ATP-induced cochlear blood flow changes involve the nitric oxide pathway

Although control mechanisms of cochlear blood flow (CBF) have been intensively studied since laser Doppler flowmetry was introduced for CBF measurement in animals and humans, the role of adenosine 5'-triphosphate (ATP) in CBF regulation is not known. Since ATP is a potent vasoactive agent in other organs, the aim of this study is to examine ATP-induced changes in CBF and to test whether the nitric oxide pathway is involved in ATP-induced CBF changes. The anterior inferior cerebellar artery (AICA) of anesthetized pigmented guinea pigs was exposed, and ATP was perfused into the AICA. For CBF measurement, the bulla was opened and the 0.7 mm laser probe of a Perimed PF2B flowmeter was positioned on the basal turn of the cochlea. AICA perfusion of an ATP solution caused dose-dependent transient CBF increases. The maximum CBF increase induced was 220% of the baseline. In some animals, CBF showed a dual effect; a transient decrease followed by a longer-lasting increase. The perfusions of sodium nitroprusside (SNP) also resulted in dose-dependent CBF changes. The intravenous application of N(omega)-nitro-L-arginine methyl ester (L-NAME) significantly attenuated ATP-induced CBF increases, and enhanced ATP-induced decreases, but did not affect SNP-induced CBF changes. The ATP-induced CBF responses indicate that ATP plays a role in CBF regulation. The biphasic characteristic of the ATP-induced CBF change suggests the involvement of both P2x- and P2y-subtype purinoceptors. That L-NAME caused attenuation of the ATP-induced CBF increase implies that the ATP-induced CBF increase is mediated by the release of endothelium-derived relaxing factor, nitric oxide, following activation of endothelial P2y-purinoceptors in the cochlear vascular bed and/or cochlear supplying vessels.

Aromatic-aromatic ring interaction revisited with model compounds of Wilcox

Aromatic-aromatic nonbonded interactions have been reexamined using model compounds of Wilcox and collaborators (J. Am. Chem. Soc. 1994, 116, 4497). It was found that at low temperatures down to 210 degrees K, the population of the folded conformers (A) is higher than that of the unfolded conformers (B), suggesting that edge-to-face aromatic-aromatic ring interactions are in effect. However, the free energy difference between the two types of conformers did not vary linearly with temperature, which is against what we expected from the thermodynamic relationship of delta G = delta H-T delta S. This suggests that in the presence of solvent molecules a free energy cancellation effect operates between the two conformers. Although A has a free energy gain of only approximately 0.5 kcal/mol over B in organic solvents, as obtained by subtracting the solvent-induced unfolding effect, it could still be a significant energy with respect to conformational preference.

[Research on basilar membrane vibration of guinea pigs elicited by direct current pulse]

To investigate the electromotility of basilar membrane (BM) of guinea pigs in vivo, a couple of Platinum-iridium wire electrodes were placed into holes drilled in the scala vestibuli and scala tympani on the basal turn of cochlea separately. The organ of Corti was stimulated with rectangular direct current pulses. The displacement and velocity of BM were measured with Laser Doppler velocimeter. The results indicated that the displacement of BM elicited by current moved toward the scala where positive current was injected. The waveform of BM displacement was corresponding to the rectangular pulse of electric current step. Ringing responses could be seen at the onset and offset of current pulse that was the transient responses of outer hair cells. The frequency of the ringing was the same as that of characteristic frequency of partition in BM. It is supposed that the ringing of BM is an active process of depletive energy and participate with cochlear amplifier. In the insensitive cochlea or dead animal, direct current can still elicit a BM displacement but the ringing response is decreased or disappeared. This phenomenon is probably because of metabolic disturbance in damaged outer hair cells. The BM vibration induced by direct current is similar to that of induced by acoustic stimulation, which can transfer to other partition of BM by traveling wave. This characteristic has laid a foundation of electromotile hearing and electrically evoked otoacoustic emission.

