Rhythmic metrazol activity and cortical spreading depression

The incidence of segments of rhythmic metrazol activity (RMA) in cortical leads and in the thalamus and hippocampus was studied in acute experiments on nine male albino laboratory rats. First of all we studied activity after administering metrazol in an i.p. dose of 50 mg/kg, without any further treatment, and then, after a control recording, we induced cortical spreading depression and observed its effect on the incidence and synchronization of RMA in the individual leads. We came to the conclusion that the thalamus is incapable of isolated production of RMA. The cortex is able to produce RMA without participation by the studied structures of the specific thalamus and hippocampus; RMA probably originates in the cortex itself. Generalization is impaired, but not eliminated, by a cortical block. The hippocampus independently produces another type of rhythmic activity.     

Influence of propranolol on rhythmic electrocorticographic activity induced by metrazol in rats

Influence of propranolol (5 mg/kg i.p.) on rhythmic metrazol activity (RMA) was studied in 11 male albino rats with chronically implanted cortical as well as subcortical (thalamic ventrobasal complex and dorsal hippocampus) electrodes. Metrazol was injected subcutaneously at a low dose of 30 mg/kg. Another group of five rats was used to study the action of propranolol on spontaneously appearing episodes of rhythmic spikes as well as on vigilance. The incidence of both rhythmic metrazol activity and episodes was significantly increased by propranolol. The latency to the first burst of rhythmic metrazol activity and to the maximum of its incidence was significantly shortened by propranolol. Propranolol also increased the incidence of relaxed wakefulness and delayed the appearance of slow wave sleep. The facilitation of RMA and spontaneous episodes could not be explained only by the increased amount of relaxed wakefulness, i.e. the vigilance level necessary for these two phenomena, because these changes did not coincide in time. In two animals, the combination of propranolol and metrazol led to the appearance of ictal activity which was sometimes accompanied by partial clonic convulsions. This phenomenon was never seen after metrazol alone (30 mg/kg s.c.) in control recordings. Propranolol was found to potentiate the possible models of human absences--spontaneous episodes, RMA and minimal clonic seizures.     

Rhythmic variations in acid phosphatase activity in the liver of newborn rats

The rhythm of acid phosphatase activity in liver homogenates of newborn rats (aged about 14 days) was compared with a similar rhythm in adult rats (aged 4.5 months). Serial chromatographic investigations demonstrating isoenzyme patterns demonstrated age-related changes of this rhythm connected with the synthesis of the enzyme in newborn rats. The averaged activity of the enzyme in the liver homogenates of newborn rats was about 4 times lower than in adult rats. The maximal values of total enzyme activity of both isoenzymes after chromatographic separation in newborn rats were shifted by about 7 hours in relation to adult animals. Similar changes were observed in the case of the greatest maximal values of the activity ratios--subunit: both isoenzymes, and isoenzyme II: isoenzyme I. In adult rats these maximal values appeared during the night hours and in newborn rats during the day.     

Rhythmic growth activity in fish scales

Changes in the growth of fish are reflected in the rate of growth of their scales. This produces the rings used in ageing temperate species. A technique has been devised for measuring the rate at which [¹⁴C] glycine is incorporated into isolated scales in vitro. This method has been used to investigate various rhythmic activities in fish growth. The results show that the amino acid is incorporated into at least two types of cell and that deposition in the scale occurs with at least two different rhythms with very different frequencies.     

