Periodical cicada: mechanism of sound production.

The species Magicicada septendecim and Magicicada cassini of the 17-year cicada produce sound by sequentially buckling a series of stiff ribs embedded in a flexible tymbal. Each such collapse excites a damped oscillation in a resonant cavity. By this means the cavity (an abdominal air sac) is excited 10 to 12 times per muscle contraction, which permits a normal muscle to perform a task requiring very rapid repetitive activity.

Pitfalls in the use of brain slices.

In vitro brain slices are the preparation of choice for the detailed examination of local circuit properties in mammalian brain. However it is the investigator's responsibility to verify that the circuits under investigation are indeed confined within the boundaries of the functional region of the slice used. The medium in which the slice is maintained is under the full control of the investigator. This places the burden on the investigator to ensure that: (1) the properties of the medium are fully under control; (2) the effects of the medium on the slice are known; (3) the conditions under which the slice is being maintained bear some reasonable relation to those it enjoys (or endures) in vivo. Generalizations to in vivo conditions must be made with caution. If at all possible, similar studies (perhaps less extensive, due to the greater technical difficulties) should be done in vivo to provide a basis for comparison. Investigators using drugs should be aware of, and respect, the basic pharmacological principles cited in the text. In particular, the substantial freedom the investigator has in defining the extracellular medium should not be abused.

The acute periventricular injury syndrome: a possible animal model for psychotic disease.

A new experimental brain syndrome involving localized periventricular damage induced by intracerebroventricular injections of lysophosphatidyl choline has been developed in adult rats. The acute periventricular injury syndrome is characterized by transient weight loss, decreased emotionality, extreme postural indifference (catalepsy), inappropriate aggressive responses, impaired grooming, cerebral ventricular enlargement, and periventricular damage to both cells and fiber sheaths. This syndrome appears to simulate several features of schizophrenia, and it may prove useful in the study of psychotic disorders in man.

Effects of temperature and temperature gradients on ion-sensitive microelectrodes.

Ion-sensitive microelectrodes are widely used in studies of mammalian tissues. Often the tissue is maintained at 37 degrees C, some 10-15 degrees C above room temperature. The temperature difference between the room and the preparation was found to be capable of altering the measured ion potential by as much as 10 mV. The change depended on 3 factors: the temperature dependence of the Nernst slope, the temperature dependence of the interference factor, and the thermoelectric potential induced by the temperature difference between the two ends of the ion-exchanger column. Certain combinations of these changes can cancel each other, resulting in spurious but apparently temperature-insensitive readings. The first two factors can produce errors when the temperature of calibration differs from the temperature of the tissue being measured. Serious errors in measurements of ion concentration can also occur, due to all 3 factors, if a temperature gradient exists across the ion exchanger column; this situation can easily occur when recording from exposed mammalian tissues. The use of a short ion-exchanger column will reduce but not eliminate effects due to a temperature gradient.

Ischemia-induced anxiety following cardiac arrest in the rat.

Male Long-Evans rats were subjected to 7 min of chest compression (CC) to produce cardiac arrest and global ischemia resulting in damage to the brain. Timidity and motor activity were evaluated using the elevated plus maze, one of the most widely accepted methods for measuring anxiety in rats. Post-ischemic rats spent much less time in the open arms (3% at day 5) than handled (54%) or sham-compressed (30%) rats. This was interpreted as increased anxiety. Thus, post-ischemic rats developed more anxiety than normal handled rats or sham-operated rats. Anxiety increased markedly on post-ischemic day 2, suggesting a delayed effect. Anxiety gradually decreased after day 5 but recovery was still incomplete up to 115 days post-ischemia. Motor activity decreased gradually during days 2-5 post-ischemia and then recovered to the normal range after day 15. These results are inconsistent with damage limited to the hippocampus and suggest that less obvious histological changes may be occurring elsewhere in the brain.

Surgical determination of the site of crossing of jaw-opening reflex evoked by tooth pulp stimulation in the cat.

Tooth pulp stimulation in the cat evokes a jaw-opening reflex that is usually bilateral. We defined the location of fibers crossing to activate the contralateral reflex by making midline sagittal transections at peripheral and central levels in 11 anesthesized cats. A local midsagittal transection of the brain stem 2-4 mm above the obex selectively eliminated the contralateral reflex response. Midline sagittal transections of the maxilla, mandible, cervical cord, or upper brain stem did not.

The stability of the hippocampal slice preparation: an electrophysiological and ultrastructural analysis.

