sfn2001

Shafi R, Berntson GG, Sarter M, Saurer T, Spino M (2001) Basal forebrain cholinergic system: Cortical activation, sleep/waking EEG and evoked potentials. Neuroscience 2001 Abstracts 533.16. Society for Neuroscience, San Diego, CA.

Summary: The role of the basal forebrain cholinergic system in cognitive functions such as arousal, attention and memory has been well documented. The purpose of the present study was to further elucidate the role of the basal forebrain in regulating cortical states and processes that may underlie these functions. Selective lesions of the cholinergic neurons of the basal forebrain were made using the immunotoxin 192 IgG-saporin, which selectively targets the p75 receptor on cholinergic neurons. The effects of these lesions on sleep structure and EEG activity and on afferent priming of cortical reactivity was evaluated. Specifically, we monitored behavioral activity and sleep states and examined the frequency distribution of power distribution in EEG frequency bands during these states. In separate sessions, we also recorded cerebral event-related potentials to auditory stimuli (100 ms, 1 K Hz at 60, 70 and 80 db) after intraperitoneal administration of saline or epinephrine (0.5 mg/kg, which we have previously found to result in priming or enhancement of the auditory evoked response). Compared to controls, lesioned animals showed a reduction in spontaneous activity, reduced power in higher frequency (primarily gamma) EEG bands during both sleep and waking, and altered sleep structure. In addition, lesioned animals displayed lower amplitude auditory evoked potentials and a loss of epinephrine-priming of the evoked response. Results support the view that the basal forebrain cholinergic system may play an important role in cortical activation and the regulation of sleep/waking states, as well as in cortical processing and its enhancement by visceral priming.

Related Products: 192-IgG-SAP (Cat. #IT-01)

Zambon NJ, Nagle R, Pokala V, Gibbs RB, Johnson DA (2001) Low dose 192 IgG-saporin selectively destroys basal forebrain cholinergic neurons and impairs acquisition of a spatial memory task. Neuroscience 2001 Abstracts 534.13. Society for Neuroscience, San Diego, CA.

Summary: We previously showed that a high dose (1 μg) of the selective cholinergic immunotoxin 192 IgG-saporin (SAP), injected into the medial septum (MS) of Sprague-Dawley rats, impeded acquisition of a delayed matching-to-position (DMP) spatial memory task, whereas injections of ibotenate (5 μg in 1 μL) did not. The present study examined the effects of lower doses of SAP (0.22 and 0.45 μg in 1 μl) on DMP acquisition. Animals received either SAP or vehicle injected directly into the MS. Two weeks later, animals were food deprived and trained to the DMP task. Rats received 8 trial pairs/day until they reached a criterion of 15/16 correct choices. Seven days later, post-criteria testing for retention was performed. Brain tissues were analyzed for choline acetyltransferase (ChAT) activity, or were processed for immunohistochemical detection of ChAT and parvalbumin. Control rats required significantly fewer days (13.1) to reach criterion than rats that received 0.22 (22.0 days) or 0.45 (20.1 days) μg SAP. There was no effect of SAP treatment on post-criteria testing. Injections of SAP produced marked depletion of ChAT-positive cells and ChAT activity, but no apparent depletion of parvalbumin staining in the MS. In contrast, ibotenate injections used in the previous study were shown to produce marked depletion of parvalbumin staining in the MS, but no significant cognitive impairment. The data suggest that selective destruction of cholinergic neurons in the MS significantly impairs acquisition of the DMP task.

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Chou TC, Gerashchenko D, Saper CB, Shiromani PJ (2001) Loss of histaminergic neurons does not produce hypersomnolence. Neuroscience 2001 Abstracts 522.21. Society for Neuroscience, San Diego, CA.

