sfn2002

Wang H, Guyenet PG (2002) Neurokinin-1 receptor immunoreactive (NK1R-ir) neurons control caudal ventrolateral medulla (VLM) gabaergic depressor neurons. Neuroscience 2002 Abstracts 862.4. Society for Neuroscience, Orlando, FL.

Summary: Depressor responses to injection of DL-homocysteic acid (DLH) into the caudal VLM are attenuated after selective unilateral lesion of the NK1R-ir cells of the VLM with a saporin-NK1R agonist conjugate (SSP-SAP)(Wang et al., J. Neurosci 2002). Here we tested whether SSP-SAP treatment destroys caudal VLM depressor GABAergic neurons thereby causing loss of DLH-induced sympathoinhibition. Two weeks after unilateral lesion of VLM NK1R-ir cells (97% reduction without loss of catecholaminergic neurons), DLH (5-10 nl, 10mM) was injected into multiple regions of the caudal and rostral VLM on both sides of the brain. The decrease in BP and sympathetic tone (SND) caused by DLH injections into caudal VLM were blunted on the lesioned side vs the intact side (p<.05, N = 7). The rise in BP and SND caused by DLH injection into rostral VLM were normal on both sides. To determine if the GABAergic barosensitive cells of the caudal VLM express NK1R, conscious rats were infused with L-phenylephrine (PE) (7μg/min, for 25 min) or saline. PE infusion raised BP by 25% and decreased HR 27% (mean; N= 4). Saline infusion produced no effect. Fos-ir neurons were mapped throughout the VLM. The caudal VLM of PE-treated rats contained many more Fos-ir cells than that of the saline controls (128.7 ± 4.2 vs. 18.7 ± 1.6, N= 4). Caudal VLM Fos-ir neurons were not NK1R-ir in either group of rats. In conclusion, the baroreceptor-activated GABAergic neurons of the caudal VLM are not NK1R-ir. The data suggests that NK1R-ir cells might provide an excitatory drive to the caudal VLM barosensitive neurons (HL 28785 to PGG).

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Nagle RA, Liberatore MA, Zombon NJ, Pokala VN, Li PK, Pokala VN, Johnson DA (2002) Effect of selective cholinergic lesioning of basal forebrain with 192 IgG-saporin on neurotransmitter concentrations in hippocampus of rat. Neuroscience 2002 Abstracts 880.6. Society for Neuroscience, Orlando, FL.

Summary: In vivo microdialysis techniques were used to examine the effects of lesioning of cholinergic neurons of the medial septum using the selective cholinergic neurotoxin 192-IgG-Saporin (SAP), on hippocampal acetylcholine (ACh), glutamate and GABA in adult male Sprague Dawley rats. High and low (1.0 and 0.22 μg) doses of SAP were used for infusion into the basal forebrain. SAP treated rats showed a significant dose dependent decrease of 74% and 59% in ACh for the high and low doses respectively, compared to controls. Glutamate decreased 50% in animals treated with 0.22 μg SAP. The data suggest that lesioning of basal forebrain neurons with SAP results in changes in neurotransmitter concentrations in the hippocampus.

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Watts AG, Sanchez-Watts G, Dinh TT, Ritter S (2002) Immunotoxic lesions of ascending catechoalminergic afferents abolish the CRH gene transcriptional response to 2-deoxyglucose in the rat paraventricular nucleus. Neuroscience 2002 Abstracts 865.2. Society for Neuroscience, Orlando, FL.

Summary: CRH neurons in the medial parvicellular (mp) part of the paraventricular nucleus (PVH) are critical for the neural control of the hypothalamo-pituitary-adrenal axis. One of their most prominent afferents sets derives from hindbrain catecholaminergic neurons that are thought to help mediate viscerosensory influences on the PVHmp. Despite the prominence of this input, its precise role in controlling CRH neuronal function remains controversial. Here we report the effect on basal and stimulated CRH gene expression of an immunotoxin that selectively destroys catecholaminergic neurons. Rats were injected in the PVH with either a saporin-anti-dopamine B-hydroxylase (DBH) conjugate (DSAP), which leads to total loss of DBH immunoreactivity in the PVH, or saporin alone (SAP), which does not. Three weeks later, animals were injected either with 250mg/kg of 2-deoxy-D-glucose (2DG) or vehicle. Thirty mins later they were anesthetized and perfused with 4% buffered paraformaldehyde. Fifteen um frozen sections were cut through the hypothalamus and hybridized for CRH mRNA, CRH hnRNA, or c-fos mRNA. DSAP treatment had no effect on CRH mRNA levels in the PVH of vehicle- or 2DG-injected animals, but abolished the CRH hnRNA and c-fos mRNA responses to 2DG. We have reported elsewhere that DSAP lesions selectively abolish the corticosterone response to 2DG, but not to swim stress, or circadian corticosterone release. We now show that catecholaminergic afferents are required for 2DG-induced CRH gene expression, but not for basal expression.