The viability and stability of the in vitro rat hippocampal slice preparation were assessed using electrophysiological and electron microscopical means. Slices exhibited lifetimes of 6-19 h. Correlation between the duration of electrical activity and changes in ultrastructure of these slices was found. Possible reasons for the wide variability in lifetime of the hippocampal slice are suggested.

Resistance to hypoxia in the rat hippocampal slice.

Rat hippocampal slices showed marked local variations in sensitivity to hypoxia within the CA1 region, judged by electrical criteria. There were also marked differences between slices, judged both by electrical and histological criteria. Local differences were attenuated by 'adapting' slices for 3-4 h in a uniformly oxygenated bath before testing. The local differences may reflect proximity to capillaries.

Chemical traumatization of adult mouse olfactory epithelium in situ stimulates growth and differentiation of olfactory neurons in vitro.

This study demonstrates that ZnSO4-induced chemical trauma results in an in situ regeneration of the olfactory epithelium which, when maintained in vitro, provides an enriched population of olfactory neurons. Therefore, the ability of the olfactory epithelium to respond to chemical trauma with increased mitotic activity can be used to increase growth of neurons in culture. Tissue obtained from normal or vehicle-treated adult mice produced few olfactory neurons, when maintained in culture, compared to cultures established from tissue following an in situ ZnSO4 trauma. Maximal neuronal yields were obtained in cultures established from tissue that was removed 4-6 days following chemical trauma. The morphological appearance and the presence of cell specific intermediate filament proteins were used to classify the cell types in these olfactory epithelial cultures. Single cells and aggregates of cells which were immunopositive for keratin, but immunonegative for neurofilament protein and GFAP, were identified as epithelioid. Flattened polygonal cells immunopositive for GFAP were identified as glia. A small population of flattened cells was immunonegative for all of the antibodies used in this study. Cells that had processes were immunonegative for GFAP and keratin. Some were immunopositive for 200 kDa and 160 kDa neurofilament proteins but immunonegative for the 68 kDa neurofilament protein. A few of these cells showed positive immunoreactivity with the olfactory marker protein (OMP) antibody and most likely represented the most mature olfactory neurons in the cultures. This trauma-induced culture model using olfactory tissue from adult mice can serve as a source of CNS neurons for comparison with cultured embryonic neurons.

Agents which block potassium-chloride cotransport prevent sound-triggered seizures in post-ischemic audiogenic seizure-prone rats.

The purpose of this study was to determine whether the loop diuretics furosemide, bumetanide and ethacrynic acid, which block the KCC1 potassium-chloride transporter in the kidney loop of Henle and the KCC2 potassium-chloride transporter in neuronal membranes, would prevent sound-triggered seizures in post-ischemic audiogenic seizure-prone rats. The rats were infused with the test agent via tail vein shortly before being tested for seizure susceptibility by exposure to loud noise (an alarm bell) for 60 s. Sound exposures were repeated at intervals to determine the time course of the seizure suppression effect. All three loop diuretics suppressed sound-triggered seizures in post-ischemic rats tested 2 days to 4 weeks after the ischemic exposure. Furosemide 200 mg/kg had no effect in 4/4 rats made acutely audiogenic seizure-prone by infusion of bicuculline into the inferior colliculus, indicating that the effect was not due to general anti-seizure activity. Mannitol 2 g/kg had no effect in 6/6 post-ischemic rats, indicating that the effect was not due to diuresis or fluid shifts. These results are consistent with the hypothesis that the exposure to global ischemia caused an upregulation of the potassium-chloride transporter KCC2 in neurons which persisted for at least 4 weeks.

Strength-duration properties of cathodal pulses eliciting spreading depression in rat cerebral cortex.

Strength-duration curves for the threshold stimulus for initiation of spreading depression were determined for durations of 2 ms to 120 s, using cathodal surface stimulation through a well-defined area. With the dura open, the strength-duration curve was of the form I square root t = constant. With extradural stimulation, the slope of the log-log plot relating current intensity to pulse duration increased gradually as the pulse duration increased.

Lactic acidosis and recovery of neuronal function following cerebral hypoxia in vitro.

