P210 / 07 Effects of age on sexually dimorphic food protection behavior associated with hippocampal cholinergic deafferentation.
featuring IT-01 192-IgG-SAP
Loss of hippocampal cholinergic projection originating from basal forebrain structures has been associated with the progression of Dementia of the Alzheimer’s Type. The role of these fibers in information processing deficits has been debated; however, spontaneous behaviors such as food protection have been observed to dissociate the contributions of hippocampal and cortical cholinergic function. Sexual dimorphism and age are critical factors in the progression of neurodegenerative disorders, yet these factors have not been evaluated in food protection behavior. The current study infused the immunotoxin 192-IgG-Saporin bilaterally into the medial septum to produce selective cholinergic deafferentation of the hippocampal formation. Female and male rats received infusion of the immunotoxin at either three or 18 months of age. Testing in the in the food protection paradigm began six weeks after the surgery. During the five days of testing, rats received two food protection sessions. Each of these sessions involved the rat (dodger) being placed in a transparent cylinder with a same sex conspecific (robber). The dodger was given a one-gram food item to consume, while the robber made multiple attempts to obtain the food item. The number, success rate, and type of food protection behaviors were recorded across all food protection sessions. Rats also received a third session each day in which the latency to consume the food item was recorded in the absence of the conspecific. Preliminary results indicate that sex and age interact with cholinergic hippocampal deafferentation to influence the organization of food protection behaviors. These observations establish a foundation for future work investigating novel therapeutic interventions that target neuroplasticity within spared cholinergic systems.
P372 / 04 Nociception impedes grasping recovery in the spinal cord injured rat.
featuring IT-10 IB4-SAP
Significant deficits in motor control and sensory function diminish an individual’s quality of life following spinal cord injury (SCI). A top priority of the injured population is regaining upper limb function. It has been shown that descending motor commands and primary afferent input, such as cutaneous feedback and proprioception, drive plasticity and recovery of function after SCI. Our lab and others have shown that primary nociceptors sprout and facilitate the maladaptive plasticity seen in chronic pain development, but their role in motor control is critically overlooked. The purpose of this experiment was to better understand the role of nociceptive input on recovery of motor function after SCI. Mechanosensitive, non-peptidergic nociceptors were ablated in Sprague-Dawley rats via intraganglionic injections of rIB4 -conjugated saporin or unconjugated (vehicle) saporin into the C7-8 dorsal root ganglia (DRGs). During the same surgery, rats received an ipsilateral C5 hemicontusion and the implantation of a braided multi-electrode probe for recording in the ipsilateral C8 gray matter. The von Frey test for allodynia and immunohistochemistry, in which cervical DRG and spinal cord sections were stained with antibodies against CGRP and isolectin-B4, were performed to confirm nociceptor ablation. The following battery of food motivated behavioral tests were performed to assess the components of the reach and grasp: single pellet retrieval, isometric pull, paw preference, Montoya staircase, and the cereal manipulation task (IBB). Results indicate that ablation of nociceptors following SCI improved the rats’ ability to grasp chocolate food pellets when compared to vehicle controls. Intraspinal recordings of local field potentials in the dorsal horn, intermediate gray, and ventral horn were obtained to measure changes in intraspinal activity in awake behaving rats. Multivariate statistical analyses of the behavioral, anatomical, and electrophysiological outcomes are underway. Increasing our understanding of the role nociceptors play in the spinal plasticity related to motor control following SCI will help guide future research and development of rehabilitative techniques.
J002 / 11 A Brief History of Saporin and its Contributions to Neuroscience
featuring All Saporin Products
When investigating the origins of targeted toxins (a drug, therapy, or scientific tool directed to a unique extracellular target), an appropriate place to begin is with the Nobel Prize-winning work of Paul Ehrlich and his concept of the “magic bullet.” Over 100 years later, the use of targeted toxins to perform molecular neurosurgery has become a vital practice that allows researchers to observe changes in organisms after eliminating a neuronal population. A prime example of this practice is the specific targeting of cholinergic neurons in the basal forebrain to mimic Alzheimer’s disease (AD). The research tool designed for this purpose is 192-IgG-Saporin, an antibody conjugated to the ribosome-inactivating protein (RIP) Saporin. Researchers have used this targeted toxin for over 30 years. A 2019 publication by Verkhratsky et al. reviews AD models and states this is the only lesion model that specifically targets cholinergic neurons.
In 1983, during a quest to find the optimal payload for a targeted toxin, Fiorenzo Stirpe and colleagues discovered Saporin, a plant protein isolated from the common soapwort plant Saponaria officinalis. Unlike ricin and abrin, Saporin does not have a binding chain and cannot enter a cell on its own.
Scientists have devised new ways to use Saporin to advance their research and drug development activities. Just a few examples include:
1. A novel suicide gene therapy approach that uses a vector encoding a double-stranded DNA aptamer to deliver the gene encoding Saporin,
2. Delivery of Saporin encapsulated in a nanotechnology system for development of cancer treatments,
3. A deeper understanding of the difference between pain and itch and the relevant pathways, and
4. Development of a stable epilepsy animal model that is used for screening specific treatments that will lead to micro-methods to eliminate the disease.
