References

Li AJ, Ritter S (2003) 2-deoxy-D-glucose (2DG) increases NPY mRNA expression in hindbrain neurons. Neuroscience 2003 Abstracts 615.7. Society for Neuroscience, New Orleans, LA.

Summary: Previous results suggest that the orexigenic peptide, neuropeptide Y (NPY), participates in glucoprivic feeding. NPY mRNA in the hypothalamus is increased by glucoprivation (Sergeyev et al, 2000; Fraley and Ritter, 2003) and injection of anti-NPY antibody into the paraventricular nucleus of the hypothalamus (PVH) impairs glucoprivic feeding (He and Edwards, 1998). The hypothalamus is innervated by both arcuate and hindbrain NPY cell bodies. NPY innervation from the hindbrain is substantial and is derived largely or entirely from cell bodies that co-express norepinephrine or epinephrine. Selective immunotoxin lesions have demonstrated that these hindbrain catecholamine neurons are required for glucoprivic feeding (Ritter et al., 2001), as well as for glucoprivic stimulation of corticosterone secretion (Ritter et al., 2003) and suppression of estrus (I’Anson et al., 2003). However, the specific contribution of hindbrain NPY to these glucoregulatory responses has not been examined. Therefore, we examined NPY mRNA expression in hindbrain catecholamine cell groups 1.5 hr after 2-deoxy-D-glucose (2DG, 250 mg/kg) injection using in situ hybridization. Cell groups A1, A1/C1, the middle portion of C1 and C2, showed a basal level of NPY mRNA signal that was dramatically increased by 2DG. In rostral C1 and in C3, where basal NPY mRNA expression was below detection threshold, the hybridization signal was also significantly increased by 2DG. In cell groups A2, A5, A6 and A7, neither basal nor 2DG-stimulated NPY mRNA expression was detected. PVH microinjection of the retrogradely transported catecholamine immunotoxin, saporin conjugated to anti-dopamine-β-hydroxylase, destroyed hindbrain catecholamine neurons and abolished basal and 2DG-stimulated increases in NPY expression in hindbrain cell groups. These data suggest that hindbrain NPY neurons with projections to the hypothalamus participate in glucoprivic feeding and other glucoregulatory responses.

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Gerashchenko D, Murillo-Rodriguez E, Lin L, Xu M, Hallett L, Nishino S, Mignot E, Shiromani PJ (2003) Relationship between CSF hypocretin levels and hypocretin neuronal loss. Neuroscience 2003 Abstracts 616.2. Society for Neuroscience, New Orleans, LA.

Summary: In the sleep disorder narcolepsy there is a massive reduction in the number of neurons containing the neuropeptide, hypocretin (HCRT). Most narcoleptic patients also have low to negligible levels of HCRT in the cerebrospinal fluid (CSF). However, the relationship between HCRT neurons and HCRT levels is not known, making it difficult for investigators to estimate how many HCRT-containing neurons might be present based on measurements of CSF HCRT levels. A relationship between neuronal loss and CSF levels of the ligand is known in other degenerative diseases, such as Parkinson’s, but not in narcolepsy. To identify this relationship, hypocretin-2-saporin, the neurotoxin that kills hypocretin neurons, or saline were administered to the lateral hypothalamus and CSF was extracted at zeitgeber times (ZT) 0 (time of lights-on) or ZT 8 at various intervals (2, 4, 6, 12, 21, 36, 60 days) after the neurotoxin administration. Compared to saline animals (n=8), rats with an average loss of 73% of HCRT neurons (n=9) had a 50% decline in CSF HCRT levels on day 60. The decline in HCRT levels was evident by day 6 and there was no recovery or further decrease. The decline in HCRT was correlated with increased REM sleep. Rats with an average loss of 14.4% of HCRT neurons (n=4) showed no significant decline in CSF HCRT levels compared to saline rats. In rats with 73% loss of HCRT neurons, the HCRT levels were not substantially increased by 6h prolonged wakefulness indicating that surviving neurons were not able to increase the output of HCRT to compensate for the HCRT neuronal loss. From these data we conclude that since most narcoleptics have more than 80% reduction of CSF HCRT that in these patients most HCRT neurons are lost.

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Pan S, Borowski T, de Lacalle S (2003) Sleep deprivation impairs retention performance on an olfactory discrimination task. Neuroscience 2003 Abstracts 616.21. Society for Neuroscience, New Orleans, LA.

