Constant light and pinealectomy disrupt daily rhythm in song production and negatively impact reproductive performance in zebra finches

We assessed the circadian clock control of singing and reproductive performance in zebra finches. Experiment 1 examined changes in body mass, testis size, and plasma corticosterone and testosterone levels in male birds exposed to constant light (LL, 100 lx) and constant darkness (DD, 0.5 lx), with controls on 12L:12D (L = 100 lx, D = 0.5 lx). There was a significant increase in the body mass and testis size under LL and a decrease in testis size under the DD. Using a similar design, experiment 2 assessed the persistence of the circadian rhythm in singing along with activity-rest pattern in cohort I birds that were entrained to 12L:12D and subsequently released in DD or LL, and in cohort II birds that were entrained to 12L:12D and following pinealectomy were released in DD. Both activity and singing patterns were synchronized with the light phase under 12L:12D, free-ran with a circadian period under DD, and were arrhythmic under the LL. There was an overall decreased and increased effect on singing under DD and LL, respectively, albeit with differences in various song parameters. The pinealectomy disrupted both activity and singing rhythms but did not affect singing or the overall song features. Pinealectomized bird pairs also exhibited a significant reduction in their nest-building and breeding efforts, resulting in a compromised reproductive performance. These results suggest a circadian clock control of singing and more importantly demonstrate a role of the pineal clock in breeding behaviors, leading to a compromised reproductive performance in diurnal zebra finches.

The effects of pinealectomy and melatonin treatment in acrylamide-induced nephrotoxicity in rats: Antioxidant and anti-inflammatory mechanisms

OBJECTIVE

Acrylamide (AA) is toxic and forms in food that undergoes high-temperature processing. This study aimed to investigate the effects of AA-induced toxicity on renal tissue in pinealectomized rats and the possible protective effect of exogenous Melatonin (ML) administration.

MATERIALS AND METHODS

Sixty rats were randomized into 6 groups (n = 10): Sham, Sham+AA, Sham+AA+ML, PX, PX+AA, and PX+AA+ML. Sham and pinealectomized rats received AA (25 mg/kg/day orally) and ML (0.5 ml volume at 10 mg/kg/day, intraperitoneal) for 21 days.

RESULTS

The results showed that malondialdehyde (MDA), total oxidant status (TOS), oxidative stress index (OSI), tumor necrosis factor-α (TNF-α), and interleukin 1β (IL-1β) levels of the kidney and urea and creatinine levels of serum in the PX (pinealectomy)+AA group were more increased than in the Sham+AA group. In addition, glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), and total antioxidant status (TAS) levels decreased more in the PX+AA group than in the Sham+AA group. Also, we observed more histopathologic damage in the PX+AA group. On the other hand, up-regulation of kidney tissue antioxidants, down-regulation of tissue oxidants, and improvement in kidney function were achieved with ML treatment. Also, histopathological findings such as inflammatory cell infiltration, shrinkage of glomeruli, and dilatation of tubules caused by AA toxicity improved with ML treatment.

CONCLUSION

ML supplementation exhibited adequate nephroprotective effects against the nephrotoxicity of AA on pinealectomized rat kidney tissue function by balancing the oxidant/antioxidant status and suppressing the release of proinflammatory cytokines.

The role of melatonin deficiency induced by pinealectomy on motor activity and anxiety responses in young adult, middle-aged and old rats

BACKGROUND

Aging affects anxiety levels in rats while the pineal gland, via its hormone melatonin, could modulate their inherited life "clock." The present study aimed to explore the impact of plasma melatonin deficiency on anxiety responses and the possible involvement of the hypothalamic-pituitary-adrenocortical (HPA) axis and heat shock proteins (Hsp) 70 and 90 in the frontal cortex (FC) and the hippocampus in young adult, middle-aged and elderly rats with pinealectomy.

RESULTS

Melatonin deficiency induced at different life stages did not affect the lifespan of rats. Pinealectomy abolished the circadian rhythm of motor activity, measured for 48 h in the actimeter, in young adult but not in middle-aged rats. Pinealectomy reduced the motor activity of the young adult rats during the dark phase and impaired the diurnal activity variations of old rats. The same generations (3- and 18 month-old rats with pinealectomy) had lower anxiety levels than the matched sham groups, measured in three tests: elevated-plus maze, light-dark test, and novelty-suppressed feeding test. While the activity of the HPA axis remained intact in young adult and middle-aged rats with melatonin deficiency, a high baseline corticosterone level and blunted stress-induced mechanism of its release were detected in the oldest rats. Age-associated reduced Hsp 70 and 90 levels in the FC but not in the hippocampus were detected. Pinealectomy diminished the expression of Hsp 70 in the FC of middle-aged rats compared to the matched sham rats.

