targeted-toxins

Browning PG, Gaffan D, Baxter MG (2007) Severe visual learning impairments in monkeys with combined but not separate lesions of the temporal cortical cholinergic system and the fornix. Neuroscience 2007 Abstracts 341.7. Society for Neuroscience, San Diego, CA.

Summary: A dense amnesia can be produced in the monkey by sectioning the anterior temporal stem, amygdala and fornix, a procedure which deafferents temporal cortex from modulatory inputs from the midbrain and basal forebrain. The present experiment investigated the neurochemical specificity of these severe learning impairments by selectively destroying cholinergic projections to the entire inferior temporal cortex by making multiple injections of the immunotoxin ME20.4-saporin into the inferior temporal cortex bilaterally. Six male macaque monkeys were preoperatively trained to learn new object-in-place discrimination problems each day until they could rapidly learn many such problems within a testing session. The monkeys then underwent surgery and received either injections of immunotoxin (n=3) or injections of saline (n=3). Both groups of monkeys were unimpaired when postoperative and preoperative performance were compared. Each monkey then underwent a second surgery to transect the fornix. After this surgery monkeys who had previously received injections of immunotoxin into temporal cortex showed a severe learning impairment, whereas monkeys who had previously received injections of saline showed a mild impairment. Monkeys with the combined immunotoxin plus fornix lesion were also severely impaired at concurrent object discrimination learning. These results suggest that different neuromodulatory inputs to inferior temporal cortex may act in concert to support cortical plasticity in visual learning such that the loss of acetylcholine only is not sufficient to disrupt normal learning behavior. The results also suggest that in monkeys, as in humans with Alzheimer’s disease, severe memory impairments occur only when a loss of acetylcholine projections to cortex is accompanied by organic tissue damage.

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

Baxter MG, Kyriazis DA, Croxson PL (2007) Cholinergic depletion of prefrontal cortex does not impair episodic memory or strategy implementation in rhesus monkeys. Neuroscience 2007 Abstracts 341.9. Society for Neuroscience, San Diego, CA.

Summary: The prefrontal cortex is involved in regulating multiple aspects of memory, decision-making, and cognitive control. Cholinergic input to prefrontal cortex is thought to be involved in supporting its functions. To examine this hypothesis we tested 4 rhesus monkeys (3 male) with cholinergic depletion of ventrolateral prefrontal cortex (N=2) or the entire prefrontal cortex, excluding its medial aspect (N=2). Selective cholinergic depletion was produced by multiple injections of the immunotoxin ME20.4-saporin (0.02 ug/ul) into the prefrontal cortex. These monkeys were tested on two tasks that each require frontal-inferotemporal interaction, as well as an intact ventrolateral prefrontal cortex. The first, strategy implementation, requires monkeys to apply different choice strategies to different categories of objects in order to maximize the rate of reward delivery, and engages decision-making and cognitive control. The second, scene memory, is a test of episodic memory in which monkeys rapidly learn 20 new object-in-place scene discrimination problems within a single test session. Cholinergic depletions of prefrontal cortex, whether they were limited to ventrolateral prefrontal cortex or included the whole of lateral and orbital prefrontal cortex, were without effect on either strategy implementation or new scene learning relative to each monkey’s preoperative performance. Thus, episodic memory and strategy implementation can proceed normally even with severely disrupted cholinergic input, so loss of cholinergic input on its own cannot explain impaired prefrontal function in conditions such as Alzheimer’s disease. Acetylcholine may work in tandem with other neuromodulators to affect prefrontal cortex function; alternatively, it may only be involved in very specific aspects of cortical function, for example representational plasticity.

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

Tai S, Ma J, Leung L (2007) Vestibular activation stimulates cholinergic system in the hippocampus. Neuroscience 2007 Abstracts 399.21/OO13. Society for Neuroscience, San Diego, CA.

