targeted-toxins

Motooka Y, Kondoh T, Nomura T, Tamaki N, Tozaki H, Kanno T, Nishizaki T (2001) Selective cholinergic denervation inhibits expression of long-term potentiation in the adult but not infant rat hippocampus. Devel Brain Res 129:119-123. doi: 10.1016/s0165-3806(01)00179-1

Summary: The authors studied the possible role of cholinergic systems in long-term potentiation (LTP), which is one of the most intensively studied models of learning and memory. 192-Saporin (4.2 µg/5 µl, Cat. #IT-01) injections were made in both infant and adult rats and the probability of LTP development was studied in hippocampal slices from animals treated 2 weeks or 2 months before. Cholinergic denervation by 192-Saporin did not affect LTP expression in the infant brain, however, the results strongly suggest that cholinergic systems in the adult brain participate in an LTP pathway.

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

Porreca F, Burgess SE, Gardell LR, Vanderah TW, Malan TP Jr, Ossipov MH, Lappi DA, Lai J (2001) Inhibition of neuropathic pain by selective ablation of brainstem medullary cells expressing the µ-opioid receptor. J Neurosci 21(14):5281-5288. doi: 10.1523/JNEUROSCI.21-14-05281.2001

Summary: The presence of descending projections in the pain pathway raises the possibility that abnormal sustained activity may perpetuate chronic pain. Using 3-ng injections of dermorphin-SAP (Cat #IT-12) on either side of the RVM in rats the authors both prevented and reversed neuropathic pain caused by spinal nerve ligation.

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

Q: What are the options for delivery of targeted toxins?

A: The options for toxin delivery are varied and limited only by investigator ingenuity. Generally, injection has been the route of choice. Some toxins can be given intravenously, such as 192-Saporin (192-IgG-SAP, Cat. # IT-01) or anti-DBH-SAP (Cat. # IT-03), in which case all cells expressing p75 or dopamine beta-hydroxylase and exposed to the systemic circulation are potential targets. Intravenous injections will not deliver toxins to the CNS.

Subarachnoid injections have been used successfully for immunotoxins and peptide toxins such as SP-SAP (Cat. # IT-07).

Direct intraparenchymal injections have been used to restrict toxin application to just a few target cells. However, intraparenchymal injections require careful attention to injection technique and are impractical for large target structures.

Q: When injecting directly into tissue, are there any special techniques that should be used?

A: Direct injections into brain or spinal cord have been used successfully by some investigators. Specifics of toxin dose, concentration, injection volume and speed of injection have varied considerably. If a high concentration of toxin is deposited locally, lesion specificity is often lost. Presumably, if toxin concentration is too high, cellular uptake by non-specific bulk fluid-phase endocytosis (pinocytosis) can internalize enough saporin to be lethal.

There is currently interest in “convective” delivery techniques developed in the laboratory of Dr. Edward Oldfield at the NIH. The basic principle is to deliver a relatively large concentration slowly over an extended period, often using a rather dilute solution. The parameters for any given species and injection site need to be determined by pilot experiments.

Q: What sort of special care should be given to the animal after administration of the targeted toxin?

A: The toxins generally bind and internalize within minutes, although some immunotoxins circulate for longer periods if injected intravenously. However, no significant amount of active toxin is excreted. So, animals can be returned to group housing immediately after toxin injection. The only special requirements may derive from the specific target being studied. For example, rats given intraventricular 192-Saporin (192-IgG-SAP, Cat. # IT-01) develop decreased fluid and food intake for several days after injection. Since the adipsia is significant, providing the animals with fresh, juicy vegetables, such as cucumber or potatoes, can help.

Rats injected intraventricularly with anti-DBH-SAP (Cat. # IT-03) will lose considerable body weight and are slow to regain. They, too, may benefit from food supplements, including nuts and other high calorie appetizing treats. Otherwise, common sense care of any neurologic deficits is indicated depending on the target and toxin being used.

See: Targeted Toxins

Lappi DA (2001) Featured Article: Dermorphin-SAP kills MOR-positive cells. Targeting Trends 2(3)

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

Read the featured article in Targeting Trends.

Browne SE, Lin L, Mattsson A, Georgievska B, Isacson O (2001) Selective antibody-induced cholinergic cell and synapse loss produce sustained hippocampal and cortical hypometabolism with correlated cognitive deficits. Exp Neurol 170:36-47. doi: 10.1006/exnr.2001.7700

Summary: The authors used 192-Saporin (two 2.5-µg bilateral injections of 1 µg/µl; Cat. #IT-01) to eliminate cholinergic neurons in the rat, then measured cerebral rates of glucose utilization. The findings show sustained reduction in glucose utilization in the brain regions showing loss of cholinergic neurons, specifically the frontal cortical and hippocampal regions. These same animals demonstrated impaired performance in a Morris water maze. The results reinforce the theory that cholinergic systems influence metabolism and cognition in the cortex and hippocampus.

