sfn2000

Siddiq MM, Tsirka SE (2000) Elimination of microglia suggests their involvement in neuronal plasticity. Neuroscience 2000 Abstracts 507.2. Society for Neuroscience, New Orleans, LA.

Summary: Reorganization of mossy fibers occurs in the mammalian hippocampus during consolidation of learning and memory. Induced low level seizures with kainic acid (KA) result in the development of new synapses and the reorganization of existing ones along the mossy fiber pathway. The serine protease tissue plasminogen activator (tPA) is expressed along the mossy fiber pathway and has been implicated in neurite remodeling after stimulation of neuronal activity. Both neurons and microglia secrete tPA. Microglial cells are thought to function only in pathological situations in the CNS, as they exhibit neurotoxic properties. However, a protective role has been observed in the regenerating optic nerve, where intervening activated microglia were involved in tissue remodeling. To investigate whether there is a role for microglia in mossy fiber remodeling, microglia were eliminated in C57/BL6 mice by immunolesioning. The reorganization of mossy fibers was evaluated. Kainate-injected wild-type mice had pronounced mossy fiber reorganization in the dentate gyrus of the hippocampal formation as detected by Timm staining, while the immunolesioned mice had significantly less and shorter mossy fibers. It is therefore suggested that activated microglia may play a role in active remodeling of mossy fibers in the hippocampus after KA-induced seizures.

Related Products: Mac-1-SAP mouse/human (Cat. #IT-06)

Mattsson A, Ögren SO, Olson L (2000) 192 IgG-saporin immunolesioning causes marked facilitation of dopamine-mediated locomotor activity in adult rats. Neuroscience 2000 Abstracts 563.7. Society for Neuroscience, New Orleans, LA.

Summary: Recent studies have indicated a possible link between changes in cholinergic mechanisms and schizophrenia. However there is limited information regarding the functional consequences of changes in ACh transmission on DA functions, which in turn are believed to be involved in schizophrenic symptoms. 192 IgG-saporin targets cells that express the low-affinity p75 neurotrophin receptor. Intracerebroventricular injection causes severe lesions of the cholinergic projections and may also damage Purkinje neurons. We have compared intracerebroventricular injections of 192 IgG SAP to adult rats (5 μg) with injections to neonate rats (0.4 μg day 4 or 0.4 μg day 4 + 0.8 μg day 13). As expected, treated adult rats are markedly impaired in the Morris swim maze both in terms of time to find the platform and in search behavior when the platform is removed, i.e. memory impairment. When tested as adults, neonatally treated animals were only modestly impaired. Interestingly, adult treated animals showed increased spontaneous motility and locomotion and markedly increased locomotor responses to amphetamine (1.5 mg/kg) as evidenced by increased rearing, motility and locomotion. These animals also responded to apomorphine (1 mg/kg) with an increased amount of rearing. There were no marked changes of locomotor activity in rats treated with 192 IgG SAP at 4 days or 4 and 13 days of age. Our results suggest that cholinergic denervation of the forebrain causes a marked enhancement of the behavior responses related to increased dopaminergic activity. However, it cannot be fully excluded that damage to non-cholinergic systems, e.g. Purkinje cells, might contribute to the effects. The striking overreaction to dopaminergic stimuli presumably caused by the cholinergic deficit is possibly relevant in relation to the role of cholinergic malfunctioning in schizophrenia.

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

De Rosa E, Hasselmo ME, Baxter MG (2000) Contribution of the cholinergic basal forebrain to proactive interference between stored odor memories during associative learning in rats: 192 IgG-saporin immunotoxic lesions. Neuroscience 2000 Abstracts 563.8. Society for Neuroscience, New Orleans, LA.