Summary: The vestibular system has been suggested to participate in spatial navigation, a function ascribed to the hippocampus. We examined the mechanisms that induced hippocampal theta, a 4-10 Hz rhythm in the electroencephalogram (EEG), during vestibular activation in rats. Freely behaving rats were rotated at various speeds, on a vertical axis, in the light or dark. Hippocampal EEGs were recorded by implanted electrodes in hippocampal CA1, and analyzed by spectral analysis. A clear hippocampal theta rhythm was induced during immobility by rotations at different speeds (20-70 rpm). The rotation-induced theta was abolished, in light and dark settings, by muscarinic cholinergic receptor antagonist atropine sulfate (50 mg/kg i.p.) but not by atropine methyl nitrate (50 mg/kg i.p.), which did not pass the blood-brain barrier. Rotation-induced theta was attenuated in rats in which the cholinergic neurons in the medial septum (MS) were lesioned by 192 IgG-saporin (0.14 µg/0.4 µl infused bilaterally into the MS 10-20 days prior to the experiments). Cholinergic lesion in the MS was confirmed by a depletion of MS neurons that stained positively for choline acetyltransferase and an absence of acetylcholinesterase histochemical staining in the hippocampus. Bilateral lesion of the vestibular receptors (by 0.1 ml intratympanic injection of 300 mg/ml sodium arsanilate) also attenuated the rotation-induced theta rhythm. Vestibular lesion was confirmed by the contact righting test where lesioned rats will “walk” upside down on a Plexiglas sheet placed in contact with the soles of the feet while intact rats will right themselves immediately. In summary, an atropine-sensitive hippocampal theta is activated by septohippocampal cholinergic neurons which are in turn activated by vestibular stimulation. Vestibular-activated septohippocampal cholinergic activity is likely an important component of spatial navigation.

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

Burk JA, Altemose KE, Lowder MW (2007) Effects of spatial cueing on visual discrimination performance of rats following loss of basal forebrain corticopetal cholinergic neurons. Neuroscience 2007 Abstracts 424.4/HHH3. Society for Neuroscience, San Diego, CA.

Summary: Basal forebrain corticopetal cholinergic neurons are necessary for normal attentional performance. However, the exact attentional task parameters that are sufficient for inducing deficits following loss of basal forebrain corticopetal cholinergic neurons remain unclear. In Experiment 1, rats were trained to perform a spatially cued visual discrimination task (press a lever under an illuminated panel light) with explicit attentional demands removed. Animals then received infusions of the cholinergic immunotoxin, 192IgG-saporin, or saline into the basal forebrain. All animals were then tested in the same task trained before surgery and then task parameters, including the duration of visual signals and the inter-trial interval, were manipulated in order to tax attentional processing. Lesioned animals exhibited an initial increase in response latencies immediately following surgery but this deficit was not observed when task demands were increased. When the task was modified to remove spatial cueing, by presenting visual signals or no signal from a centrally-located panel light, lesioned animals exhibited an increase in lever press latencies compared to sham-lesioned animals. In Experiment 2, rats were trained in a visual discrimination task that, within each session, had blocks of trials with or without spatial cueing, using procedures similar to Experiment 1. After receiving intra-basalis infusions of 192IgG-saporin or saline, animals were tested for 12 sessions in the same task trained before surgery followed by one session in which the inter-trial interval was decreased. Lesioned animals did not exhibit deficits immediately following surgery, but did show elevated lever press latencies compared to sham-lesioned animals when the inter-trial interval was decreased. There was a trend for this lesioned-induced deficit to be more pronounced when spatial cues were not present. These experiments indicate that cortical acetylcholine is critical for maintaining normal visual discrimination performance when spatial cueing is not available. We speculate that, under conditions in which spatial cueing is unavailable, the lesion-induced increased lever press latencies reflect a disruption in recalling rules for an appropriate response.

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

Butt AE, Amodeo D, Flesher M, Marsa K, Holt R, Lladones R, Olney R, Haynes J, Kinney-Hurd BL, Dach N (2007) 192 IgG-saporin lesions of the cholinergic basal forebrain disrupt selective attention and trace conditioning but spare delay and long-delay conditioning. Neuroscience 2007 Abstracts 424.9/HHH8. Society for Neuroscience, San Diego, CA.