The tonic sympathetic input to the cochlear vasculature in guinea pig

Vascular tones is an essential component in maintaining steady regional blood flow and dynamic responsiveness of a vascular bed. Sympathetic innervation can contribute to vascular tone. Although certain studies have reported evoked changes in cochlear blood flow (CBF) with activation of the sympathetic fibers to the cochlear vasculature, other studies have failed to show evidence of sympathetic contribution to CBF regulation when the cervical sympathetic fibers were unilaterally sectioned. We hypothesized that the bilateral 'sympathectomy of the stellate ganglia' would remove sufficient sympathetic input to the cochlea to yield a change in CBF resting level. To test this hypothesis a new technique was used to expose the stellate ganglia (SG) bilaterally and induce a chemical sympathectomy. We observed that unilateral SG blockade with 2 microliters of 4 mM lidocaine hydrochloride on either side produced a 5-10% increase in CBF, which recovered to baseline during the following 2 min. A subsequent blockade of the contralateral SG produced a rapid 25-35% increase, which then recovered partially during the following 3-4 min, remaining 5-15% above the baseline over a 20 min measurement period. Superior cervical ganglion transection did not affect CBF. Our results provide evidence for the existence of a tonic sympathetic component in the control of vascular tone in guinea pig cochlea. This neural effect is derived bilaterally from SG. This result is consistent with previous anatomical studies showing the bilateral innervation of the cochlea by the SG sympathetic fibers and with previous physiological studies on the bilaterality of evoked changes in CBF due to electric stimulation of SG.

Electrically evoked cubic distortion product otoacoustic emissions from gerbil cochlea

It has been demonstrated that electrical stimulation of the cochlear partition results in basilar membrane vibration and otoacoustic emissions. Electromotility of stimulated outer hair cells (OHCs) elicits the electrically evoked otoacoustic emissions (EEOAEs). Although electrically evoked upper and lower sideband distortion products (DPs) have been reported, electrically evoked cubic DP has not been investigated. Since the acoustically evoked cubic DP is the most commonly used otoacoustic measure of cochlear nonlinearity, this study tested whether electrical stimuli evoke a cubic DP otoacoustic emission. An electrical current containing the frequency component f1 and f2 (f1 < f2) was delivered to the round window niche of the gerbil, and electrically induced sound pressure change in the external ear canal was measured with a microphone. It was found that, in addition to f1 and f2 EEOAEs, cubic DP (2f1-f2) and other emissions at 3f1-2f2, 2f2-f1 and f2-f1 frequencies are electrically evoked. The electrically evoked cubic DP growth is similar to that of an acoustically evoked cubic DP. An electrical stimulus at f1 or f2 and an acoustic stimulus at f2 or f1 produce an identical cubic DP to that evoked by two electrical stimuli and/or two acoustic stimuli at f1 and f2 frequencies. An acoustic suppressor at a frequency near f2 can completely suppress an electrically evoked cubic DP emission. These data demonstrate that DPs can be provoked by a complex two frequency electrical current delivered to the round window niche. These stimuli elicit mechanical vibrations, from stimulated OHCs near the round window, which propagate apically toward their characteristic frequency places on the basilar membrane, and produce combination DPs. Electrically evoked cubic DPs appear to be produced by the same nonlinear mechanism that generates acoustically evoked DPs.

Electrophysiological and morphological evaluation of the acute ototoxicity of sodium nitroprusside

Nitric oxide (NO) is a messenger molecule that mediates several physiological functions and pathological processes. Sodium nitroprusside (SNP), a potent vasodilator, when given clinically as an anti-hypertension agent, exerts its function by releasing NO. It was reported recently that SNP causes a loss of auditory nerve compound action potential (CAP) after topical application of SNP on guinea pig round window membrane (RWM). The current study was designed to investigate the ototoxic target of SNP through both electrophysiological and morphological approaches. The CAP threshold at frequencies ranging from 2 to 36 kHz, the cochlear microphonic quadratic distortion product (cmQDP, F2-F1, where F1 = 17.1 kHz; F2 = 18 kHz), and the cochlear microphonic (CM) at the frequency of F1 were recorded via a round window electrode before and up to 2 h after RWM application of 1 microliter of drug solution. Cochlear blood flow (CBF) and arterial blood pressure were monitored. The cochleae were then processed for morphological examination. The effect of SNP on endocochlear potential (EP) was also studied. Results showed that cmQDP, CM, and CAP, as well as EP, were suppressed in varying amounts, while CBF was substantially increased following drug application. Morphological evaluations showed swelling of the afferent inner radial dendrites within the basal cochlear turn in the higher concentration groups of SNP, while the hair cells presented no evidence of damage at the light microscopic level. The results indicate that SNP has an acute ototoxic effect in a concentration- and time-dependent manner. The targets of SNP ototoxicity are at least the afferent dendrites and stria vascularis.

