Spontaneous recovery of excitation and inhibition.

In two conditioned suppression experiments with rats as subjects, the authors examined two classes of accounts of spontaneous recovery of excitation and inhibition. One view suggests that spontaneous recovery occurs due to greater temporal instability of inhibitory associations, whereas the other posits that spontaneous recovery occurs due to greater temporal instability of second-learned associations. These accounts diverge in predictions concerning spontaneous recovery when the first-learned association is inhibitory and the second-learned association is excitatory.

Overshadowing and CS duration: counteraction and a reexamination of the role of within-compound associations in cue competition.

In the present experiments, we examined the role of within-compound associations in the interaction of the overshadowing procedure with conditioned stimulus (CS) duration, using a conditioned suppression procedure with rats. In Experiment 1, we found that, with elemental reinforced training, conditioned suppression to the target stimulus decreased as CS duration increased (i.e.

Overexpectation and trial massing.

Three experiments were conducted to examine the interaction of overexpectation treatment and trial massing using a Pavlovian fear conditioning procedure with rats. In first-order conditioning, Experiment 1 found the overexpectation effect (i.e.

Fibrogenesis imperfecta ossium (Baker's disease): a case studied at autopsy.

A man aged 40 years showed radiographic changes in the form of generalized increased bone density and patchy rarefaction. Urinary calcium was increased and serum alkaline phosphatase was elevated; serum calcium and phosphate levels were normal. Multiple fractures developed.

Fibrous dysplasia of bone: case report with autopsy study 80 years after the original clinical recognition of the bone lesions.

We present a report of the histological features of the bone lesions in a case of polyostotic fibrous dysplasia studied at autopsy in a patient aged 88 years. While much of the fibrous tissue of the lesions contained the trabeculae of non-lamellar bone that are a feature of fibrous dysplasia in young patients, other parts of the lesions showed evidence of osteoclastic remodelling of bone trabeculae, and even of the replacement of some of these structures by mature lamellar bone.

The World Health Organization's histologic classification of bone tumors. A commentary on the second edition.

Background: The World Health Organization's histologic classification of bone tumors was revised in 1993.

Methods: The first edition was reviewed by an international panel of pathologists from nine countries and modified to incorporate advances made in the twenty years since it appeared.

Results: The framework and concept of the classification remain the same (i.

Calcified spherules in fibro-osseous lesions of bone.

We present 20 examples of fibro-osseous lesions of bone, characterized by the presence of varying numbers of rounded calcified structures (calcified spherules). In the past, such lesions have been regarded as ossifying fibromas or cementifying fibromas, the latter because of their histologic similarity to jaw lesions known by that name. In the present series, six lesions showed, in addition to the calcified spherules, typical histologic features of fibrous dysplasia, while a further seven showed atypical bony structures that also suggest a link with fibrous dysplasia.

Membranous bone lengthening: a serial histological study.

Bone lengthening using the process of corticotomy and gradual distraction of callus is applicable to the membranous bone of the canine mandible. In this study the precursors to bone formation, in the area between the distracted bone edges, are analyzed in an attempt to determine the mechanism of bone formation. Ten mongrel dogs 5 months of age were studied.

Pathology of osteonecrosis of the femoral head. A review of experience at the Hospital for Joint Diseases, New York.

Pathological examination of the resected femoral heads from approximately 2000 total hip replacement operations carried out at the Hospital for Joint Diseases from 1984 to 1989 identified the presence of osteonecrosis in 345 patients (377 femoral heads). In 232 patients the osteonecrosis, referred to as "idiopathic," had occurred in the absence of a subcapital fracture. The present paper describes the pathology of the necrotic lesions in these 232 patients.

Case report 662. Bilateral avascular necrosis of femur, with supervening suppurative arthritis of right hip.

We present a case of suppurative arthritis occurring in a patient with bilateral osteonecrosis of the femoral head. Predisposing factors were chronic alcoholism (osteonecrosis) and septicemia due to intravenous drug abuse (suppurative arthritis). Although the association of suppurative arthritis and osteonecrosis is rarely reported in the literature, the prevalence of osteonecrosis and of various factors predisposing to the development of suppurative arthritis should remind us of the possibility that a patient with osteonecrosis who develops sudden worsening of joint pain or fever may have developed suppurative arthritis of the affected joint, particularly when there is evidence of bone destruction.

Bone lengthening in the craniofacial skeleton.

The process of bone lengthening by cortical fracture and gradual distraction of callus has become well established in the enchondral bones of the extremities. In this study the principles of bone lengthening were applied to the membranous bone of the craniofacial skeleton using the growing dog mandible as a model. Six mongrel dogs five months of age were studied.

A light and scanning electron microscopic study of osteocyte activity in calcium-deficient rats.

