Bioactive glass granules as extender of autogenous bone grafting in cementless intercalary implant of the canine femur

BACKGROUND AND AIMS

Ceramic bone graft substitutes have a potential to be used as replacement of allogeneic bone grafting and, under optimal distribution of particle size, they may even provide mechanical support. The current study examined the efficacy of bioactive glass granules as an extender of autogenous bone grafting in a segmental bone replacement model of the canine femur.

MATERIAL AND METHOD

A 16 mm long segment of the femur shaft was bilaterally replaced with an intercalary titanium implant in eight animals. The implant had cementless grooved proximal and distal stems. In one leg, the peri-implant space was packed with composite graft consisting of a mixture of bioactive glass granules and autogenous bone graft in proportion of 50:50. In the opposite leg, the peri-implant space was treated with autogenous bone graft alone. After surgery, unlimited functional loading was allowed. The outcome was evaluated at three months.

RESULTS

Eight out of sixteen autografted implants and seven out of sixteen composite-grafted implants were radiographically incorporated and clinically stable at three months. In the paired comparison, the proximal components of composite-grafted implants showed lower maximum load under torsional testing (p = 0.068), less new bone in the longitudinal grooves of the stems (p = 0.036) and lower affinity of new bone to implant surface (p = 0.046). The distal components of the two sides showed a similar trend for less new bone in the grooves and lower bone affinity of new bone in the distal composite-grafted components.

CONCLUSIONS

The current study suggests that supplementation of periprosthetic bone graft with bioactive ceramic particles may not help to promote healing of cementless implants under high dynamic loading conditions.

Orbital floor reconstruction with poly-L/D-lactide implants: clinical, radiological and immunohistochemical study in sheep

In this study the reconstruction capacity of orbital wall in sheep was evaluated when poly-L/D-lactide (PLDLA96) implants were used for large blow-out defects in 18 sheep. The contralateral side, where the defects healed spontaneously, served as controls. The follow-up was 12, 16, 22 and 36 weeks. Healing was evaluated clinically, radiologically, histologically and immunohistochemically. Physiochemical properties of the implants were also studied. At first, the implants were surrounded by elastic capsules, which gradually ossified. At 36 weeks, 60% were still visible and deformed but surrounded by bone. Light microscopy revealed a low grade inflammatory reaction. Expression of Tn-c and cFn was intense throughout the study. Shear strength decreased gradually and was not measurable after 16 weeks. Crystallinity increased steadily from 1.5 to 29.30% and molecular weight decreased from 49,000 to 4186. In CT, the final bony defect was smaller in the reconstructed sides than in the controls. Based on this study it can be concluded that PLDLA96 implant provokes a local inflammation, which does not prevent bone healing. The deformation of the implant, however, indicates that this PLDLA96 plate is not suitable for orbital floor reconstruction.

The introns of the canine rod opsin gene show higher sequence homology to the human than to the rodent introns

Using genomic DNA from late-onset retinal degenerate and wild type Labrador Retrievers as templates and canine exon-specific oligonucleotides as primers in polymerase chain reaction, all four introns of opsin were cloned and sequenced. Dot-matrix comparisons were made for human, murine and canine introns. Selected sequences containing either intronic or coding sequences were aligned and used for phylogenetic relationship analysis. The opsin gene introns are conserved between the human, the mouse and the dog with regards to number and length. In addition there is an astonishingly high degree of sequence homology between the second and fourth introns. Introns 2(1277 bp in dog) and 4 (863 bp in dog) are 72% and 71% homologous to the human introns, and 57% and 52% homologous to the mouse introns, respectively. The coding sequence (CDS) of the dog shows 93% homology to human CDS and 88% homology to mouse CDS. A phylogenetic analysis of the intronic sequences 2 and 4 confirms the higher relatedness between dog and human than between mouse and human opsin genes. As there are good reasons to believe that the primate and rodent lineages are closer to each other than to the Canis familiaris, there must be some functional constraints on the evolution of human and dog opsins.