Acoustic modulation of electrically evoked distortion product otoacoustic emissions in gerbil cochlea

In order to study the linearity of outer hair cell fast electromotility in vivo, an acoustic tone was used to interact with the electrically evoked distortion product otoacoustic emissions. Otoacoustic emissions at the primary frequencies (f1, f2, where f1 < f2) and the distortion frequencies (2f1 - f2 and f2 - f1) were evoked by a complex current, with f1 and f2 components, delivered to the gerbil round window. An externally given acoustic tone at the frequency f1 or f2 with appropriate phase and level can completely abolish both the 2f1 - f2 and f2 - f1 distortion tones. Because the external tone causes basilar membrane vibration at its natural topographic locations, this result indicates that the observed distortion tones were generated near the locations of f1 and f2 frequencies on the basilar membrane and that no distortion occurred from the stimulated cells near the electrode. The study strongly suggests a linear electromechanical transduction of the outer hair cells in the sensitive cochlea.

Extracochlear electrically evoked otoacoustic emissions: a model for in vivo assessment of outer hair cell electromotility

Cochlear outer hair cell (OHC) motion in response to changes in membrane potential (electromotility) has been extensively studied in vitro. Electromotility is thought to actively control the micromechanical properties of the sensory epithelium. In order to understand how OHC electromotility contributes to normal cochlear responses, its role must be assessed in vivo. We have developed a novel animal model for the study of electromotility in vivo. Alternating current is delivered by an electrode to the round window (RW) of gerbil cochlea and the electrically evoked otoacoustic emission (EEOE) is measured from the external ear canal. As much as 45 dB SPL sound could be generated by about 200 micro A RMS extracochlear current delivered to the RW. Except for the fine structure of EEOE transfer function curves, the magnitude of the EEOE has a bandpass appearance ranging from about 4 to 32 kHz and shows a positive linear relationship to the current intensity. The phase has a linear relationship with frequency and shows no significant change with current intensity. Local intracochlear perfusion of 4% paraformaldehyde caused EEOE to decrease by approximately 20 dB. These results indicate that the EEOE is probably generated by OHCs near the electrode location and propagates to the external ear canal. In addition, the force generated by OHCs in vivo is a linear function of the electrical stimulus. The major advantages of our model include: (1) non-invasive procedure and normal cochlea; (2) wide dynamic range of the measurement; (3) simple and easy preparation. With these features this model has potential applications in basic hearing research and in the diagnosis and treatment of otological patients.

Electromotile hearing: evidence from basilar membrane motion and otoacoustic emissions

Electrical stimulation of the cochlea is known to cause auditory sensations in humans and other animals. It also has been shown to produce emissions of sound from the inner ear. In the current study we investigate the relationship between electrically induced motion of the basilar membrane (BM) and the production of otoacoustic emissions. We test the hypothesis that electrical current-induced movements of the outer hair cell (OHC electromotility) result in intracochlear acoustic pressure which causes traveling waves on the BM. Our results demonstrate that the dominant response of the guinea pig inner ear to electric stimulation, at the round window membrane (RW) or across the cochlear duct, is a mechanical response of the organ of Corti. We observed that electrical stimulation of the cochlea produced traveling wave activity on the BM, measured with a laser Doppler velocimeter. The BM motion was accompanied by sound emitted by the cochlea for frequencies up to at least 25 kHz. Furthermore, bipolar rectangular current stimulation produced steady, bipolar displacements of the BM (to 2 nm), indicating functional elongation or contraction of OHCs occurs depending on the polarity of the current pulse. All of the evoked responses were absent after drug treatments eliminated the OHCs. Our data indicate that OHCs undergo electrically evoked displacements capable of producing high-fidelity, high-frequency acoustic energy. The electrically evoked intra-cochlear energy results in conventional traveling waves within the cochlea, as well as emissions of sound from the cochlea. These data provide direct support for a mechanism of cochlear sensitivity and tuning involving high-frequency OHC electromotility. Moreover, the data also indicate that any intra- or extracochlear electric current which affects the electric polarization of OHCs could induce BM traveling waves and cause 'electromotile hearing'. This form of hearing would be one component under the more general definition of the electrophonic effect.

