sfn2016

Kelly SC, Nelson PT, Counts SE (2016) The locus coeruleus: a potential link between cerebrovascular and neuronal pathology in Alzheimer’s disease. Neuroscience 2016 Abstracts 786.11 / H7. Society for Neuroscience, San Diego, CA.

Summary: Noradrenergic locus coeruleus (LC) neuron loss is a major feature of Alzheimer’s disease (AD). The LC is the primary source of norepinephrine (NE) in the forebrain, where it modulates attention and memory in vulnerable cognitive regions such as prefrontal cortex and hippocampus. Furthermore, LC-mediated NE signaling is thought to play a role in blood brain barrier maintenance and neurovascular coupling, suggesting that LC degeneration may impact the high comorbidity of cerebrovascular disease (CVD) and AD. However, the extent to which LC projection system degeneration occurs in the earliest stages of AD is not fully characterized to date. To address these issues, we analyzed LC tissue samples from University of Kentucky AD Center subjects who died with a premortem diagnosis of no cognitive impairment (NCI) and Braak stages 0-II at autopsy, NCI subjects with Braak stages III-V thought to be in a preclinical AD (PCAD) stage, and subjects with mild cognitive impairment (MCI) or mild AD (n = 5-6 cases/group). Paraffin-embedded pontine tissue blocks containing the LC were cut at 20µm, immunostained with tyrosine hydroxylase (TH, a marker for NE synthesis), and analyzed by stereology to estimate total LC neuron number (total number of neuromelanin-containing LC neurons) and the percentage of TH+ LC neurons. Preliminary analysis reveal a ~20% loss of both total and TH+ LC neurons in PCAD (p = 0.08), a ~30-35% loss of these neurons in MCI (p < 0.05), and a ~45-50% loss of total and TH+ neurons in AD (p < 0.01) compared to NCI. Studies were also performed to compare additional LC neuronal pathologies (phospho-tau, TDP-43, and 8dOHG) in the diagnostic groups. A substantial increase in 8dOHG and phospho-tau is observed in PCAD compared to NCI. The morphometric data will be correlated with postmortem neuropathologic and CVD variables (e.g., microinfarcts and cerebral amyloid angiopathy) to gauge the relationship between LC neurodegeneration and cerebral AD and vascular pathology. To model these relationships in vivo, we stereotactically lesioned LC projection neurons innervating the PFC, a major LC projection zone, in the TgF344-19 rat model of AD (6 months old) using the noradrenergic immunotoxin, dopamine-β-hydroxylase-saporin, or a control lesion (n = 8/group). Prior to sacrifice at 9 months, immunotoxin- and control-lesioned rats will be tested behaviorally on the Barnes maze task. Postmortem PFC will be analyzed for LC fiber innervation, NE and NE metabolite levels, CVD pathology and AD-like pathology. Taken together, these data will shed light on the multifactorial noradrenergic pathways contributing to neuronal and vascular pathologies during the onset of AD.

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ATS Poster of the Year Winner. Read the featured article in Targeting Trends.

Ruiz AD, Hays S, Berry A, Vallejo S, Barron L, Carrier X (2016) Enhanced motor recovery by vagus nerve stimulation requires cholinergic innervation in a rat model of ischemic stroke. Neuroscience 2016 Abstracts 807.20 / HH11. Society for Neuroscience, San Diego, CA.

Summary: Stroke is a debilitating neurological insult that affects approximately 795,000 people in the U.S. each year. Following a stroke, many patients are left with impairment in upper extremity function, even after intensive rehabilitation therapy. Recent studies indicate that vagus nerve stimulation (VNS) paired with rehabilitative training significantly enhances recovery of forelimb function in models of ischemic stroke, intracerebral hemorrhage, and traumatic brain injury. Nevertheless, the mechanisms that underlie VNS-dependent enhancement recovery are largely unknown. The cholinergic nucleus basalis (NB) is a critical substrate in cortical plasticity, and several studies suggest that VNS activates cholinergic circuitry. Previous studies demonstrated that cholinergic innervation of the motor cortex is required for VNS-dependent enhancement of cortical plasticity. In this study we examine whether cholinergic innervation is required for VNS-dependent enhanced recovery in a rat model of ischemic stroke. A cohort of rats was trained to proficiency on the isometric force task, an automated and qualitative measure of forelimb function and then received a cortical ischemic lesion to impair the trained forelimb. Rats then received injections of the highly selective immunotoxin IgG-192-saporin into the nucleus basalis to deplete cortical cholinergic innervation (NB-) or control injections (NB+). Two weeks after stroke and immunolesion, rats underwent rehabilitative training for 6 weeks with or without VNS paired with forelimb movement. At the conclusion of behavioral testing, pseudorabies virus labelling was performed to assay anatomical plasticity in motor circuits controlling the forelimb. Preliminary findings indicate that VNS-dependent enhancement of stroke recovery requires cholinergic innervation.