Inflammatory cells in experimental intervertebral disc injury

STUDY DESIGN

Inflammatory cells were located by immunocytochemistry in areas of experimental intervertebral disc injury in pigs.

OBJECTIVES

To study the occurrence of T lymphocytes and macrophages 1 week, 1 month, and 3 months after partial-thickness transverse scalpel injuries in pig lumbar discs.

SUMMARY OF BACKGROUND DATA

Inflammatory cells and mediators recently have been observed in disc herniation tissue that was removed at disc prolapse surgery. The prevalence of inflammatory cell infiltrates in such clinical disc tissue material also has been studied. There are no studies, however, that have analyzed, using immunocytochemical methodology, the occurrence of, types of, and time dependence of inflammatory cells in an experimental disc injury model. The role of inflammation in intervertebral disc injury and repair has not been determined.

METHODS

Transverse scalpel injuries 5-mm long and 4-mm deep were cut in the anterolateral anulus of L5-L6 and L4-L5 discs in 16 pigs. The cuts in the center of the anulus did not reach the nucleus pulposus and never produced a disc prolapse. In every pig, two non-adjacent lumbar discs (L1-L2 and L2-L3) were used as controls. Four discs per animal were studied in parallel by two different complementary immunohistochemical staining protocols. T lymphocytes and macrophages were located immunohistochemically using CD3 and CD68 antibodies, respectively. Discs were removed for analysis from four pigs at 1 week, from six pigs at 1 month, and from six pigs at 3 months. Inflammatory cells were categorized by two independent observers as being entirely absent (-), only few scattered cells (+), and at least one larger cellular infiltrate (+2).

RESULTS

In none of the discs could extensive inflammatory cell infiltration be observed. T lymphocytes were present in significantly more sections cut from injured discs than in sections cut from control discs. The difference was highly significant particularly at 1 week and 1 month after disc removal. Only the 1-month-after-injury sections from injured discs exhibited significantly more macrophages than those from control discs.

CONCLUSIONS

The results suggest the presence of only modest inflammatory cell infiltration in experimental intervertebral disc injury at all follow-up times. The inflammatory response in partial-thickness anterior experimental intervertebral disc injury, in the absence of disc prolapse, seems to be dominated by a T lymphocyte response. The macrophage response is apparently strongest at 1 month after such injury. These findings differ from what has been observed in herniated disc tissue.

The use of a coral composite implant containing bone morphogenetic protein to repair a segmental tibial defect in sheep

A composite implant consisting of a coral cylinder, moose bone morphogenetic protein and type IV collagen was used to repair a segmental tibial defect in sheep. Healing, related variance in mechanical strength and immune responses were evaluated. In comparison with a coral control, a larger amount of newly formed external callus was observed in the composite group at 6 weeks. The maximal torque capacity, maximal angular deformation at failure and bone stiffness of a healed osteotomised tibia recovered 113%, 117% and 120% in the coral controls and 67%, 92% and 79% in the composite implants against the corresponding contralateral tibia at 16 weeks respectively. A significantly elevated anti-BMP antibody was detectable in the composite group at 3 and 6 weeks. Augmented bone formation at an early stage and weakened torsional performance at a later stage in the composite implants may indicate the phase-specific osteoinduction and the immune response of xenogenic BMP with time.

Cloning and analysis of the cDNA encoding the rod G-protein transduction alpha, beta1 and gamma1 subunits from the canine retina

The canine (Canis familiaris) retinal rod transducin (G(T)) alpha, beta1 and gamma1 subunits were sequenced. Cloning of the cDNAs was accomplished by polymerase chain reaction (PCR) using degenerate and wild type retinal cDNA libraries as templates. The deduced amino acid sequences were highly similar to rod transducins from other species: G(T alpha) differed by 5 amino acids from the corresponding human sequence, whereas beta1 and gamma1 were identical to human sequences. The coding sequence of rod transducin was evaluated as a possible cause for the recessively inherited retinal rod-cone degeneration: there were no nucleotide differences between the wild type and retinal degenerate strains.

