Neuroprotective effects of intramuscular ketamine in rabbit retinas after pars plana vitrectomy and silicone oil injection.
OBJECTIVE
To investigate potential retinal neuroprotective effects of intramuscular ketamine in rabbits after pars plana vitrectomy (PPV) and intravitreal silicone oil injection (SOI).


METHODS
Twelve New Zealand rabbits (weight, 2.0-2.5 kg) underwent PPV with SOI in the right eye. Postoperatively, six rabbits received a daily intramuscular injection of ketamine for 4 weeks (ketamine-operated eyes), and six rabbits received a daily intramuscular injection of saline (saline-operated eyes). The retina from the left eye of each rabbit served as a control (ketamine-control and saline-control eyes). The animals were euthanized at 4 weeks after surgery. Qualitative and quantitative analyses were performed using the Zeiss Axiophot microscope and KS 400 software.


RESULTS
Qualitative analysis using light microscopy demonstrated more extensive edema and cell disorganization in saline-operated retinas than in ketamine-operated, ketamine-control, and saline-control retinas. Quantitatively, the cell densities (cell/mm) in the outer nuclear layer (ONL), inner nuclear layer (INL), and ganglion cell layer (GCL) in saline-operated retinas were significantly (P < 0.05) lower than those in these layers in ketamine-operated, ketamine-control, and saline-control retinas. The cell density in the ONL in saline-operated retinas was 52% lower than that in ketamine-operated retinas, 55% lower than that in ketamine-control retinas, and 56% lower than that in saline-control retinas. The cell density in the INL in saline-operated retinas was 44% lower than that in ketamine-operated retinas, 48% lower than that in ketamine-control retinas, and 49% lower than that in saline-control retinas. The cell density in the GCL in saline-operated retinas was 60% lower than that in ketamine-operated retinas, 64% lower than that in ketamine-control retinas, and 64% lower than that in saline-control retinas.


CONCLUSIONS
PPV with SOI was associated with retinal cell death and disorganization in rabbit eyes. Intramuscular ketamine administration provided protection against these effects.
Department of Ophthalmology, Otorhinolaryngology and Head and Neck Surgery, Ribeirão Preto School of Medicine, University of São Paulo, Av. Bandeirantes 3900, Cep. 14049-900 Ribeirão Preto, São Paulo, Brazil.
Mila W
MW
Paques
Renato
R
Guizzo
Rubens C
RC
Siqueira
Antônio R M
AR
Silva
José A
JA
Cardillo
Ingrid U
IU
Scott
Harry W
HW
Flynn
Wagner F
WF
Santos
Rodrigo
R
Jorge
D000818:Animals; D017209:Apoptosis; D002452:Cell Count; D018691:Excitatory Amino Acid Antagonists / Q000008:administration & dosage / Q000627:therapeutic use*; D005260:Female; D007267:Injections; D007273:Injections, Intramuscular; D007649:Ketamine / Q000008:administration & dosage / Q000627:therapeutic use*; D009474:Neurons / Q000187:drug effects* / Q000473:pathology; D018696:Neuroprotective Agents / Q000008:administration & dosage / Q000627:therapeutic use; D011183:Postoperative Complications / Q000517:prevention & control*; D011817:Rabbits; D012160:Retina / Q000187:drug effects* / Q000473:pathology; D012164:Retinal Diseases / Q000517:prevention & control*; D012827:Silicone Oils / Q000008:administration & dosage*; D014821:Vitrectomy
D018691:Excitatory Amino Acid Antagonists; D018696:Neuroprotective Agents; D012827:Silicone Oils; D007649:Ketamine