A reversible ischemia model in gerbil cochlea

A completely reversible cochlear-ischemia animal model was developed, and an initial study of ischemia/reperfusion-induced cochlear function change is presented. The bulla of the anesthetized gerbil was opened through a ventral approach and the anterior inferior cerebellar artery and its branches were exposed. Cochlear blood flow (CBF) from the basal turn of the cochlea was monitored with a laser Doppler flowmeter. An electrically isolated microclamp was used to occlude the labyrinthine artery (LA). During LA clamping, the cubic distortion product (DP) was continuously recorded. The LA was repeatedly clamped for different durations in all animals, and CBF consistently showed full recovery after clamp release. No obvious change in vessel diameter or flow pattern was observed under a stereomicroscope. Mean blood pressure did not show significant change during clamping. Immediately upon LA clamping, CBF decreased rapidly nearly to zero. After clamp release, CBF demonstrated an immediate rapid increase, followed by a secondary gradual recovery to baseline. CBF recovery patterns were clamp duration-related. Within a few seconds of occlusion, DP decreased and reached a minimum of approximately 24% of the initial level in less that 30 s. Following reperfusion of the cochlea, DP gradually increased, decreased again, then slowly recovered. Time delay between CBF reperfusion and the first increase of DP was proportional to clamping duration, and the increased amplitudes demonstrated a negative relationship to clamp duration. We assume that the first decrease in DP during clamping was caused by ischemia in the cochlea; the second decrease, during the cochlear reperfusion, could be a form of reperfusion-induced change in cochlear function. This ischemia/reperfusion model in gerbil cochlea demonstrates excellent repeatability and reversibility. Since DP and other measurements can be used to dynamically monitor cochlear or hair cell functions, this model is useful in studies of auditory physiology and pathophysiology.

Heart beat modulation of spontaneous otoacoustic emissions in guinea pig

It has been reported that background variation in the frequency of spontaneous otoacoustic emission (SOAEs) may arise from the cardiovascular system and that the side-bands in the spectra of SOAEs may be modulated by heartbeat. For better understanding of the mechanical influence of the cardiac cycle on cochlear functions under physiological and pathophysiological conditions, this study investigated heartbeat-induced modulation of SOAEs in guinea pig. Possible mechanisms of these phenomena are also discussed. The external ear canal acoustic signal, round window electric signal, and the ECG were recorded for off-line analysis from five pigmented guinea pigs with SOAEs. Time and frequency domain averages with synchronization of the heartbeat indicate that both the external ear canal acoustic and round window electric signal contain some component contributed by ECG and phonocardiography. High resolution FFT spectra suggest that SOAEs were modulated by heartbeat and respiration. Theoretically the change in the SOAEs could be from frequency modulation or a combination of frequency and amplitude modulations. Results of a heartbeat-synchronized average of a wave analyzer output at SOAE frequency indicates that amplitude modulation of SOAE does occur. Data obtained in the current experiment support the hypothesis that the heartbeat-related modulation of SOAE in guinea pig is a combination of frequency and amplitude modulation. The proposed mechanism is that pulsatile cochlear blood flow may cause oscillations in cochlear pressure and affect cochlear performance, resulting in heartbeat modulation of SOAEs.