Rhythmic autocrine activity in cultured insect epidermal cells

It is now well established that ecdysteroids can be produced in insects in the absence of prothoracic glands. In this respect, it has been shown that cells in culture can produce ecdysteroids. Our aims were: (1) to determine whether ecdysteroid target cells of epidermal origin could also be the source of ecdysteroids; (2) to monitor more accurately the kinetics of ecdysteroid production; and (3) to check for possible relationships between this synthetic activity and dynamics of cell division. An insect cell line (IAL-PID2) established from imaginal discs of the Indian meal moth, Plodia interpunctella, with wild-type sensitivity to ecdysteroids was used in our study. Our results showed that the Plodia cell line exhibited autocrine activity. When division of IAL-PID2 cells was synchronized, a rhythmic production of ecdysteroids was observed. However, further experiments indicated that this rhythmicity could be cell autonomous. This led us to anticipate the existence of two cell subpopulations that would be able to produce ecdysteroids rhythmically, a minor one that would be cell cycle serum-independent population, and a major population that would need serum growth factors to proliferate and produce ecdysteroids. Qualitative study of the ecdysteroid content of the media clearly showed that ecdysone was the major immunoreactive product. Taken together, our findings clearly show that an insect cell line of epidermal origin is capable of rhythmic autocrine production of ecdysteroids. These results support the hypothesis that alternate sites for ecdysteroid production in vivo may exist and could play a role in local regulation of development. We now plan to determine the cellular basis of this rhythmic autocrine activity and to confirm the existence of growth factor-autonomous cells in the culture as well as the potent role played by ecdysteroids in the cross-talk between various cell subpopulations.     

Rhythmic photostimulation and a number of alpha-rhythm dipoles in the human brain

Dynamic study of the equivalent current dipoles (ECDs) of alpha rhythm in the human brain was performed in a one-dipole model. The number of ECDs was shown to be dependent on the time course of visual stimulation, on the phase shift of triggering of flickers with alpha-rhythm frequency from alpha-wave, as well as on the type of visual illusions produced in subjects by this stimulation. The data are discussed in accordance with the "scanning hypothesis" that predict a certain functional meaning of the spreading alpha-wave for cortical processing of sensory information in the human brain.     

Full-thickness human foreskin transplantation onto nude rats as an in vivo model of acute human wound healing

Current wound-healing models do not fully duplicate the in vivo human environment. The feasibility of grafting human full-thickness foreskin onto nude rats, as a model of acute wound healing, was evaluated. Incisions were then created on the grafted skin, and wound healing was evaluated. Full-thickness human skin was obtained after elective circumcision and was grafted subcutaneously onto the dorsal thorax of nude rats. At 10 days after transplantation, graft beds were judged for graft viability, on the basis of gross appearance, texture, and adherence. Full-thickness wounds were then made in the foreskin. Graft wounds were left to close by secondary intention. The wounds were allowed to heal for 7 days. Wounds were excised and tested for breaking stress. Histological evaluations included proliferating cell nuclear antigen, factor VIII, hematoxylin and eosin, and trichrome staining. Twenty grafts were performed, with 100 percent viability. Upon incision, all grafts bled freely, indicating a rich vascular supply and tissue viability. Graft viability was confirmed by the presence of proliferating cells in the parabasal stratum of the epithelium. Furthermore, there was evidence of angiogenesis, as confirmed by staining for factor VIII. Breaking stress was evaluated by tensiometry, 7 days after wounding. Histological evaluations revealed viable grafts and active wound-healing events. Full-thickness human skin can be successfully transplanted onto nude rats, providing a larger, more physiological model of human wound healing. This model closely parallels the in vivo situation, providing a promising model for study of the complex biological processes of acute human wound healing, in a reproducible manner.     

Influence of phenobarbital on ECoG phenomena induced by metrazol in rats during ontogenesis.

Effect of phenobarbital (PhB, 20 and/or 40 mg/kg) on epileptic ECoG phenomena induced by metrazol was studied in acute experiments in rats aged 7, 12, 18, 25 and 90 days. Fractionated administration of metrazol (20 mg/kg i.p. each 300 s) was used to quantify the effects of PhB. First signs of metrazol action (sharp elements and/or rhythmic metrazol activity) were not reliably influenced by PhB. On the contrary, the latency of the first EEG seizures as well as of the first generalized EEG seizures was prolonged and thus a dose necessary for their elicitation was increased in all age groups. These differences reached statistical significance in 12-, 18- and 25-day-old rats. A lack of effect of PhB against the rhythmic metrazol activity supports the adequacy of this activity as a model of human absences. Differences between the development of antiepileptic and hypnotic effects of PhB (described earlier) suggest two different mechanisms of action.