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Ritter S, Dinh TT, Pedrow C, Roellich K (2002) Immunotoxic lesion of catecholamine afferents to paraventricular hypothalamus (PVH) impairs the corticosterone response to glucoprivation but not the basal secretory rhythm or response to swim stress. Neuroscience 2002 Abstracts 865.4. Society for Neuroscience, Orlando, FL.

Summary: Catecholamine afferents from the hindbrain densely innervate the medial parvicellular part of the PVH, which contains CRH neurons critical for control of corticosterone (CORT) secretion. However, the precise role of these afferents in control of CORT secretion is unclear. Here the immunotoxin, saporin conjugated to anti-dopamine B-hydroxylase(DSAP), which selectively lesions norepinephrine and epinephrine neurons, or unconjugated saporin (SAP) control solution, was microinjected into the PVH. After extensive habituation to testing conditions, DSAP and SAP rats were injected with 2-deoxy-D-glucose (2DG, 250mg/kg) or vehicle or subjected to a 5-min forced swim. Blood was sampled remotely between 0 and 240 min for radioimmunoassay of CORT. In a third test, blood was sampled every 4 hr for 24 hr to assess the basal secretory rhythm of CORT. Subsequently, loss of dopamine B-hydroxylase containing terminals without destruction of CRH neurons in the PVH of DSAP rats was confirmed by immunohistochemistry. In DSAP rats, the CORT response to 2DG was reduced dramatically to 29% of the response in SAP controls. In contrast, DSAP and SAP rats did not differ in their basal secretory rhythm or their CORT response to swim stress, indicating for the first time a stimulus-specific role of catecholamine afferents in control of CORT secretion. This finding is complemented by other work in which we (with A.G. Watts and G. Sanchez-Watts) show that these catecholamine afferents are required for 2DG-induced CRH gene expression, but not basal expression.

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McGaughy JA, Rubin S, Stollstorff M, Baxter MG, Eichenbaum HB (2002) 192 IgG-saporin-induced cortical, cholinergic deafferentation in rats produces a dissociation in the function of prelimbic/infralimbic and orbitofrontal cortex in an attentional set-shifting task. Neuroscience 2002 Abstracts 674.4. Society for Neuroscience, Orlando, FL.

Summary: Converging data support the hypothesis that cholinergic afferents to the cortex mediate attentional processes. Rats with selective cholinergic lesions of the nucleus basalis magnocellularis produced by 192 IgG-saporin (SAP) show deficits in attentional performance. These deficits are highly correlated with diminished cholinergic efflux in the infralimbic/prelimbic (IL/PL) cortex during attentional testing. Excitotoxic lesions of the IL/PL in rats trained in an attentional set-shifting task did not impair the initial discimination, a novel discrimination with the previously relevant dimension (intradimensional shift; IDS) or reversal learning, but did impair the ability to shift attention to the previously irrelevant stimulus dimension (extradimensional shifting; EDS). It is not known from the previous study whether the loss of cortical, cholinergic afferents alone would be sufficient to produce the EDS deficit. Consequently, infusions of SAP(0.01 μg/μl; 0.25 μl) were made into either the IL/PL or the orbitofrontal (OF) cortex. Rats were then trained in the same attentional set-shifting task. Subjects had to discriminate between stimuli based on one of two perceptual dimensions, odor or digging media with both dimensions present on all trials. Preliminary analyses show that neither OF nor IL/PL lesions impair the initial discrimination or the IDS. However, IL/PL lesions impair the EDS whereas OF lesions impair reversal learning. These data support dissociable roles of cholinergic afferents to OF and IL/PL in attentional set-shifting.

