sfn2000

Han JS, Bizon JL, Chun HJ, Maus CE, Gallagher M (2000) Feedback HPA axis to stress is impaired in rats with selective removal of hippocampal cholinergic input. Neuroscience 2000 Abstracts 388.16. Society for Neuroscience, New Orleans, LA.

Summary: Activation of intracellular glucocorticoid receptors (GRs) may play a permissive role in mechanisms that lead to degeneration of hippocampal neurons in pathological conditions such as Alzheimer’s disease (AD). A previous study demonstrated that loss of cholinergic input from cells in the basal forebrain, a prominent feature of AD, reduced glucocorticoid receptor mRNA expression in the hippocampus in rats (Bizon et al., 1999). This experiment was conducted to see if reduced GRs after loss of cholinergic input would impair the function of the HPA axis in response to acute restraint stress. The cholinergic lesion was made by microinjections of the immunotoxin 192-IgG-saporin into the medial septal area and the vertical limb of the diagonal band. About 2 weeks later, rats were prepared with intravenous silastic catheters in the right jugular vein. After 5 days recovery, restraint stress for 1 hr was performed at 9:00 (a.m.). Blood (∼|50ul) was sampled repeatedly via the jugular catheter immediately (0 min) and at various times following the termination of the stressor (1 hr, 2 hr, 4 hr). For each group, negative feedback after a peak response to restraint was evident as a general trend of decreasing corticosterone that approached basal values by four hours after the cessation of stress. However, the speed of recovery to baseline differed between groups. Rats with loss of cholinergic input had higher corticosterone concentrations for a longer period after restraint stress than control rats, reflecting a diminished negative feedback function. These results suggest a mechanism whereby loss of basal forebrain cholinergic neurons in AD could contribute to a dysregulation of the HPA axis and more protracted exposure to high amounts of glucocorticoids. As an extension of the glucocorticoid cascade hypothesis, glucocorticoids might then be a factor in endangering hippocampal neurons in this disease.

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

Jasmin L, Arsenault P, Ohara PT, Marchand S (2000) Chronic noradrenergic spinal denervation in rats does not produce long-term hyperalgesia. Neuroscience 2000 Abstracts 243.7. Society for Neuroscience, New Orleans, LA.

Summary: Pharmacological studies have established that noradrenaline tonically inhibits spinal nociceptive transmission. We tested the hypothesis that chronically decreasing spinal noradrenaline would result in a disinhibition of nociceptive afferents resulting in behavioral hyperalgesia. We destroyed noradrenergic cells innervating the spinal cord using dopamine beta-hydroxylase antibodies linked to the neurotoxin saporin (anti-DBH-Sap). Male rats (n=6) were injected intrathecally with 4µg/10µl of anti-DBH-Sap, and their responses to nociceptive and non-nociceptive stimuli was monitored over a period of 65 days. Compared to controls (n=6), a significant (p< 0.05) decrease to hot plate (46oC) nociceptive responses could be observed during the first week post-treatment, but no differences were found at later times. At no point was there any altered response to innocuous stimuli. When tested for response to cold water stress, both treated and control animals showed analgesia, demonstrating that descending pain inhibition could still be activated. At 65 days, a formalin test showed no difference between treated (1.1 +/-0.5) and control (0.8 +/-0.5) groups. Post-mortem immunostaining of spinal cords for DBH, however, confirmed that noradrenergic denervation of the spinal cord had occurred in treated animals. These results suggest that a reorganization of the spinal cord following noradrenergic denervation is sufficient to reestablish normal nociceptive responses.

Related Products: Anti-DBH-SAP (Cat. #IT-03)

Miller SA, Lappi DA, Wiley RG (2000) Intrathecal dermorphin-saporin decreases morphine effect in hotplate algesia testing. Neuroscience 2000 Abstracts 212.8. Society for Neuroscience, New Orleans, LA.

