Development and characteristics of a synovial-like interface membrane around cemented tibial hemiarthroplasties in a novel rat model of aseptic prosthesis loosening.

OBJECTIVE: Aseptic prosthesis loosening (APL) is related to the formation and aggressive growth of a synovial-like interface membrane (SLIM) between prosthesis and bone. However, investigation of the early phases of SLIM development in humans presents major difficulties. This study was undertaken to develop and characterize the usefulness of a novel animal model of APL that is based on an established model of defined exercise in a running wheel by Wistar rats that have been subjected to intracranial self-stimulation (ICSS). METHODS: Cemented tibial hemiarthroplasties were implanted into the left knees of 7 male Wistar rats. After 2 weeks, exercise in a running wheel was started in all rats, with a running-load of 2 hours/day for 5 days/week. Six months postoperatively, the knee joints were removed, decalcified, and embedded in paraffin. Histologic evaluation on hematoxylin and eosin-stained sections was performed to investigate the development of a SLIM and the presence of cement debris particles. To characterize the SLIM on a molecular level and investigate growth-regulating factors, the expression of transforming growth factor beta (TGFbeta) and the anti-apoptotic molecule Bcl-2 was analyzed by immunohistochemistry. RESULTS: Although the prostheses appeared mechanically stable after 6 months, the development of SLIM with areas of bone resorption was seen in all samples. Resembling human SLIM, these membranes consisted of loose fibrous tissue, with cement debris particles located particularly at sites originally attached to the prostheses. Immunohistochemistry studies revealed the expression of TGFbeta and Bcl-2 in all specimens. Interestingly, staining for TGFbeta and Bcl-2 was restricted to areas where the SLIM were attached to bone. In contrast, there was only negligible expression of both proteins at sites adjacent to the prostheses. CONCLUSION: Our findings demonstrate that the ICSS Wistar rat model constitutes a feasible tool for studying early stages of APL, and specifically the effect of defined running exercise on SLIM formation. The results further suggest that both cellular proliferation, as stimulated by TGFbeta, and altered apoptosis contribute to early stages of SLIM formation. The expression patterns of TGFbeta and Bcl-2 indicate that the growth of the SLIM is initiated and promoted from the bone rather than from the prosthesis.

[Joint loading as a possible etiology for arthrosis development. Results of animal experiment studies of the rat model]. / Gelenkbelastung als eine mögliche Ursache der Arthroseentstehung. Ergebnisse tierexperimenteller Untersuchungen am Rattenmodell.

We review our results with an animal model for investigations on the development of osteoarthritis (OA). This model is based on running exercises of wistar rats performed in a running wheel using intracranial self-stimulation to motivate rats to excessive running. In our studies a total of 49 rats was divided into groups with running exercises of 15 km, 20 km, and 30 km respectively. In order to investigate the influence of altered sensible joint innervation on the development of OA, in addition to a total running load of 20 km in another group of 8 rats we performed Capsaicin (8 Methyl-N-vanillyl-6-noneamide) mediated partial sensible knee joint denervation. Complete knee joint sections of all rats were evaluated histologically using Mankins grading system. In addition, we performed semiquantitative assessment of the immunoreactivity of the chondrocytes to MMP-3 by immunostaining with monoclonal MMP-3 IgG antibodies. Histological assessment and immunostaining for MMP-3 of the knee joint sections revealed a significant increase in osteoarthritic changes with higher running load. Moreover, osteoarthritic changes in the knee joints of the rats with sensible joint denervation and running exercises were significantly greater as compared to those with sole running load. In conclusion, our studies revealed a significant relationship between the development of knee osteoarthritis and the extent of joint load. Hereby, an alteration of the sensible joint innervation seems to have a promoting effect on the development of osteoarthritic changes. This model offers a wide range of further approaches to studying different processes of the development of OA.

Central vasopressin administration failed to influence anxiety behavior after pinealectomy in rats.

