The effects of lesions rostral to the brain stem on breathing responses to hypoxia were determined in chronically catheterized fetal sheep (>0.8 term). These studies were designed to test the hypothesis that the diencephalon is involved in hypoxic inhibition of fetal breathing. As in normal fetuses, hypoxia inhibited breathing with transection rostral to the thalamus or transection resulting in virtual destruction of the thalamus but sparing most of the parafascicular nuclear complex. Neuronal lesions were produced in the fetal diencephalon by injecting ibotenic acid through cannulas implanted in the brain. Hypoxic inhibition of breathing was abolished when the lesions encompassed the parafascicular nuclear complex but was retained when the lesions spared the parafascicular nuclear region or when the vehicle alone was injected. A new locus has been identified immediately rostral to the midbrain, which is crucial to hypoxic inhibition of fetal breathing. This thalamic sector involves the parafascicular nuclear complex and may link central O2-sensing cells to motoneurons that inhibit breathing.

Saliva samples collected from 393 subjects with and without oral diseases were examined for concentrations of mycoplasmas and Mycoplasma species. Mycoplasmas were isolated from 383 (97%) of the 393 subjects. Viable counts ranged from zero to 7.6 x 107 CFU/ml (median, 6.9 x 104) and were significantly (P < 0.01) higher in diseased subjects, except for those with arthrosis temporomandibularis, than in controls. Of 1,400 isolates, 897 (64%), 442 (30%), and 8 (1%) were identified as Mycoplasma salivarium, M. orale, and M. hominis, respectively, and the remaining 73 isolates (5%) were unidentifiable. More than two-thirds of the isolates from diseased subjects versus only half from controls were identified as M. salivarium. In diseased subjects other than those with ostitis (especially those with arthrosis temporomandibularis), the incidence of M. salivarium was higher than that of M. orale, whereas the former occurred about as frequently as the latter in the controls. Antibodies to M. salivarium were also measured in sera from some subjects by the metabolism inhibition test. Sera with metabolism inhibition titers of 16 or greater were rated positive. There was no significant difference in the prevalence of antibodies between diseased subjects (60%) and controls (40%), but the mean titers (97 to 220) of all positive sera from diseased subjects were two to four times those for sera from controls. In addition, a fourfold or greater rise or fall of antibody titers to the organism was shown in paired sera from some subjects. On the basis of these results, M. salivarium was strongly suggested to participate etiologically in some cases of oral infection.

The effects of diencephalic lesions on respiratory responses to intra-arterially infused adenosine (ADO) were determined in chronically catheterized fetal sheep (>0.8 term). These studies were designed to test the hypothesis that the inhibitory effects of ADO on fetal breathing, like those of hypoxia, are mediated by the parafascicular nuclear complex (Pf) of the posteromedial thalamus. ADO inhibited breathing [control (C): 26 +/- 2.6, ADO: 4 +/- 1 min/h] in normal fetuses and in a fetus with a lesion that virtually destroyed the thalamus but left intact most of Pf. Neuronal lesions in the diencephalon, produced by injecting ibotenic acid, abolished the inhibitory effects of ADO on breathing (C: 31 +/- 5.1, ADO: 30 +/- 4.5 min/h) when the lesions encompassed Pf or the sector immediately rostral to Pf that retained the capacity to regulate hypoxic inhibition. Smaller lesions created by the insertion of needles also eliminated the depressant effects of ADO when disruptions were within Pf or a rostral component of the thalamic cortical activating system. It is concluded that 1) a medial thalamic sector is critically involved in ADO-induced apnea and 2) ADO-dependent and ADO-independent mechanisms mediate hypoxic inhibition.

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