Increased Intracranial Pressure Damages Optic Nerve Structural Support.

Optic nerve sheath diameter (ONSD) is used clinically as a noninvasive measure for elevated intracranial pressure (ICP). This study had two purposes: to investigate the immediate effects optic nerve sheath (ONS) dilation post-ICP increase on trabecular fibers connecting the optic nerve to the ONS and to document any changes in these fibers 30 days post-increased ICP. In a swine model, ICP was increased by inflating a Foley catheter balloon in the epidural space. Three control pigs received the catheter insertion without inflation (no increase in ICP) and four experimental pigs received the catheter with inflation (increased ICP). The control and two randomly selected pigs with increased ICP were euthanized immediately after the procedure. The two other pigs were euthanized 30 days post-catheter inflation. For all pigs, the ONS was removed and imaged using a scanning electron microscope, calculating percent porosity values. Porosity values for the experimental groups (Immediately measured [IM] µ = 0.5749; Delayed measured [DM] µ = 0.5714) were larger than the control group (µ = 0.4336) and statistically significant (IM vs. Control, p = 0.0018; DM vs. Control, p = 0.0092). There was no significant difference (p = 0.9485) in porosity of the DM group when compared with the IM group. This study demonstrated that the trabecular fibers immediately post-increased ICP (ONS dilation) were more porous than the control and remained statistically different (more porous) after 30 days. These results suggest a structural change that occurs in the ONS with elevations in ICP.

Comparison of Serial Blood Collection by Facial Vein and Retrobulbar Methods in C57BL/6 Mice.

Many biomedical research protocols for mouse models involve serial blood collection and analysis. Two common techniques for serial blood collection in this species are the retrobulbar (RB, also called retroorbital) and facial vein (FV) methods. However, previous studies comparing these methods typically evaluated collection at a maximum of 2 time points. Here we compared hematologic values, adverse clinical effects, and histopathologic lesions in mice bled either once or serially (6 times) by using the FV or RB method. Mice (n = 48) were divided into 4 groups: single FV, single RB, serial FV and serial RB. Mice in the single-collection groups underwent a single blood collection by the indicated method, whereas those in the serial-collection groups were sampled once weekly for 6 consecutive weeks. All animals were euthanized and necropsied 2 wk after their last blood collection. Compared with all other groups, the serial FV group experienced more serious clinical adverse events, including 33% mortality, convulsions, head tilt, and hemorrhage from the ear canal and nares. In addition, mice in the FV groups had a significantly greater acute body weight loss compared with mice in the RB groups. Histologically, mice in both serial-collection groups had an increased incidence of tissue lesions compared with their respective single-collection groups. Importantly, only mice in the serial FV group had life-threatening histopathologic lesions, including cerebral hemorrhage or ischemia. Given these data, we conclude that serial blood collection in mice causes increased incidence of tissue damage compared with single sampling, and serial blood collection by the FV method causes substantial morbidity and mortality compared with the RB method.

Target engagement and histopathology of neuraxial resiniferatoxin in dog.