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

Sarter MF, Draut A, Herzog CD, Bruno JP (2002) Effects of septohippocampal cholinergic deafferentation on attention and learning. Neuroscience 2002 Abstracts 674.8. Society for Neuroscience, Orlando, FL.

Summary: In contrast to the extensively studied attentional functions mediated via basal forebrain corticopetal cholinergic projections, the role of septohippocampal cholinergic projections in attention and memory have remained poorly understood. For example, selective lesions of this system have limited, if any, effects on spatial memory performance. The present experiment initially tested the effects of intraseptal injections of the cholinergic neurotoxin 192-IgG saporin (SAP) on the performance of rats in an operant procedure designed to assess sustained attention. Despite almost complete hippocampal cholinergic deafferentation, the lesioned animals’ attentional performance remained identical to that of controls. Task parameter manipulations designed to further increase the demands on attentional processing also failed to reveal an effect of the lesions. However, lesioned animals were superior in acquiring a version of this task in which the propositional rules of the task were reversed. Lesioned rats achieved >65% hits after 14 training sessions, while intact rats did not reach this level of performance after 50 sessions of training. As the acquisition of the reversal of such extensively practiced response rules suffers from interference from the rather automatic processing of the original rules, loss of hippocampal cholinergic inputs may have reduced the interference that resulted from the processing of the original rules. Thus, hippocampal cholinergic inputs are speculated to modulate, but not to be necessary for, the recall of propositional rules. Collectively, the available data completely dissociate the functions of septo-hippocampal and corticopetal cholinergic projections.

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Harrell LE, Parsons DS, Conger K, Kolasa K (2002) ß1 adrenergic antagonist effect on brain muscarinic cholinergic receptors. Neuroscience 2002 Abstracts 685.13. Society for Neuroscience, Orlando, FL.

Summary: Degeneration of basal forebrain cholinergic system and sympathetic ingrowth appear to be pathologic changes in Alzheimer’s Disease (AD). An imbalance between these systems may mediate cognitive deficit in AD. To model this situation, 192-IgG-Saporin, a specific cholinergic immunotoxin, was infused intraventricularly to induce cholinergic denervation and sympathetic ingrowth into cortex and hippocampus. After 8 weeks of intraperitoneal injection of Metoprolol, β1 antagonist, at 2.5 mg/kg and 5 mg/kg, the Kd and Bmax of dorsal hippocampus (DH), anterior (AC) and entorhinal (EC) cortex was determined via [3H]-QNB, muscarinic antagonist, binding. Low dose Metoprolol increased Kd in the sympathetic ingrowth, cholinergic denervation, ganglionectomized groups compared to control and vehicle groups (p<.05). Affinity of AC=DH but was > than EC (p<.02). Bmax was greater in AC than DH (p<.05) > than EC (p<.02). Controls and ganglionectomized had > Bmax in AC and EC (p<.03). EC had > Bmax in control and ganglionectomized animals (p<.04). High dose Metoprolol induced a greater affinity in DH>AC>EC (p<.05). No effect was found on Bmax.The results of our study suggest that a β1 antagonist, which is used clinically, can alter the number and affinity of cholinergic receptors, which in turn could potentially alter the AD patients' response to cholinergic therapy.

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

Rudick CN, Gibbs RB, Woolley CS (2002) Estrogen-induced disinhibition of hippocampal CA1 pyramidal cells depends on basal forebrain cholinergic neurons. Neuroscience 2002 Abstracts 740.6. Society for Neuroscience, Orlando, FL.

