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The response of periodontal ligament mechanoreceptors to mechanical stimuli was studied at different temperatures in anaesthetized cats. Recordings were made from functionally single fibres in the inferior alveolar nerve from mechanoreceptors which were located in the ligament by dissection and punctate stimulation and electrical stimulation. A thermode was used to alter and maintain small areas of periodontal ligament at temperatures ranging from thermode tip temperatures of 3 degrees C to 57 degrees C. The response to ramp-plateau mechanical stimuli applied to the tip of the crown of the canine tooth was greatest when the thermode temperature was 37.5 degrees C +/- 6.5 degrees C. The effect was similar for all receptors studied.

During the course of a study on the morphology of periodontal ligament mechanoreceptors it was observed that a direct relation, without intervening bone, existed between the mandibular canine and first premolar tooth roots in the cat. An area, representing a window in the alveolar septal bone, extended 2–3 mm from the apex towards the tooth crown. Ruffini nerve terminals were observed amongst the collagen bundles in the ligament between the roots of the two teeth. Light and electron microscopy were used to identify the receptors. It is proposed that a periodontal ligament mechanoreceptor can respond to forces applied to adjacent teeth; movement of both teeth need not occur. This may explain the observation made in the past that single periodontal ligament mechanoreceptors respond to forces applied to more than one tooth.

A correlative morphological study was carried out on two electrophysiologically identified and located periodontal ligament mechanoreceptors in anaesthetised cats. One mechanoreceptor had its cell body in the mesencephalic nucleus and the other had its cell body in the trigeminal ganglion. Physiological recordings were made from each of their cell bodies. The two receptors were located by punctate and electrical stimuli in the labial aspect of the periodontal ligament of the left mandibular canine tooth. Both receptors had similar positions relative to the tooth apex and fulcrum and were situated in the labial part of the ligament in each tooth. The receptor loci were marked, and these regions were studied in a series of semi-thin and ultra-thin sections. Only Ruffini nerve endings were observed under each ink mark. Both Ruffini nerve endings branched, were unencapsulated and were incompletely surrounded by terminal Schwann cells with extensions projecting towards collagen bundles. The results indicate that periodontal ligament mechanoreceptors with cell bodies in the mesencephalic nucleus and those with their cell bodies in the trigeminal ganglion can both be Ruffini nerve endings. Furthermore, there was no apparent morphological difference between the two periodontal ligament mechanoreceptors.

1. In anaesthetized cats the left maxillary and mandibular canine and incisor teeth were extracted. Nine weeks later the animals were anaesthetized again and titanium implants were placed into the edentulous ridge of the maxilla and mandible. 2. Terminal experiments were performed between 9 weeks and 10 months after inserting the implants. Recordings were made from the trigeminal ganglia and peripheral nerves of anaesthetized cats. Neurones were identified which responded to forces applied to the maxillary teeth but none was found which responded to forces applied to the implant. 3. The responses of motor units in the temporalis muscle were studied in response to ramp-plateau forces applied to the maxillary canine tooth and maxillary implant using peristimulus time histograms and cumulative sum (cusum) analysis. A small amount of inhibition of the motor units was observed in response to the applied forces to the implant. However, the inhibition was much more profound when similar forces were applied to the tooth. 4. The results confirm that when forces are applied to a tooth, periodontal mechanoreceptors are stimulated which evoke reflex inhibitions to motor units in the jaw-closing muscles. However, there is evidence that mechanoreceptors situated distant to the periodontium can also evoke such reflexes. 5. The results are discussed in relation to the overall functional role of periodontal mechanoreceptors in the reflexes of mastication.

Mathematical models for the analysis of pulse-cytophotometric (PCP) data are described. With computer programs based on these models the fractions of cells in G1-, S- and (G2 + M)-phase are obtained. The methods are applied to PCP-measurements of Ehrlich ascites tumor cells, human bone marrow cells and L-929-cells in culture. The results of the L-cell experiment are compared with autoradiographic results; for both methods the duration of the various phases has been calculated. Two different mathematical models for PCP-data evaluation and the autoradiographic method yielded results agreeing within statistical error. The application of the two models on different types of DNA-histograms is discussed: One model is suitable for asynchronous cell populations with a low fraction of S-phase cells, the other can be applied for partially synchronized cells and high S-phase fractions as well.

The proliferation parameters of the Walker carcinoma were estimated from both in vivo and in vitro measurements. tthe transplantable Walker carcinoma 256 was grown in male inbred BD1 rats. During exponential growth, 5--6 days after transplantation, a PLM curve was performed, yielding estimates of TC approximately equal to 18-0 hr, TS approximately equal to 6-4 hr, TG2+M approximately equal to 4-1 hr. With the double labelling technique in vitro under 2-2 atm oxygen we obtained: TC approximately equal to 18-2 hr, TS approximately equal to 8-2 hr, TG2+M approximately equal to 2-0 hr. From pulse cytophotometry DNA content histograms the fractions of cells in the cell cycle phases were calculated using a computer program: fG1 approximately equal to (47-6 +/- 1-1)%, fS approximately equal to (34-1 +/- 1-0)%, fG2+M approximately equal to (18-3 +/- 1-5)%. These fractions remained constant between the fifth and the twelfth day after transplantation. At that time the tumour growth had already slowed down appreciably. The growth fraction determined by repetitive labelling was 0.96 on the fifth and 0-93 on the seventh and eleventh day. The cell loss factor was phi approximately equal to 17% during exponential tumor growth and increased to about 100% between the tenth and twelfth day. The agreement of the cell kinetic data determined by autoradiography from solid tumours in vivo (PLM, continuous labelling) and autoradiography as well as pulse cytophotometry from in vitro experiments (excised material) was satisfactory.