Summary: The targeted cytotoxin, dermorphin-saporin, selectively destroys cells expressing MOR. In the present study, we gave dermorphin-saporin by lumbar i.t. injection and sought to determine if destroying dorsal horn neurons expressing MOR would alter thermal sensitivity and/or response to systemic morphine (MS) using hotplate testing under various conditions. 16 male Sprague-Dawley rats were tested on constant temperature (0.3, 44 and 47 C) and incremental (0.1 C/sec from 28 to 57 C) hotplates. Then 8 rats received lumbar intrathecal injections of derm-sap (465 ng) and 8 received vehicle using a subarachnoid PE-10 catheter that was removed 10 mins after injection. Retesting rats after toxin/vehicle injection showed no change in responses to any of the hotplate conditions. However, vehicle but not derm-sap rats showed increased lick latency on the incremental hotplate 20 mins after MS, 2.5 mg/kg, s.c. At 5 mg/kg of MS, vehicle and dermorphin-saporin rats showed identical responses. Capsaicin cream (0.94%) applied to the plantar surface of both hindpaws 3 hrs before testing on the 44 C hotplate produced decreased lick latencies in both groups of rats. MS, 5 mg/kg, s.c., produced increased lick latencies in capsaicin treated vehicle but not derm-sap rats. At 10 mg/kg, MS produced identical effects in capsaicin treated vehicle and toxin rats. These results indicate that i.t. derm-sap produced no change in baseline thermal sensitivity but did diminish the effect of low dose MS under conditions that preferentially test C nociceptor function suggesting that MOR-expressing dorsal horn neurons play a role in the analgesic action of low dose MS.

Related Products: Dermorphin-SAP / MOR-SAP (Cat. #IT-12)

Vierck CJ, Belford PM, Iqbal MA, Camara C, Kline RH, Lappi DA, Wiley RG (2000) Altered operant and reflex responses to noxious heat in rats with central noradrenergic lesions using antiDßH-saporin. Neuroscience 2000 Abstracts 247.10. Society for Neuroscience, New Orleans, LA.

Summary: We sought to determine effects of a selective lesion of pontine NA neurons on thermal sensitivity, using an operant escape task and hotplate tests. 8 rats received ICV injections of 10 ìg of anti-DβH-saporin, an immunotoxin that selectively destroys NA neurons, or vehicle. The rats were trained to escape a dark chamber with a hot floor to a brightly lit room-temperature shelf. There was no difference between groups at 39o, 44oor 47o C. However, at 44o C, application of mustard oil to the dorsal surface of both hindpaws or 0.94% capsaicin cream to the plantar surfaces increased escape durations only for vehicle rats. Also, at 44o C, toxin-treated rats were more sensitive than vehicle rats to morphine (0.5-5 mg/kg, s.c.) and clonidine (0.125 mg/kg, s.c.). The toxin-injected rats were insensitive to yohimbine (2.5 and 5 mg/kg, s.c.). Postmortem analysis for DβH showed that toxin-treated rats lost all pontine NA neurons, with preservation of medullary NA cells. To determine the role of NA projections to the spinal cord, two groups of rats were injected with 200-300 ng of antiDβH-saporin or vehicle via a lumbar intrathecal catheter. There were no consistent changes in baseline responses, and no differences between toxin and vehicle injected rats to 44o C after capsaicin or morphine (2.5 mg/kg, s.c.). However, the toxin treated rats were more sensitive to clonidine (0.03 mg/kg, s.c.). Thus, spinally projecting NA neurons appear not to mediate some modulatory effects of pontine NA neurons on nociception.

Related Products: Anti-DBH-SAP (Cat. #IT-03)

Easton A, Ridley RM, Baker HF, Gaffan D (2000) Crossed unilateral lesions of the cholinergic basal forebrain (by me20.4IgG-saporin) and fornix from inferior temporal cortex produce severe learning impairments in rhesus monkeys. Neuroscience 2000 Abstracts 205.8. Society for Neuroscience, New Orleans, LA.

Summary: Section of the anterior temporal stem, amygdala and fornix in monkeys results in a dense anterograde amnesia. We have proposed that this impairment is a result of isolating the medial temporal lobe and inferior temporal cortex from their basal forebrain afferents. Evidence suggests that the cholinergic cells of the basal forebrain are important for learning and memory. In the present experiment we have made an immunotoxic unilateral lesion (ME20.4IgG-saporin), specific for the cholinergic cells of the basal forebrain, in combination with unilateral fornix damage in the same hemisphere, and a lesion of the inferior temporal cortex in the opposite hemisphere to disconnect these cholinergic cells from the medial temporal lobe and inferior temporal cortex. These monkeys were severely impaired at scene learning and concurrent visual discrimination learning, both of which are sensitive to sections of the anterior temporal stem, amygdala and fornix. This deficit is strongly correlated with the degree of acetylcholine loss in the basal forebrain in the hemisphere with the immunotoxic lesion. This result strengthens the proposal that the cholinergic cells of the basal forebrain are essential for new learning, and that their interaction with the medial temporal lobe and inferior temporal cortex is required for normal learning in monkey and man.

Related Products: ME20.4-SAP (Cat. #IT-15)

Schreihofer AM, Stornetta RL, Guyenet PG (2000) Regulation of sympathetic vasomotor tone and arterial pressure by the rostral ventrolateral medulla after elimination of C1 neurons in rat. Neuroscience 2000 Abstracts 310.7. Society for Neuroscience, New Orleans, LA.

