Simplified Surgical Placement and Stabilization Methods for Intracerebroventricular Cannulas in Rat Lateral Ventricles

Extracellular signal-regulated kinase-dependent phosphorylation of histone H3 serine 10 is involved in the pathogenesis of traumatic brain injury

Traumatic brain injury (TBI) induces a series of epigenetic changes in brain tissue, among which histone modifications are associated with the deterioration of TBI. In this study, we explored the role of histone H3 modifications in a weight-drop model of TBI in rats. Screening for various histone modifications, immunoblot analyses revealed that the phosphorylation of histone H3 serine 10 (p-H3S10) was significantly upregulated after TBI in the brain tissue surrounding the injury site. A similar posttraumatic regulation was observed for phosphorylated extracellular signal-regulated kinase (p-ERK), which is known to phosphorylate H3S10. In support of the hypothesis that ERK-mediated phosphorylation of H3S10 contributes to TBI pathogenesis, double immunofluorescence staining of brain sections showed high levels and colocalization of p-H3S10 and p-ERK predominantly in neurons surrounding the injury site. To test the hypothesis that inhibition of ERK-H3S10 signaling ameliorates TBI pathogenesis, the mitogen-activated protein kinase–extracellular signal-regulated kinase kinase (MEK) 1/2 inhibitor U0126, which inhibits ERK phosphorylation, was administered into the right lateral ventricle of TBI male and female rats via intracerebroventricular cannulation for 7 days post trauma. U0126 administration indeed prevented H3S10 phosphorylation and improved motor function recovery and cognitive function compared to vehicle treatment. In agreement with our findings in the rat model of TBI, immunoblot and double immunofluorescence analyses of brain tissue specimens from patients with TBI demonstrated high levels and colocalization of p-H3S10 and p-ERK as compared to control specimens from non-injured individuals. In conclusion, our findings indicate that phosphorylation-dependent activation of ERK-H3S10 signaling participates in the pathogenesis of TBI and can be targeted by pharmacological approaches.

Tympanic Membrane Rupture During Stereotaxic Surgery Disturbs the Normal Feeding Behavior in Rats

Stereotactic surgery is a widely used procedure in neuroscience research to study the brain’s regulation of feeding behavior. In line with this notion, this study aims to assess how food consumption and feeding patterns are affected in response to the use of auditory bars that preserve or damage the tympanic membrane during stereotactic surgery. Our previous observations led us to hypothesize that the traumatic tympanic membrane rupture affects food intake and feeding patterns in rats undergoing stereotactic procedures. Thereby, female and male rats were cannulated in the third ventricle (3V) using both types of auditory bars. Post-surgical pain was assessed using the grimace scale. Food intake, meal patterns and weight gain or loss were analyzed for 5–7 consecutive days after surgery. Normal food intake, increased body weight and regular meal patterns were observed from postoperative day 2 when the stereotactic procedure was performed using auditory bars that maintain the integrity of the tympanic membrane. However, tympanic membrane rupture prevented the expected recovery of food intake and body weight. This effect was accompanied by an alteration in eating patterns, which was persistent over 7 days of recovery. Thus, tympanic membrane preservation during surgery is necessary to evaluate short-term feeding patterns. This study demonstrates auditory bars that do not damage the tympanic membrane should be used when performing stereotactic surgery for subsequent analysis of rat behavior.

Peripheral-to-central immune communication at the area postrema glial-barrier following bleomycin-induced sterile lung injury in adult rats