The rat hippocampal slice preparation was used to study the combined effects of hypoxia and lactic acidosis on neuronal function. Control slices were exposed to a standard hypoxic insult while being perfused with normal artificial cerebrospinal fluid (ACSF). Experimental slices were perfused with ACSF containing 1.0, 2.0, 10.0 or 20.0 mM lactic acid, 30 min before and during the same standard hypoxic insult. Following at 30-min recovery period the ability of these slices to respond to orthodromic stimulation by displaying a population spike (synaptic function) was tested. No significant decreases in the recovery rate of synaptic function were found between control and experimental groups, excluding the combination of 20 mM lactic acid and 10 min hypoxia, where such a decrease was found. The combination of 10 mM lactic acid and 12 min hypoxia brought about an increase in the recovery rate of synaptic function. Thus, the adverse effects attributed to lactic acid in vivo were not seen in the present in vitro study. Neuronal tissue appears to be able to handle excess lactic acid by yet, unknown mechanism (high intracellular buffer capacity?). The suggested in vivo damage due to lactic acidosis could originate in the cerebrovascular system. On the other hand, the possibility that lactic acidosis is harmless under hypoxic conditions should also be considered.

Early, but not late, antiepileptic treatment reduces relapse of sound-induced seizures in the post-ischemic rat.

Global ischemia was used to induce a sensitivity to sound-triggered generalized seizures in 24 male Long-Evans rats. All showed a generalized seizure when exposed to a 108 dB bell for 1 min. They were assigned randomly to 3 groups of 8, and received 30 additional sound exposures. The early treatment group was injected with valproate (200 mg/kg i.p) 1 h prior to each of the first 10 sound exposures. The late treatment group received the same treatment during the second set of 10 sound exposures after 10 sound exposures without treatment. The third group was untreated. Both early and late treated groups had a significant reduction in seizure incidence during the treatment period, i.e. both groups showed seizure control. However, in the late group seizures returned promptly when valproate treatment was discontinued, while the early group showed a sustained reduction in seizure susceptibility. Since this outcome corresponds to seizure remission, the findings of this study favor early treatment.

Administration of human chorionic gonadotropin affects sleep-wake phases and other associated behaviors in cycling female rats.

We investigated the possible effects of human chorionic gonadotropin (hCG) on sleep-wake phases and other associated behaviors controlled by the medial preoptic area, cerebral cortex and hippocampus. Chronic epidural electroencephalographic (EEG) and temporal muscle electromyographic (EMG) electrodes were placed in cycling female rats. After a week of recovery, rats were injected intraperitoneally at 3.00 pm on the day of proestrus with either saline or highly purified hCG or indomethacin or hCG plus indomethacin. Three hours after injection, EEG, EMG and behavioral activities were recorded for 3.5 h. The administration of hCG increased high and low amplitude sleep, resting phase and decreased active awake phase, walking, sniffing and chewing as compared to the controls. While the administration of indomethacin alone had no effect, coadministration inhibited hCG effects. Medial preoptic area, cerebral cortex and hippocampus contain immunostaining for LH/hCG receptors. The administration of hCG resulted in an increase of immunoreactive PGD2 and a decrease of PGE2 in median preoptic area, cerebral cortex and hippocampus as compared to the controls. In summary, hCG administration affects sleep-wake phases and other associated behaviors in rats which can collectively be described as decreased activity. These effects are probably mediated by increasing PGD2 and decreasing PGE2 in areas of brain which control these activities. The above findings may be relevant to pregnant women who experience decreased activity when hCG is present in the circulation and cerebrospinal fluid.

Adaptation of adult brain tissue to anoxia and hypoxia in vitro.

The rat hippocampal slice preparation was used in the present study to demonstrate the ability of adult brain tissue to adapt to anoxic and hypoxic conditions. Adaptation was induced by pre-exposure of hippocampal slices to a short (5 min) anoxic episode. The evoked electrical activity of pre-exposed slices recovered from a subsequent, longer anoxic insult, while that of controls (without pre-exposure), receiving the same insult, did not. The adaptation process is time-dependent; an interval of 0.5 h between the pre-exposure and the subsequent anoxic insult allowed slices to resist anoxic periods of 13 +/- 2 min while after an interval of 2 h an anoxic period of 16 +/- 2 min could be tolerated. Evoked electrical activity persisted in adapted slices during exposure to hypoxia while their non-adapted controls exhibited synaptic silence under hypoxic conditions.

Increased glucose improves recovery of neuronal function after cerebral hypoxia in vitro.