Experiments were performed to measure the influence of centrally applied arginine vasopressin (AVP) on anxiety-related behavior in pinealectomized (PE) rats and sham-operated (SO) controls. In the PE animals, microdialysis application of 200 pg AVP into the mediolateral septum, as well as intracerebroventricular administration of 10 ng AVP, failed to influence anxiety-related behavior measured in the elevated plus-maze test. However, in SO animals, the percentage of time spent on the open arms of the elevated plus-maze was found to be higher in both experiments. Pinealectomy alone was without effect in this respect. The results suggest that central AVP may be involved in the modulation of anxiety-related behavior in rats, even though this modulation is dependent on an intact pineal function.

Increased plasma ACTH in rats exposed to the elevated plus-maze is independent of the pineal gland.

The involvement of the pineal gland in activation of the hypothalamic-pituitary-adrenocortical (HPA) axis evoked by a stressful stimulus (exposure to the elevated plus-maze) was investigated. Plasma ACTH levels were measured in pinealectomized and pineal-intact rats (sham-operated and non-operated) immediately after a 5 min placement into a plus-maze. A statistically significant elevation in plasma ACTH was measured within all groups; however, no statistical differences between pinealectomized and pineal-intact rats were observed. Similarly, comparison of the plasma ACTH basal values obtained from animals only kept in their home cages did not reveal any statistical differences between pinealectomized and pineal-intact rats. From these results it can be concluded that the pineal gland is not involved in anxiety-related behavior and ACTH response.

The effect of combined oestrogen and progesterone replacement on the renal responses to oxytocin and vasopressin in ovariectomized rats.

OBJECTIVE: Renal responsiveness to the neurohypophyseal hormones, oxytocin and vasopressin, has been shown in the rat to vary during pregnancy and lactation. A study was performed to determine whether ovarian steroids could contribute to the observed changes. DESIGN: Using a previously validated method, fluid excretion during infusion of oxytocin or vasopressin was monitored in ovariectomized animals with and without chronic administration of oestrogen and progesterone. METHODS: After 14 days treatment with vehicle or 12.5 mg hydroxyprogesterone caproate and 0.25 mg oestradiol valerate injected every 3 days, rats were infused with 0.077 mol/l NaCl for an equilibration period of approximately 2.5h. Timed urine collections for the determination of volume and electrolytes were then made during a control period of at least 45 min and for 60 min while the infusate was supplemented with vasopressin (40 fmol/min) or oxytocin (50 fmol/min). Further observations were made for a final 90 min of hypotonic saline infusion. In control infusions saline alone was given. RESULTS: Treatment with ovarian steroids did not affect the volume of urine excreted during hormone infusion. Electrolyte excretion, however, was affected with lower concentrations of sodium and chloride on oxytocin infusion being seen in the steroid-treated animals. During vasopressin infusion, peak electrolyte concentrations were also achieved later in this group of animals. CONCLUSION: The increased circulating concentrations of oestrogen and progesterone seen during pregnancy could contribute to variations in the natriuretic response to neurohypophyseal hormones observed in the rat.

[Deterioration of sensory joint innervation as an enabling factor for development of arthrosis. An animal experiment study of the rat model]. / Störung sensibler Gelenkinnervation als begünstigender Faktor für die Arthroseentstehung. Eine tierexperimentelle Untersuchung am Rattenmodell.

In the present study we investigated the influence of an altered sensible joint innervation on the development of knee osteoarthritis in a wistar rat model of osteoarthritis. Capsaicin (8-methyl-N-vanillyl-6-noneamide) mediated partial sensible knee joint denervation was performed in a group of 16 male wistar rats. Twelve rats without alterations of the sensible knee joint innervation served as controls. In both groups, half of the rats underwent strenuous running exercises (total running load of 20 km) in a running wheel by intracranial self-stimulation, while the other half did not have any running load. In rats without running, there were no histological sings of knee osteoarthritis according to the Mankin score. In contrast, in rats running a total of 20 km significant osteoarthritis changes were observed. Hereby, in rats without altered sensible knee joint innervation, osteoarthritis was mostly classified as mild or moderate, while severe osteoarthritis was the predominant finding in the knee joints of the rats with partial sensible knee joint denervation. In conclusion, our study gives strong evidence for the hypothesis that an altered sensible joint innervation works as a contributing factor in the development of osteoarthritis.