Cloning of the cDNA encoding rod photoreceptor cGMP-phosphodiesterase alpha and gamma subunits from the retinal degenerate Labrador retriever dog

The nucleotide (nt) sequence of the cDNA encoding the retinal rod cyclic 3'5'-GMP phosphodiesterase (PDE) alpha and gamma subunits from two strains of dogs-(i) Labrador Retrievers homozygous for autosomally recessively inherited rod-cone degeneration and (ii) the wild-type Beagle-are reported. Cloning of these subunits was accomplished by polymerase chain reaction using retinal cDNA libraries as templates. The nt sequence of alpha PDE predicts a 861-amino-acid polypeptide which is 97.7 per cent and 96.9 per cent identical to the bovine and human counterparts, respectively. PDE gamma encodes an 87-amino-acid polypeptide differing from bovine and murine gamma subunits by only one amino acid. Since no differences were found between these two strains of dogs, the cause of the Labrador Retriever's degeneration remains to be determined.

Impaired retinal function in young labrador retriever dogs heterozygous for late onset rod-cone degeneration

Xenon-flash d.c.-electroretinograms were recorded from dark adapted, rod-cone degenerate homozygote affected (n = 6), heterozygote carrier (n = 3) and control retinas (n = 4) at 3 and 4 months of age, starting at 0.6 log units below control PII threshold. One log unit higher stimuli were necessary to evoke PII in heterozygote and affected retinas compared to controls. Unique to the heterozygotes, double peaked PII responses that were evoked by -2 log relative units intensity stimulation were significantly (P = 0.028) lower in amplitude than those of controls. PII amplitudes of homozygotes were significantly (P = 0.005) lower in amplitude than those of controls at both ages examined in response to -2 and 0 log relative intensity stimulation. No differences were found in scotopic threshold response amplitudes or times to peak between the three groups. Homozygote affected PII times to peak were significantly (P = 0.005) shorter in relation to controls at -2 log units. Findings suggest that heterozygotes exhibit an impaired retinal function which can be demonstrated at 3 and 4 months in this mutant.

Morphological and biomechanical difference in healing in segmental tibial defects implanted with Biocoral or tricalcium phosphate cylinders

To evaluate the effects of two bioceramics on bone regeneration during repair of segmental bone defects, Biocoral and tricalcium phosphate cylinders were implanted in osteotomized sheep tibial defects 16 mm in length and followed up for 16 weeks. In comparison with the TCP-implanted defect, a significant increment in area and density of external callus was quantified radiomorphometrically at 3 weeks, and a marked increase in maximal torque capacity, maximal angle of deformation and absorption of energy was demonstrated mechanically in the Biocoral-implanted tibia at 16 weeks after implantation. Better bone integration with the substratum was microscopically observed in Biocoral cylinders. With good osteointegration and biomechanical-performance, Biocoral seems to be superior to TCP in repair of segmental defects in weight-bearing limbs.

Stabilization of an inserted tricalcium phosphate spacer enhances the healing of a segmental tibial defect in sheep

The effect of inserting a tricalcium phosphate (TCP) spacer stabilized by a rigid or non-rigid fixation technique on the healing of segmental tibial defects of critical size was established. The osteotomized tibiae, 11 with and 8 without TCP spacers, were fixed by an external circular device in 11 mature sheep and by plates in 8 mature sheep, respectively. Healing was evaluated roentgenographically 16 weeks after the operation. Compared with the defects without TCP spacers, enhanced stability and healing were observed in the defects with TCP spacers under an identical external fixation. Furthermore, a significantly higher incidence of healing was obtained with plate fixation than with external device fixation in the TCP-implanted defects (P < 0.04). An abundant bridging callus was roentgenograpically demonstrated in most of the healed defects, but none in the unhealed defects. The TCP spacer with its mechanical integrity enhances the stability of external fixation, and the stable immobilization provided by rigid fixation is essential for osteoconduction of an inserted TCP spacer in the healing of segmental diaphyseal defects in sheep.