CONCLUSIONS

Our results suggest that while melatonin hormonal dysfunction impaired the motor activity in the actimeter and emotional behavior in young adult and elderly rats, the underlying pathogenic mechanism in these generations might be different and needs further verification.

Therapeutic role of melatonin on acrylamide-induced hepatotoxicity in pinealectomized rats: Effects on oxidative stress, NF-κB signaling pathway, and hepatocellular proliferation

Acrylamide (AA) is formed in some foods by the cooking process at high temperatures, and it could be a carcinogen in humans and rodents. The purpose of the current study was to reveal the possible protective effects of melatonin against AA-induced hepatic oxidative stress, hepatic inflammation, and hepatocellular proliferation in pinealectomized rats. Hence, the sham and pinealectomized rats were consecutively given AA alone (25 mg/kg) or with melatonin (10 mg/kg) for 21 days. Melatonin acts as an antioxidant, anti-inflammatory, and antiapoptotic agent and introduces as a therapeutic strategy for AA-induced hepatotoxicity. Melatonin supplementation reduced AA-caused liver damage by decreasing the serum AST, ALT, and ALP levels. Melatonin raised the activities of SOD and CAT and levels of GSH and suppressed hepatic inflammation (TNF-α) and hepatic oxidative stress in liver tissues. Moreover, histopathological alterations and the disturbances in immunohistochemical expression of NF-κB and Ki67 were improved after melatonin treatment in AA-induced hepatotoxicity. Overall, our results demonstrate that melatonin supplementation exhibits adequate hepatoprotective effects against hepatotoxicity of AA on pinealectomized rat liver architecture and the tissue function through the equilibration of oxidant/antioxidant status, the regulation of cell proliferation and the suppression of the release of proinflammatory cytokines.

A surgical modification in the technique of rat pinealectomy

BACKGROUND

Several experimental intents require pineal gland removal. The main challenge of the pinealectomy surgical procedure is the hemorrhage due to the transverse sinus torn. The study aimed to modify the rat pinealectomy surgical procedure to reduce the risk of bleeding and the mortality rate.

METHODS

Adult male rats experienced pinealectomy surgery. A mini-drill was used to remove a small skull area in the junction of the lambda and sagittal sutures. The pineal gland was removed using a curved-head hook. Animals experienced intensive post-surgical care. Locomotion, cerebellar motor function, working memory, and anxiety were evaluated 2 weeks after pinealectomy by the open field, rotarod, Y maze, and the elevated plus maze, respectively.

RESULTS

Surgical modification reduced the bleeding risk and animal mortality rate. No significant alteration was found in locomotion and working memory. However, the pinealectomy was anxiogenic and decreased entry to the open arm. The cerebellar motor performance did not change in the rotarod test. Hematoxylin-Eosin staining of removed tissue confirmed the histology of the pineal gland.

CONCLUSION

Advantages of this technique were removing a small skull area, modifying the hook insertion point to prevent damaging the brain veins, reducing the bleeding risk and the mortality rate. Surgery modification was associated with a decreased final number of animals used. Regardless of the melatonin shortage, pinealectomy affects different organs, which should be considered in the research study design.

Crocin treatment exerts anti-inflammatory and anti-oxidative effects in liver tissue damage of pinealectomized diabetic rats

Diabetes mellitus (DM) is a chronic metabolic disorder with an increasing global prevalence that leads to significant morbidity and mortality. The liver plays a vital role in glycemic regulation in physiological and pathological conditions such as DM. Free radical formation and inhibition of antioxidant defense systems play a role in the liver damage pathogenesis in diabetic patients The antioxidant, anti-diabetic, anti-inflammatory, and radical scavenging properties of crocin are known. This study was designed to determine the possible protective effects of crocin against liver tissue damage in pinealectomized diabetic rats. Sixty rats were divided into six groups: Control, Sham+streptozotocin (STZ), Pinealectomy (PINX), PINX+STZ, PINX+Crocin, and PINX+STZ+Crocin. PNX procedure was carried out on the first day of the experiment. Intraperitoneal (i.p.) injection of 50 mg/kg STZ was performed on the 30th day of the experiment to induce DM. Crocin (50 mg/kg; i.p.) was applied for 15 days after the pinealectomy procedure and induction of DM. Crocin decreased the markers (alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), interleukin-1β (IL-1β), and malondialdehyde (MDA)) of liver damage and increased antioxidant enzyme levels and tissue total antioxidant status. Histological results showed that the administration of crocin exhibited a protective effect against liver damage caused by STZ. These results indicate that crocin evidence protection against liver injury caused by STZ.