Summary: Recent research suggests that Pavlovian trace conditioning, but not delay conditioning, is a form of declarative memory that requires attention, where both of these processes depend on specific brain systems. For example, past research has shown that although amnesiac humans with damage to the hippocampus (HPC) acquire a normal conditioned response (CR) in delay conditioning paradigms, where the conditioned stimulus (CS) and unconditioned stimulus (US) partly overlap, they fail to acquire the CR in trace conditioning paradigms, where the CS and US are separated in time. Others have shown that the anterior cingulate cortex (ACC) in rats and the medial prefrontal cortex (mPFC) in rabbits are similarly necessary for trace but not delay conditioning. The basal forebrain cholinergic system (BFCS) has projections to the mPFC, ACC, and HPC. Given that each of these regions is critical for trace but not delay conditioning, we hypothesized that lesions of the BFCS using 192 IgG-saporin (SAP) would selectively impair trace but not delay or long-delay appetitive conditioning in rats. Additionally, given evidence suggesting BFCS involvement in attention, it was hypothesized that the addition of varying levels of distraction during the trace conditioning task would cause progressively greater degrees of impairment in the BFCS lesion groups compared to controls. In contrast, neither the control groups nor the BFCS lesion groups were expected be negatively affected by the addition of a distracting stimulus in the delay and long-delay conditioning tasks. Rats received bilateral SAP lesions or sham lesions of the BFCS prior to conditioning with a white noise CS and sucrose pellet US in either a delay, long-delay, or 10 s trace conditioning paradigm. Separate groups of BFCS lesion and control rats were subjected to varying levels of visual distraction (flashing house light) in each paradigm; no distraction, low distraction (continuously blinking light), and high distraction (intermittent, unpredictable flashing light). Results supported our hypotheses, with the BFCS lesion groups showing normal delay and long-delay conditioning regardless of level of distraction. In contrast, trace conditioning was impaired in the BFCS lesion groups, with progressively greater degrees of impairment occurring with greater levels of distraction, and complete disruption of learning in the high distraction condition. Together, these experiments suggest that the BFCS is necessary for normal trace conditioning, and that the BFCS is critically involved in selective attention tasks where animals must discriminate relevant stimuli from distracting background stimuli.

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

Likhtik E, Popa D, Apergis-Schoute J, Fidacaro GA, Pare D (2007) Lesion of intercalated (ITC) amygdala neurons interfere with extinction of classically conditioned fear responses. Neuroscience 2007 Abstracts 426.6/HHH29. Society for Neuroscience, San Diego, CA.

Summary: The acquisition of conditioned fear responses (CRs) is thought to involve the potentiation of synapses conveying information about the conditioned stimulus (CS) to the basolateral (BLA) amygdala. Expression of CRs would depend on the transfer of potentiated CS inputs by the BLA to the central amygdala (CE). In contrast, the mechanisms of extinction remain controversial. It has been proposed that ITC neurons, which receive BLA inputs and generate feedforward inhibition in CE, are in a key position to mediate extinction. In this view, NMDA-dependent potentiation of BLA inputs to ITC cells during extinction training, would dampen the impact of CS-related BLA activity on CE neurons, inhibiting CRs. However, this idea is difficult to test because ITC cells occur in small, lateromedially dispersed clusters, making conventional lesioning methods inadequate. Here, we took advantage of the fact that, compared to the rest of the amygdala, ITC cells express a much higher concentration of mu opioid receptors (muORs). As a result, we could lesion them by performing local injections of a peptide-toxin conjugate (demorphin conjugated to saporin, D-Sap) that selectively targets cells expressing muORs. Control rats received injections of saporin conjugated to a blank peptide (B-Sap). On Day 1, intact rats were subjected to a standard cued fear conditioning protocol in context A. On Day 2, they received 20 CS alone presentations in a different context (B). On Day 3, rats then received either D-Sap or B-Sap injections in the ITC cell masses. One week later, extinction recall was tested in context B with 10 CS alone presentations. Compared to control (B-Sap) rats (n=10), ITC-lesioned rats (n=5) had an extinction deficit (ANOVA, F=11.687, p = 0.005). Post-hoc t-tests comparing % time freezing during the first five or last five CSs revealed that rats with ITC lesions had significantly higher freezing levels throughout the extinction recall test (p<0.002 for both tests). These differences were not attributable to a non-specific increase in freezing or anxiety levels as exploratory behaviors in a novel open field in control and ITC-lesioned rats were indistinguishable. Overall, these results indicate that ITC cells are involved in the expression of extinction.

Related Products: Dermorphin-SAP / MOR-SAP (Cat. #IT-12), Blank-SAP (Cat. #IT-21)

Stornetta RL, Takakura AC, Moreira TS, Mulkey DP, Bayliss DA, Guyenet PG (2007) Phox2b-expressing neurons of the retrotrapezoid nucleus (RTN) and central respiratory chemoreception in rats. Neuroscience 2007 Abstracts 230.9. Society for Neuroscience, San Diego, CA.