Summary: Estrogen (E) increases dendritic spine and synapse density on hippocampal pyramidal cells, both in vivo and in vitro. In both cases, the increase in spine/synapse density is preceded by transient disinhibition. Based on in vitro studies, this transient disinhibition is likely to be involved in the mechanism of the subsequent increase in spine density. In adult female rats, where E increases spine/synapse density on CA1 pyramidal cells, it is unknown whether E acts within the hippocampus itself and/or through hippocampal afferents to regulate synaptic changes. Considerable evidence suggests that the basal forebrain (BF) cholinergic system could be involved in mediating E’s effects in the hippocampus. Therefore, we tested the ability of E to disinhibit CA1 pyramidal cells in adult female rats in which BF cholinergic neurons were eliminated by infusion of 192IgG-saporin toxin (SAP) into the medial septum. Two weeks after SAP or SHAM lesion, rats were ovariectomized and treated with E or oil (O) 3 days later. Synaptically evoked inhibitory postsynaptic currents (eIPSCs) and miniature IPSCs (mIPSCs) in CA1 pyramidal cells were evaluated 24h after E or O, the timepoint at which disinhibition occurs. As previously shown, E decreased eIPSC amplitude and mIPSC frequency at 24h. Additionally, E-induced disinhibition was significantly reduced in SAP lesioned rats, but it was not completely blocked. These data demonstrate that the BF cholinergic system is involved in E-induced disinhibition of CA1 pyramidal cells, but that other cells may also be involved.

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Sherren N, Pappas BA (2002) Neonatal dopamine lesions: Cognitive impairment or hyper-sensitivity to stress. Neuroscience 2002 Abstracts 782.19. Society for Neuroscience, Orlando, FL.

Summary: Neonatal rat pups given a selective cholinergic immunotoxin exhibit large reductions in cortical (30-70%) and hippocampal (75%) choline acetyltransferase (ChAT) activity which persist into adulthood. However these rats do not show spatial learning deficits in the Morris water maze despite the sensitivity of this task to muscarinic receptor blockade and hippocampal damage. We hypothesized that while the developing brain may be able to compensate for early loss of ACh transmission, it may also become more vulnerable to additional disruptions in other systems. We combined postnatal day 7 i.c.v. administration of 192 IgG-saporin with 6-hydroxydopamine (6-OHDA) to lesion either or both ACh and DA terminals respectively. 6-OHDA treatment produced a 90% loss in striatal and a 75% loss in frontocortical DA levels. No differences in exploratory behaviour were found between ACh, DA and ACh/DA lesioned rats. However upon placement in the Morris water maze, DA depleted rats displayed behaviour suggestive of panic and were unable to search for the hidden platform effectively. In order to determine whether the DA depletion was producing a spatial learning deficit or an exaggerated reaction to a stressor (the hidden platform task), a separate cohort of lesioned rats was tested in the cued platform version of the maze. Just prior to testing, the rats received 4 days of shaping in order to gradually habituate them to the pool and teach them the task. Platform location improved in half of the DA and ACh/DA rats, but never approached control or ACh only levels. Thus rats with neonatal DA lesions may be particularly sensitive to stressful tasks. This sensitivity may be partly dependent on lesion extent.

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Fraley GS (2002) Role of hindbrain catecholaminergic afferents to the medial hypothalamus in the regulation of penile reflexes in the rat. Neuroscience 2002 Abstracts 681.4. Society for Neuroscience, Orlando, FL.

Summary: The use of ex copula erections, or reflexive erections, has been used for decades in the study of the central pathways and neuroendocrinology of penile erections. However, the exact neuroendocrine pathways involved in developing penile erections are not known. This study utilized molecular neurosurgical techniques combined with behavioral, histological, and molecular analyses to determine a central link between metabolic state and penis erectile function. Utilizing saporin-conugate immunolesion techniques (DSAP), hindbrain catecholaminergic afferents to the hypothalamus that are reported to be glucoresponsive were eliminated. DSAP-lesioned rats had a significantly attenuated glucoprivic feeding response and significantly attenuated penile reflexes compared to controls. Analysis of Nissl-stained spinal cord sections demonstrated a significant reduction in the size of sexually dimorphic motoneurons. Furthermore, qualitative analysis of calcitonin gene-related immunoreactivity (CGRPir) in alternate spinal sections revealed a decrease in CGRPir in sexually dimorphic motor pools. Analysis of hypothalamic mRNA levels showed a significant increase in both oxytocin and neuropeptide Y mRNA, but not b-actin mRNA. No significant differences were seen, however, in the weight of the perineal muscles, seminal vessicles, or in plasma testosterone levels. These data indicate a novel hindbrain-hypothalamic-spinal cord pathway by which potential glucoresponsive neurons effect the ability to achieve penile erection based upon availability of metabolic fuel.

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