Relative blood velocity measurement in individual microvessels using the self-mixing effect in a fiber-coupled helium-neon laser

A system has been developed for the measurement of relative blood velocity in micro-vessels by using the self-mixing effect of a laser. A helium-neon laser was coupled to a single-mode optical fiber and the pulled fiber tip (approximately 30 microns diameter) was positioned on a single microvessel. The backscattered Doppler-shifted laser light from moving red blood cells enters the laser cavity and modulates the laser output by influencing internal laser parameters. The signal of the laser output intensity change was produced using a fiber-coupled photodiode and processed by a signal processor. This processor yields an output signal proportional to the first moment of the power spectral density, i.e., the mean frequency of the Doppler shift, corresponding to the blood flow velocity on an arbitrary instrument scale. Results of the in vitro experiment demonstrated that the current method can detect moving particles in fluid and moving red blood cells in a small plastic tube. Data from the in vivo study showed that this system is capable of measuring relative blood velocity in arterioles and venules and can easily follow the cardiac cycle up to 360 beats/min. Primary data suggest that, in addition to high sensitivity, good spatial and temporal resolution, and convenience of use, the self-mixing technique may have an even greater capacity for analysis of blood flow in microvessels than explored in this study, since information on the absolute velocity and velocity distribution of red blood cells is available in self-mixing signal. Further study on its hematocrit dependence and particle bias effect is needed.

Cochlear blood flow measured by averaged laser Doppler flowmetry (ALDF)

This report describes a new approach to estimate the hydromechanical properties of a vascular system. Averaged laser Doppler flowmetry (ALDF) was developed by averaging the flux signal of a laser Doppler flowmeter (LDF) synchronized to the heart cycle. The usefulness of this method was verified by manipulation of the cochlear microvasculature. Twelve pigmented guinea pigs under pentobarbital/fentanyl anesthesia were used. The cochlea was surgically exposed and the LDF probe placed on the bony surface of the first turn to monitor cochlear blood flow (CBF). The LDF flux signal (0.2 s time constant) was sampled by an A/D board at 2 kHz for 255 ms and averaged with synchronization to the heart beat. The mean blood flow, peak to peak amplitude, and time (phase) delay of pulsatile flow were measured from the averaged signal. According to a transmission line model of the vascular system, under a given perfusion pressure, mean flow reflects resistance while amplitude and time delay of the pulsatile flow are related to the reactance component of the impedance of the vascular system. During the formation of photochemically-induced thrombosis in the cochlear microvasculature, there was a dramatic mean flux decrease (90.1 +/- 3.4% from baseline (BL), N = 6). Additionally, a time-dependent decrease in amplitude and time delay of pulsatile flow were indicated by ALDF. These results suggest a large increase in vascular resistance and significant decrease in compliance.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamic response of cochlear blood flow to occlusion of anterior inferior cerebellar artery in guinea pigs

In this study we investigated the autoregulation and hemodynamics of cochlear blood flow (CBF) as measured by laser-Doppler flowmetry. When the anterior inferior cerebellar artery was clamped, CBF decreased approximately 40% (not to "biological zero"), followed by a gradual increase. When the clamp was released, CBF quickly increased to as much as 167% of the baseline level and then slowly returned to baseline. We assume that the dynamic CBF response to anterior inferior cerebellar artery clamping reflects primarily a combination of passive elastic properties of the cochlear vessels and active autoregulatory mechanisms. The decrease portion of the negative phase and the increase portion of the positive phase reflect mainly passive behavior, static compliance, and resistance of vessels, whereas the slow exponential negative and positive changes indicate an active response of vessels: an autoregulatory mechanism based on compensatory vascular dilation and constriction. Our preliminary data show a very strong CBF autoregulatory response to a change in intravascular pressure. Sympathetic stimulation can enhance this autoregulation, and CO2 inhalation promotes compensatory dilation and inhibits compensatory vascular constriction.

Contribution of the anterior inferior cerebellar artery to cochlear blood flow in guinea pig: a model-based analysis

This study was performed to determine the contribution of the anterior inferior cerebellar artery (AICA) to cochlear blood flow (CBF) in guinea pig. The AICA and the basilar-vertebral arterial complex in twelve animals was exposed through the basal portion of the skull. The cochlea was ventrally approached and the CBF of the apical area monitored with laser Doppler flowmetry. A specially designed microclamp was held in a micromanipulator and used to obstruct the AICA. When the AICA was clamped, CBF decreased to approximately 60% of baseline (BL) (not to 'biological zero'), followed by a gradual increase. When the clamp was released, CBF quickly increased to more than 160% BL and then slowly declined to baseline. To quantify the contribution of AICA to CBF, we formulated an electrical analog model of the cochlear vessel system. With this model, AICA contribution to CBF and the relationship among blood pressure, blood flow, and vascular resistance or vascular conductance in the cochlea can be explored. Results in the present study indicate that the AICA contributes only about 45% of CBF to the cochlea; 55% of CBF must come from other supplying vessels. Contrary to previous reports, CBF response to AICA clamping did not exhibit a stable or constant decrease but showed time-dependent dynamic changes. In addition, the cochlear vascular system showed a marked autoregulatory response, instead of a passive response, to the perfusion pressure change. AICA clamping is, therefore, not a suitable model for investigation of ischemia effects in the guinea pig cochlea, but it is a useful approach to study autoregulation and the myogenic mechanism of the cochlear vascular system.