Summary: The rostral ventrolateral medulla (RVLM) tonically stimulates sympathetic preganglionic neurons to maintain arterial pressure (AP). Although the C1 neurons in the RVLM may have a sympathoexcitatory function, it is not known whether they are the essential presympathetic RVLM neurons. In the present study, we selectively destroyed spinally projecting C1 cells (∼84%) with bilateral microinjections (spinal segments T2-T3) of an anti-dopamine-betahydroxylase antibody conjugated to saporin (anti-DβH-SAP). 3-5 weeks later these rats had a normal AP and splanchnic nerve activity (SNA) under chloralose anesthesia. Extracellular recording and juxtacellular labeling of bulbospinal barosensitive neurons in RVLM revealed that after anti-DβH-SAP only the lightly myelinated RVLM neurons with no or very low levels of tyrosine hydroxylase immunoreactivity were preserved. In these rats, inhibition of RVLM (muscimol 100 pmol/100 nl/side) eliminated SNA and decreased AP as seen in control rats. However, treatment with anti-DβHSAP reduced the sympathoexcitatory and pressor responses to electrical stimulation in RVLM. Although treatment with anti-DβH-SAP also eliminated A5 noradrenergic cells, rats with selective lesions of A5 cells (local microinjection of 6-hydroxydopamine) displayed no deficits to stimulation of the RVLM. These data suggest basal sympathetic vasomotor tone relies primarily on non-catecholaminergic presympathetic cells in the RVLM. In contrast, bulbospinal adrenergic neurons are important for the increased SNA and AP produced by stimulation of the RVLM.

Related Products: Anti-DBH-SAP (Cat. #IT-03)

Gunhan-Agar E, Choudary P, Landerholm TE, Chalupa LM (2000) Depletion of cholinergic amacrine cells does not perturb the segregation of on and off cone bipolar cell projections. Neuroscience 2000 Abstracts 119.3. Society for Neuroscience, New Orleans, LA.

Summary: The pathways signaling onset and offset of light are segregated in the retina with On-cone and Off-cone bipolar cells terminating on the stratified dendrites of On and Off retinal ganglion cells (RGCs). During development the axons of On and Off cone bipolar cells form two strata in the IPL in a remarkably precise manner, without any obvious refinements. Moreover, such a precise ingrowth pattern occurs even after RGCs have been depleted (J. Neurosci., 2000, 201:306-314). Here we show by immunostaining that two bands of cholinergic processes are present in the rat retina as early as P1, some 7 days before the formation of segregated bipolar inputs. Double labeling of retinal sections with the antibody to recoverin (that recognizes On and Off cone bipolar cells) and the antibody for VACHT (which labels cholinergic processes) revealed that the segregated terminals of cone bipolar cells are juxtaposed with the two bands of cholinergic fibers. These observations suggested that the cholinergic fibers could serve as a scaffold for the later ingrowing bipolar cell axons. To test this hypothesis, we devised a novel method for depleting retinal cholinergic amacrine cells with a VACHT-saporin immunotoxin. A single treatment of the developing retina with this immunotoxin was found to eliminate virtually all cholinergic cells and processes. Recoverin labeling of bipolar cells showed that the axons of these neurons still form two stratified terminal bands within the IPL. Thus, neither RGCs nor cholinergic amacrine cell processes are required for the formation of segregated ON and Off cone bipolar cell projections.

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Bitner RS, Nikkel AL, Decker MW (2000) Immunohistochemical detection of alpha-7 nicotinic receptor expression by two distinct cell types in the dorsal raphe and locus coeruleus of rat. Neuroscience 2000 Abstracts 41.7. Society for Neuroscience, New Orleans, LA.