Enhanced healing of segmental tibial defects in sheep by a composite bone substitute composed of tricalcium phosphate cylinder, bone morphogenetic protein, and type IV collagen

Diaphyseal segmental defects in the tibia of 18 sheep were used to evaluate the healing potential of a composite bone substitute device (CBS) composed of a tricalcium phosphate cylinder (TCP), naturally occurring sheep bone morphogenetic protein (sBMP), and type IV collagen. A total of 100 mg of sBMP and 20 mg of type IV collagen in the high-dose group (CBSH), and 13 mg of sBMP and 2.5 mg of type IV collagen in the low-dose group (CBSL) were adsorbed to TCP cylinders, respectively. TCP cylinders impregnated with type IV collagen alone (TCPC) were used as control. A significantly larger area and more highly integrated intensity of newly formed external callus between CBSH and CBSL or TCPC group were quantified by computerized image analyzer at both 3 and 6 weeks. A torsion test showed that the maximal torque capacity, maximal angular deformation, and bone stiffness of healed osteotomized tibia with implants recovered 117-125% in CBSH, 72-109% in CBSL, and 63-80% in TCPC, compared with the corresponding contralateral tibia at 16 weeks. A healing superiority of the segmental bone defects replaced by the implants was demonstrated in the CBSH group. Thus, the composite bone substitute device defined in this study was shown to possess osteoinductivity, osteoconductivity, and mechanical strength.

Xenogeneic moose (Alces alces) bone morphogenetic protein (mBMP)-induced repair of critical-size skull defects in sheep

A standardized skull defect in adult sheep was used to test the healing capacity of xenogeneic, partially purified, moose-derived bone morphogenetic protein (mBMP) extracted from the fresh long bones of moose (Alces alces) calves. An amount of 52 mg of mBMP mixed with 13 mg of purified type IV collagen (5:1) (mBMP/COL) in gelatin capsules was implanted into six 22-mm-diameter skull defects in adult sheep for comparison with six defects implanted with fresh autogenous bone marrow (BM) and six other controls implanted with a gelatin capsule containing 13 mg of type IV collagen (C). The amount of new bone formed was quantified from radiographs by computerized image analysis and histology. The healing percentage in the mBMP/COL group was significantly higher (93.18 +/- 4.51%) than in the BM (33.17 +/- 20.05%) or C group (31.32 +/- 17.41%) at 16 weeks after implantation. The difference between BM and C was not statistically significant. The level of anti-BMP antibody in the serum showed a significant increase in the group implanted with mBMP, but returned to normal after 6 weeks. The experiment demonstrated that xenogeneic mBMP possesses a strong osteoinductive capacity and weak immunogenicity.

Propofol influences the electroretinogram to a lesser degree than thiopentone

BACKGROUND

The Electroretinogram (ERG) is used clinically to assess the function of retina. Anaesthetic agents are known to affect ERG, and as anaesthesia is often needed in children and uncooperative patients, knowledge about its effects is of clinical importance. Barbiturates selectively depress ERG components, and we compared thiopentone with propofol to assess if the latter preserved retinal function better.

METHODS

Ten pigs, average weight 17 kg (SD +/- 2 kg) were anaesthetized randomly with propofol 10 mg kg-1 or thiopentone 30 mg kg-1. Anaesthesia was maintained by 65% nitrous oxide in oxygen and continuous infusion of the induction agent, i.e. 10 mg kg-1 h-1 of propofol, or 10 mg kg-1 h-1 for the first hour, then 5 mg kg-1 h-1 of thiopentone, with doses being based on pilot studies. After an interval of one week the programme was repeated using the other agent. After 40 minutes dark-adaptation, responses to single flashes of graded intensities from a xenon flashlamp were recorded at five-minute intervals. The a- and b-wave amplitudes and implicit times (time to peak), and a-wave slopes were determined.