Summary: Electrolytic lesions of the posterior hypothalamus (PH) produce long-lasting hypersomnolence (1,2). The PH contains histaminergic neurons in the tuberomammillary nucleus (TMN) that project diffusely throughout the brain. Because histamine promotes wakefulness while antihistamines are sedating, the TMN is thought to be critically involved in maintaining wakefulness. To test this hypothesis, we placed cell-specific lesions in the PH and TMN of rats and measured sleep-wake behavior. Lesions were produced using either the conventional excitotoxin ibotenic acid, or the novel toxin orexin (hypocretin) conjugated to the ribosomal toxin saporin (ORX/HCRT-SAP). Ibotenic acid injections were ineffective at lesioning the TMN; most histaminergic neurons were selectively spared while neurons in surrounding regions such as the mammillary bodies and supramammillary area were completely lesioned. In contrast, ORX/HCRT-SAP injections into the TMN lesioned up to 95% of histaminergic neurons, as determined by adenosine-deaminase immunostaining, with a similar loss of neurons in adjacent areas. Surprisingly, neither group of rats showed changes in NREM or REM sleep time or circadian distribution of sleep relative to saline-injected controls for up to 2 weeks after surgery. Thus, the waking state may not be critically dependent on the PH or TMN in rats. Further research is needed to reconcile the sedating effects of antihistamines with the current findings. 1. Ranson 1939, Archiv Neurol and Psychiatry 41(1):1-23. 2. Swett and Hobson 1968, Arch Ital Biol 106(3):283-293.

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Sherren N, Pappas BA (2001) Behavioural and neurochemical changes associated with single and combined acetylcholine and dopamine lesions in neonatal rats. Neuroscience 2001 Abstracts 539.5. Society for Neuroscience, San Diego, CA.

Summary: The functional outcomes of neonatal ACh or DA lesions are frequently less severe or qualitatively different from those seen in adult rats, and may be due to compensatory neurochemical changes. Given that these transmitter systems interact in the adult brain and that ACh and DA hypofunction may underlie the cognitive and motor disabilities seen in Rett syndrome, we hypothesized that combined neonatal ACh/DA lesions may produce a profile of neurochemical changes and behavioural impairments which are more severe or distinct from that caused by either lesion alone. Rats were lesioned at postnatal day 7 with 192 IgG-saporin (ACh rats), 6-OHDA with NE receptor blockade (DA rats), or both (ACh/DA rats). Behavioural testing occurred at 4 months of age. In the open field, only ACh/DA rats exhibited locomotor hyperactivity whereas all lesioned groups exhibited reduced exploratory behaviour. Neither DA nor ACh/DA rats were able to solve the Morris water maze, however ACh rats were indistinguishable from controls. 192 IgG-saporin treatment produced a 75% decrease in hippocampal ChAT activity, and cortical decreases of 30%, 70% and 40% in the frontal/cingulate (FC), retrosplenial (RS) and partietotemporal (PT) regions respectively. 6-OHDA treatment produced a 90% decrease in striatal DA levels and a 75% decrease in FC cortex. Interestingly PT DA levels were 68% higher in ACh rats but 47% lower in ACh/DA rats compared to control, while DA rats showed a decrease which was not significantly different from control. Thus sparing of spatial learning ability in ACh rats may be mediated by increases in PT DA levels, whereas combined ACh/DA lesions exacerbate DA loss in this region.

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Pau K (2001) Immunolesioning of brainstem DBH neurons on the mating-induced LH and prolactin surge in the rabbit. Neuroscience 2001 Abstracts 466.7. Society for Neuroscience, San Diego, CA.

Summary: Coitus induces a surge release of norepinephrine (NE) that is accompanied by a preovulatory gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) surge. Prazosin, an alpha-1 adrenergic antagonist, attenuates the GnRH/LH surge, and tyrosine hydroxylase (TH) gene expression in brainstem NE areas increases within 30 min after coitus. Here, we determined the coitus-induced LH/prolactin surge after specific lesioning of dopamine beta-hydroxylase (DBH) neurons in the brainstem with monoclonal anti-DBH sera conjugated with the ribosomal cytotoxin saporin (DBH-SAP). Female NZW rabbits received 3rd cerebroventricular injection (Day 0) of either DBH-SAP (20 µg, n=4) or SAP (3 µg, n=4). On day 14, the four DBH-SAP females were paired with stud males, but none of them mated. After daily injection of estradiol benzoate (EB, 3 µg) for 3 days, all eight females mated. Blood samples were taken once before, and at 10-min intervals for 4 hours after, coitus. Brainstems were prepared for immunocytochemical detection of DBH and TH. Coitus increased both LH and prolactin release in either DBH-SAP or SAP animals. However, postcoital LH and prolactin levels were 55% lower and 50% higher, respectively, in DBH-SAP rabbits than in SAP animals. The number of DBH neurons was near zero in the A6 and reduced by 80% in the A1 and 70% in the A2 noradrenergic areas in DBH-SAP animals. The number of TH neurons was reduced by 95% and 30% in the A6 and A1 areas, respectively, and did not change in the A2 area. The results suggest that the presence of intact brainstem NE neurons are critical for sexual performance and production of normal LH/prolactin surge after coitus in female rabbits.