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Gulino R, Forte S, Parenti R, Gulisano M (2016) Novel targets for modulation of plasticity in a mouse model of motoneuron degeneration. Neuroscience 2016 Abstracts 812.14 / OO13. Society for Neuroscience, San Diego, CA.

Summary: A successful spinal cord repairing strategy should involve the activation of neural precursor cells. Unfortunately, their ability to generate neurons aſter injury appears limited. Another process promoting functional recovery is synaptic plasticity. We have previously studied some mechanisms of spinal plasticity by using a mouse model of motoneuron depletion induced by cholera toxin-B saporin. TDP-43 is a nuclear RNA/DNA binding protein involved in amyotrophic lateral sclerosis. Although considerable attention has been devoted to the toxic effects of the TDP-43 cytoplasmic aggregates, the functional role of this factor remains poorly investigated. Notably, TDP-43 is present in the dendrites where it behaves as a modulator of local RNA translation. Moreover, it is crucial for synaptic plasticity and locomotion in Drosophila. Here, we would like to deepen the investigation of this model of spinal plasticity. Aſter lesion, we observed a glial reaction and an activity-dependent modification of Synapsin-I, Shh, Noggin, Numb and TDP-43 proteins. Multivariate regression was used to model the possible association between these proteins, as well as with the motor performance. We found that Shh and Noggin could affect motor performance and that these proteins could be associated with both TDP-43 and Numb, thus suggesting that TDP-43 is likely an important regulator of synaptic plasticity. Given the well-known role of morphogens such as Shh, Noggin and Numb in neurogenesis and the above described functions of TDP-43, we believe that an in vivo manipulation of their signaling pathways after lesion could represent a putative method of improving regeneration and recovery by affecting synaptic plasticity and/or neurogenesis.

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Leong CS, Maness EB, Baraki DI, Burk JA (2016) Effects of protein kinase C activation on attention deficits following loss of corticopetal cholinergic neurons. Neuroscience 2016 Abstracts 833.03 / HHH22 . Society for Neuroscience, San Diego, CA.

Summary: Alzheimer’s disease (AD) is a neurodegenerative dementia characterized by memory loss, cognitive impairment, and attention deficits. Damage to corticopetal cholinergic neurons originating in the basal forebrain is thought to contribute to the attention deficits. Recent evidence had identified G-protein decoupling at the M1 muscarinic acetylcholine receptor as well as decreased levels of protein kinase C (PKC) in rat AD models and the human AD brain. PKC is a signaling kinase that can affect neurite outgrowth, synaptic formation, and neurotransmitter release. PKC activation additionally may affect voltage-gated calcium currents. Previous research in this lab has shown that inhibition of PKC by chelerythrine chloride decreased signal detection in a sustained attention task. The present experiment evaluates the effect of PKC activation on sustained attention following loss of cortical cholinergic projections induced by infusions of 192 IgG-saporin into the basal forebrain. Male and female Sprague-Dawley rats were trained to discriminate between signals (illumination of a central panel light) and nonsignals (no panel light illumination) in a two-lever sustained attention task. Each rat received intraventricular infusions of the PKC activator bryostatin-1 (0, 0.5, 2.0, and 4.0pM) prior to testing. In the middle block of trials, a flashing houselight distracter was included to increase attentional demands. Compared to sham-lesioned animals, lesioned animals showed poorer signal detection in the distracter block of the task, but no differential effects of lesion on nonsignal trials. Distracter scores (initial block of trials with no distracter – distracter block) were calculated for each behavioral measure. For signal detection, there was a dose × group interaction (F(3,30) = 3.069, p = 0.043). Bryostatin-1 attenuated signal detection deficits in lesioned animals. Sham-treated animals showed decreased performance with increased bryostatin-1 dosage. Following the highest bryostatin-1 dose, there were no difference in signal detection between the sham and lesioned animals. The present results support the hypothesis that Bryostatin-1 can improve performance in a visual attention task following damage to corticopetal cholinergic neurons.