RESULTS

The b-wave implicit time was significantly shorter during propofol anaesthesia than when using thiopentone. The effect was most pronounced at the lowest intensities (P < 0.01). No statistically significant differences were found in the amplitudes of the b-waves. The a-wave appeared at lower stimulus intensity (P < 0.05) and the a-wave slopes were significantly steeper (P < 0.01) during propofol anaesthesia.

CONCLUSION

Propofol accordingly appeared to preserve the photoreceptor response better than thiopentone, and may therefore be considered to be more suitable for ERG recordings than thiopentone.

Elevation of cGMP with normal expression and activity of rod cGMP-PDE in photoreceptor degenerate labrador retrievers

Cyclic guanosine 3',5'-monophosphate (cGMP) levels were determined in retinas from a strain of Labrador Retrievers with inherited retinal dystrophy manifesting at early stages of retinal differentiation. The cGMP contents of dystrophic retinas of dogs from 1 to 4 months of age (n = 7) were significantly higher (p = 0.001) than in age-matched controls of the same breed (n = 11). Ultrastructure along the vertical retinal meridian was studied in developing retinas and findings were related to those of age-matched wild-type controls of the same breed. Slow central to peripheral progression of degeneration was observed in affected dogs. No differences were found in total cGMP-phosphodiesterase (PDE) activity, in PDE subunit composition as determined by Western blotting of 2-month-old homozygote affected retinas, or in the amino acid sequence deduced from the nucleotide sequence of the PDE beta-subunit as compared to controls. This model of photoreceptor degeneration thus is the first case of an apparent abnormality of cGMP metabolism that is not associated with a defect in the PDE catalytic subunits, and it is also the first reported model not associated with severe developmental abnormalities and rapid degeneration.

Microscopic evaluation of bone-implant contact between hydroxyapatite, bioactive glass and tricalcium phosphate implanted in sheep diaphyseal defects

In order to compare morphological discrepancies in bone-implant contact in vertebrates, cylinders of hydroxyapatite, bioactive glass and tricalcium phosphate were implanted in segmental defects of the tibia in sheep. Three types of visible bone-implant contact were observed microscopically at 4 months after implantation. The trabecular web-like bone-implant contact noted in tricalcium phosphate seemed superior to the disseminated patchy bone-implant contact in bioactive glass and the buttressed bone-implant contact in hydroxyapatite with respect to both bone ingrowth and bioresorption of the implant. Differences of physicochemical properties on the surface among the three kinds of bioceramic implants probably give rise to different types of bone-implant contact.

The late positive retinal potential in dogs

The late positive potential of the mammalian electroretinogram has been called the 'PI' or the 'c-wave' potential. It is unusual among retinal potentials because its peak implicit time increases in response to increasing stimulus intensity and because it cannot be demonstrated consistently in small samples of normal humans or normal dogs. We recorded wideband (DC-1 kHz) responses from 34 normal Beagles or dogs of similar size. Of the 34, 11 produced a late positive potential set that satisfied the criteria for c-waves. Multiple aspartate injections always increased c-wave amplitude and stimulus-response linearity in all 'producers'. Non-producers were never converted to producer status by aspartate blocking of the inner retina. Interaction of late positive and negative potentials and the possible influence of normal individual variations in the trans-epithelial potential are discussed. Individual mammal c-wave production is controlled by outer retinal phenomena which vary between individuals.

Early morphometry of a retinal dystrophy in Labrador retrievers

Retinal morphometry was assessed in 7 dogs from a colony of Labrador Retrievers with dystrophic retinas at 1,2,3,4 and 18 months of age. Rod outer segment length and outer nuclear layer width were measured in the central, midperipheral and peripheral retina at six locations along the vertical meridian. Early striking regional differences in onset and rate of progression were characteristic for this inherited retinal degeneration. Notably, some areas of the retina developed fully and normally before degenerating. The central parts of the vertical meridians showed slightly disorganized rod outer segments already at 1 month of age and they were significantly shorter than those of control animals at 3 and 4 months (p < 0.01 and p < 0.001, respectively). The rod outer segments of the midperipheral and peripheral regions were, however, comparable to control animals as late as at 4 months of age. At 18 months the rod outer segments of dystrophic animals were significantly shorter in all retinal regions (p < 0.0005). At the age the outer nuclear layer of the dystrophic animals had become significantly thinner than that of control animals in all retinal regions (p < 0.001), indicating a clear visual cell loss. It is reasonable to characterize this as a retinal degeneration having a relatively slow progression, which enhances its relevance to conditions of clinical significance.