Interleukin-1 activation of FOS proto-oncogene protein in the rat hypothalamus

The activation of FOS proto-oncogene protein has been used as an anatomical marker of activated brain areas. Immunocytochemical detection of FOS can provide information about the sites of action of extracellular stimuli, in spite of the relative absence of specific receptors, at the level of single cell resolution. Following the intracerebroventricular (i.c.v.) injection of recombinant human interleukin-1 (alpha) the c-fos mRNA levels isolated from rat hypothalamus were activated rapidly. In association with c-fos mRNA activation, the i.c.v. injection of interleukin-1 (alpha and beta) markedly induced the FOS immunoreactivity in the hypothalamus including periventricular (PE), paraventricular (PVN), supraoptic (SON), arcuate (ARC), and supramammillary (SuM) nuclei. Within the magnocellular neurons of the SON and PVN, activation of FOS by IL-1 appeared to be greater in areas known to have a high proportion of oxytocin-containing cells than in those of vasopressin-containing cells. Parvocellular neurons were also activated in the PVN. These data suggest sites of action of interleukin-1 in the rat hypothalamic areas reported to have relative absence of interleukin-1 receptor expression.

Effects of stellate ganglion stimulation on bilateral cochlear blood flow

The effect of intraneural electrical stimulation of the stellate ganglion (SG) on bilateral cochlear blood flow (CBF) was investigated with laser-Doppler flowmetry. The SG of 15 anesthetized guinea pigs was exposed by a novel surgical approach and stimulated with a specially designed intraneural bipolar platinum-iridium electrode. Bilateral CBF was continuously monitored. Stimulation of 0.25 mA caused a detectable increase of the systemic blood pressure (BP) and a bilateral decrease of the cochlear vascular conductance (R, defined as the ratio CBF/BP). A stimulus of 0.5 mA elicited a statistically significant ipsilateral CBF (CBFi) decrease of 3.6% +/- 5.1% from the baseline and a contralateral CBF (CBFc) decrease of 3.1% +/- 5.5%. That no statistical difference was found between CBFi and CBFc indicates that a unilateral sympathetic stimulation of the SG can cause equal bilateral responses. These responses were accompanied by a significantly increased BP (8.7% +/- 5.2% of baseline) and consequently a greatly decreased R (12.2% +/- 6.5%) of the ipsilateral cochlea. Bilateral sections of the cervical sympathetic trunk below the level of the superior cervical ganglion did not alter the evoked changes in CBF, BP, and R. It is concluded that SG stimulation can decrease the conductivity of the cochlear vessels or the supplying vessels of the cochlea. Additionally, the SG nerve fibers that cause these effects do not pass through the superior cervical ganglion.

Betahistine-induced vascular effects in the rat cochlea

Betahistine (BH) has been used widely to treat cochlear disorders, such as tinnitus and Meniere's disease. The mechanism of action of BH in the cochlea is assumed to be based on its histamine-like effect on H1 receptors in the cochlear vasculature, leading to an increased cochlear blood flow (CBF). Recently it has been shown that BH can strongly affect H3 heteroreceptors (a novel histamine receptor subclass) in the periphery, via an autonomic ligand. This mechanism may also contribute to the BH effects on CBF. This study was to validate BH effects in the cochlear vasculature and to investigate the possible mechanisms of action of this drug in the inner ear vasculature. We assessed the effects of BH on CBF with the laser Doppler flowmeter in 23 rats and concluded that BH affects vascular conductivity in the cochlea in a dose-dependent fashion; betahistine diffuses through the round window, but does not have access to vascular receptors or ligands once in the labyrinthine fluids; and the H1 receptors mediate the systemic and peripheral vascular effects of BH, whereas the cochlear effect involves cholinergic receptors.

