Multiple Synapse Formation: A Possible Compensatory Mechanism for Increased Cell Size in Rat Supraoptic Nucleus

Magnocellular neuroendocrine cells of the rat supraoptic nucleus undergo numerous morphological changes during chronic dehydration of the animal. These changes include increases in cell size, the percentage of neuronal membrane in direct apposition and formation of new multiple synapses (i.e. terminals which form more than one synapse with adjacent somata and/or dendrites). Previous studies of multiple synapse formation in the supraoptic nucleus did not include adjustments for changes in somatic size, thus the full extent of synapse formation relative to increases in cell size was not known. That multiple synapse formation is a compensatory mechanism for increased somatic size was investigated by comparing animals that were either chronically dehydrated (by drinking 2% saline) or were well hydrated. Using morphometric techniques the percentage of somatic membrane contacted by single and multiple synapses was obtained. Estimates of somatic surface area were used together with stereologically derived estimates of the number of synapses per μm² to calculate the number of single and multiple axo-somatic synapses per neuron. Measures of soma-somatic and soma-dendritic membrane apposition and glial coverage were made to confirm earlier estimates of these parameters. Somatic surface area increased by more than 70% in dehydrated animals. Percentage of somatic membrane contacted by single synapses was lower (by 41%) and that contacted by multiple synapses was higher (by 100%) in dehydrated as compared to control animals. The number of single synapses was not different between the two groups but dehydrated animals had more multiple synapses per soma (23) than controls (6). With dehydration, there was an eight-fold increase in the percentage of somatic membrane contacted by adjacent somatic/dendritic membrane. The surface area per somain such direct apposition was fifteen-fold higher in dehydrates compared to controls. Glial processes covered the same proportion of somatic membrane in the two groups, while the actual area covered by glial processes per soma was higher in dehydrated animals. These results are consistent with the hypothesis that multiple synapse formation at least partially compensates for probable relative decreases in synaptic efficacy as synaptic density decreases when cells increase in size due to dehydration. This altered synaptic input as well as the increased direct apposition between adjacent neurons probably contribute to their enhanced activation during periods of increased hormone demand.     

Activation of excitatory amino acid inputs to supraoptic neurons. II. Increased dye-coupling in maternally behaving virgin rats

Electrical stimulation of the lateral olfactory tract (LOT) has been shown to excite, monosynaptically, supraoptic nucleus (SON) neurons in slices of hypothalamus taken from male, virgin female or lactating rats. Only in the last of these, however, did 10 min of 10 Hz stimulation produce an increase in the incidence of Lucifer yellow dye-coupling, an indicator of electrotonic interactions. This coupling is virtually exclusively dendrodendritic. Since virgin females that have been induced to show full maternal behavior have altered dendritic morphology reminiscent of lactating animals (but different from males and untreated virgins) we investigated the effects of LOT stimulation in slices from maternally behaving virgins. Similar to the data for lactating rats, electrical stimulation of this tract, the terminals of which release excitatory amino acid transmitter, increased the incidence of dye-coupling by 112% (P less than 0.01). Also similar to lactating rats, the coupling was dendrodendritic and the increase was due entirely to increasing the number of neurons coupled to the injected neuron. No increase in coupling was seen in stimulated slices from pup-exposed control rats. We conclude that the maternal behaviors engaged in by both real mothers and induced virgins 'primes' the supraoptic neurons to increase coupling in response to olfactory system stimulation. This priming may occur via olfactory and vomeronasal stimulation during such behaviors as sniffing and anogenital licking of the pups. That coupling increased in tissue from maternally behaving virgins comparably to that from nursing mothers further suggests that SON neurons may play a role in maternal behavior independent of its well-documented role in the milk ejection reflex.     

Mammographic findings after breast cancer treatment with local excision and definitive irradiation

Following local excision and definitive irradiation of 163 breast cancers in 160 women, alterations in mammographic patterns were observed for up to 7 years. Skin thickening was observed in 96% of mammograms obtained within 1 year of completing therapy and was most pronounced in women treated with iridium implant, chemotherapy, or axillary dissection. In 76% of mammograms, alterations in the parenchymal pattern, including coarsening of stroma and increased breast density, were seen at 1 year. Neither skin nor parenchymal changes progressed after 1 year. Within 3 years of treatment the parenchymal density, which usually regressed, did not change in all patients. At 3 years skin thickness and the parenchymal pattern had returned to normal in less than 50% of the breasts of these women. Scars developed in approximately one-quarter of women. They were present on the initial post-treatment mammogram and remained unchanged on serial studies. Coarse, benign calcifications also developed in the breasts of about one-quarter of women. Microcalcifications developed in 11 breasts; biopsy specimens of six were benign. Benign microcalcifications may be related to therapy.     