Pigment epithelial function in canine retina

The lateral distribution and temporal changes in the eye standing potential of 15 dogs with normal eyes (as determined by use of an ophthalmoscope and electroretinography) were measured by use of noninvasive methods. The standing potential was converted to an alternating potential by controlled eye movement. The light peak occurred 6 minutes after a stimulus intensity increase of 4 log units. The ratios of the highest measured voltage after the light step divided by the voltage measured immediately before the light step ranged from 1.27 to 2.07 (mean 1.74 +/- SEM, 0.064). The responses typically decayed slowly after the light peak. The potential after the light peak did not return to prelight step values during the observation period. The field potential of the standing potential decreased nonlinearly in temporal direction from the outer canthus.

Ultrastructural and ERG findings in progressive rod-cone dystrophy in a litter of Labrador retrievers

Early ultrastructural findings of a progressive photoreceptor dystrophy and corresponding ERG findings are reported in 3 Labrador Retrievers from a litter of 7 pups bred from 2 dogs clinically and electroretinographically affected with generalized progressive retinal dystrophy. The pups were euthanized at 5, 11 and 15 months post partum. The most prominent ultrastructural finding was photoreceptor dystrophy. At 5 months the outer nuclear layer (ONL) consisted of 8-10 layers and seemed reduced in thickness, pyknotic nuclei were seen in this layer. The receptor outer segments (OS) were short and swollen. Some disorientation of OS discs occurred. In the 11-months specimen 7-8 ONL layers were identified. Overall thinning of the neuro-retina had occurred and fewer receptors compared to the 5-months specimen were present. By 15 months the ONL was further reduced to about 4 layers. Enlarged internuclear spaces were present in the ONL as well as around inner segments (IS). Phagocytic cells were frequent among remains of OS. The pigment epithelium appeared normal. The dark adapted ERG b-wave amplitudes and photopic 30 Hz flicker responses were low in comparison to controls of the same breed, and decreased with age. The condition represents a progressive rod-cone dystrophy which shares similarities with primary receptor dystrophy in man such as retinitis pigmentosa.

A DC electroretinography method for the recording of human a-, b- and c-waves

In the clinical ERG the c-wave is not usually recorded due to methodological problems. Because of the potential importance of the c-wave recording in assessing the function of the pigment epithelium in several retinal diseases, we describe a DC ERG method which is convenient for the patient and suitable also for clinical practice. The light stimuli are provided by a Ganzfeld stimulator and the potentials are recorded with a disposable corneal wick electrode. The method allows the recording of the c-wave from co-operative subjects as well as to study the a- and b-wave properties.

A late receptor dystrophy in the Labrador retriever

Dark adapted single flash and light adapted 30 Hz photopic flicker ERGs were recorded from a litter of seven Labrador Retrievers bred from parents affected with generalized progressive rod-cone dystrophy. After an initial increase of b-wave amplitudes from 5 weeks to 4 months similar to the controls, the b-wave amplitudes of the litter were significantly decreased (P less than 0.005) at 7 months. At 21 months the b-wave amplitudes were very low, although some response to 30 Hz photopic flicker was still left. The ERG changes indicated a late onset progressive rod-cone dystrophy which developed after maturation of the retina. The development of this photoreceptor dystrophy has not previously been described.