Summary: Previous electrophysiological studies and a computational model suggest that cholinergic neuromodulation may reduce olfactory associative interference during learning (Hasselmo & Bower, 1993; Hasselmo et al., 1992). Using a simultaneous discrimination task where rats were required to learn a baseline odor pair (A+B-) and then two novel odor pairs: A-C+ (with an overlapping component A) and D+E- (with no overlapping component), De Rosa & Hasselmo (2000) demonstrated that a 0.25 mg/kg systemic dose of scopolamine (SCOP) selectively increased proactive interference. Under the influence of SCOP, the rats were impaired on acquiring the odor pair AC and not the odor pair DE relative to their normal saline performance. To localize this effect male Sprague-Dawley rats, with bilateral selective cholinergic lesions of the horizontal limb of the diagonal band of Broca (HDB group) or of all of the cholinergic nuclei of the basal forebrain (BF group), were tested on our task. Neither lesion impaired normal acquisition of either odor pair relative to the sham-operated control rats. However, the BF group, but not the HDB and control groups, were sensitive to a lower dose of SCOP (0.125 mg/kg) than in the previous study: this dose selectively impaired the BF group on acquiring the odor pair AC and not the odor pair DE relative to their normal saline performance, suggesting that weaker cholinergic modulation after removing the majority of cholinergic neurons in the basal forebrain makes the system more sensitive to proactive interference during blockade of remaining cholinergic effects.

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

Rogers SD, Salak-Johnson JL, Schwei MJ, Pomonis JD, Mantyh PW (2000) Reduced anxiety related behavior following ablation of amygdala neurons expressing substance P receptor. Neuroscience 2000 Abstracts 571.2. Society for Neuroscience, New Orleans, LA.

Summary: The neurokinin substance P (SP) is localized in brain regions that coordinate stress response and may play a role in modulating anxiety. Effects of ablation of substance P receptor (SPR)-expressing neurons by administration of a substance P-toxin conjugate, substance P-saporin (SP-SAP), in the amygdala (a brain region known to modulate stress and anxiety responses) were examined immunohistochemically and behaviorally thirty days following SP-SAP treatments. Rats were bilaterally injected in basolateral amygdala nuclei with 5μl of sterile saline, 1 μM saporin (SAP), or 1 μM SP-SAP. SPR-immunofluoresence levels and number of SPR-IR positive neurons in amygdalar subnuclei decreased following SP-SAP treatment. SP-SAP did not induce significant gliosis or non-specific neuronal death. Interestingly, after SP-SAP treatment, the number of NPY-IR neurons were also decreased, and combined SPR and NPY immunofluorescence demonstrated a large number of NPY-IR neurons colocalize with SPR-IR neurons in the amygdala. Thirty days following SP-SAP treatment, rats were tested in elevated plus maze (EPM) and open field (OF). Anxiety level and exploratory behavior displayed by SP-SAP treated rats were altered; they had significantly more entries into and spent more time in EPM open arms than did saline- or SAP-injected rats. In the OF, SP-SAP treated rats spent less time frozen than saline or SAP treated rats. These results suggest that SPR expressing neurons in the amygdala plays a pivotal role in generation of anxiety behaviors and that SP may play a modulatory role in stress-induced anxiety behavior.

Related Products: SP-SAP (Cat. #IT-07)

Vulchanova L, Olson TH, Elde R, Honda CN (2000) Role of IB4-binding sensory neurons in the effects of intradermal capsaicin injection. Neuroscience 2000 Abstracts 212.7. Society for Neuroscience, New Orleans, LA.

Summary: We have shown previously that a unilateral injection of a conjugate of the lectin IB4 and the toxin saporin (IB4-SAP) into sciatic nerve of rats results in loss of IB4-binding neurons and transient increase in thermal and mechanical nociceptive thresholds. The thresholds were maximally increased 10 days post-treatment and returned to baseline levels by day 21. In the present study, we examined the responses of IB4-SAP treated rats after intradermal injection of capsaicin, which results in acute nocifensive behavior followed by thermal and mechanical hyperalgesia. The nocifensive behavior of IB4-SAP treated rats 10, 21 and 42 days post-treatment was 6%, 36% and 47%, respectively, of the behavior of control treated rats. IB4-SAP treated rats injected with capsaicin did not develop thermal or mechanical hyperalgesia at any of the time points examined. These results suggest that the increase in thermal nociceptive thresholds after IB4-SAP treatment is due to loss of VR1-expressing IB4-binding neurons since the nocifensive behavior is most likely mediated by the capsaicin receptor VR1, which also transduces noxious thermal stimuli. In addition, VR1 in surviving neurons may contribute to the recovery of thermal nociceptive thresholds. Finally, our results suggest that IB4-binding neurons are required for development of capsaicin-mediated hyperalgesia, and that the recovery of the responsiveness of IB4-SAP treated rats to noxious stimuli under normal conditions is not accompanied by recovery of the mechanisms underlying hyperalgesia.