Neuroprotection by melatonin against acrylamide-induced brain damage in pinealectomized rats

The current study aimed to evaluate the neuroprotective effect of exogenous melatonin against acrylamide (ACR)-induced oxidative stress and inflammatory and apoptotic responses in the brain tissues in pinealectomized rats (PINX). ACR is a toxic chemical carcinogen that occurs owing to the preparation of carbohydrate-rich foods at high temperatures or other thermal processes. The rats who underwent pinealectomy and sham pinealectomy were exposed to ACR (25 mg/kg b.w., orally) alone or with exogenous melatonin (10 mg/kg b.w., i.p.) for 21 consecutive days. Alterations of brain oxidant/antioxidant status, dopamine (DA), Brain-Derived Neurotropic Factor (BDNF) inflammatory mediator and apoptosis during exposure to ACR in pinealectomized rats were more than without pinealectomized rats. Histopathological changes were more in brain tissue of pinealectomized rats after ACR administration. Exogenous melatonin treatment in ACR -exposed rats following pinealectomy increased the activities of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) and improved brain total antioxidant status (TAS) compared to PINX+ACR. Moreover, melatonin suppressed lipid peroxidation, inflammatory pathways and apoptosis in ACR-intoxicated brain tissues. In addition, after exposure to ACR on pinealectomized rats, melatonin treatment ameliorated BDNF and DA levels in brain tissues. Furthermore, exogenous melatonin intervention in ACR-intoxicated rats significantly rescued the architecture of neuronal tissues. In summary, the present study, for the first time, suggested that exogenous melatonin treatment could reduce oxidative damage by increasing the activities of antioxidant enzymes, inhibiting lipid peroxidation and inflammation, and improving histopathological alterations in the brain tissue of pinealectomized rats after ACR administration.

Metabolic footprint in young, middle-aged and elderly rats with melatonin deficit

The pineal gland is suggested to be an essential area involved in the programming of fertility, growth, aging, and death of mammals via the released hormone melatonin.The present study aimed to ascertain the effect of melatonin deficit on several physiological and metabolic parameters, closely associated with the aging process, at certain stages of ontogenesis. Sham and rats with pinealectomy, operated at ages 3, 14, and 18-months, respectively, were tested two months later. Sham rats demonstrated an age-related decline of muscle strength, exercise endurance, motor activity, food intake, calorimetric parameters, and impaired lipid profile. Pinealectomy reduced the maximal time to exhaustion and body weight gain while diminished motor activity, food intake, O₂ consumption, CO₂ production, and energy expenditure during the Dark phase in the youngest rat group. In addition, melatonin deficit elevated arterial blood pressure (systolic, diastolic, and mean arterial pressure) and increased serum glucose and triglyceride level in 3-month-old rats while decreased the liver enzyme activity in 14-month-old rats. In conclusion, the present study brought new insights confirming the complex impact of melatonin deficit on important physiological, metabolic and biochemical markers related to aging and demonstrated for the first time that the lack of melatonin hormone is harmful in young adult rats.

Influence of Pinealectomy and Long-term Melatonin Administration on Inflammation and Oxidative Stress in Experimental Gouty Arthritis

Gout is an inflammatory arthritis characterized by the deposition of monosodium urate (MSU) crystals in the joints or soft tissue. MSU crystals are potent inflammation inducers. Melatonin (MLT) is a powerful endogenous anti-inflammatory agent and effective in reducing cellular damage. In the present study, possible underlying mechanisms associated with anti-inflammatory and antioxidative effects were investigated in rats with gouty arthritis and melatonin deprivation treated with MLT. Fifty-six rats were divided into seven groups: control, sham control, pinealectomy (PNX), MSU (on the 30th day, single-dose 20 mg/ml, intraperitoneal), MSU + MLT (10 mg/kg/day for 30 days, intraperitoneal), MSU + PINX and MSU + PINX + MLT. PNX procedure was performed on the first day of the study. As compared to the controls, the results showed that MSU administration caused significant increases in oxidative stress parameters (malondialdehyde and total oxidant status). Besides, significant decreases in antioxidant defense systems (glutathione, superoxide dismutase and total antioxidant status) were observed. A statistically significant increase was found in the mean histopathological damage score in the groups that received MSU injection. It was found that histopathological changes were significantly reduced in the MSU + MLT group given MLT. In our study, it was determined that many histopathological changes, as well as swelling and temperature increase in the joint, which are markers of inflammation, were significantly reduced with MLT supplementation. These results suggest that melatonin ameliorates MSU-induced gout in the rat through inhibition of oxidative stress and proinflammatory cytokine production.