Effects of intracamerally or subconjunctivally injected cross-linked hyaluronic acid on the intraocular pressure and on the anterior segment of the rabbit eye

Cross-linked hyaluronic acid (CLH), a viscoelastic substance with a high viscosity, was injected into the left anterior chamber of 5 rabbits without simultaneous withdrawal of aqueous humour. The right eyes of the same rabbits received an equal amount of sodium hyaluronate (Healon). The intraocular pressure (IOP) of the CLH injected eyes increased four-fold immediately after the injection. One week post injection the IOP had decreased to the pre-injection level where it remained until the euthanatization of the animals 32 days post injection. Biomicroscopically CLH was seen as a slightly opaque curly mass in the anterior chamber in the eyes that otherwise were quiet in four of the rabbits. In one rabbit the injected cross-linked substance reacted immediately with aqueous and turned white. The eye was quiet and showed no inflammatory signs. In all intracamerally injected eyes, slight to moderate aqueous flare was present 4 h post injection. Aqueous flare was still present 1 day post injection in 4 eyes, but was absent 4 days post injection. Histologically no apparent inflammatory reaction was present. Occasional giant cells were seen on the anterior surface of the iris in three animals. Slight accumulation of mononuclear cells was found in the iridocorneal angle of the CLH injected eyes. At histology few mononuclear cells were also found surrounding the subconjunctivally injected CLH still present in 4 additional rabbits when euthanatized 28, 42 and 49 days post injection. The contralateral eye of these 4 animals received an equal amount of sodium hyaluronate subconjunctivally. The substance had been resorbed completely. No reactive or inflammatory signs were present.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of thiopentone halothane-nitrous oxide anaesthesia compared to ketamine-xylazine anaesthesia on the DC recorded dog electroretinogram

Eleven ophthal-moscopically healthy dark adapted dogs were examined by DC ERG technique with single flash full field illumination starting with near b-wave threshold blue (tests 1-3) and white (tests 4-6) stimuli of different intensity and ending with 30 Hz photopic flicker smuli (test 7) after light adaptation. All animals were anaesthetized using 2 different anaesthetic methods: Anaesthesia I (A I): Induction with thiopentone sodium, continued with halothane and nitrous oxide in oxygen. Anaesthesia II (A II): Praemedication with xylazine hydrochloride followed by anaesthesia with ketamine hydrochloride. A minimum interval of 1 week was kept between all anaesthesias.

The a- and b-wave amplitudes and latencies were determined. Statistical analysis of results indicated that the a- and b-waves were elicited by weaker intensities in A II. In Tests 3-6 the a-wave was highly significantly (P < 0.001), higher in amplitude in AII than in A I. Differencies in b-wave amplitudes were not statistically significant (except Test 1). The b-wave latencies were longer in AI in Test 2 (using low intensity blue light). The a-wave latencies were slightly shorter in AII in Test 6 (using high intensity white light).

In additional experiments the selective action of the different agents (except N₂O) used in AI and AII was studied. Thiopentone alone given to 3 dogs seemed to depress the a-wave selectively.

Halothane given separately to 3 dogs lowered both the a- and b-wave amplitudes. Ketamine given with a neuromuscular blocking agent to three dogs resulted in responses almost identical to those in AII.

Xylazine with vecuronium given to 4 dogs resulted in responses with slighly depressed a- and b-waves in comparison to ketamine with vecuronium.

The results indicate that when developing an animal model for the electrophysiologic study of human retinal dystropies, the actions of different anaesthetics upon the ERG components are of great importante.

The DC-recorded dog electroretinogram in ketamine-medetomidine anaesthesia

A new selective alpha 2-adre-noreceptor agonist, medetomidine hydrochloride was combined with low dosage ketamine hydrochloride and vecuronium bromide for d.c. (direct current) recordings of fast electroretinographic (ERG) components in nine ophthalmoscopically healthy dark adapted dogs. The dogs were tracheally intubated and manually ventilated. They were given full field single flash stimuli of different intensities starting with near b-wave threshold blue light (tests 1-3), followed by white light (tests 4-6) and 30 Hz photopic flicker (test 7). The a- and b-wave amplitudes and flicker responses were measured from the base line. The latencies were measured from the stimulus moment to the highest point of the different waves.