Related Products: IB4-SAP (Cat. #IT-10)

Martin JL, Sloviter RS (2000) Focal hippocampal hyperexcitability after focal interneuron ablation in the rat by substance P-saporin. Neuroscience 2000 Abstracts 389.13. Society for Neuroscience, New Orleans, LA.

Summary: Hyperexcitability after prolonged seizures or head trauma may result from interneuron malfunction or loss; but a causal relationship is in doubt because global insults produce widespread brain damage and other effects. We have therefore sought to destroy interneurons selectively using stable Substance P-saporin (SSPsap; ATS); a neurotoxin internalized by SP receptor (SPR)-expressing neurons. Improved immunofluorescent methods revealed that most GABA-; parvalbumin (PV)-; and somatostatin (SS)-positive (+) cells of all hippocampal regions (dentate gyrus and areas CA1-CA3) are SPR+; but that granule cells; mossy cells; and CA1-3 pyramidal cells are not. Intrahippocampal injections of SSPsap or vehicle were made under urethane anesthesia in 3 sites (20nl/site) of the dorsal hippocampus of 6 male Sprague-Dawley rats/group. After 5-90 days; rats were blindly evaluated in two sites for CA1 pyramidal cell and dentate granule cell responses to perforant path stimulation (PPS). SSPsap-treated rats exhibited relatively normal responses in some sites; but pathophysiology at other sites that was virtually identical to that seen after prolonged PPS or kainate (multiple population spikes and paired-pulse disinhibition in response to 0.1-2.0Hz perforant path (PP) stimuli). Abnormal responses were observed at the earliest time tested (5 days); and at 90 days. Anatomical analysis revealed selective loss of SPR+; PV+; SS+; and GABA+ neurons; and survival of principal cells and extrinsic afferents. Importantly; “epileptic” pathophysiology was observed exclusively in areas of interneuron loss. These data indicate that the pathophysiology produced by status epilepticus or head trauma can be replicated focally by selective interneuron loss alone; and provide the first direct evidence that highly focal interneuron loss per se is capable of replicating “epileptic” disinhibition and hyperexcitability. In addition; the pathophysiology is restricted to the region of the affected interneuron somata; suggesting a highly localized influence of inhibitory interneurons. Supported by: NIH grant NS18201.

Related Products: SSP-SAP (Cat. #IT-11)

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

Petruska JC, Johnson RD (2000) Differential input to a nociceptive specific reflex by trka-positive and trka-negative small diameter DRG afferents. Neuroscience 2000 Abstracts 354.7. Society for Neuroscience, New Orleans, LA.

Summary: The cutaneus trunci muscle (CTM) reflex is a nociceptive specific reflex in the rat. We examined whether particular subtypes of afferents may be differentially involved in the reflex. In particular, we wanted to determine if there were differences in input to the reflex between those expressing trkA receptors, and those lacking trkA receptors. We approached this question with two techniques. The selective neurotoxin 192-saporin was injected into the left T13 DRG to destroy the p75 receptor-bearing neurons. Two to three weeks following injection, the ability of the injected DRG to elicit the CTM reflex was examined in contrast to uninjected DRG. The ganglia were also retrieved for histochemical examination. In all cases where histochemical examination revealed a clear depletion of the neurotrophin-bearing neurons the injected DRG lacked the ability to induce the CTM reflex. Histochemical markers for the trkA-negative small diameter afferents appeared normal in all cases. The second approach utilized the trans-synaptic neuronal tracer pseudorabies virus (PRV). PRV was injected into the CTM to generate a retrograde tracing of the reflex circuit, including the afferents involved. This resulted in specific labelling of many small diameter DRG neurons, the vast majority of which expressed trkA. The CTM reflex may therefore not be a suitable monitor for inputs from the trkA-negative small diameter afferents, especially as regards its use in collateral sprouting experiments. These data indicate that inputs from the two populations of afferents are likely processed differently.