Summary Cell doubling time, DNA distribution pattern, frequency distribution of chromosome numbers per cell and degree of synchrony obtained after mitotic selection were studied in 4 different sublines of mouse fibroblast cells, NCTC L-929, in culture. The 4 sublines did not differ with respect to their cell kinetic data but showed changes of the chromosome pattern compared to the stemline and compared to each other suggesting that chromosome analysis provides a very sensitive means to detect evolutianary changes of a permanent cell line.

Mouse fibroblast L-929 cells synchronized by mitotic selection were irradiated during the G1-phase of the cell cycle with a dose of 1000 rad. The rate of DNA synthesis was measured by3H-thymidine incorporation, and the progression of the cells through the cell cycle was determined using a pulse-cytophotometer. Irradiation caused a decrease in the rate of DNA synthesis to half the control value, and an extension of the S-phase to twice its normal duration.

THE detection of growth fraction and the characterisation of non-proliferating cells are extremely important in human tumour therapy1,2. Cytological criteria for individual objective discrimination in vivo between non-proliferating and proliferating cells with the same DNA content have not been previously available3. It has been shown recently, in vitro, that the transition from the non-proliferating to proliferating state (G0—G1) of WI-38 cells—human diploid fibroblasts—can be objectively characterised in the intact cell by flow microfluiorimetry4 and geometric–densitometric texture analysis5. Similar differences in nuclear morphometry and chromatin conformation between proliferating G1 and non-proliferating ‘G0 + Q’ cells are reported here for the first time for tumour cells in vivo, by parallel utilisation of objective image analysis and multiparameter laser flow microfluorimetry, both correlated with autoradiography.

Mechanically synchronized cultures of L-cells were treated in various phases of the cell cycle with daunomycin. After incubation for 4 hr at a concentration of 1 μg/ml the percentage of cells in the various phases was determined using an impulse-cytophotometer † . Applying daunomycin in G1 phase produced an arrest of cells in G1 that had not been observed so far or had been considered negligible. When daunomycin was applied in S phase the progression of cells throughout this phase was not influenced and the end of S phase was not delayed, indicating that DNA synthesis of cells having already started DNA synthesis, is not disturbed by daunomycin at this low concentration. Daunomycin treatment in the late S phase or in the G2 phase resulted in an accumulation of cells in G2 (G2 block).

1. In anaesthetized cats recordings have been made in the mesencephalic nucleus of the fifth cranial nerve and the trigeminal ganglion from neurones that respond when forces are applied to the mandibular canine tooth. The site of the mechanoreceptors in the periodontal ligament and their distribution around the tooth root have been determined. 2. Receptors with their cell bodies in the mesencephalic nucleus were found to be situated in the periodontal ligament in a discrete area intermediate between the fulcrum and apex of the tooth, while those in the trigeminal ganglion were situated in the whole area of the periodontal ligament between the fulcrum and apex of the tooth. 3. All of the located mechanoreceptors responded maximally when that part of the ligament in which they lay was put under tension. 4. The directional sensitivities of the mechanoreceptors suggested that there was an uneven distribution around the tooth root of receptors with cell bodies in the mesencephalic nucleus. In contrast mechanoreceptors with cell bodies in the trigeminal ganglion were distributed more equally around the tooth root. The rationale for the differences requires further investigation.

1. Micro-electrode recordings were made from intra-oral mechanoreceptor neurones in the trigeminal ganglion and mesencephalic nucleus of the fifth nerve in the cat. 2. The effect of cervical sympathetic trunk stimulation on the discharge of the mechanoreceptors to a controlled force was observed. 3. Almost half of the mechanoreceptor neurones studied were modulated by sympathetic stimulation. Sympathetic stimulation both decreased the impulse frequency to a controlled force application and raised the threshold in these receptors. The remainder were unaffected by sympathetic stimulation. 4. In previous studies involving recordings from either the trigeminal ganglion or mesencephalic nucleus no spontaneously active slowly adapting intra-oral mechanoreceptors have been observed, yet in peripheral alveolar nerve studies many workers have reported spontaneously discharging neurones. In the present study spontaneous activity has been recorded from intra-oral mechanoreceptors both in the trigeminal ganglion and in the mesencephalic nucleus after cutting the cervical sympathetic trunk. The spontaneous activity could be abolished in all cases but one, by sympathetic stimulation. It is suggested that reported spontaneous activity from intra-oral mechanoreceptors could be due to cutting the peripheral nerve and therefore the sympathetic supply, thus removing an inhibitory influence from the sensory unit. The means by which the sympathetic supply inhibits the sensory unit has not been resolved.