Septal vasopressin modulates motility and passive avoidance in pinealectomized rats.

Experiments were performed to investigate the role of central arginine vasopressin (AVP) in an interrelationship with the pineal gland on motility and passive avoidance response in rats. The involvement of the pineal gland in behavioral paradigms was examined using pinealectomized (PE) and pineal-intact (sham-operated and nonoperated) animals. Central administration of 200 pg AVP or 40 ng of the AVP receptor antagonist, d(CH2)sThyr(Et)VAVP (AAVP) was performed into the mediolateral septum by means of microdialysis probes. The blockade of vasopressinergic neurotransmission or neuromodulation into the septal area by AAVP decreased the motility in both pineal-intact groups, whereas AVP was without effect. In PE rats during AVP administration an increased motility was found, but AAVP was without effect. In pineal-intact rats the avoidance latency of passive avoidance retrieval was not influenced after application of both AVP and AAVP. However, an increase in avoidance latency was found both immediately and 24 h after AVP or AAVP administration into the septum of PE rats. The results support the hypothesis that septal AVP modulate motility and passive avoidance behavior and this modulation is influenced by the pineal gland.

Differential behavioral effects of TFF peptides: injections of synthetic TFF3 into the rat amygdala.

TFF peptides (formerly named P-domain peptides or trefoil factors) are also released from the brain as well as being secreted typically by mucin producing cells. The amygdala, besides the hypothalamus, represents a defined neuronal locality of TFF3 synthesis. In a passive avoidance test synthetic TFF3/monomer or 0.9% sodium chloride (control) was injected bilaterally into the basolateral nucleus of the amygdala of male rats either immediately (consolidation test) or 23 h after a footshock (retrieval test). Application of a low TFF3 dose (2 x 6 pg) decreased avoidance latency in a time dependent manner. In contrast, a high dose (2 x 60 pg) increased avoidance latency. Maximal effects of TFF3 were observed about 24 h after the injection. This bidirectional effect was also observed using the elevated plus-maze test. The locomotor activity on the open arms was significantly increased 24 h after a low dose injection of TFF3 into the amygdala. In contrast, a high-dose injection significantly decreased the activity on the open arms. The results of both tests can be explained by an anxiolytic effect at a low dose and an anxiogenic effect at a high dose of synthetic TFF3/monomer.

Vasopressin administration modulates anxiety-related behavior in rats.

Experiments were performed to measure the influence of centrally and peripherally applied arginine vasopressin (AVP) on anxiety-related behavior as indicated by the elevated plus maze test. Central administration was performed into the septum using a microdialysis technique. In initial experiments, the microdialysis probes were characterized for substance application in vivo by means of 125I AVP, measuring the substance-specific percent passover and the spatial distribution around the microdialysis membrane within the brain. Both microdialysis administration of 200 pg of AVP into the septum and and intraperitoneal application of 500 ng of AVP induced an increase in the percentage of time spent on the open arms of the elevated plus maze. The blockade of vasopressinergic neurotransmission or neuromodulation into the septal area by 40 ng of the AVP receptor antagonist d(CH2)5Thyr(Et)VAVP failed to induce a significant effect in this respect. The observation that neither centrally nor peripherally applied AVP influenced the locomotor activity on the elevated plus maze supports the hypothesis that AVP is involved in the modulation of anxiety-related behavior in rats.

Development of osteoarthritis in the knee joints of Wistar rats after strenuous running exercise in a running wheel by intracranial self-stimulation.