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

Vogt LJ, Sim-Selley LJ, Childers SR, Wiley RG, Vogt BA (2000) Distribution of mu-opioid receptors and activated G-proteins in rat cingulate cortex and alterations following removal of noradrenergic afferents. Neuroscience 2000 Abstracts 238.1. Society for Neuroscience, New Orleans, LA.

Summary: Anterior cingulate cortex (ACC) is involved in acute and chronic pain processing. Here we define opioid architecture throughout rat cingulate cortex, relate mu-opioid receptor and G-protein stimulated binding in particular layers, and localize binding to noradrenergic terminals with immunotoxin lesions (anti-DBH-saporin). [3H]DAMGO binding was highest in areas 32 and 24 with a peak in layer I. Midcingulate area 24′ and posterior area 29 had lower and homogeneous binding. DAMGO stimulated [35S]GTPγS binding in area 24′ was similar to that in areas 32 and 24, while area 29 had very low and homogeneous binding. Undercut lesions reduced [3H]DAMGO binding in all layers with greatest loss in layer I, while DAMGO-stimulated [35S]GTPγS binding losses occurred only in layers I-III. Since neurons in the midline thalamic nuclei and locus coeruleus synthesize mu-opioid receptors, noradrenergic afferents were removed with anti-DBH-saporin. This toxin reduced [3H]DAMGO binding only in layer I of areas 32 and 24, while DAMGO-stimulated [35S]GTPγS binding increased in layer II of areas 32 and 24, had no changes in area 24′, and decreased binding in layer I of area 29. Thus, in addition to their actions on ACC neurons, other sites of opiate drug actions are through mu-opioid heteroreceptors on glutamatergic thalamic and noradrenergic locus coeruleus afferents to ACC.

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

Burgess SE, Vanderah TW, Mantyh PW, Malan Jr TP, Ossipov MH, Lappi D, Lai J, Porreca F (2000) Dermorphin-saporin targets tonic descending facilitation in the rostral ventromedial medulla to block and reverse neuropathic pain. Neuroscience 2000 Abstracts 243.6. Society for Neuroscience, New Orleans, LA.

Summary: The hypothesis that chronic pain from L5/L6 spinal nerve ligation (SNL) is due to tonic activation of descending pain facilitation mechanisms was explored by selective targeting mu (μ) opioid receptor expressing cells in the RVM (i.e., presumably, ON cells). Rats were treated with a single RVM injection of dermorphin (DERM)(μ agonist), saporin (SAP), or dermorphin-saporin conjugate (DERM-SAP) and responses to non-noxious (von Frey filaments) or noxious (Hargreave’s test) stimuli characterized. DERM-SAP retained high affinity for μ receptors and acutely produced antinociception (tail-flick test), indicating agonist actions of the conjugate. Decreased staining of μ receptor-expressing cells was seen in superficial dorsal horn and in dorsal root ganglia 28 days after intrathecal injection of DERM-SAP, but not DERM or SAP. RVM DERM-SAP, DERM or SAP did not significantly alter baseline thresholds to von Frey filaments or noxious heat applied to the paw over 28 days. At day 28, RVM pretreated rats were subjected to sham- or SNL surgery and responses to tactile and heat stimuli monitored 7 days later (i.e., 35 days after the RVM pretreatment). DERM and SAP pretreated SNL rats showed the expected development of tactile allodynia and thermal hyperalgesia, while DERM-SAP pretreated rats did not. The RVM pretreatments did not alter responses in sham-operated controls. Administration of RVM DERM-SAP, but not SAP or DERM, to SNL rats showed full reversal of established allodynia/hyperalgesia by day 14. RVM pretreatment with β-funaltrexamine (β-FNA; opioid μ antagonist) prevented the antiallodynic and antihyperalgesic effects of subsequent DERM-SAP injection. These data, together with findings of blockade of SNL pain with RVM lidocaine or lesions of the dorsolateral funiculus, support the possibility of tonic activation of descending facilitation as a basis for chronic neuropathic pain.

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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)