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Phillips KB, Sarter M (2016) Cholinergic-dependent shifts to cue-directed behavior. Neuroscience 2016 Abstracts 833.11 / HHH30. Society for Neuroscience, San Diego, CA.

Summary: Successful cue detection requires cortical cholinergic signaling. Recent evidence has elucidated the role of phasic, short-timescale, regionally-specific cholinergic signals, termed “cholinergic transients”, in cue detection. Cholinergic transients in the right prefrontal cortex were exclusively observed in trials in which cues were detected and when such trials followed non-cued trials yielding correct rejections or falsely perceived non-cued trials (cues that were missed). Thus, these cholinergic transients were interpreted as mediating shifts from performance guided by internally-guided attention to cued-directed behavior (Howe et al., 2013). In contrast to cholinergic transients mediating shift-hits, such transients were not observed during consecutive hits. Transients may be actively suppressed during consecutive hits in order to constrain a potential detection bias and maintain behavioral flexibility (Sarter et al., 2015). Here we removed cholinergic innervation to the right prefrontal cortex in rats to test the hypothesis that the right hemispheric cortical cholinergic projection system is necessary for shift-hits. Rats were trained on a sustained attention task (SAT) consisting of a random sequence of signal trials and non-signal trials, both requiring a distinct lever response from the subject. Following stable task performance, half of the subjects received right unilateral cholino-selective lesions of the basal forebrain by infusions of the immunotoxin 192 IgG-saporin, while the remaining subjects received sham surgeries. Rats were then familiarized with performing a modified version of SAT which consisted of engineered trial sequences to provide an “aggressive” test of the hypothesis based on the performance of pre-defined trials. In particular, the modified SAT included long strings of non-cued trials that were followed by a cued trial, with lesioned animals expected to miss specifically that latter trial. Conversely, neither hits during long strings of cued trials, nor correct rejections during non-cued trials that followed long strings of consecutive hits were expected to be affected by the lesion. Results indicate that right cholinergic losses selectively impair shift-hits. These findings are consistent with recent results from our optogenetic studies showing that cortical cholinergic transients are necessary and sufficient for the detection of cues (Gritton et al., 2016) and they extend these findings by specifying that in the absence of cortical cholinergic activity, subjects remain arrested in a state of perceptual or intrinsic attention.

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Maness EBL, Leong CS, Burk JA (2016) Effects of N-desmethylclozapine on attentional performance following loss of basal forebrain corticopetal cholinergic inputs. Neuroscience 2016 Abstracts 833.15 / HHH34. Society for Neuroscience, San Diego, CA.

Summary: Corticopetal cholinergic neurons play a vital role in attentional processing, and dysregulation of this system contributes to central nervous system disorders whose main attributes include an inability to engage in sustained attention, such as Alzheimer’s disease. The cholinergic muscarinic-1 (M1) receptor is known to be necessary for normal attentional processing. In general, there has been a trend towards supporting drugs that provide allosteric agonism of cholinergic receptors as an approach that may yield greater benefits than drugs that act at orthosteric receptor sites. There exists contention in the literature regarding the action of N-desmethylclozapine (NDMC), a partial M1-preferring agonist, that is thought to act at an allosteric site on the M1 receptor. The goal of the present experiment is to further evaluate NDMC’s activity at these sites in a lesion model of cholinergic dysfunction using an operant task assessing attentional capacity. After training in an attention-demanding task requiring differentiation between signal trials (500, 100, and 25ms illumination of a central panel light) and non-signal trials (no light illumination), Sprague Dawley rats received intrabasalis infusions of either saline or the cholinergic neurotoxin 192 IgG-saporin, and attentional performance was later measured following intracerebroventricular infusions of NDMC. In general, NDMC impaired attentional performance, particularly for lesioned animals. These findings suggest that NDMC may functionally decrease acetylcholine stimulation of M1 receptors or that the actions of NDMC at other receptor sites disrupt any beneficial effects of NDMC at the M1 receptor.

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Kucinski AJ, De Jong IEM, Sarter M (2016) Preventing falls in PD in a rat model of impaired cognitive control of complex movements by a pro-cholinergic combination treatment. Neuroscience 2016 Abstracts 835.15 / III34. Society for Neuroscience, San Diego, CA.