Lymphangiomas in children: MR imaging

Seventeen lymphangiomas in 15 patients were imaged with magnetic resonance (MR) to define the nature, extent, and anatomic relationships of these lesions. The MR and pathologic findings were then compared to determine the histologic basis for the signal-intensity characteristics of these lesions. The signal intensity of 13 lesions was similar to or slightly less than that of muscle on T1-weighted images and greater than that of fat on T2-weighted images. This appearance correlated with the presence of ectatic lymphatic channels containing clear fluid on histologic section. Four lymphangiomas had high signal intensity, approximately equal to that of fat, on T1-weighted images, reflecting the presence of clotted blood or small cystic spaces with a higher ratio of fat to fluid. Sixteen of 17 lesions had visible septations on MR images. The authors' experience suggests that most lymphangiomas have a characteristic appearance on MR images. The information obtained with MR imaging can help in providing a preoperative diagnosis, in planning surgical resection, and in defining recurrence.     

Liver metastases: detection by phase-contrast MR imaging

Forty patients with biopsy-proved metastatic liver cancers were studied by magnetic resonance (MR) imaging using one or more conventional (in-phase) pulse sequences and a corresponding phase-contrast (opposed-phase) pulse sequence. Pulse-sequence performance was quantitated by measuring signal-difference-to-noise (SD/N) ratios between cancerous tissue and liver. The SD/N performance of T2-weighted spin-echo (SE) pulse sequences improved when used with the phase-contrast technique. SE 2,000/30 opposed-phase images showed improved (P less than .001) SD/N in 72% of patients over in-phase images. The SD/N of T1-weighted SE or inversion recovery pulse sequences deteriorated when used with the phase-contrast technique. Changes in measured SD/N correlated well with image appearance and actual lesion detectability in individual cases. Phase-contrast imaging should be employed routinely when T2-weighted SE pulse sequences are relied on to detect liver cancer.     

Temperature rise due to finishing of direct restorative materials

An in vitro study was performed to evaluate the effect of four variables on the temperature rise produced by the finishing of restorations. The four variables were: restorative material, finishing agent, finishing time, and depth of dentin under the restoration. Class V preparations were cut on extracted premolars and restored with amalgam, composite, or glass ionomer cement. Finishing was done with wet pumice and cup, wet pumice and a brush, a grit rubber polishing point, and an aluminum oxide- coated disc. Finishing time was continuous or intermittent for up to 1 minute. Dentin thickness under the restoration was 0.5 mm to 3.0 mm. Amalgam produced the highest temperature rises at the pulp, while composite and glass ionomer were no different than the untreated (virgin) tooth. Aluminum oxide discs produced the largest temperature rise, wet pumice with a brush the least. Temperature rise increased almost linearly with continuous finishing, while intermittent finishing significantly reduced temperature rise in all cases. Thickness of remaining dentin was only significant for the amalgam restoration, and then only at 1.0 and 0.5 mm.     

Low-speed rotational angioplasty in chronic peripheral artery occlusions: experience in 83 patients. Work in progress

Between December 1986 and October 1988, 83 patients with chronic peripheral artery occlusions were treated with a new technique. In 56 patients, the superficial femoral artery was completely occluded; in 21 patients, the popliteal artery; and in six patients, the iliac artery. The length of occlusion ranged from 5 to 35 cm (mean, 12.5 cm). The duration, estimated by history, was 5-48 months (mean, 16.5 months). In seven patients, durations of 6-36 months were documented angiographically. A flexible, blunt, motor-driven rotating catheter was introduced through an 8-F sheath, and rotational angioplasty was performed at low speed (up to 200 rpm). In 49 of 60 (82%) patients in whom this new technique was used as the primary intervention, the occlusions were successfully reopened. In 23 patients in whom conventional methods had failed more than 4 weeks earlier, the success rate for rotational angioplasty was 67% (12 of 18 patients); when the time interval was less than 4 weeks, only one of five patients was treated successfully. In none of the 83 patients did a perforation occur. This new technique can reopen chronic artery occlusions with a high degree of success and without the danger of vessel-wall perforation, even after failure of conventional techniques.     

Collateral input to the paraventricular and supraoptic nuclei in rat. I. Afferents from the subfornical organ and the anteroventral third ventricle region

Injections of two fluorescent retrograde tracers were used to investigate the existence of collateral branching of input to the hypothalamic magnocellular neuroendocrine neurons. Injection of one tracer (either Fluoro-Gold or rhodamine-labeled microspheres) into the supraoptic nucleus and the other tracer into the ipsilateral paraventricular nucleus produced labeled neurons within the subfornical organ and the anteroventral third ventricle area. Some labeled cells were found to contain both fluorescent tracers (double-labeled cells), suggesting that they project to both the paraventricular and supraoptic nuclei via branching axons. Most double-labeled cells were found within the subfornical organ. Fewer of these cells were located within the nucleus medianus preopticus, and still fewer were distributed in the organum vasculosum lamina terminalis, the bed nucleus of the stria terminalis, and the medial and the lateral preoptic areas. These data present the first direct evidence that single cells may provide input to more than one magnocellular neuroendocrine nucleus. Hypothetically, hormonal release would require coordinated firing of many magnocellular cells. Thus, the branched input to these neurons may assist in the organization and the timely activation of this system in response to physiological stimuli.