The influence of excessive running load on the development of knee osteoarthritis (OA) was investigated in male Wistar rats. Running exercises were performed in a running wheel using intracranial self-stimulation to motivate Wistar rats to run daily distances of 500 m at 5 days/week. Hereby, ten rats ran a distance of 15 km within three weeks while a further ten rats run a total of 30 km within six weeks. Thirteen Wistar rats without running exercises served as controls. Complete knee joint sections of all rats were evaluated histologically using MANKINs grading system with categorization of the findings into non, mild moderate, and severe osteoarthritis. In addition, immunoreactivity of the chondrocytes to MMP-3 as an important cartilage degrading enzyme in OA was assessed by immunostaining with monoclonal MMP-3 IgG antibodies. Histological assessment of the knee joint sections revealed a significant increase in osteoarthritic changes with higher running load. While in rats with 15 km running all but two knee joints showed mild OA, moderate OA was the predominant finding in rats with 30 km running. In contrast, no OA was found in the controls. Immunostaining for MMP-3 revealed a significant increase in immunoreactivity of the chondrocytes to MMP-3 with higher running load, indicating a running load-depending production of this cartilage-degrading enzyme in the course of increasing OA. Compared to 47.4% immunoreactive chondrocytes to MMP-3 in the controls, this ratio rose to 70.4% in rats with 15 km running and even up to 89.9% in rats with 30 km running. In conclusion, in Wistar rats, excessive running load leads to marked, running distance-depending osteoarthritic changes which are caused, at least in part, by an increase in MMP-3 production rising with greater running distance. Within this exercise model of OA, intracranial self-stimulation is an effective method to motivate Wistar rats to extremely excessive running in a running wheel. This model offers a wide range of further approaches to studying different processes of the development of OA.

Effects of methylphenidate on oxytocin and vasopressin levels in pinealectomized rats during light-dark cycle.

Although previous reports have shown that methylphenidate (MPH), in addition to its known behavioral effect, can influence the hypothalamo-pituitary-adrenal axis by increasing the plasma ACTH, the pineal gland seems to be involved in neuroendocrinological processes too, e.g., in hypothalamic synthesis and release of oxytocin (OXY) and vasopressin (AVP). Therefore, a study was performed to measure the OXY and AVP content of the hypothalamus, neurohypophysis, and plasma after application of MPH in the morning and evening in pinealectomized (PE) as well as sham-operated control (SO) rats. Pinealectomy influenced both the daily pattern (reversed in the neurohypophysis) and the levels of OXY and AVP. Starting from this different situation, application of MPH produced diverse effects. Hypothalamus: PE, increase in both hormones in the morning and evening; SO, decrease in morning OXY level. Neurohypophysis: PE, increase in morning OXY level; SO, decrease in both hormones even though in the morning only. Plasma: PE, decrease in morning OXY concentration; SO, increase in both hormones in the morning and decrease in the evening. The present results indicate that MPH application influences the hypothalamo-neurohypophysial system. Furthermore, the hypothesis has been supported that this influence may be dependent on the circadian activity of the pineal gland as well.

Effect of pinealectomy and melatonin on vasopressin-potentiated passive avoidance in rats.

The pineal indoleamine, melatonin, and the hypothalamic neuropeptide, vasopressin, facilitate passive avoidance behaviour in rats. The similarity of the effects suggest that interaction might occur between the two substances. Therefore, the effect of intraperitoneally applied vasopressin and/or melatonin on one-trial learning passive avoidance behaviour was studied in pinealectomized rats. Intraperitoneal treatment with 500 ng vasopressin 1 hr before the retention test increased passive avoidance latency of sham-operated rats. In pinealectomized rats, an identical amount of vasopressin was ineffective. In sham-operated rats, melatonin blocked the effect of vasopressin. It is concluded that vasopressin needs a regulated pineal function for developing effects in passive avoidance behaviour.

Intracerebroventricular but not intraperitoneal administration of aluminum attenuates vasopressin-enhanced retrieval of a passive avoidance task in rats.