Summary: Parkinson’s disease (PD) patients, in addition to primary motor symptoms resulting from extensive losses of striatal dopamine (DA), suffer from an interrelated group of motor-control symptoms including postural instability, gait deficits, and a propensity for falls. These levodopa-insensitive symptoms are associated with losses of cortically-projecting cholinergic neurons of the basal forebrain (BF), as well as cognitive impairments such as poor attention. Given the high prevalence and severe consequences of falls in levodopa-treated patients, alternative treatment options are urgently needed. To assess potential treatments we have developed behavioral models of falls in rats including a test system (Michigan Complex Motor Control Task, MCMCT) that requires persistent control of gait, limb coordination, and carefully timed and placed steps during traversals of dynamic surfaces (rotating square rods). Rats with bilateral cholinergic lesions of the BF using 192 IgG-saporin and 6-OHDA lesions to the dopaminergic dorsomedial striatum (dual lesions, DL) exhibit falls while traversing rotating rods and these falls correlate with impaired performance of a sustained attention task. DL rats’ falls have been hypothesized to result from interactions between disruption of normally cholinergically-driven transfer of extero- and interoceptive cue information from cortex to striatum and impaired striatal action sequencing. Here we tested the hypothesis that falls are reduced by co-treatment with acetylcholinesterase inhibitor donepezil and a 5-HT6 receptor antagonist. This combination treatment was previously reported to exhibit synergistic pro-cholinergic activity in rats and improved cognition in patients with moderate Alzheimer’s disease. Overall, drug-treated rats fell less frequently from the rotating rods and were particularly more efficient at reinstating forward movement after sudden stoppages of forward movement with a passive (doorframe) distractor task. This treatment combination may benefit fall propensity in PD patients via maintaining planned movement sequences in working memory and improving the vigor of executing such movements following brief periods of freezing of gait. The neuropharmacological interactions of this treatment may involve diverse signaling pathways converging onto striatal output neurons. Results from current experiments using microdialysis and HPLC-mass spectrometry to simultaneously assess release of striatal ACh, animo acids and monoamines during rotating rod traversals will assist in elucidating potential targets for therapeutic prevention of falls. Supported by a grant from H. Lundbeck A/S

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Rajakumar R (2016) Developmental disturbances in thalamocortical connection are sufficient to produce almost all features of schizophrenia. Neuroscience 2016 Abstracts 845.01 / LLL41. Society for Neuroscience, San Diego, CA.

Summary: Partial ablation of subplate of the developing frontal cortex was achieved by two different approaches in PD1 S-D rat pups: infusions of either P75 receptor antibody-conjugated to saporin or β-nerve growth factor, and both resulted in identical changes: ~20% loss of subplate and aberrant distribution of thalamocortical fibers within the cortex. Control littermates received similar infusions of vehicle. Pups were allowed to grow under standard care. All animals survived, and showed no noticeable differences in milestones or activities. No differences were observed between lesioned and control groups in standard behavioral tests at 6-8 weeks of age. However, lesioned group showed significantly increased stress- or amph-induced locomotor activity, PPI deficit, social interaction deficits, and executive functional deficits after 9 weeks of age. A month-course of haloperidol or risperidon completely ameliorated locomotor abnormalities but did not affect social interaction deficit. Histological examination revealed several interesting changes: (1) 18% loss of gray matter thickness in the mPFC and no change in thickness in other cortical areas at 12 weeks, while at 20 weeks PFC loss remained at 18% but parietal and temporal cortices showed progressive thinning (20-36%); (2) significant loss of neuropil in the mPFC characterized by loss of synaptophysin and spinophilin labeling; (3) no changes in the number of neuronal cell bodies in PFC; (4) significantly increased lateral and third ventricular volume; (5) significant loss of dopaminergic fibers in lower layers of the PFC; (6) significant loss of GAD67-IR terminals in PFC; (6) significant decrease in the intensity of PAR labeling and abnormal distribution of PAR-IR terminals/cell bodies without loss of neurons; (7) significant loss of GAT-1-IR terminals only in upper layers of the PFC; (8) loss of PAR-IR terminals and cell bodies in the hippocampus; (9) abnormal distribution but no loss of CR-IR neurons in the entorhinal cortex; and (10) significantly reduced volume of basolateral amygdala. No changes were seen in ChAT neurons of the septum or N. basalis. All structural changes noted above were seen as early as 12 weeks and were not affected by antipsychotic treatment between 12 and 16 weeks. Results suggest that disturbances in thalamocortical pathfinding (due to genetic or other mechanisms) are sufficient to cause features of schizophrenia in normal animals.

