Changes in vestibular postural response determined by information content of visual feedback

Electrical unipolar monoaural stimulation of the labyrinth led to body sway mainly on a frontal plane in normal human subjects in a standing position. Early and late stages of response with latencies of 120–200 and 200–500 msec respectively changing in size in accordance with conditions of visual control were distinguished in the stabilographic response. Maximum response was recorded when the eyes were closed. Response declined upon opening the eyes, fixing the gaze on a static target, and with visual feedback according to stabilograms. The early and late components declined by 10–20 and 50–70% respectively in all cases. Fixing the gaze, in darkness, on an illuminated light spot stationary in relation to the head had no effect on level of response. Once the expected direction of body sway had been imparted, a significant and almost identical decrease of 70–80% in both components took place with the gaze fixed, however. Early and late components of vestibulomotor response are thought to be mediated by regulatory mechasisms with differing time courses and functional connections.Institute of Research into Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vo. 22, No. 1, pp. 80–87, January–February, 1990.     

Nephrotoxic effect of the specific brain serotonin depletor para-chlorophenylalanine

Brain serotonin depletion induced by peripheral parachlorophenylalanine (pCPA) is frequently used to evaluate the role of the central serotoninergic system in the regulation of a number of physiological functions, including the secretion of renin by the kidney. We found that due to the treatments applied in the protocol used for the investigation of pCPA effect on renin and vasopressin secretion in rats (300 mg/kg i.p. 64 and 40 h before sacrifice) renal injury was induced as well. Typical changes indicating acute renal failure were observed--an initial polyuria, natriuresis and body mass loss, succeeded by oliguria, decreased glomerular filtration rate, and salt and creatinine retention. Morphological changes in the glomeruli included a thickening of the basal membranes, a confluence and a reduced number of podocyte pedicles. A slight to moderate granular degeneration was observed in epithelial cells of the proximal convoluted tubule, combined with mitochondrial changes--an increase in number, matrix disorganization, and myelin degeneration. In conclusion, the renal function changes after i.p. pCPA may be due not to brain serotonin depletion-alone, but also to nephrotoxic effect.     

Frequency tuning curves of the dolphin's hearing: envelope-following response study

Simultaneous tone-tone masking in conjunction with the envelope-following response (EFR) recording was used to obtain tuning curves in dolphins (Turslops truncatus). The EFR was evoked by amplitude-modulated probes of various frequencies. A modulation rate of 600 Hz was found to fit the requirement to have a narrow spectrum and evoke EFR of large amplitude. Tuning curves were obtained within the frequency range from 11.2 to 110 kHz. The Q₁₀ values of the obtained tuning curves varied from 12–14 at the 11.2 kHz center frequency to 17–20 at the 64–90 kHz frequencies.Abbreviations ABR auditory brainstem response - EFR envelope following response - ERB equivalent rectangular bandwidth     

Ontogeny of positive phonotaxis in female crickets,Gryllus bimaculatus De Geer: dynamics of sensitivity,frequency-intensity domain,and selectivity to temporal pattern of the male calling song

1. The ontogeny of positive phono taxis (PPT) in female crickets, Gryllus bimaculatus was followed in tethered flight. During the first day of adult life many females already demonstrated PPT to the calling song (CS) of conspecific males. The average threshold of PPT at 5 kHz, the dominant frequency of the CS, decreased by 30 dB by the time of sexual maturity (Fig. 1).
2. No correlates of this decrease were found in the activity of the most sensitive ascending prothoracic neuron tuned to 5 kHz recorded in the neck connective. This is presumably the AN1 neuron which is known to be involved in PPT realization. Its threshold at 5 kHz in young animals was the same as in adults. Therefore, ascending circuits of PPT seem to be mature by the first day of imago life and there should be some other mechanisms preventing performance of PPT by young walking females until maturation.
3. The PPT of females in flight is tuned to 5 kHz, much sharper than in walking (Fig. 2). In flight, the carrier frequency of a signal is probably an important parameter driving PPT, at least in a no-choice situation, whereas on the substrate, at close range, temporal parameters become decisive.
4. The ontogenetic development of the selectivity of a female's PPT to temporal parameters of a signal passes 3 successive steps: 1) response mainly to the trill with pulse repetition rate as in the CS; 2) response mainly to the actual CS with chirp structure; 3) destruction of selectivity (Figs. 3–6). The existence of steps 1 and 2 strengthens our hypothesis, that in phylogeny, the trill (pulse rate) detector of the CS “recognizer” in the CNS appeared earlier, and was later accompanied by the chirp detector.
5. Joint breeding of female larvae with males accelerates maturation of the CS recognizer.