Summary: The RTN contains glutamatergic interneurons that are strongly activated by CO2 via acidification. These chemosensitive neurons are non-catecholaminergic and they express the transcription factor Phox2b. Although RTN chemoreceptors innervate selectively the brainstem regions that contain the respiratory rhythm and pattern generator (CPG), it is not yet clear whether these neurons drive inspiration or expiration, pump or airway muscles, autonomic circuits or all of the above. To determine whether RTN neurons drive inspiration, we examined whether their selective destruction modifies the CO2 sensitivity of the phrenic nerve discharge (PND) in anesthetized vagotomized rats. Using electrophysiological recordings in vivo and in slices, we found that the chemosensitive neurons of RTN express substance P receptors. We also found that these cells can be destroyed by local injection of a substance P agonist conjugated with saporin (SSP-SAP). The kill rate of RTN chemoreceptors was determined by counting the number of residual Phox2b-expressing non-catecholaminergic neurons present in this structure 15 days after toxin injection. Unilateral injection of 0.6 ng SSP-SAP destroyed 75% of the presumptive chemoreceptors on the injected side only. The lesion was selective because nearby neurons such as facial motoneurons, catecholaminergic and serotonergic cells were spared. SSP-SAP also spared the ventral respiratory column caudal to RTN except for a small amount of damage in the Bötzinger region closest to RTN. Unilateral lesion of the Phox2b-expressing neurons of RTN had no effect on PND and on respiratory chemoreception. However, in such rats, a single injection of the GABA-mimetic muscimol into the contralateral intact RTN instantly eliminated PND. After muscimol, PND did not usually reappear in the presence of hypercapnia up to 10% end-expiratory CO2. However, PND could typically be reactivated by strong stimulation of peripheral chemoreceptors which suggests that the respiratory oscillator had remained functional after muscimol. Unilateral injection of a lower dose of SSP-SAP (0.15 ng) had no effect on the Phox2b-expressing neurons of RTN. In such rats, unilateral injection of muscimol into the contralateral RTN had no detectable effect on PND and central chemoreception.

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

Masawaki A, Sugiyo S, Shimoda T, Sakai Y, Ohyamaguchi A, Uehashi D, Moritani M, Yoshida A, Niwa H, Takemura M (2007) Effects of systemic bicuculline on the formalin-induced nociceptive response in the lip and c-Fos expression in the SP-Saporin-treated rats. Neuroscience 2007 Abstracts 186.16/RR16. Society for Neuroscience, San Diego, CA.

Summary: This study examines the effect of systemic bicuculline (2 mg/kg, ip) on formalin-induced pain-related behavior in the lip (PRB; face scrubbing behavior) and c-Fos expression in the trigeminal nucleus caudalis (SpVc) 2hrs after formalin injection and 2-4 weeks after intra cisterna magna (i.c.m.) injection of substance P (SP) conjugated to neurotoxin, saporin (SP-Sap; 3 µM, 5 µl), blank-Sap- or saline-treatment. In SP-Sap-treated rats, the number of NK-1- immunoreactive (NK-1-IR) neurons in lamina I of the SpVc decreased compared with that of saline- or blank-Sap-treated rats. In SP-Sap-treated rats, PRB at phase 2 decreased compared with that of saline- or blank-Sap-treated rats. In SP-Sap-treated rats, the number of c-Fos-IR cells in the VcI/II decreased compared with that in the saline- or blank-Sap-treated rats. In saline- and blank-Sap- treated rats but not SP-Sap-treated rats, systemic bicuculline decreased the number of PRB at phase 2. These results indicate that i.c.m. injection of SP-Sap eliminates NK-1-bearing neurons in L1 of SpVc, and that NK-1-bearing neurons in the SpVc have pivotal role in formalin-induced PRB at phase 2 and c-Fos expression in the SpVc. The decremental effects of systemic bicuculline on the formalin-induced nociceptive responses at phase 2 and c-Fos expression in the VcI/II are secure in the presence of NK-1 receptor bearing neurons in the Vc.

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

Gray PA, Vandunk C (2007) Developmental origins of ventral medullary NK1r neurons. Neuroscience 2007 Abstracts 187.15/SS7. Society for Neuroscience, San Diego, CA.

