title: Direct injection into the dorsal root ganglion: technical, behavioral, and histological observations.
abstract: Direct injection of agents into the dorsal root ganglia (DRGs) offers the opportunity to manipulate sensory neuron function at a segmental level to explore pathophysiology of painful conditions. However, there is no described method that has been validated in detail for such injections in adult rats. We have found that 2 μl of dye injected through a pulled glass pipette directly into the distal DRG, exposed by a minimal foraminotomy, produces complete filling of the DRG with limited extension into the spinal roots. Injection into the spinal nerve required 3 μl to achieve comparable DRG filling, produced preferential spread into the ventral root, and was accompanied by substantial leakage of injected solution from the injection site. Injections into the sciatic nerve of volumes up to 10 μl did not reach the DRG. Transient hypersensitivity to mechanical stimulation at threshold (von Frey) and noxious levels (pin) developed after 2 μl saline injection directly into the DRG that was in part attributable to the surgical exposure procedure alone. Only minimal astrocyte activation in the spinal dorsal horn was evident after DRG saline injections. Injection of adeno-associated virus (AAV) vector conveying green fluorescent protein (GFP) transgene resulted in expression as soon as 1 day after injection into the DRG, including fibers in the spinal dorsal horn and columns. AAV injection into the DRG produced additional thermal hypersensitivity and withdrawal from the stroke of a brush and compromised motor performance. These findings demonstrate a method for selective injection of agents into single DRGs for anatomically restricted actions.
authors.affiliation: Department of Anesthesiology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA. gfischer@mcw.edu
authors.forename: Gregory
authors.initials: G
authors.lastname: Fischer
authors.forename: Sandra
authors.initials: S
authors.lastname: Kostic
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nakai
authors.forename: Frank
authors.initials: F
authors.lastname: Park
authors.forename: Damir
authors.initials: D
authors.lastname: Sapunar
authors.forename: Hongwei
authors.initials: H
authors.lastname: Yu
authors.forename: Quinn
authors.initials: Q
authors.lastname: Hogan
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D002478:Cells, Cultured; D003080:Cold Temperature / Q000009:adverse effects; D004396:Coloring Agents / Q000008:administration & dosage / Q000493:pharmacokinetics; D000229:Dependovirus / Q000235:genetics; D005727:Ganglia, Spinal / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D017930:Genes, Reporter; D015316:Genetic Therapy / Q000379:methods; D005822:Genetic Vectors / Q000008:administration & dosage; D049452:Green Fluorescent Proteins / Q000032:analysis; D006358:Hot Temperature / Q000009:adverse effects; D006930:Hyperalgesia / Q000139:chemically induced* / Q000503:physiopathology; D007211:Indoles / Q000008:administration & dosage / Q000493:pharmacokinetics; D008297:Male; D008845:Microinjections / Q000379:methods*; D009437:Neuralgia / Q000188:drug therapy / Q000209:etiology / Q000503:physiopathology*; D011597:Psychomotor Performance / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D012584:Sciatic Nerve; D011984:Sensory Receptor Cells / Q000502:physiology; D012965:Sodium Chloride / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology / Q000633:toxicity; D012996:Solutions / Q000008:administration & dosage / Q000493:pharmacokinetics; D013126:Spinal Nerve Roots / Q000648:ultrastructure; D013314:Stress, Mechanical
chemical_list: D004396:Coloring Agents; D007211:Indoles; D012996:Solutions; D049452:Green Fluorescent Proteins; D012965:Sodium Chloride; C007293:DAPI