Treatment with crocin suppresses diabetic nephropathy progression via modulating TGF-β1 and oxidative stress in an experimental model of pinealectomized diabetic rats

One of the most common complications of diabetes is diabetic nephropathy (DN). Uncontrolled hyperglycemia leads to histopathologic alterations in the kidney that prevent normal renal function. This study aimed to explore the effects of crocin treatment via virtue of its numerous beneficial properties in streptozotocin-induced pinealectomized diabetic rats. The pinealectomy procedure was conducted on the first day of the study. On the 30th day following pinealectomy, streptozotocin (STZ) (50 mg/kg) was administered intraperitoneally in Wistar rats for induction of diabetes. Diabetes was confirmed on the 3rd day following STZ administration by determining the glucose levels. Daily crocin treatment intraperitoneally for 15 days (50 mg/kg) ameliorated impaired renal oxidant/antioxidant balance, reduced TGF-β1 immuno-staining around tubules, and promoted improvement of renal architecture. Moreover, crocin administration improved altered renal function parameters, including serum Cr and BUN, and also increased creatinine clearance. In conclusion, the protective effects of crocin on diabetic nephropathy might be associated with its powerful antioxidant properties, its ability to improve tissue antioxidant status, and its ability to prevent inflammatory pathways.

Pinealectomy in Rats

The pinealectomy technique consists of the surgical removal of the superficial pineal gland. This procedure allows the ablation of circulating indoles produced by this gland. Withdrawal of systemic melatonin, a pineal hormone, affects animal circadian rhythms and induces several physiological changes that are the subject of many investigations. In this chapter, we describe the pinealectomy protocol adapted to rats. We describe the animal placement on the stereotaxic fixation system, and the procedure for the pineal gland removal and animal recovery from surgery.

Effect of melatonin on T/B cell activation and immune regulation in pinealectomy mice

Melatonin is an indole neuroendocrine hormone that is mainly secreted by the pineal gland to regulate circadian rhythm, antioxidation, and immune regulation. Melatonin plays an important role in T cell-mediated immune responses against cancer, infections, and the development of many autoimmune diseases. The aim of this study was to investigate the immunomodulatory effects of melatonin on T/B cell activation in pinealectomy mice. The improved pinealectomy procedure for mice presented in this study is a good animal model to be used in follow-up studies on melatonin. After pinealectomy, the tissue removed was identified as the pineal body using HE staining. The effects of melatonin supplementation on T cell activation and activation-related changes to the MAPK/NF-κ B pathways were analyzed by flow cytometry and real-time PCR. We found that expression levels of Th1, Th2 and Th17-related cytokines in peripheral blood were lower in mice that had undergone pinealectomy, compared with normal mice. After melatonin supplementation, cytokine levels rapidly increased within a short period of time, which resulted in the gradual recovery of cytokine expression levels. Moreover, activation of T/B cells in mice was weakened and decreased after pineal gland removal. Melatonin was found to inhibit the expression of TLR3, p38, JNK, and MAPK/NF-κ B within a short period (2 weeks) of melatonin replenishment. This inhibition gradually weakened with time, since the degree of inhibition is negatively related with the dosage of melatonin. In conclusion, melatonin may regulate the activation of T/B cells, playing a critical role in the regulation of immune balance.

Effect of pinealectomy on the circadian clock of the chick retina under different monochromatic lights