Summary: Sleep deprivation is known to adversely affect learning and memory. We examined the effects of sleep deprivation on attentional and memory processes in rats that received unilateral cholinergic lesions with 192IgG-saporin. Young Fisher 344 male rats were evaluated on an olfactory discrimination learning task both before and after exposure to 8 hours of sleep deprivation. Prior to testing, rats were trained to associate a particular scent with a food reward. They were then tested on their ability to successfully distinguish between two randomly placed, differently scented cups to retrieve the food reward. On a second experiment we investigated the effect that chronic estrogen administration may exert on the cognitive response to sleep deprivation. Gonadectomized rats were implanted s.c. with a pellet containing estrogen or placebo, and tested before and after sleep deprivation, one month after treatment. Untreated rats displayed impaired performance on the retention of the olfactory discrimination task; sleep deprivation resulted in an inability to remember the association of the baited scent from the previous day of testing. However, hormonal treatment appeared to have no significant effect on olfactory discrimination performance. These findings suggest a beneficial effect of sleep in learning and memory. Further research is needed to unravel the role of steroid hormones in modulating sleep-deprived learning deficits in rodents.

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Lee R, Gallegos RA, Crawford EF, Wills DN, Zhukov VI, Huitron-Resendiz S, Criado JR, Henriksen SJ (2003) Ventral tegmental area lesions alter EEG power spectrum across the sleep/wake cycle. Neuroscience 2003 Abstracts 616.5. Society for Neuroscience, New Orleans, LA.

Summary: The ventral tegmental area (VTA) has long been implicated in reward and drug abuse. We previously demonstrated (Lee et al, J. Neurosci. 2001) a role for VTA GABAergic neurotransmission in REM sleep. In continuing studies the potential role of the VTA in modulating electroencephalogram (EEG) activation was explored by selectively lesioning mu-opioid receptor expressing cells, or NMDA-lesioning cells, in the VTA. Under sodium pentobarbital anesthesia rats received either (1) a sham operation (2) a saporin injection (3) an injection of a dermorphin-saporin (DERM-SAP) conjugate (Advanced Targeting Systems, San Diego, CA) (4) or a bilateral VTA injection of NMDA. All injections were delivered in a volume of 0.5 to 1.0 µL over 4 to 8 minutes. Animals were also implanted with electrodes for recording the EEG & EMG. The filtered EEG & EMG were recorded continuously for 24 hours beginning 21 days after surgery. Frequency analysis of the EEG in 15-sec epochs revealed differences in the distribution of relative power in the DERM-SAP or NMDA-lesioned animals, compared to controls. Higher frequency components (12-25 Hz) were reduced in DERM-SAP lesioned animals during waking and slow wave sleep. Histology demonstrated gliosis of GAD-stained neurons in the VTA 3 to 4 weeks after injection of DERM-SAP. These data suggest that long-projecting GABA neurons of the VTA have a desynchronizing influence on cortical EEG arousal mechanisms. This is supported by anatomical evidence of both direct and indirect non-thalamic GABAergic projections to widespread areas of cortex in the rodent. Supported by: DA08301 to SJH.

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Reynolds JN, Sutherland JM, Sutherland RJ (2003) A novel nitrate ester enhances performance in a spatial memory task in rats with forebrain cholinergic depletion. Neuroscience 2003 Abstracts 626.11. Society for Neuroscience, New Orleans, LA.

Summary: Forebrain acetylcholine (ACh) depletion is associated with a variety of cognitive problems, including memory deficits. Here we evaluate the efficacy of a novel nitrate ester, GT 1061, a potential cognition enhancer, in reversing the memory deficit produced by ACh depletion. Long-Evans hooded rats were stereotaxically injected with 192-IgG-saporin intraventricularly or into basal forebrain cell regions to effect loss of cholinergic cells in the basal forebrain and depletion of cholinergic input to neocortex and hippocampus. The rats were postoperatively tested in a version of the Morris water task in which the location of the hidden platform was changed every second day. This version allows for repeated testing of new spatial learning and 24-hr memory retention. ACh depletion causes statistically reliable deficits in new learning and retention components of the task. We examined the effects of oral (0.5, 1, 5, and 10 mg/kg) and intraperitoneally injected (1, 10, 25 and 50 mg/kg) GT 1061 and donepezil oral (0.05, 0.5, 0.1, 1 mg/kg) and intraperitoneal (0.5 mg/kg) on performance of ACh depleted rats. Both oral and injected GT1061 (10 mg/kg oral, and 1 mg/kg i.p.) and donepezil improved new learning and retention performance. The improvement was especially evident during the 24-hr retention tests when GT1061 treated rats performed as well as normal rats. On this measure 10 mg/kg GT 1061 and 1 mg/kg donepezil administered orally were equipotent.