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Ricceri L, Scattoni ML, Calamandrei G (2001) Neonatal cholinergic lesions alter reactivity to a GABAergic agonist in 18-day-old rats. Neuroscience 2001 Abstracts 541.14. Society for Neuroscience, San Diego, CA.

Summary: We have shown previously that neonatal intracerebroventricular (icv) injections of the selective cholinergic immunotoxin 192 IgG-saporin on postnatal day (pnd) 7induces learning impairments on pnd 15 and disruption of reactivity to spatial novelty on pnd 54. The same neonatal treatment also induces a permanent cholinergic loss in both hippocampus and neocortex. In the present study we analyzed behavioral effects induced by a GABAergic drug (muscimol, a GABAa receptor agonist) in rats neonatally lesioned with 192 IgG-saporin (icv on pnd 7). On pnd 18 192 IgG-saporin lesioned and sham rats were injected with muscimol (0.1, 0.5 mg/kg ip) and placed in an open field arena for 20 min; locomotion, wall rearing and rearing responses were measured. In sham animals, as expected, 0.1 muscimol decreased locomotion, wall rearing and rearing responses. In saporin lesioned animals 0.1 muscimol increased locomotion, left wall rearing responses unchanged and decreased only rearing responses. In a 60s hot-plate test, 0.1 muscimol induced comparable analgesic responses in both sham and saporin-lesioned animals. The 0.5 muscimol dose resulted cataleptic for both saporin and sham lesioned rats. Neonatal saporin per se also reduced wall rearing and rearing responses. These data suggest that only in selective behavioral patterns — associated with locomotion and exploration of the environment — reactivity to a GABAergic agonist is reduced following neonatal cholinergic lesions, probably because of a decrease of GABAa receptors in the medial septal nucleus.

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Harrell LE, Kolasa K, Parsons DS, Conger K (2001) α-1 adrenergic agonist effect on cholinergic muscarinic receptors. Neuroscience 2001 Abstracts 549.16. Society for Neuroscience, San Diego, CA.

Summary: Degeneration of the basal forebrain cholinergic system and sympathetic ingrowth appear to be pathological changes in Alzheimer’s Disease patients (AD), leading to an alteration in the balance between both systems and may mediate cognitive deficits in AD. In an attempt to model this situation, intraventricular injection (ivc) of a specific cholinergic immunotoxin, 192-IgG-saporin, has been used to induce peripheral noradrenergic fibers to grow into cortex and hippocampus after cholinergic denervation of rat cortex (CCD) and hippocampus (HCD). This adrenergic reorganization has been termed cortical (CSI) and hippocampal (HSI) sympathetic ingrowth. 192-IgG-saporin ivc injection was followed by intraperitoneal (ip) treatment with α1 agonist methoxamine. Thus the effects on choline acetyltransferase (ChAT) activity, norepinephrine (NE) level and muscarinic acetylcholine receptors (mAChR) were studied in rat hippocampal and cortical brain tissue. We found that 192-IgG-saporin produced significant decrease in ChAT activity in all experimental groups and areas. Methoxamine (3 and 6 mg/kg ip) did not affect NE levels. It produced significant decrease in mAChR affinity in the cholinergic denervation group and no significant increase in mAChR density in cholinergically denervation groups of dorsal hippocampal and cortical areass. Results of the present study indicate the influence of α1 agonist treatment on mAChR and may provide new concepts for the future combination drug therapy for AD patients.

Related Products: 192-IgG-SAP (Cat. #IT-01)

Kolasa K, Harrell LE, Parsons DS, Conger K (2001) α-1 adrenergic antagonist effect on cholinergic muscarinic receptors. Neuroscience 2001 Abstracts 549.17. Society for Neuroscience, San Diego, CA.