The avian circadian rhythm pacemaker is composed of the retina, pineal gland and suprachiasmatic nucleus. As an intact input-pacemaker-output system, each of these structures is linked within a neuroendocrine loop to influence downstream processes and peripheral oscillations. While our previous study found that monochromatic light affected the circadian rhythms of clock genes in the chick retina, the effect of the pineal gland on the response of the retinal circadian clock under monochromatic light still remains unclear. In this study, a total of 144 chicks, including sham-operated and pinealectomized groups, were exposed to white, red, green or blue light. After 2 weeks of light illumination, the circadian expression of six core clock genes (cClock, cBmal1, cCry1, cCry2, cPer2 and cPer3), melanopsin (cOpn4-1, cOpn4-2), Arylalkylamine N-acetyltransferase (cAanat) and melatonin was examined in the retina. The cBmal1, cCry1, cPer2, cPer3, cOpn4-1, cOpn4-2 and cAanat genes as well as melatonin had circadian rhythmic expression in both the sham-operated and pinealectomized groups under different monochromatic lights, while cClock and cCry2 had arrhythmic 24 h profiles in all of the light-treated groups. After pinealectomy, the rhythmicity of the clock genes, melanopsins, cAanat and melatonin in the chick retina did not change, especially the mesors, amplitudes and phases of cBmal1, cOpn4-1, cOpn4-2, cAanat and melatonin. Compared to the white light group, however, green light increased the mRNA expression of the positive-regulating clock genes cBmal1, cAanat, cOpn4-1 and cOpn4-2 as well as the melatonin content in pinealectomized chicks, whereas red light decreased their expression. These results suggest that the chick retina is a relatively independent circadian oscillator from the pineal gland, whose circadian rhythmicity (including photoreception, molecular clock and melatonin output) is not altered after pinealectomization. Moreover, green light increases ocular cAanat expression and melatonin synthesis by accelerating the expression of melanopsin and positive-regulating clock genes cBmal1 and cClock.

Melatonin and cortisol secretion profile in patients with pineal cyst before and after pineal cyst resection

A pineal cyst is a benign affection of the human pineal gland on the borderline between pathology and normality. Only a small percentage of patients present with symptoms and a surgical treatment is indicated in highly selected cases. A melatonin secretion in patients with a pineal cyst before and after a pineal cyst resection has not been studied yet and the effect of surgery on human metabolism is unknown. The present study examined melatonin, cortisol and blood glucose secretion profiles perioperatively in a surgical group of 4 patients. The control group was represented by 3 asymptomatic patients with a pineal cyst. For each patient, 24-h circadian secretion curves of melatonin, cortisol and glycemia were acquired. An analysis of melatonin profiles showed an expected diurnal pattern with the night peak in patients before the surgery and in the control group. In contrast, melatonin levels in patients after the surgery were at their minimum throughout the whole 24-h period. The cortisol secretion was substantially increased in patients after the surgery. Blood glucose sampling showed no statistically significant differences. Clinical results demonstrated statistically significant headache relief measured by Visual Analogue Scale in patients after the surgery. Despite the small number of examined patients, we can conclude that patients with a pineal cyst preserved the physiological secretion of the hormone melatonin while patients who underwent the pineal cyst resection experienced a loss of endogenous pineal melatonin production, which equated with pinealectomy. Surprisingly, cortisol secretion substantially increased in patients after the surgery.

Effects of pinealectomy on the neuroendocrine reproductive system and locomotor activity in male European sea bass, Dicentrarchus labrax

The seasonally changing photoperiod controls the timing of reproduction in most fish species, however, the transduction of this photoperiodic information to the reproductive axis is still unclear. This study explored the potential role of two candidate neuropeptide systems, gonadotropin-inhibitory hormone (Gnih) and kisspeptin, as mediators between the pineal organ (a principle transducer of photoperiodic information) and reproductive axis in male European sea bass, Dicentrarchus labrax. Two seven-day experiments of pinealectomy (Px) were performed, in March (end of reproductive season) and August (resting season). Effects of Px and season on the brain expression of gnih (sbgnih) and its receptor (sbgnihr), kisspeptins (kiss1, kiss2) and their receptors (kissr2, kissr3) and gonadotropin-releasing hormone (gnrh1, gnrh2, gnrh3) and the main brain receptor (gnrhr-II-2b) genes, plasma melatonin levels and locomotor activity rhythms were examined. Results showed that Px reduced night-time plasma melatonin levels. Gene expression analyses demonstrated a sensitivity of the Gnih system to Px in March, with a reduction in sbgnih in the mid-hindbrain, a region with bilateral connections to the pineal organ. In August, kiss2 levels increased in Px animals but not in controls. Significant differences in expression were observed for diencephalic sbgnih, sbgnihr, kissr3 and tegmental gnrh2 between seasons. Recordings of locomotor activity following surgery revealed a change from light-synchronised to free-running rhythmic behavior. Altogether, the Gnih and Kiss2 sensitivity to Px and seasonal differences observed for Gnih and its receptor, Gnrh2, and the receptor for Kiss2 (Kissr3), suggested they could be mediators involved in the relay between environment and seasonal reproduction.