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

Martin JL, Sloviter RS (2001) Focal inhibitory interneuron loss and principal cell hyperexcitability in the rat hippocampus after microinjection of a neurotoxic conjugate of saporin and a peptidase-resistant analog of substance P. J Comp Neurol 436:127-152. doi: 10.1002/cne.1065

Usage: The authors used SSP-SAP (0.4 ng/10 nl; Cat. #IT-11).

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

Read the featured article in Targeting Trends.

Ferreira G, Meurisse M, Tillet Y, Lévy F (2001) Distribution and co-localization of choline acetyltransferase and p75 neurotrophin receptors in the sheep basal forebrain: implications for the use of a specific cholinergic immunotoxin. Neuroscience 104(2):419-439. doi: 10.1016/s0306-4522(01)00075-6 PMID: 11377845

Summary: ME20.4 is a monoclonal antibody (Cat. #AB-N07) that has been shown to bind the p75 receptor in rabbit, sheep, dog, cat, raccoon, pig, and several primate species. Ferreira et al. investigate ME20.4-SAP (bilateral, 150 µl per ventricle, 50-150 µg total; Cat. #IT-15) use in sheep to assess distribution and localization of p75. The authors demonstrate 80-95% loss of basal forebrain cholinergic neurons and acetylcholinesterase-positive fibers in the hippocampus, olfactory bulb, and entorhinal cortex.

Related Products: ME20.4-SAP (Cat. #IT-15), NGFr (ME20.4, p75) Mouse Monoclonal (Cat. #AB-N07)

Hartlage-Rübsamen M, Schliebs R (2001) Sequential upregulation of cell adhesion molecules in degenerating rat basal forebrain cholinergic neurons and in phagocytotic microglial cells. Brain Res 897(1-2):20-26. doi: 10.1016/s0006-8993(01)02093-5

Summary: Neurodegeneration, found in brain disorders such as Alzheimer’s, Parkinson’s, and Huntington’s diseases, is marked by a significant microglial response. This microglial activation is characterized by increased migratory activity and potential cytotoxic action on injured neurons. The interaction of microglial cells with degenerating axons and neural somata is known to be mediated by expression of cell adhesion molecules. The authors use a single intracerebroventricular injection of 192-Saporin (4 µg; Cat. #IT-01) to initiate neurodegeneration of choline acetyltransferase-immunoreactive neurons and follow the expression of two cell adhesion molecules, ICAM-1 and LFA-1, using immunohisto-chemistry. The results indicate that these adhesion molecules may function as intercellular recognition signals through which degenerating cholinergic neurons actively participate in their own targeting and removal by microglia.

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

Sarter M, Givens B, Bruno JP (2001) The cognitive neuroscience of sustained attention: where top-down meets bottom-up. Brain Res Brain Res Rev 35(2):146-160. doi: 10.1016/s0165-0173(01)00044-3

Summary: The findings from human and animal studies provide the basis for a relatively precise description of the neuronal circuits mediating sustained attention, and the dissociation between these circuits and those mediating the ‘arousal’ components of attention.

Usage: The absence of attentional effects of infusions of 192-IgG-SAP into the primary and secondary visual cortex supports the notion that performance in such a task cannot be attributed solely to the ACh-mediated enhancement of the primary processing of sensory stimuli serving as targets in this task.

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

See Also:

• Gill TM et al. Sustained visual attention performance-associated prefrontal neuronal activity: evidence for cholinergic modulation. J Neurosci 20:4745-4757, 2000.

de Rosa E, Hasselmo ME, Baxter MG (2001) Contribution of the cholinergic basal forebrain to proactive interference from stored odor memories during associative learning in rats. Behav Neurosci 115(2):314-327.

Summary: Proactive interference (PI) is the damaging effect of previously learned information on the acquisition of new, related information. Human patients with basal forebrain (BF) damage due to aneurysms are sensitive to PI. The authors administered 192-Saporin (Cat. #IT-01) to the horizontal limb of the diagonal band of Broca (two 0.2-µl injections of 0.175 µg/µl in each hemisphere) in rats and evaluated performance in an olfactory discrimination task. The treated rats had more difficulty acquiring an overlapping odor pair when muscarinic receptors were blocked by scopalomine. These results indicate that cholinergic neurons have a role in the modulation of PI in associative learning.

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