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Wiley RG, Yezierski R, Vierck Jr CJ (2016) Cerebral cholinergic mechanisms in pain: CBF lesions vs systemic scopolamine. Neuroscience 2016 Abstracts 525.15 / SS2. Society for Neuroscience, San Diego, CA.

Summary: Cholinergic inputs to the cerebral cortex and limbic system, originating primarily from the cholinergic basal forebrain (CBF), play an important role in cortical sensory processing, largely through modulation of inhibitory interneurons. Cholinergic agonists given spinally, intracerebroventricularly (ICV) or systemically depress reflex nocifensive responses, but systemic cholinergic antagonists also depress some affective responses to pain and impair attention to aversive stimuli and stress reactions. In the present study, we determined the effects of selective cerebral cholinergic denervation, using ICV microinjection of 4 ug of 192-saporin in 10 μl (Advanced Targeting Systems, San Diego, CA) on operant thermal escape responses to aversive thermal stimuli (10° C, 44.5° C) and hyperalgesic effect of sound stress (ten X 30 sec bursts of 100 dB white noise over a 15 min period, 20 mins prior to thermal escape testing) in normal and CBF-lesioned rats compared to effects of systemic cholinergic antagonism (0.1 mg/kg, i.p., scopolamine, 20 minutes prior to thermal escape testing) in intact, normal rats. All rats were on the thermal escape task prior to either scopolamine, or sound stress testing and prior to ICV 192-saporin. At the conclusion of behavioral testing, choline acetyltransferase immunohistochemistry confirmed that 192-sap produced 62-81% loss of CBF cholinergic neurons. CBF-lesioned rats showed decreased thermal escape responses to both temperatures (10°C and 44.5°C) for >19 weeks. There also was no increase in escape responding (hyperalgesia) after sound stress as seen in normal rats. Scopolamine in normal rats produced decreased thermal escape responses to cold (2° C, 6°C and 10° C) and to heat (44.5° C). These results suggest that systemic scopolamine mimics the effects of CBF destruction on pain and together the overall results are interpreted to indicate an important role for the CBF in cerebral pain processing. These findings may be relevant to clinical pain care in patients with cerebral cholinergic dysfunction, such as Alzheimer’s disease.

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Vitale EM, Holschbach MA, Lonstein JS (2016) Maternal aggression is impaired by prepartum serotonin-specific lesions of the midbrain dorsal raphe. Neuroscience 2016 Abstracts 338.01 / SS14. Society for Neuroscience, San Diego, CA.

Summary: The postpartum period in laboratory rats and other animals is characterized by increased maternal responsiveness, decreased anxiety, and increased aggression. Pharmacologically manipulating the serotoninergic system during the postpartum period alters all of these behaviors, and our lab recently found that lesioning serotonergic neurons in the dorsal raphe (DR; primary source of forebrain serotonin) after parturition decreases maternal aggression as well as pup licking in laboratory rats. This demonstrates serotonin’s importance for these behaviors during the postpartum period, but no studies have evaluated the function of serotonin during pregnancy, a highly sensitive period when hormones and peptides alter neurochemistry to initiate maternal responsiveness. Given serotonin’s role in hormone and neuropeptide release, DR serotoninergic activity beginning during pregnancy may be particularly important for the onset of postpartum changes in anxiety, maternal responsiveness, and maternal aggression. To test this hypothesis, we destroyed serotonergic cells with a neurotoxin targeting the serotonin transporter (anti-SERT-saporin; Advanced Targeting Systems) infused into the DR on pregnancy day 15. After parturition, we observed subjects’ maternal caregiving behaviors, maternal motivation during retrieval tests, maternal aggression, and anxiety-like behaviors. We found that DR lesions during pregnancy greatly reduced maternal aggression towards an intruder, and that lesioned mothers also showed increased contact with pups immediately after disruption of the nest site during retrieval tests. Preliminary analysis of serotonin fiber innervation in several forebrain regions indicates tremendous reduction in serotonin fiber density in the amygdala and medial prefrontal cortex of lesioned subjects, but much less so in the medial preoptic area (MPOA). These findings demonstrate that prepartum serotonin-specific lesions of the DR affect particular maternal behaviors, especially aggression, and likely do so by reducing serotonergic innervation of the forebrain in a site-specific manner.

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