Stellate ganglion drives sympathetic regulation of cochlear blood flow

The functional properties of the sympathetic fibers innervating the cochlea are not well understood. Adrenergic fibers supplying lateral wall structures of the cochlea have been observed terminating on radiating arterioles and collecting venules. Adrenergic fibers also terminate as 'free' endings in the spiral osseous lamina. Stimulation or transection of sympathetic fibers originating from superior cervical chain and supplying the cochlea have yielded mixed results concerning many aspects of cochlea physiology. In order to clarify the origin of sympathetic fibers and their role in control of cochlear blood flow (CBF), we examined the effect of electrical stimulation of the stellate ganglion (ESS) and transection of postganglionic fibers from the stellate on CBF measured by laser Doppler flowmetry and on systemic blood pressure (BP) in the guinea pig. ESS produced a 20-35% increase in BP and 10-15% decrease in CBF. The decrease in CBF presumably reflects the net result of increased perfusion pressure, local autoregulatory mechanisms, and a direct sympathetic-induced vasoconstriction. Section of the immediate postganglionic sympathetic trunk had little or no effect on the ESS-related change in BP; however, it eliminated the CBF reduction. Intravenously infused beta 1-blocker diminished the BP increase due to ESS, while the electrically-evoked reduction in CBF remained. Local application of an alpha-blocker on the round window blocked ESS evoked CBF reductions without altering the BP increase. These data confirm the functional role of sympathetic projections from the stellate ganglion in CBF regulation in guinea pig.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of c-fos immunostaining in the rat brain after the systemic administration of nicotine

To search for evidence of altered neuronal gene expression in response to exposure to the highly addictive drug nicotine, rat brains were examined by immunocytochemistry for the fos protein after the systemic administration of nicotine. The drug was administered as an IV infusion over 1 h At a dose of 2 mg/kg, the most dramatic nicotine-induced fos nuclear immunostaining was seen in central visual pathways, including the superficial superior colliculus and the medial terminal nu. of the accessory optic tract, in the interpeduncular nu. Notably, many regions with high levels of nicotine binding sites, including the medial habenula, thalamus, substantia nigra, and ventral tegmental area, failed to express the c-fos gene with this schedule of nicotine administration. A minimal increase in fos immunostaining was seen after a nicotine dose of 0.5 mg/kg, with a much greater response after 1 or 2 mg/kg. The response was seen as soon as 60 min after the beginning of the infusion, was maximal at 2-3 h, and declined thereafter. c-fos expression was substantially attenuated in the superficial gray layer of superior colliculus, medial terminal nucleus of the accessory optic tract, and the interpeduncular nucleus by pretreatment with the centrally acting nicotine antagonist mecamylamine, 5 mg/kg IP, but not with the peripherally acting antagonist hexamethonium, 4 mg/kg IP. These observations identify a subset of central nervous system neurons that respond to nicotine with altered expression of the immediate early gene c-fos. These neurons presumably undergo long-term changes in gene expression as a result of acute exposure to high doses of nicotine.

Dispersion of Small Ceramic Particles (Al 2 O 3 ) with Azotobacter vinelandii

The high surface charge of small ceramic particles such as alumina particles prevents them from dispersing evenly in aqueous suspensions and forming high-density compacts. However, suspensions of 400-nm-diameter alumina particles treated with alginate from the bacterium Azotobacter vinelandii were well dispersed. The alginate bound firmly to the particle surface and could not be removed by repeated washing with distilled water (2.82 mg of the bacterial alginate adsorbed to 1 g of the alumina particles). Furthermore, A. vinelandii grew and produced alginate in the presence of up to 15% (vol/vol) alumina particles. These results suggest that an in situ process using this bacterium to coat ceramic particles with alginate might be developed. In in situ processing experiments, the particle-packing densities were significantly increased and the viscosities of 5 and 10% (vol/vol) suspensions were reduced 4- and 60-fold, respectively, over those of controls. The bacteria were readily removed from the alumina particles by washing.