The material herein is an extension of an earlier study of osteocyte lacunae in calcium-deficient rats, utilizing morphometric measurements in undecalcified bone sections and scanning electron microscopy. The results confirm our earlier finding that bone resorption resulting from a low-calcium diet is not accompanied by osteocytic resorption.

The role of rigid skeletal fixation in bone-graft augmentation of the craniofacial skeleton.

The type of fixation (rigid skeletal vs. wire) was assessed against embryologic origin (membranous vs. endochondral) and recipient site (depository vs.

Tumoral calcium pyrophosphate deposition disease.

A report of two patients in which a soft tissue mass, initially regarded as a malignant tumor, was shown to be the result of calcium pyrophosphate deposition disease. The first case, a woman aged 71 years, presented with a mass involving the right fifth finger. In the second case, also a woman aged 71 years, the lesion involved the tissues adjacent to the right hip.

Aneurysmal bone cyst. A review of 123 cases including primary lesions and those secondary to other bone pathology.

A group of 639 bone lesions was reviewed in order to study the features of the aneurysmal bone cyst and its association with other conditions. A diagnosis of primary aneurysmal bone cyst not associated with any other bone lesion was made in 87 patients. In 36 additional patients the gross and microscopic changes of aneurysmal bone cyst were identified as part of some other solid bone lesion.

Malignant transformation of fibrous dysplasia. A case report and review of the literature.

A 34-year-old man developed a spindle-cell sarcoma originating in a preexisting lesion of monostotic fibrous dysplasia. A review of the literature reveals 83 cases of a malignant degeneration in fibrous dysplasia; osteosarcoma was the most common type of tumor. The next most common were fibrosarcoma and chondrosarcoma.

Expression of Ia and monocyte-macrophage lineage antigens in giant cell tumor of bone and related lesions.

An immunohistochemical study of six giant cell tumors of bone and eight related lesions (aneurysmal bone cyst, fibrous histiocytoma, and giant cell tumor of tendon sheath) was performed using a panel of monoclonal antibodies directed to the Ia and monocyte-macrophage lineage antigens. In all types of lesion, osteoclastlike multinucleate giant cells were negative for both types of antigen, but a proportion of mononuclear cells gave positive reactions. While the possibility that these cells are reactive cannot be excluded, in giant cell tumor and malignant fibrous histiocytoma, their frequency and their morphologic similarity to the rest of the tissue suggest that they may be an intrinsic part of the neoplasm.

Lysozyme and alpha 1-antitrypsin in giant-cell tumor of bone and in other lesions that contain giant cells.

We performed an immunohistochemical study of 24 giant-cell tumors of bone and 30 other lesions (fibrous histiocytoma, nonossifying fibroma, and giant-cell tumor of the tendon sheath) using lysozyme and alpha 1-antitrypsin as markers for histiocytic cells. The presence of histiocytic cells in giant-cell tumors of bone is confirmed by the finding of a positive reaction for alpha 1-antitrypsin in both multinucleate giant cells and mononuclear stromal cells in some cases. It is not clear whether the positive cells are to be regarded as neoplastic or reactive and alpha 1-antitrypsin is not considered as a diagnostically useful marker for giant-cell tumor of bone.

The effect of discography on the canine intervertebral disc.

With increasing use of chemonucleolysis, interest and use of discography is at an all-time high. Various reports in past years have disagreed on the safety and efficacy of intradiscal injections of contrast mediums. This experimental study was devised to determine the effects of discography on the gross and histologic appearance of the lumbar intervertebral disc.

Mechanisms of bone resorption in calcium-deficient rats.

A study of surface remodeling activity and osteocyte lacunar area was made in young and adult rats maintained on a low-calcium diet, to explore cellular mechanisms of bone resorption. The diet produced active remodeling of the endosteal part of the femoral cortex, with a decrease in the amount of bone present. Surface resorption, with numerous osteoclasts, was evident, but there was no evidence of osteocytic osteolysis in bone which, by tetracycline labeling, could be identified as existing at the commencement of the experimental period.

Radiographic hallmarks of peripheral chondrosarcoma.

Ten peripheral chondrosarcomas, nine arising in the cap of an osteochondroma and one developing as a primary periosteal tumor, are reported. The radiological and histological features of these tumors are compared with those of 203 benign osteochondromas and two soft-tissue chondrosarcomas. In 3 of the 10 cases, cytological evidence of malignancy could not be demonstrated, although the size of the tumors and the presence of extension into adjacent soft tissues indicated that they were low-grade chondrosarcomas.

Delineation of four cell types comprising the giant cell tumor of bone. Expression of Ia and monocyte-macrophage lineage antigens.

Giant cell tumors of bone dissociated by collagenase digestion were found to be composed of four different cell types defined by morphology, growth in culture, and pattern of staining with monoclonal antibodies. Giant cells comprised an average of 0.8% of the cells recovered, with the remainder consisting of small stromal cells.