targeted-toxins

Gerashchenko D, Blanco-Centurion CA, Miller JD, Shiromani PJ (2006) Insomnia following hypocretin2-saporin lesions of the substantia nigra. Neuroscience 137(1):29-36. doi: 10.1016/j.neuroscience.2005.08.088

Objective: To investigate which regions of major arousal areas might be responsible for the changes in sleep-wake architecture

Summary: It is known that orexin (also known as hypocretin) is involved in waking. The results suggest that motor activity is under inhibitory control of the substantia nigra.

Usage: Bilateral injection of Orexin-SAP (92 and 184 ng/ml, 0.25 ml in the ventral tegmental area and 0.5 ml in the substantia nigra) of rats induced insomnia, as well as hyperactivity and stereotypic movements.

Related Products: Orexin-B-SAP (Cat. #IT-20)

Mattsson A, Lindqvist E, Ogren SO, Olson L (2005) Increased phencyclidine-induced hyperactivity following cortical cholinergic denervation. Neuroreport 16(16):1815-1819. doi: 10.1097/01.wnr.0000185018.29316.87

Summary: A potential contribution to schizophrenia is altered cholinergic function. The authors investigated how lesioning cholinergic corticopetal projections might affect glutaminergic activity. Rats were injected with 0.134 µg of 192-IgG-SAP (Cat. #IT-01) into the nucleus basalis magnocellularis. The authors found that cholinergic lesioning of the neocortex led to enhanced sensitivity to phencyclidine, which has been shown to induce clinical symptoms similar to those of schizophrenia. These data suggest that glutaminergic dysfunction may be relevant to schizophrenia pathophysiology.

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

Q: We just completed surgeries where we implanted third ventricular cannulas and temporary bilatera cannulas directed into the nucleus tractus solitarius in the brainstem of animals. We injected either the Blank-SAP control toxin (Cat. #IT-21) or the experimental material Oxytocin-SAP into the bilateral NTS cannulae over a 30-second period. However, within the next week — two weeks post-surgery, we lost 13 of the 19 animals treated; they appeared not to be able to groom properly and lost over 20% of their body weight. This was apparent in both the Blank-SAP and the Oxytocin-SAP groups. We gave a dose of 40 ng/300 nl for each of the reagents. This dose was determined based on a published article using another of ATS’s targeted toxins. I’m very surprised by my results. Can you offer any explanation/advice?

A: This is a particularly disturbing result; it appears that a dose was chosen by comparison to one used with another targeted toxin. Although this can be a good approximating tool to begin a dose-ranging study, it usually doesn’t take into account the tissue, system, target molecule — so many parameters that are important to determining the proper dosage. The literature is quite extensive on targeted toxins, and so there may be a comparable starting dose that has been published. Let’s use, for example, 4 mg. Reduce that amount by 20% quantities (4, 3.2, 2.4) and test in a small number of animals to determine a value that is safe and effective. If no trouble is seen at the highest dose, and the effect is minimal, that would indicate a higher dose may be acceptable. You can then test doses in 20% increased increments (4.8, 5.6, 6.4). The effects you see in your animals should only be reflective of the particular cell type you are eliminating. In the case of control reagents, such as Blank-SAP, no cell type is being targeted, so if you are seeing any kind of result, then you are certainly over-dosing.

Q: Is there some kind of formula that one can use that will help determine a starting point for establishing a range of doses to test in animals prior to initiating a study? For example, if the targeted toxin is administered intravenously, does it take more or less material than when administered directly into tissue?

A: Start with a few animals and do dose-ranging as discussed in the previous question. The various modes of application are really too wide to discuss in any detail here, but I, a biochemist by training, always like the approach of thinking about what sort of concentration will be needed to have a cytotoxic effect. Generally, these molecules have an ED50 in the nanomolar to picomolar range. Obviously if you inject systemically, the material from the first becomes greatly diluted, relative to an injection directly into tissue, and so you’ll need a lot more. If you inject directly into tissue the local concentration can be quite high.

See: Targeted Toxins, Control Conjugates

Thinschmidt JS, Frazier CJ, King MA, Meyer EM, Papke RL (2005) Septal innervation regulates the function of alpha7 nicotinic receptors in CA1 hippocampal interneurons. Exp Neurol 195(2):342-352. doi: 10.1016/j.expneurol.2005.05.006

Summary: The authors examined whether hippocampal innervation by medial septum/diagonal band of Broca projections is necessary for normal a7 receptor function. 1 µg of 192-Saporin (Cat. #IT-01) was injected into the medial septum of rats. Various methods, including whole-cell patch clamping and immunohistochemistry, were used to evaluate the effects of these lesions. Lesioning with 192-Saporin did not affect a7 receptor currents, indicating that cholinergic neurons are not linked to a7 function.