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Dudkin KN, Chueva IV, Makarov FN, Beach TG, Roher AE (2003) Impairments of working memory processes on a model of Alzheimer’s disease in monkeys. Neuroscience 2003 Abstracts 626.8. Society for Neuroscience, New Orleans, LA.

Summary: We have investigated the characteristics of visual working memory in a delayed-discrimination task in a model of Alzheimer’s disease (AD) in rhesus monkeys. Three animals received unilateral stereotaxic intracerebroventricular injection of the nucleus basalis of Meynert and three monkeys received sterile saline injections and thus served as controls. The lesioning agent consisted of a ribosomal toxin, saporin, conjugated to monoclonal antibodies against (the nbM lesion) the p75 neurotrophin receptor (p75NTR), which is expressed almost exclusively on cholinergic neurons of the nbM. The rationale for the model is the same as for a rabbit model of AD (Roher et al, Ann. NY Acad Sci. 2000). The monkeys were trained to discriminate stimuli with different types of visual information (spatial frequency gratings, color, spatial choice, spatial relationships between components of objects). The data obtained demonstrate that the nbM lesioning agent had a weak effect on visual differentiation without delay (long-term memory), but significantly decreased the duration of information storage (by a factor of 2 – 3) in working memory later two months after injection. These changes depended on temporal stage after injection and stimulus properties, and were accompanied by increase of motor reaction time and of refusal of task decision. In monkeys that were sham injected, there were no alterations in working memory characteristics. The results suggest that considerable worsening of the working memory characteristics for monkeys after lesion of the nbM reflects the formation of an AD model in these monkeys. The principles of functional organization of working memory and role of pathology of the cortical mechanisms in an impairment of memory characteristics are discussed.

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Kim I, Wilson RE, Wellman CL (2003) Cholinergic deafferentation increases expression of the glur-1 subunit of the AMPA receptor in frontal cortex of young adult but not aging rats. Neuroscience 2003 Abstracts 633.9. Society for Neuroscience, New Orleans, LA.

Summary: Previously, we demonstrated that plasticity of frontal cortex is altered in aging rats: cholinergic lesions of the nucleus basalis magnocellularis (NBM) produce larger declines in dendritic morphology in frontal cortex of aged rats compared to young adults. In addition, these lesions result in upregulation of dendritic spines in frontal cortex of young adult but not aging rats. To begin to identify possible mechanisms underlying age-related differences in plasticity after NBM lesion, we assessed immunohistochemical labeling of the AMPA receptor subunit GluR1 in young adult and aging rats after either sham or 192 IgG saporin lesions of the NBM. Young adult (N=17), middle-aged (N=16), and aged rats (N=13) received unilateral sham or 192 IgG saporin lesions of the NBM. Two weeks later, brains were processed for immunohistochemical labeling of the GluR1 subunit of the AMPA receptor. An unbiased stereological technique was used to estimate density of labeled neurons in layer II-III of frontal cortex. Cells were identified as neurons based on standard morphological criteria and counted. Using a computerized image analysis system interfaced with a microscope, the average optical density of the white matter below frontal cortex was determined; neurons with optical densities at least one standard deviation above this mean were identified as intensely labeled. In young adult rats, lesions produced a 55% increase in the density of intensely GluR1-immunopositive neurons in frontal cortex. On the other hand, lesions had no effect on counts of GluR1-immunoreactive neurons in middle-aged and aged rats. This age-related difference in lesion-induced expression of AMPA receptor subunit protein could underlie the age-related differences in dendritic plasticity after NBM lesions.

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Fletcher BR, Baxter MG, Rapp PR, Shapiro ML (2003) 192-IgG saporin lesions of the medial septum and vertical diagonal band impair cognitive flexibility. Neuroscience 2003 Abstracts 425.8. Society for Neuroscience, New Orleans, LA.

Summary: Learning and memory remain largely intact following selective basal forebrain cholinergic lesions. By comparison, single unit recording studies have documented reliable effects of such lesions, including abnormally rigid hippocampal place fields when animals are confronted with changes in the configuration of the testing environment. The present experiment tested the prediction that cholinergic lesions of the basal forebrain would impair performance of tasks requiring cognitive flexibility. Rats received 192-IgG saporin or control vehicle injections into the medial septal nucleus and vertical diagonal band, and were tested on cued and spatial delayed match-to-place tasks in a radial arm water maze. Test sessions consisted of four sample trials in which animals searched for a cued or hidden escape platform located in a fixed position at the end of one arm (60 sec cutoff, inter-trial interval = 15 sec). A memory delay was imposed by returning rats to the home cage for a variable delay (15 sec. – 6 hrs), followed by two test trials. The lesion and control groups learned at similar rates in both versions of the task, and performed comparably on the critical test trials, independent of the length of the retention interval. However, lesioned rats were impaired during the transition from the cued to spatial variants of testing. Specifically, the lesion group made significantly more errors on an early sample trial in the spatial task, returning to the location that was previously correct during cued training. Pending histological confirmation of the extent and selectivity of the experimental lesions, this pattern of results suggests that damage to the basal forebrain cholinergic system spares spatial learning but impairs cognitive flexibility when task contingencies are changed.