     

ABR frequency tuning curves in dolphins

Tone-tone masking was used to determine auditory brain-stem response tuning curves in dolphins (Tursiops truncatus) in a simultaneous-masking paradigm. The Q ₁₀ of the curves was as large as 16–19 in the frequency range 64–128 kHz. In the range 45–16 kHz, Q ₁₀ decreased proportionally to the frequency with the bandwidth of the curves being constant, about 3.5–4 kHz at the 10-dB level. Tuning curves below 45 kHz are supposed to reflect broad spectral bandwidth of the probe's effective part which is no longer than 0.5 ms, irrespective of actual probe duration. Tuning curves above 64 kHz are supposed to reflect the real frequency tuning of the dolphin's auditory system.Abbreviations ABR auditory brain stem response - AP action potential     

Biochemical changes accompanying the long-term starvation of Micrococcus luteus cells in spent growth medium

Changes in the biochemical properties of Micrococcus luteus cells were studied during the transition to a dormant state after incubation in an extended stationary phase. The overall DNA content after 150 days of starvation was similar to its initial level, while the RNA content decreased by 50%. Total lipids and protein, phospholipids and membrane proteins declined rapidly within the first 1–10 days of starvation. After 180 days of starvation, cells contained 43% of the protein and 35% of the lipid initially present. Starvation for 120 days resulted in the loss of phosphatidylglycerol and, to some extent, of phosphatidylinositol, giving a membrane whose phospholipids consisted mainly of cardiolipin. The membrane fluidity declined during starvation, as judged by diphenyl hexatriene fluorescence anisotropy measurements. Oxidase activities declined to zero within the first 20–30 days of starvation, while the dehydrogenases and cytochromes were more stable. The activities of some cytoplasmic enzymes were lost very rapidly, while NADPH-linked isocitrate dehydrogenase had 30% of its initial activity after 120 days of starvation. For all parameters tested there were significant fluctuations during the first 10–20 days of starvation, which may reflect cryptic growth in the culture.Abbreviations MPN Most probable number - DPH Diphenyl hexatriene     

Morphological aspects of the hypothalamic-hypophyseal system

Summary The ultrastructure of the tanycyte ependyma in male 160–180 g Wistar albino rats was studied under normal conditions and in experiments involving long-term suppression of ACTH secretion and its long-term stimulation. The former was accomplished by daily (for 8 days) intraperitoneal administration of dexamethasone phosphate at low (5 g/100 g) and high (100 g/100 g) concentrations. The effectiveness of suppression of the hypothalamic-hypophyseal-adrenal system in the experimental animals was judged by their reaction to two-minute ether stress (determination of plasma corticosterone) and by the results of measurement of the adrenal weights. Stimulation of ACTH secretion was achieved by bilateral adrenalectomy; the animals were examined on days 8, 10, 14, and 22 following the operation. The results obtained were in agreement with the previously established fact that there is a negative correlation between tanycyte activity and hypophyseal adrenocorticotrophic function (Akmayev and Fidelina, 1974). They also testified to the predominant involvement of the median eminence tanycyte ependyma (beta-tanycytes according to the authors' nomenclature) in these relationships.It is supposed that these correlations are regulated by a feedback mechanism and attest to the involvement of beta-tanycytes in the inhibiting control of hypophyseal adrenocorticotrophic function. The mechanism of this control may be explained alternatively: either the tanycytes transport ACTH-suppressing substances (catecholamines, corticosteroids, ACTH) from the CSF to the hypophyseal portal system or they themselves secrete substances possessing ACTH-suppressive activity. The authors distinguish several types of vesicles in the beta-tanycytes, the number of which changed with experimentally induced shifts in hypophyseal adrenocorticotrophic function. These vesicles are discussed in connection with the transport and secretory activity of the tanycytes and are considered to be a possible substrate of the hypothalamic inhibiting effect on ACTH secretion.