This review will focus on Saporin as the payload delivered to cells. Targeted toxins (typically targeted by an antibody or peptide chemically linked or genetically fused) provide robust tools for neuroscience where ablation of specific neuronal populations is used to study behavior and function. Saporin is an ideal molecule because of its extreme resistance to high temperatures and denaturation, retention of catalytic activity after conjugation, and lack of a binding chain to allow entrance to the cytoplasm of cells on its own. As a result, it is one of the most studied RIPs used for its vigorousness, potency, safety, and ease of use in the laboratory. The information presented will shed light on the history of Saporin, current applications, and what the future holds for this protein in the neuroscience field.
P377 / 07 Contribution of small diameter non-peptidergic primary afferent neurons to central neuropathic pain in a new, more clinically relevant mouse model of multiple sclerosis
featuring IT-10 IB4-SAP
Over 50% of multiple sclerosis (MS) patients suffer from neuropathic pain (MSNP). Current treatments give inadequate relief due to incomplete understanding of underlying mechanisms. Recent electrophysiological recordings of primary afferent neurons (PAN) in the dorsal root ganglion (DRG) following experimental autoimmune encephalomyelitis (EAE), a mouse model of MS, revealed increased afterhyperpolarization in small-diameter fibers. These data form the premise of our goal to understand the contribution of small-diameter (peptidergic or non-peptidergic) PANs to MSNP. Arguably the most common method to induce EAE is administration of myelin oligodendrocyte glycoprotein (MOG) to generate an autoimmune response targeting the myelin sheath. A MOG fragment is typically given with two adjuvants: complete Freund’s adjuvant (CFA) to boost immunogenicity and pertussis toxin (PTX) to breakdown the blood-brain barrier and facilitate CNS immune cell infiltration. However, PTX can disrupt G-protein coupled receptors, cause pain, and alter autoimmune response gene expression. In 10-week-old C57BL/6 mice, we conducted the first rigorous comparison of a classic PTX EAE model with the novel non-PTX (nPTX) EAE model. We found that both PTX and nPTX EAE mouse models showed the same degree of: 1) motor deficits; 2) plantar hindpaw mechanical and cold hypersensitivity (except cold hypersensitivity resolved more quickly after PTX EAE than nPTX EAE); and 3) lumbar spinal cord demyelination. Unlike most rodent models of MS including PTX EAE, the nPTX EAE group exhibited somatosensory cortex demyelination, a core feature of MS in human patients and cold hypersensitivity. We suggest nPTX EAE to be the most clinically relevant rodent model available to study not only MSNP, but MS in general. To evaluate the contribution of peptidergic and non-peptidergic neurons to MSNP, we induced nPTX EAE. After 12 days we administered capsaicin (10µg/mouse, i.t.) or IB4-saporin (1.5µg/mouse, i.t.) to primarily ablate peptidergic or nonpeptidergic C-fibers, respectively. Ablation efficacy was successfully confirmed with dramatic loss in DRG of TRPV1/CGRP immunoreactivity (peptidergic C-fibers) following capsaicin, and IB4 immunoreactivity (nonpeptidergic C-fibers) following IB4-saporin. IB4-saporin, but not capsaicin, partially reduced mechanical hypersensitivity and reversed cold hypersensitivity within 9 days. These data suggest nonpeptidergic but not peptidergic C-fibers contribute to MSNP. Our next studies will use genetic knockout, chemogenetic, and optogenetic strategies using MrgprdCreER mice to modulate the activity of nonpeptidergic C-fibers.
P747 / 06 The Role of the Patch Compartment of Striatum in Reward-Driven Behaviors
featuring IT-12 Dermorphin-SAP
The striatum is a neural structure that plays a critical role in cognitive functions, behavioral decision-making, and reward generation. The striatum exhibits a heterogeneous composition, containing neurons belonging to the patch compartment—which is thought to be involved in habitual reward-related behaviors—surrounded by neurons belonging to the matrix compartment—which is thought to be involved in adaptive motor control. Additionally, the striatum is further subdivided into the dorsolateral striatum (DLS) and the dorsomedial striatum (DMS), each with their own patch and matrix compartments. The DMS has been associated with goal-oriented behavior seen during the initial stages of addiction. Conversely, the DLS has been associated with habitual behaviors seen during late-stage addictive behaviors that are inflexible. It is thought that drug addiction is initially mediated by the DMS before DLS activity becomes predominant. Previously, it has been shown that the patch compartment of the DLS is necessary for development of habitual behavior, but the role of the patch compartment of the DMS is less clear. Our study intends to demonstrate that selective ablation of DMS patch compartment neurons will result in a negative impact on the initial development of reward-driven behaviors during the early stages of drug addiction. Since patch compartment neurons express a high level of mu opioid receptors compared to the surrounding matrix, we used dermorphin-saporin, a toxin that selectively destroys mu opioid receptor-containing neurons to target patch compartment neurons in the DMS and DLS for ablation. Following infusion in the DMS or DLS with dermorphin-saporin (17 ng/μl) or vehicle, rats were trained to self-administer cocaine (0.4 mg/kg/infusion) on progressive ratio schedule of reinforcement, starting with fixed ratio of 1 and ending with a fixed ratio of 5. Ablation of the patch compartment altered the level of responding for cocaine as the schedule of reinforcement became progressively labor-intensive. These data suggest that the patch compartment contributes to reward-driven behaviors.