Melatonin is a redundant entraining signal in the rat circadian system

The role of melatonin in maintaining proper function of the circadian system has been proposed but very little evidence for such an effect has been provided. To ascertain the role, the aim of the study was to investigate impact of long-term melatonin absence on regulation of circadian system. The parameters of behavior and circadian clocks of rats which were devoid of the melatonin signal due to pinealectomy (PINX) for more than one year were compared with those of intact age-matched controls. PINX led to a decrease in spontaneous locomotor activity and a shortening of the free-running period of the activity rhythm driven by the central clock in the suprachiasmatic nuclei (SCN) in constant darkness. However, the SCN-driven rhythms in activity and feeding were not affected and remained well entrained in the light/dark cycle. In contrast, in these conditions PINX had a significant effect on amplitudes of the clock gene expression rhythms in the duodenum and also partially in the liver. These results demonstrate the significant impact of long-term melatonin absence on period of the central clock in the SCN and the amplitudes of the peripheral clocks in duodenum and liver and suggest that melatonin might be a redundant but effective endocrine signal for these clocks.

Anxiolytic-like effects of a new 1-N substituted analog of melatonin in pinealectomized rats

In spite of the wide variety of drugs available for treating anxiety, this disorder continues to represent a worldwide health problem that is classified within the first 10 causes of disability. Therefore, the search continues for new antianxiety agents, particularly those not related to benzodiazepines. Even though melatonin has been prescribed as an anxiolytic drug, its use is currently limited due to its short half-life and photo-sensitivity, among other disadvantages. The present study explores the antianxiety properties of a new 1-N substituted melatonin analog, M3C, in pinealectomized rats submitted to two behavioral tests (the cumulative burying behavior paradigm and the elevated plus-maze). Results from both tests show that M3C is effective as an anxiolytic-like agent, at doses lower than any other melatonin analog previously reported. The blocking of these actions by luzindole together with the available data suggests that the anxiolytic properties of M3C are mediated by MT1 and MT2 receptors.

Pinealectomy in a broiler chicken model impairs endochondral ossification and induces rapid cancellous bone loss

BACKGROUND CONTEXT

Adolescent idiopathic scoliosis (AIS) in humans is a lateral curvature of the spine often associated with osteopenia. It has recently been accepted that the development of AIS is closely associated with spinal overgrowth. Pinealectomy (PNX) in a chicken model consistently induces scoliosis with anatomic features similar to human AIS; however, the mechanism of PNX inducing scoliosis is poorly understood.

PURPOSE

This experimental study attempts to improve the understanding of the mechanisms underlying the onset of scoliosis in a PNX broiler chicken model.

METHODS

A histomorphometric study was performed to analyze longitudinal bone growth and cancellous bone remodeling before the development of scoliosis. Static and dynamic parameters in cancellous bone and chondro-osseous junction of the 7th thoracic vertebral body at 9 days after hatching were compared between PNX chickens (n=9) and control chickens with no surgery (n=5).

RESULTS

PNX resulted in a rapid and marked loss of cancellous bone volume (7.9±0.9% vs. 14.2±1.8%, mean±SD, p<.0005) and profoundly disrupted trabecular structure with increases in dynamic formative parameters, such as mineralizing surface, mineralization apposition rate, and adjusted appositional rate. In the chondro-osseous junction, activated osteoclasts phagocytized degenerating chondrocytes, leaving a minimal amount of cartilage matrix and activated osteoblasts, losing their scaffolding for bone formation, and directly covering the hypertrophic zone cells. The osteoid surface and thickness in the chondro-osseous junction were significantly increased in PNX chickens (43.1±14.2% vs. 11.6±5.7% and 4.1±0.2 μm vs. 2.9±0.4 μm). In the subjacent cartilage regions being protected from further resorption, abundant labeled cartilage remained with higher cellularity.

CONCLUSIONS

It is known that fast-growing birds have a unique paradigm of rapid bone elongation with minimal metaphyseal bone production. A bone-forming surface exists at the front of cartilage ossification in the growth plate; therefore, papillae of hypertrophic chondrocytes become included between the trabeculae of metaphyseal bone and the overall thickness of the growth plate increases considerably in addition to distal expansion. Our results indicate that the unique mechanism for rapid bone elongation in chicken is more pronounced after PNX. PNX also induces high turnover osteoporosis, which may also contribute to the development of scoliosis in the chicken.