulted in a marked deficit of one-trial step-through passive avoidance (PA) at 24 hours. Cholinesterase inhibitors including physostigmine, N-ethylaklylphenyl carbamate (RA-6), and N,N-methylethylphenyl carbamate (RA-7) were administered in separate experiments, for 2 days before retrieval testing or for 3 consecutive days during consolidation immediately following training. Nonsignificant improvements in PA latency were produced using 0.32 mg/kg physostigmine and 2.5 mg/kg RA-6 administered before retrieval testing. The results suggest that destruction of cholinergic neurons in the nBM are involved in the PA deficit, but does not exclude the possibility that damage to other neuronal systems may contribute to the observed behavioral deficit.