Summary: Cholinergic denervation of cortex and hippocampus in rat causes an unusual neuronal rearrangement, in which peripheral sympathetic fibers, originating from superior cervical ganglia, grow into the cholinergically denervated areas. This process has been termed cortical (CSI) and hippocampal sympathetic ingrowth (HSI). A similar process may occur in Alzheimer’s Disease (AD). Recent studies suggest that the balance between central adrenergic and cholinergic systems may be important for normal learning and memory, while the alterations of these systems may play a critical role in cognitive deficits of AD. To better understand this situation specific cholinotoxin, 192-IgG-saporin, was intraventricularly (ivc) injected to produce a selective loss of cholinergic cells in rat basal forebrain nuclei, cholinergically denervating hippocampal (HCD) and cortical areas (CCD). This effect was confirmed by significant decrease in choline acetyltransferase activity in all groups and brain structures.192-IgG-saporin injection was followed by a treatment with α1-adrenergic antagonist prazosin to determine the effect on hippocampal and cortical muscarinic acetylcholine receptors (mAChR) and norepinephrine (NE) level. Prazosin (0.5 & 2 mg/kg ip) produced decreases in NE levels of HSI and CSI and induced no significant increase in mAChR affinity in HSI and CSI groups in dorsal hippocampus,anterior and entorhinal cortex. Injected at the dose of 2 mg/kg it increased mAChR density in CSI of both cortical areas. The present results began to define the interaction between adrenergic and cholinergic systems, as α1 antagonist treatment affects mAChR,a potential therapeutic target in AD.

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Wang H, Guyenet PG (2001) DL-homocysteic (DLH)-induced tachypnea is eliminated by ablation of neurokinin-1 receptor immunoreactive (NK1R-ir) neurons of the preBötzinger complex (preBötc). Neuroscience 2001 Abstracts 633.4. Society for Neuroscience, San Diego, CA.

Summary: We identified a hot spot of the ventrolateral medulla (VLM) where tachypnea is produced by small injections of the excitatory amino acid DLH in urethane-anesthetized vagotomized rats. We sought to determine its anatomical location relative to a group of NK1R-ir cells that may be a marker of the preBötC. We also determined the location of the hot spot relative to VLM pressor and depressor sites. The VRG was located by recording respiratory units and then 5-10 nl of 10 mM DLH were injected into the VRG at 200 mm interval from Bregma -12.1 to -13.3 mm. DLH produced site-specific changes in respiratory rate and mean arterial blood pressure (MAP). At rostral levels (Bregma -12.1 mm) PND rate decreased and MAP increased (-57 ± 11% and 9.4 ± 0.9%; N= 4-6). At more caudal levels these effects gradually reversed (cross-over point at -12.4 mm). Tachypneic responses were restricted between Bregma -12.5 and -13.1 mm with a sharp peak (88.7 ± 12.8% increase in rate) at -12.7 mm. The hot spot corresponded to where most pre-inspiratory neurons are found. It overlapped with VRG NK1R-ir cells but was more restricted than the distribution of these cells. Depressor responses were maximal at -12.7 mm and stable at more caudal levels. After unilateral ablation of the NK1R-ir cells (N=3) with a saporin-NK1R agonist conjugate, the DLH-induced tachypnea disappeared bilaterally. In conclusion, the tachypnea hot spot corresponds to the defined preBötC. It overlaps with the rostral end of the VLM depressor area and the NK1R-ir neurons of the preBötC may be responsible for DLH-induced tachypnea.

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Motooka Y, Kondoh T, Nomura T, Tamaki N, Nishizaki T (2001) Poster: Selective cholinergic denervation inhibits expression of long-term potentiation in the adult but not infant rat hippocampus. Neuroscience 2001 Abstracts 599.7. Society for Neuroscience, San Diego, CA.

Summary: The present study assessed the role of the cholinergic systems on the expression of perforant path long-term potentiation (LTP) in rat hippocampal slices from the infant and adult brain. To denervate the cholinergic systems, 192 1gG-saporin was injected into the lateral ventricle of the infant (2 weeks old) and adult (6 weeks old) rat brain. There, choline acetyltransferase immunoreactive fibers were little detectable two weeks and two months after injection for both the groups. For the infant rats, perforant path LTP was not affected by selective cholinergic denervation; the probability of LTP development was 0.83 (5/six slices) and 0.78 (7/nine slices) at 2 weeks and 2 months later in 192 IgG-saporin-treated slices, as compared with 0.83 at each period in control saline-treated slices. In contrast, the expression of the LTP was blocked by selective cholinergic denervation for the adult rats; the probability of LTP development was 0 (0/ten slices) and 0.38 (3/eight slices) at 2 weeks and 2 months later in 192 IgG-saporin-treated slices, as compared with 0.8 (8/ten slices) and 0.83 (5/six slices) at each period in control saline-treated slices. The results of the present study thus suggest that the cholinergic systems play a crucial role in the expression of LTP in the adult brain and that the denervated systems in the infant brain could be compensated by the sprouting of non-cholinergic fibers.

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