We studied the influence of single intracerebroventricular (ICV) and intraperitoneal (IP) injections of the neurotoxin aluminum on the retrieval of a passive avoidance task in rats and on the vasopressin-evoked improvement of the recall of the task. It was found that ICV administration of the metal alone strongly decreases the retention time of a passive avoidance task, whereas IP application of aluminum prolongs it. Vasopressin given ICV and IP leads to an enhancement of retrieval (prolongation of the retention time). Vasopressin in combination with aluminum does not improve the recall of the task when both substances are given ICV. Intraperitoneal injection of the neuropeptide together with the metal improves the recall of the task. Our data point to the crucial importance of the route of application of aluminum for behavioral studies.

Effect of perinatal dexamethasone treatment on conditioned taste aversion in rats.

Effect of perinatal dex Rats received a single subcutaneous injection of 1 mg/kg dexamethasone at the age of seven days. One hundred days after the treatment, conditioned taste aversion was determined in the adult animals. Perinatally applied dexamethasone did not affect water consumption but caused a significant attenuation of conditioned taste aversion. These findings may be explained by dexamethasone effects upon brain development which cause impairment of memory functions or, alternatively, decreased responsiveness to aversive stimuli.

Increased locomotor activity of rats by self-stimulation in a running wheel.

A method was developed in which the intracranial self-stimulation of rats was dependent on their locomotor activity. During each rotation of a running wheel (= 0.75 m), six stimulus trains were administered via electrodes in the medial forebrain bundle. Under these conditions, animals increased their locomotor activity 112-fold, compared to a control condition without self-stimulation. This method may be a valuable procedure in various research fields where extreme increases in motor activity of laboratory animals are advantageous.

Intracerebroventricular administration of insulin attenuates retrieval of a passive avoidance response in rats.

The effect of intracerebroventricularly applied insulin on one-trial learning passive avoidance behaviour has been studied in rats. Treatment with 10.3 pmole insulin 1 hr before the 24 hr retention test attenuated passive avoidance behaviour at both the 24 hr and 48 hr retention trials. The data suggest that insulin may play a role in processes relating to the retrieval of information stored in the brain.

Measurement of septal release of vasopressin and oxytocin by the push-pull technique following electrical stimulation of the paraventricular nucleus of rats.

The release of vasopressin (AVP) and oxytocin (OXT) within the septum was studied with the push-pull perfusion technique in 6 conscious, freely behaving male rats. Push-pull perfusion was performed via a chronically implanted cannula and samples collected for 3 consecutive 30-min periods. Stimulating electrodes were implanted in both the left and right paraventricular nuclei 4 days before the experiment. Bilateral electrical stimulation (10-s trains every 4 min) of the paraventricular nuclei during the second 30-min period resulted in a significant increase in the release of both AVP and OXT (128% and 159% of control values respectively); release returned to the pre-stimulation value during the final 30-min collection.

Central and peripheral release of vasopressin and oxytocin in the conscious rat after osmotic stimulation.

Vasopressin (AVP) and oxytocin (OXT) were measured by radioimmunoassay in push-pull perfusates and tissue samples of various brain areas, plasma and cerebrospinal fluid (CSF) of male rats in response to osmotic stimulation. Hypertonic saline caused a significant rise in plasma AVP and OXT and different changes in peptide contents, in the septum and hippocampus at 30 and 60 min after intraperitoneal injection. Push-pull perfusion (20 microliters artificial CSF/min, 30-min periods) of the septum and dorsal hippocampus of conscious, unrestrained animals revealed a significant, stimulus-evoked release of both AVP and OXT. This release was: (1) not always reflected by corresponding changes in the regional peptide content; (2) simultaneous with the peripheral release from the posterior pituitary; and (3) probably the result of synaptic/parasynaptic events as suggested by use of agents in the artificial CSF which either inhibit or facilitate the release from intact fibre terminals.