The pathways for peripheral-to-central immune communication (P → C I-comm) following sterile lung injury (SLI) are unknown. SLI evokes systemic and central inflammation, which alters central respiratory control and viscerosensory transmission in the nucleus tractus solitarii (nTS). These functional changes coincide with increased interleukin-1 beta (IL-1β) in the area postrema, a sensory circumventricular organ that connects P → C I-comm to brainstem circuits that control homeostasis. We hypothesize that IL-1β and its downstream transcriptional target, cyclooxygenase-2 (COX-2), mediate P → C I-comm in the nTS. In a rodent model of SLI induced by intratracheal bleomycin (Bleo), the sigh frequency and duration of post-sigh apnea increased in Bleo- compared to saline- treated rats one week after injury. This SLI-dependent change in respiratory control occurred concurrently with augmented IL-1β and COX-2 immunoreactivity (IR) in the funiculus separans (FS), a barrier between the AP and the brainstem. At this barrier, increases in IL-1β and COX-2 IR were confined to processes that stained for glial fibrillary acidic protein (GFAP) and that projected basolaterally to the nTS. Further, FS radial-glia did not express TNF-α or IL-6 following SLI. To test our hypothesis, we blocked central COX-1/2 activity by intracerebroventricular (ICV) infusion of Indomethacin (Ind). Continuous ICV Ind treatment prevented Bleo-dependent increases in GFAP + and IL-1β + IR, and restored characteristics of sighs that reset the rhythm. These data indicate that changes in sighs following SLI depend partially on activation of a central COX-dependent P → C I-comm via radial-glia of the FS.

Mechanisms Underlying Neuroprotection by the NSAID Mefenamic Acid in an Experimental Model of Stroke

Stroke is a devastating neurological event with limited treatment opportunities. Recent advances in understanding the underlying pathogenesis of cerebral ischemia support the involvement of multiple biochemical pathways in the development of the ischemic damage. Fenamates are classical non-steroidal anti-inflammatory drugs but they are also highly subunit-selective modulators of GABA_A receptors, activators of I_KS potassium channels and antagonists of non-selective cation channels and the NLRP3 inflammosome. In the present study we investigated the effect of mefenamic acid (MFA) in a rodent model of ischemic stroke and then addressed the underlying pharmacological mechanisms in vitro for its actions in vivo. The efficacy of MFA in reducing ischemic damage was evaluated in adult male Wistar rats subjected to a 2-h middle cerebral artery occlusion. Intracerebroventricular (ICV) infusion of MFA (0.5 or 1 mg/kg) for 24 h, significantly reduced the infarct volume and the total ischemic brain damage. In vitro, the fenamates, MFA, meclofenamic acid, niflumic acid, and flufenamic acid each reduced glutamate-evoked excitotoxicity in cultured embryonic rat hippocampal neurons supporting the idea that this is a drug class action. In contrast the non-fenamate NSAIDs, ibuprofen and indomethacin did not reduce excitotoxicity in vitro indicating that neuroprotection by MFA was not dependent upon anti-inflammatory actions. Co-application of MFA (100 μM) with either of the GABA_A antagonists picrotoxin (100 μM) or bicuculline (10 μM) or the potassium channel blocker tetraethylammonium (30 mM) did not prevent neuroprotection with MFA, suggesting that the actions of MFA also do not depend on GABA_A receptor modulation or potassium channel activation. These new findings indicate that fenamates may be valuable in the adjunctive treatment of ischemic stroke.

Successful intracerebroventricular cannulation of a eusocial mammal

BACKGROUND

Manipulating neural activity in live animals within a colony would allow researchers to more fully explore the neurobiology of complex social behaviors. However, some colony-living animals like the naked mole-rat (Heterocephalus glaber) cannot be reintroduced to a colony after the extended recovery time required following cranial surgery. Furthermore, the colony setting creates increased risk of infection and interruption of cranial surgical sites.

NEW METHOD

A protocol for intracerebroventricular cannulations was developed for securing and minimizing exposure of the intracranial apparatus. We tested whether animals could be reintroduced to the colony immediately following surgery and whether they showed full recovery and expression of normal behavior a week later, after intracerebroventricular infusion of saline.

RESULTS

Animals were successfully reincorporated into their home colony and showed normal behavior. No animals lost guide cannulae within their colony and loss of dummy cannulae was minimized. Any loss of animals was due to surgical complications or multiple intracerebroventricular infusions of saline rather than recovery in the colony, per se.