OBJECTIVE: To evaluate target engagement of intracisternally (IC) delivered TRPV1 agonist, resiniferatoxin (RTX), as measured by primary afferent and dorsal horn substance P immunoreactivity (sP-IR), histopathology and thermal escape latencies in dogs. STUDY DESIGN: Prospective experimental trial. ANIMALS: Fourteen adult male Beagle dogs, weighing 10.3-13.2 kg; 11 dogs surviving to scheduled euthanasia. METHODS: Anesthetized dogs were randomly assigned to be administered IC RTX (3.6 µg, 0.1 mL kg-1) in a hyperbaric (hRTX, n = 6), normobaric (nRTX, n = 4) vehicle or a hyperbaric vehicle (hVehicle, n = 4). Over 16 days, animals were examined for thoracic and pelvic limb paw thermal withdrawal latencies and neurologic function. Spinal cords, trigeminal ganglia and dorsal root ganglia (DRGs) were assessed for morphologic changes and sP-IR. RESULTS: IC RTX in anesthetized dogs resulted in a < 1 hour increase in blood pressure. Acute reactions leading to euthanasia within 8 hours occurred in three dogs (two hRTX, one nRTX). All other animals recovered with normal neurologic, bowel and bladder function. Final groups were: vehicle n = 4, hRTX n = 4 and nRTX n = 3. Animals in nRTX and hRTX showed increases in escape latencies in thoracic paws and, to a lesser extent, in pelvic paws, correlating to a loss of sP-IR in cervical cord with smaller reductions in thoracic and lumbar cord. In animals surviving to euthanasia, thickening of the arachnoid membrane (predominantly in the cervical region) was the most consistent change. This change, present in controls, was interpreted to be vehicle related. There was no evidence of structural changes in brain and spinal cord. CONCLUSIONS AND CLINICAL RELEVANCE: IC RTX produced localized loss of spinal and DRG sP with a corresponding thermal analgesia, absent motor impairment or spinal pathology. Loss of three animals emphasizes the need to refine the use of this promising therapeutic modality in managing companion animal pain.

Current and Future Issues in the Development of Spinal Agents for the Management of Pain.

Targeting analgesic drugs for spinal delivery reflects the fact that while the conscious experience of pain is mediated supraspinally, input initiated by high intensity stimuli, tissue injury and/or nerve injury is encoded at the level of the spinal dorsal horn and this output informs the brain as to the peripheral environment. This encoding process is subject to strong upregulation resulting in hyperesthetic states and downregulation reducing the ongoing processing of nociceptive stimuli reversing the hyperesthesia and pain processing. The present review addresses the biology of spinal nociceptive processing as relevant to the effects of intrathecally-delivered drugs in altering pain processing following acute stimulation, tissue inflammation/injury and nerve injury. The review covers i) the major classes of spinal agents currently employed as intrathecal analgesics (opioid agonists, alpha 2 agonists; sodium channel blockers; calcium channel blockers; NMDA blockers; GABA A/B agonists; COX inhibitors; ii) ongoing developments in the pharmacology of spinal therapeutics focusing on less studied agents/targets (cholinesterase inhibition; Adenosine agonists; iii) novel intrathecal targeting methodologies including gene-based approaches (viral vectors, plasmids, interfering RNAs); antisense, and toxins (botulinum toxins; resniferatoxin, substance P Saporin); and iv) issues relevant to intrathecal drug delivery (neuraxial drug distribution), infusate delivery profile, drug dosing, formulation and principals involved in the preclinical evaluation of intrathecal drug safety.

Epigenetic and gene expression changes related to transgenerational carcinogenesis.

Transgenerational carcinogenesis refers to transmission of cancer risk to the untreated progeny of parents exposed to carcinogens before mating. Accumulated evidence suggests that the mechanism of this process is epigenetic, and might involve hormonal and gene expression changes in offspring. To begin to test this hypothesis, we utilized a mouse model (NIH Swiss) in which exposure of fathers to Cr(III) chloride 2 wk before mating can alter incidence of neoplastic and nonneoplastic changes in offspring tissues. Utilizing a MS-RDA approach, we found that the sperm of these fathers had a significantly higher percentage of undermethylated copies of the 45S ribosomal RNA gene (rRNA); this finding was confirmed by bisulfite sequencing. Because gene methylation is a known mechanism of expression control in germ cells, and ribosomal RNA levels have been linked to cancer, these findings are consistent with the hypothesis. Secondly, we observed that offspring of Cr(III)-treated fathers were significantly heavier than controls, and had higher levels of serum T3. Possible effects of T3 levels on gene expression in the offspring were examined by microarray analysis of cDNAs from liver. A total of 58 genes, including 25 named genes, had expression ratios that correlated significantly with serum T3 ratios at P