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

Pang K, Smith H (2005) Featured Article: Effects of intraseptal orexin-saporin on spatial memory. Targeting Trends 6(4)

Related Products: Orexin-B-SAP (Cat. #IT-20)

Read the featured article in Targeting Trends.

See Also:

• Smith HR et al. Orexin-saporin lesions of the medial septum impair spatial memory. Neuroscience 132(2):261-271, 2005.

Suzuki R, Rahman W, Rygh LJ, Webber M, Hunt SP, Dickenson AH (2005) Spinal-supraspinal serotonergic circuits regulating neuropathic pain and its treatment with gabapentin. Pain 117(3):292-303. doi: 10.1016/j.pain.2005.06.015

Summary: The anticonvulsant, gabapentin, is thought to modulate calcium channel function. In animals, it also affects abnormal pain function. 10 µl of 1 µM SP-SAP (Cat. #IT-07) was injected into the subarachnoid space of rats. It was found that the effects of gabapentin were blocked when NK-1r expressing neurons in the dorsal horn were eliminated. The results suggest that not only is the NK-1r pathway a determinant of neuronal and behavioral manifestations of neuropathy, it is also involved in the action of gabapentin.

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

Sherren N, Pappas BA (2005) Selective acetylcholine and dopamine lesions in neonatal rats produce distinct patterns of cortical dendritic atrophy in adulthood. Neuroscience 136(2):445-456. doi: 10.1016/j.neuroscience.2005.08.053

Summary: In this work the authors examined lesions of acetylcholine afferents in 7-day-old rat pups, and the effect on dendritic development. 600 ng of 192-IgG-SAP (Cat. #IT-01) were administered to the ventricles of test animals. Various morphological changes in the retrosplenial cortex were observed, including smaller apical tufts and fewer basilar dendritic branches in layer V medial prefrontal cells. The data demonstrate that ascending acetylcholine afferents are very important in the development of cortical cytoarchitecture.

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

Schechter LE, Smith DL, Rosenzweig-Lipson S, Sukoff SJ, Dawson LA, Marquis K, Jones D, Piesla M, Andree T, Nawoschik S, Harder JA, Womack MD, Buccafusco J, Terry AV, Hoebel B, Rada P, Kelly M, Abou-Gharbia M, Barrett JE, Childers W (2005) Lecozotan (SRA-333): a selective serotonin 1A receptor antagonist that enhances the stimulated release of glutamate and acetylcholine in the hippocampus and possesses cognitive-enhancing properties. J Pharmacol Exp Ther 314(3):1274-1289. doi: 10.1124/jpet.105.086363

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

Fontan-Lozano A, Troncoso J, Munera A, Carrion AM, Delgado-Garcia JM (2005) Cholinergic septo-hippocampal innervation is required for trace eyeblink classical conditioning. Learn Mem 12(6):557-563. doi: 10.1101/lm.28105

Summary: Classical conditioning of eyeblink responses can be used to evaluate cognitive deficits. The authors lesioned the medial septum/diagonal band of rats with 200 ng of 192-IgG-SAP (Cat. #IT-01), then examined classical and instrumental conditioning paradigms. Lesioned animals displayed a deficit in the acquisition, but not retrieval of eyeblink classical conditioning. The deficit was reversed by carbachol, a cholinergic muscarinic agonist, suggesting a role for the muscarinic system in the acquisition of new motor abilities.

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

Hawkes C, Jhamandas JH, Kar S (2005) Selective loss of basal forebrain cholinergic neurons by 192 IgG-saporin is associated with decreased phosphorylation of Ser glycogen synthase kinase-3beta. J Neurochem 95(1):263-272. doi: 10.1111/j.1471-4159.2005.03363.x

Summary: Glycogen synthase kinase-3ß (GSK-3ß) is an enzyme involved in a variety of biological events. In this study the authors examined the potential role of GSK-3ß in degeneration of basal forebrain cholinergic neurons. Rats were treated with 2.0 µg per ventricle injections of 192-IgG-SAP (Cat. #IT-01), then GSK-3ß and other cholinergic marker levels were assayed. The results indicate that increased GSK-3ß activity can provide some protection from 192-IgG-SAP-induced degeneration of forebrain cholinergic neurons.

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