COMPARISON WITH EXISTING METHODS

Standard cranial cannulation methods for small rodents were used with the addition of implanting a shortened guide cannula under the skin for limited exposure of cannulae to the external environment. Furthermore, dummy cannulae were sealed to guides to avoid loss in-colony.

CONCLUSION

The use of intracranial cannulations is a viable option for colony-living rodents when the proper care is taken to minimize cannula exposure and when animals are carefully and promptly reintroduced to the colony setting after surgery.

Domoic acid preconditioning and seizure induction in young and aged rats

Clinical reports suggest that the elderly are hypersensitive to the neurological effects of domoic acid (DOM). In the present study we assessed DOM-induced seizures in young and aged rats, and seizure attenuation following low-dose DOM pretreatment (i.e. preconditioning). Seizure behaviours following saline or DOM administration (0.5-2mg/kg i.p.) were continuously monitored for 2.5h in naïve and DOM preconditioned rats. Competitive ELISA was used to determine serum and brain DOM concentrations. Dose- and age-dependent increases in seizure activity were evident in response to DOM. Lower doses of DOM in young and aged rats promoted low level seizure behaviours. Animals administered high doses (2mg/kg in young; 1mg/kg in aged) progressed through various stages of stereotypical behaviour (e.g., head tics, scratching, wet dog shakes) before ultimately exhibiting tonic-clonic convulsions. Serum and brain DOM analysis indicated impaired renal clearance as contributory to increased DOM sensitivity in aged animals, and this was supported by seizure analysis following direct intrahippocampal administration of DOM. Preconditioning young and aged animals with low-dose DOM 45-90 min before high-dose DOM significantly reduced seizure intensity. We conclude that age-related supersensitivity to DOM is related to reduced clearance rather than increased neuronal sensitivity, and that preconditioning mechanisms underlying an inducible tolerance to excitotoxins are robustly expressed in both young and aged CNS.

Validation of a method for localised microinjection of drugs into thalamic subregions in rats for epilepsy pharmacological studies

OBJECTIVES

To validate a method for the chronic implantation of micro-cannulae to examine the effect of drug administration to two small brain regions critical to the control of generalised seizures, the reticular nucleus of the thalamus (Rt) and the ventrobasal thalamus (VB), in a genetically epileptic rat model.

METHOD

Micro-cannulae guides (length 9 mm, 26G, i.d. 0.24 mm, o.d. 0.46 mm) were implanted bilaterally into either the Rt or the VB of 11- to 13-week-old Genetic Absence Epilepsy Rats from Strasbourg (GAERS) using a stereotaxic head frame. After a seven-day recovery period the animals were injected with 0.2 microl of methylene blue. The animals were allowed to move freely in their cages for a further 90 min while a post-drug EEG recording was acquired and then brains were perfused with 4% paraformaldehyde and extracted. Twenty-micrometer slices were cut on a cryostat and the site and extent of the methylene blue staining in the brain determined. The implantation co-ordinates were adjusted accordingly, and then a validation study was performed on a further cohort of rats (n=8 Rt, n=7 VB).

RESULTS

The co-ordinates that were found to most accurately localise the Rt were: AP -3mm, ML 3.6mm, DV -5.8mm (relative to Bregma). Those that accurately localised the VB were: AP -3mm, ML 2.6mm, DV -5.5mm. In the validation study, the dye staining was measured to diffuse an average radius of 520+/-120 microm from the centre of the injection site for the 0.2 microl injection in both brain hemispheres. For the VB injections the dye remained confined within the structure, however, for the smaller Rt there was spread to surrounding structures in the axial plane. The radial diffusion for the 0.5 microl injection was similar, but more of the dye was found to spread back up the cannula tract away from the target zone.

CONCLUSION

These studies have validated a method for accurate and localised injection of drugs into the VB and Rt for neuropharmacological studies in a rat model of generalised epilepsy. This method allows the measurement of localised drug effects on EEG and generalised seizure activity at these sites.