Dark Neurons of the Sensorimotor Cortex of White Rats after Acute Incomplete Ischemia in Terms of Artifacts Fixation and Neuroglial Relationships

The aimof research was to study morphofunctional signs of the sensorimotor "dark neurons" formation in the cerebrum of sexually mature white rats under normal conditions and in 40 minutesafter the common carotid arteries (CCA) occlusion.Material and methods.Acute ischemia was simulated in white Wistar rats by a 40-min CCA occlusion. The brain was fixed by immersion and perfusion methods. A comparative morphometric assessment of cyto-and gliocytoarchitectonics of the neocortex was carried out under normal conditions (n = 6), 1 (n = 6), 3 (n= 6), and in 7 days (n = 6) after the common carotid arteries (CCA) occlusion. The Nissl staining, hematoxylin and eosin staining, immunohistochemical typing NSE, MAP-2, HSP-70, p38, CASP3, GFAP and AIF1 were applied. The numerical density of normochromic and hyperchromic (dark) pyramidal neurons, oligodendrocytes, microgliocytes, and the relative area of edema –swelling zones were determined. Statistical hypotheses were tested by nonparametric methods using Statistica 8.0 software.Results.The method of the brain fixation significantly influenced the content of the artifact dark neurons,which are similar in morphology and tinctorial properties to degeneratively altered dark neurons. The appearance of reversibly and irreversibly degeneratively altered dark neurons in the sensorimotor cortex after the CCA occlusion was accompanied by an increase in the relative area of edema –swelling zones (control –5.4%, 1st day –17.6%). The maximum content of degeneratively altered dark neurons (53%) was found in layer V in 7 days after ischemia. According to the findings of immunohistochemical typing NSE, MAP-2, HSP-70, p38, CASP3, the specific proteins of the most degeneratively altered dark neurons were retained, ensuring their restoration and the neural network functioning. The total number density of sensorimotor neurons decreased by 26.4% (p =0.001) in layer III, and by 18.5% in layer V (Mann –Whitney U Test; p = 0.01) in 7 days after the intervention. The revealed changes were of a diffuse focal character. In the zones of degeneratively altered dark neurons accumulation, the content of astrocytes, microgliocytes and oligodendrocytes increased. The neuro-astroglial index (control –1.62) increased to 2.72 in 3 days after the CCA occlusion. The peak in the number density of microgliocyte s was noted in 1 day, and the oligodendrocytes in 7 days after acute incomplete ischemia (Mann –Whitney U Test; p0.001).Conclusion.After a 40-minute common carotid arteries occlusion, dark neurons were detected in layers III and V of the sensorimotor cortex with underlying hydropic dystrophy; their cytomorphological pro perties indicated the dynamics of their in vivo degenerative changes. Restoration of degeneratively altered dark neurons was accompanied by an increase in the number of satellite oligodendrocytes, astrocytes and microgliocytes. The revealed changes were considered as one of the variants of reversible changes in neurons in response to moderate ischemic damage.

Temperature and state dependence of dynamic phrenic oscillations in the decerebrate juvenile rat

The aim of the present study was to determine characteristics of fast oscillations in the juvenile rat phrenic nerve (Ph) and to establish their temperature and state dependence. Two different age-matched decerebrate, baro- and chemodenervated rat preparations, in vivo and in situ arterially perfused models, were used to examine three systemic properties: 1) generation and dynamics of fast oscillations in Ph activity (both preparations), 2) responses to anoxia (both preparations), and 3) the effects of temperature on fast oscillations (in situ only). Both juvenile preparations generated power and coherence in two major bands analogous to adult medium- and high-frequency oscillations (HFO) at frequencies that increased with temperature but were lower than in adults. At < 28°C, however, Ph oscillations were confined primarily to one low-frequency band (20–45 Hz). During sustained anoxia, both preparations produced stereotypical state changes from eupnea to hyperpnea to transition bursting (a behavior present only in vivo during incomplete ischemia) to gasping. Thus the juvenile rat produces a sequential pattern of responses to anoxia that are intermediate forms between those produced by neonates and those produced by adults. Time-frequency analysis determined that fast oscillations demonstrated dynamics over the course of the inspiratory burst and a state dependence similar to that of adults in vivo in which hyperpnea (and transition) bursts are associated with increases in HFO, while gasping contains no HFO. Our results confirm that both the fast oscillations in Ph activity and the coherence between Ph pairs produced by the juvenile rat are profoundly state- and temperature-dependent.