The rat hippocampal slice preparation was used to evaluate the effect of increasing glucose levels in the perfusion medium on the recovery of synaptic function after a standardized hypoxic insult. Slices exposed to low glucose (5 mM) did not recover from a standard hypoxic insult (10 min of 95% N2/5% CO2 atmosphere). Following the same insult, 39% of the control (10 mM glucose) slices recovered their synaptic function, while 93% of the slices provided with high glucose level (20 mM) exhibited recovery of synaptic function. Thus, a dose-dependent effect of glucose on recovery of neuronal function following an intermediate period (10 min) of oxygen deprivation was found. The high-glucose-treated slices could tolerate a severe hypoxic insult of 15 min or even 20 min from which 94% and 81% of them recovered, respectively. Only 21% of the control (10 mM glucose) slices recovered their synaptic activity following 15 min of hypoxia, and none survived 20 min of that insult. The adverse effects of hyperglycemia reported in vivo were not seen in our study. This may be due to the sustained perfusion of the brain slice preparation, which could limit accumulation of lactic acid during hypoxia. However, treatment of slices with lactic acid prior to and during the hypoxic insult did not worsen the outcome. Alternatively, glucose may protect against the damaging effects of oxygen free radicals formed during reoxygenation. Nevertheless, the antihypoxic effect of glucose appears to be a metabolic one, since L-glucose (the non-metabolic analog of D-glucose) was innocuous in this respect.

Correlates of delayed neuronal damage and neuroprotection in a rat model of cardiac-arrest-induced cerebral ischemia.

Numerous studies over the past three decades have used rodent models of cerebral ischemia. To measure the postischemic outcome, the majority of these studies used histopathology as the method of choice both quantitatively and qualitatively. No functional measure of postischemic outcome has been proved to correlate well with the histopathological one. The rat chest compression model of cardiac-arrest-induced global cerebral ischemia was used in the present study. Two separate measures of neuronal damage at 7 days postischemia were performed: (a) histologically, by counting normal pyramidal cell bodies in the mid-CA1 hippocampal region of the rat brain, in hematoxylin-eosin-stained, paraffin-embedded 6-microm sections, and (b) electrophysiologically, by counting the number of 400 microm hippocampal slices in which it was possible to evoke a normal (>/=10 mV) CA1 population spike by orthodromic stimulation of the Schaffer collaterals. The correlation between these two measures was tested in the following groups of rats: (a) control, untreated group, (b) MK-801-treated groups (0.03 to 1.0 mg/kg given i.p. shortly after ischemia), (c) diltiazem-treated (DILT) groups 1.0 to 30 mg/kg, given i.p. shortly after ischemia, and (d) a group treated with a combination of the two drugs together (0.1 mg/kg MK-801+3.0 mg/kg DILT given i.p. shortly after ischemia). The two measures of postischemic outcome were highly correlated in all groups studied. Both MK-801 and DILT exhibited a dose-dependent neuroprotective effect. When administered together, a synergy between the neuroprotective effect of MK-801 and DILT was observed. At the doses used, minimal or no side effects of either MK-801 or DILT were observed.

Dimethylsulfoxide (DMSO) blocks conduction in peripheral nerve C fibers: a possible mechanism of analgesia.

Dimethylsulfoxide (DMSO) is readily absorbed through skin, and relieves musculoskeletal pain when applied topically to painful areas. We studied the effects of DMSO on C-type nerve fibers, which mediate pain sensation. DMSO was applied directly to exposed cat sural nerves. C fiber conduction velocity was slowed by DMSO, even in low concentrations (5-7% v/v). Higher concentrations completely blocked C fiber conduction, with a minimum blocking concentration of 9%. Onset of nerve block was almost immediate with 15% DMSO or higher concentrations. C fiber blockade may account for analgesia with DMSO.

The mRNA level of the potassium-chloride cotransporter KCC2 covaries with seizure susceptibility in inferior colliculus of the post-ischemic audiogenic seizure-prone rat.

Cardiac arrest and resuscitation were used to induce brain damage and susceptibility to sound-triggered seizures in Sprague-Dawley rats. Glucose preloading was used to vary seizure susceptibility. Because loop diuretics can block these seizures, we investigated changes in KCC2, a potassium-chloride cotransporter, in the inferior colliculus - the origin of the seizures. Using polymerase chain reaction (PCR), we found that collicular KCC2 mRNA levels covaried with seizure susceptibility in these animals. Using quantitative PCR, we found that a fivefold increase in collicular KCC2 mRNA levels was associated with a doubling of seizure incidence. A hypothesis linking KCC2 activity to seizure susceptibility is presented.

Impedance of amalgam-dentin interface in cat tooth.

The impedance between two amalgam electrodes implanted in the maxillary canine of a cat was measured at various frequencies between 0.02 kilohertz (kHz) and 100 kHz. When plotted on the X-R plane as a function of frequency, two types of impedance loci were obtained. One resembled a circular are at low frequencies, whereas the other was parabolic or exponential in formmthe circular-arc loci are similar to those calculated from membrane models. The parabolic or exponential loci are predicted by a polyelectrolyte model.