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


METHODS
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.


CONCLUSIONS
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.
Lohman
Rink-Jan
RJ
Department of Pharmacology, The University of Melbourne, Parkville, Victoria, Australia.
Liu
Lige
L
Morris
Margaret
M
O'Brien
Terence J
TJ
D000818:Animals; D000927:Anticonvulsants / Q000008:administration & dosage; D004396:Coloring Agents; D004058:Diffusion; D004195:Disease Models, Animal; D016503:Drug Delivery Systems / Q000295:instrumentation / Q000379:methods*; D004569:Electroencephalography / Q000187:drug effects; D004827:Epilepsy / Q000188:drug therapy* / Q000235:genetics / Q000503:physiopathology; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D020646:Intralaminar Thalamic Nuclei / Q000187:drug effects / Q000503:physiopathology / Q000601:surgery; D008751:Methylene Blue; D008845:Microinjections / Q000295:instrumentation / Q000379:methods*; D051381:Rats; D011922:Rats, Mutant Strains; D015203:Reproducibility of Results; D013238:Stereotaxic Techniques / Q000295:instrumentation*; D013788:Thalamus / Q000187:drug effects* / Q000503:physiopathology / Q000601:surgery*; D020651:Ventral Thalamic Nuclei / Q000187:drug effects / Q000503:physiopathology / Q000601:surgery
D000927:Anticonvulsants; D004396:Coloring Agents; D008751:Methylene Blue