Summary: The α7 nicotinic acetylcholine receptor (nAChR) subunit can be assembled to form a homomeric-pentamer with high permeability to calcium, in contrast to other neuronal nAChR subunit-comprised ligand-gated cation channels. Although the expression of the α7-nAChR has been demonstrated throughout the CNS, the neurochemical phenotype of neurons expressing α7 remains to a large extent unknown. Using a polyclonal antibody raised against the carboxyl terminus (amino acids 460-479) of the α7 nAChR subunit (goat IgG, Santa Cruz Biotech.), immunohistochemical staining was observed in rat dorsal raphe (DR) and locus coeruleus (LC), serotonergic and noradrenergic brainstem nuclei, respectively. In both the DR and LC, there appeared to be two histologically distinct α7-expressing cell types as distinguished by size, i.e. large vs. small diameter. In rats treated with either a selective serotonergic (5,7-dihydroxytryptamine 150 μg i.c.v.) or noradrenergic (anti-dopamine-β-hydroxylase saporin 5 μg i.c.v.) neurotoxin, α7 immunostaining was seen only in small diameter cells, suggesting that the large diameter α7-expressing cells were serotonergic DR and noradrenergic LC neurons. Indeed, double-labeling experiments revealed in the large, but not small, cell types coexpression of α7 with tryptophan hydroxylase in the DR and tyrosine hydroxylase in the LC of saline-treated rats. In contrast, there was no coexpression in the neurotoxin-treated rats due to the loss of serotonergic or noradrenergic neurons, with only small diameter α7-expressing cells remaining. The results of these studies suggest that both serotonergic and noradrenegic neurons express α7 nAChRs. In addition, there appears to be a small diameter, non-serotonergic/noradrenergic cell-type in both the DR and LC that also expresses α7.

Related Products: Anti-DBH-SAP (Cat. #IT-03)

Rahimi O, Tatham D, Juliano SL (2000) Sensory training improves the ability to process stimuli in barrel cortex after basal forebrain lesion. Neuroscience 2000 Abstracts 51.22. Society for Neuroscience, New Orleans, LA.

Summary: Lesions of the basal forebrain deplete the cerebral cortex of acetylcholine and result in decreased ability to process stimuli. Using a model of unilateral basal forebrain lesion (BFL), we previously determined that the ability to perceive simple touch to the whiskers is impaired after BFL, but improves over time. Functional responses in barrel cortex, however, as measured by 2-deoxyglucose uptake (2DG) or electrophysiological recordings, remain reduced even after long survival times. We questioned whether the impaired cortical responses could be improved with behavioral training involving sensory discrimination using the whiskers. To do this, one group of rats was trained to discriminate between different textures using the whiskers on one side of the face, which projected to the lesioned hemisphere. After learning the task, this group of rats received a BFL using the immunotoxin, 192-IgG Saporin. They then continued the sensory discrimination task for at least 2 months. The second group of rats received a BFL, but no sensory training. They survived after the lesion for comparable periods of time; each rat of both groups then underwent a 2DG experiment. During the 2DG study, 1-4 matched sets of whiskers on both sides of the face were stimulated using an electromagnetic device. The magnitude of the response was measured in barrel cortex by preparing 2-dimensional maps of the label evoked by whisker stimulation. The area of barrel cortex activated in each hemisphere by whisker stimulation was measured and expressed as a ratio of the lesioned to normal hemisphere. We found that the evoked response in the lesioned hemisphere remained diminished compared to the normal side regardless of training. When the magnitude of response was compared between the trained and untrained group, however, the area of 2DG uptake in each barrel in response to stimulation was significantly increased in the animals receiving sensory discrimination training. These findings suggest that sensory training plays a role in improving cortical responses to stimulation after lesion of the basal forebrain.

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

Daniels D, Miselis RR, Flanagan-Cato LM (2000) Local immunotoxin treatment prevents transneuronal labeling of the intermediolateral column; but not the ventral horn; of the spinal cord after tracer injection into lumbar epaxial muscle. Neuroscience 2000 Abstracts 77.13. Society for Neuroscience, New Orleans, LA.

Summary: Pseudorabies virus (PRV) has been used as a transneuronal tracer to study central neural circuits that control various peripheral targets. Our laboratory has injected PRV into the lumbar epaxial muscles that produce the lordosis posture to label sequentially specific brain regions along the neuraxis. However, concomitant uptake of PRV through sympathetic innervation of nearby vasculature has made the interpretation of higher-order labeling problematic. To avoid this confound, we have designed a procedure for focal sympathetic denervation using dopamine-β-hydroxylase immunotoxin (DHIT). Five days after injecting DHIT (5 μg) into the medial portion of lateral longissimus, the Bartha strain of PRV was injected into the pre-treated area. After survival times of 72 or 96 h, animals were sacrificed and the spinal cords were immunostained for PRV. In preliminary studies, DHIT treatment was not effective in all animals, as determined by PRV labeling in the sympathetic preganglionic neurons that reside in IML. However, at each survival time, in 50% of the animals DHIT virtually eliminated PRV-labeling in cells within IML of the thoracic and lumbar spinal cord, whereas robust labeling of motoneurons in the ventral horn was retained. These preliminary results suggest that this procedure for local sympathectomy may allow for selective transneuronal labeling of somatic motor pathways.

Related Products: Anti-DBH-SAP (Cat. #IT-03)