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Nelson LE, Franks NP, Maze M (2003) Discrete lesioning of orexin (hypocretin)-containing neurons potentiates dexmedetomidine- but not pentobarbital-induced hypnosis. Neuroscience 2003 Abstracts 426.13. Society for Neuroscience, New Orleans, LA.

Summary: Introduction: Recent work suggests that anesthetics putatively modulated by the α2-adrenoceptor (e.g. dexmedetomidine (DEX)) or the GABAA receptor (e.g. pentobarbital (PTB)) elevate and depress c-Fos expression, respectively, in the orexinergic perifornical area (PeF)1. Here the hypnotic effects of DEX and PTB are assessed after selective lesion of the PeF by orexin-B conjugated to saporin (OX-SAP). Methodology: Anesthetized Fischer rats were administered stereotaxic PeF injections of saline (0.5µl/side) or OX-SAP (490ng/0.5μl/side; as described2). Loss of righting reflex (LORR) induced by DEX (150μg/kg, SC), PTB (50mg/kg, SC), and saline was tested 1 day pre- and 1, 4, 8, and 12 days post-surgery, then lesions were assessed histologically. All data are presented as means±SEMs (n=6; comparisons by unpaired t-tests and ANOVA, Newman-Keuls). Results: Bilateral PeF lesions enhanced DEX-induced hypnosis at days 8 (281.2±15.8 min; p<0.05) and 12 (322.7±15.93 min; p<0.001) as compared to naïve (234.5±9.0 min) and saline sham animals (day 8, 236.7±9.8 min; day 12, 242.8±10.80 min). In contrast, PTB-induced LORR remained unaffected at day 12 (124.8±6.8 min) relative to naïve (119.4±4.6 min) and sham (120.8±5.3 min). These results agree with previous reports that by day 12, PeF-microinjected OX-SAP induces roughly 80% cell loss2. Conclusion: The absence of a functional PeF potentiates hypnosis induced by DEX but not PTB, as perturbation of the PeF by microinjected GABAA receptor antagonist gabazine is known to 1. References: 1 Nelson et al. (2002) SfN abstract 776.14/M20; 2 Geraschenko et al. (2001) J Neurosci 21:7273-83.

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Sherren N, Pappas BA (2003) Dendritic dysgenesis in midline cortical regions following selective acetylcholine and dopamine lesions in neonatal rats. Neuroscience 2003 Abstracts 457.11. Society for Neuroscience, New Orleans, LA.

Summary: Both acetylcholine (ACh) and dopamine (DA) afferents reach their cortical targets during periods of synaptogenesis, and are perfectly positioned to influence the cytoarchitectural development of cortical neurons. Thus the behavioural outcomes of these lesions may be related to the development of appropriate dendritic morphology in neurons from cortical regions involved in cognition. Previous studies have either used non-specific lesion techniques or have not examined long-term effects. We lesioned rat pups at P7 with either 600 ng of the selective immunotoxin 192 IgG-saporin, or 150 ug of 6-hydroxydopamine preceded by desmethylimipramine, or both, and aged them to four months. One squad of rats was sacrificed for neurochemistry and another was prepared for morphological analysis using Golgi-Cox stain. The ACh lesion caused a 32% decrease in choline acetyltransferase activity in the frontal/cingulate cortex and a 72% reduction in retrosplenial cortex (RSC). This was associated with reductions in total dendritic length of the apical tree of layer V pyramidal cells in the medial prefrontal cortex (mPFC), the apical tree of layer III pyramidal cells in the anterior cingulate cortex (ACC), and the basal tree of layer III pyramidal cells in RSC. The DA lesion caused a 76% reduction in DA levels in frontal/cingulate cortex and no change in RSC levels. This was associated with reductions in total dendritic length of the basal and apical trees of layer V pyramidal cells in mPFC, and the basal tree of layer III pyramidal cells in ACC. No changes in layer III pyramidal cells were noted in RSC following the DA lesion. These data demonstrate that ascending ACh and DA afferents play a vital role in the cytoarchitectural development of the cortex. This is particularly important considering that hypofunction in these systems is a characteristic feature of neurodevelopmental disorders involving mental retardation, such as Rett and Down syndrome.

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