Statistical analysis of results gave individual differencies which had a good constancy. This showed that the dogs had an individual ERG profile according to the standardized method. The latencies varied very little as expected, but the amplitudes differed individually and showed a good constancy as seen by reproducibility tests made nine to ten days later on three of the dogs’ ipsilateral eyes. The combination of drugs used in this study was considered suitable for short term (10-12 minutes) stable d.c.–ERG recordings in dogs as the rod and cone responses had higher amplitudes when compared to an identical examination made with other anaesthetic combinations on the same dogs.

Involuntary eye movements and other involuntary muscular activity caused by ketamine in dogs were negligible when using medetomidine premedication and was completely absent when using vecuronium.

The anaesthetic method described can be recommended for ambulatory ERG recordings in dogs because of the above mentioned advantages.

Electroretinography in Labrador retrievers given ketamine-xylazine anesthesia

Electrophysiologic examination of scotopic and photopic retinal function was done in 31 young healthy Labrador Retrievers and 6 Labrador Retrievers with ophthalmoscopic signs of generalized progressive retinal atrophy (PRA). Scotopic responses to 4 stimulus intensities (b-wave threshold and 0.65-, 1.60-, and 2.59-log relative units above b-wave threshold, tests 1, 2, 3, and 6, respectively) were determined, using single-flash stimulation. Alternating current recorded single-flash c waves (stimulus intensity 3.18-log relative units above b-wave threshold, test 4) and 30-Hz photopic flicker (stimulus intensity 1.92-log relative units above b-wave threshold, test 7) responses were recorded. Results of the single-flash recordings from 31 healthy dogs were analyzed statistically. The method used allowed for a separation of rod and cone function. Tests 3, 6, and 7 were most useful in determination of retinal disease, when results of the healthy young dogs were compared with results obtained from generalized PRA-affected dogs. Various doses of ketamine and xylazine in dogs with ophthalmoscopically normal fundi had no significant effects on a- and b-wave amplitudes when dogs were given single-flash stimuli 1.60-log relative units above b-wave threshold (test 3). Three 3-year-old dogs, with ophthalmoscopic signs of generalized PRA, had greatly reduced a- and b-wave amplitudes and unaltered or slightly shortened a- and b-wave latencies. One 3-year-old dog with normal-appearing fundi had responses similar to those of dogs with generalized PRA of the same age. On repeated examination 6 months later, this dog had ophthalmoscopic and angiographic signs of generalized PRA.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluorescein angiography in homozygote and carrier state of progressive retinal atrophy of the poodle; comparative aspects with human retinitis pigmentosa

Fluorescein angiographic findings in 7 carriers and 7 homozygotes of a recessively inherited disease, generalized progressive retinal atrophy of the poodle, are described in detail and comparisons with 24 healthy control poodles are presented. Two angiographic types of the disease could be distinguished. These are: Type 1, a diffuse, widespread choriocapillaris atrophy associated with retinal vascular and depigmentation changes and Type 2, a predominantly retinal involvement combined with focal choroidal atrophic patches lineating major vessels. These findings share similarities with the observations made of the human disease, retinitis pigmentosa. Unaffected carriers of the disease showed characteristic fundus changes in angiography: patchy, hyperfluorescent depigmentation changes and often minor narrowing and irregularities of the arterioles and poorly visible capillary bed.

Fluorescein angiography of the canine ocular fundus in ketamine-xylazine anesthesia

Fluorescein fundus angiography was performed on 30 dogs with no pathologic fundus findings using a Canon CF 60 Z wide angle camera. In serial photography of the dye passage 4 different circulatory phases could be distinguished: choroidal, retinal anteriolar, capillary and venous phase. The dye passage in the retinal vessels was described in detail. For aesthesia the combination of ketamine and xylazine proved to be suitable.