Summary: Breathing is a fundamental neural behavior generated by neurons within the brainstem. In the adult rat, bilateral injection of substance P conjugated to saporin (SSP) in the preBötzinger Complex (preBötC) eliminates normal breathing. Unilateral injection produces sleep disordered breathing and eliminates the effects of excitatory amino acid injection on breathing and blood pressure. SSP injection in the RTN region, in contrast, blunts chemosensitivity. The extent these different effects are due to ablation of anatomically, functionally, or genetically distinct populations are unknown. Further, the extent NK1R expression identifies unique populations in neonatal mice is unknown. Transcription factors are fundamental to determining the properties of neurons and it has been proposed a “combinatorial code” of transcription factor expression defines each distinct functional population. From a genome-scale analysis of over 1000 transcription factors and transcriptional co-factors we identified several genes expressed in respiratory regions of the brainstem. Using immunohistochemistry, we analyzed gene expression patterns of NK1R expressing neurons of the ventral medulla in embryonic and neonatal mice. We find there are at least four genetically distinct, partially overlapping populations of NK1R expressing neurons in the ventral medulla. These differ in the transcription factors they express, their onset of NK1R expression, and their co-expression of peptides and g-protein coupled receptors. At the level of the preBötC, there are two populations of NK1R expressing neurons derived from distinct developmental progenitor populations. One population corresponds to the preBötC as defined in rats and co-expresses the peptide somatostatin. A second population is continuous with, and genetically identical to the subCVLM population important for respiratory-cardiovascular coordination. Both populations co-express the somatostatin 2a receptor (SST2aR). At the level of the RTN/pFRG, there are also two populations of NK1R expressing neurons that are derived from similar developmental precursors as the preBötC. Neither of these populations expresses SST2aR. Whether either of these populations corresponds to the RTN or pFRG is currently unknown. These data suggest both the preBötC and RTN/pFRG regions contain developmentally related NK1R expressing populations. Further, they identify the developmental origin of preBötC neurons known to be essential for normal breathing and provide a foundation for understanding the genetic origin of an important neural circuit.

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

Radley JJ, Sawchenko PE (2007) Noradrenergic denervation of dorsal medial prefrontal cortex (mPFC) modulates paraventricular hypothalamic responses to acute restraint stress. Neuroscience 2007 Abstracts 198.4/ZZ13. Society for Neuroscience, San Diego, CA.

Summary: The dorsal mPFC is implicated in restricting the hypothalamo-pituitary-adrenal (HPA) axis response to acute emotional stress via its influence on neuroendocrine effector mechanisms represented in the paraventricular hypothalamic nucleus (PVH). The afferents that provide for mPFC engagement during stress may include ascending noradrenergic projections from the locus coeruleus (LC), which are known to be stress-responsive and capable of modulating attentional mechanisms and other aspects of mPFC function. Arguing against such a role for LC-mPFC projections is evidence that LC lesions attenuate PVH/HPA responses to acute emotional stress. Here we sought to clarify the role of the noradrenergic innervation of mPFC in acute stress-induced PVH activation. Rats received injections of the axonally transported catecholamine immunotoxin, anti-dopamine-β-hydroxylase (DBH)-saporin, centered in the prelimbic area, or sham injections of IgG-saporin or saline. 14 days later, rats were subjected to 30 min of restraint and perfused 2 h later. Immunohistochemical localization of the immediate-early gene product, Fos, was employed as an index of cellular activation in PVH. Cell counts revealed that acute stress reliably provoked marked increases in the number of Fos-labeled neurons in the PVH of all restrained groups relative to unstressed controls. Among stressed groups, anti-DBH-saporin lesions in the dorsal mPFC decreased activational responses in the PVH by 30%, relative to sham-lesioned animals, that were focused in the hypophysiotropic (dorsal medial parvocellular) subdivision. DBH immunostaining revealed a virtually complete noradrenergic denervation of the prelimbic area in immunotoxin-treated animals, while the ventral mPFC (infralimbic area) remained intact. Cortical fields dorsally and laterally adjoining the target area displayed a partial denervation, consistent with local collateralization of prelimbic-projecting LC neurons. While these data are consistent with a role for LC-mPFC projections in facilitating restraint-induced PVH engagement, it remains to be determined how this perspective may be reconciled with prior evidence indicating that mPFC serves normally to inhibit PVH/HPA responses to acute emotional stress.

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