Effects of betahistine and of its metabolites on vestibular sensory organs

Betahistine is widely used in the treatment of peripheral and central vestibular disorders. Till now the anti-vertigo effect of the drug was though to be mainly due to an action of betahistine on inner ear or cerebral microcirculation or on some structures of the CNS, chiefly the vestibular nuclei. Vertigo, however is, in most cases, of peripheral origin but it remains unknown whether betahistine, or some of its metabolities, may directly affect the vestibular system at peripheral level. Pharmacokinetic studies have in fact demonstrated that betahistine is transformed, mainly at the hepatic level, in aminoethylpyridine (M1), hydroxyethylpyridine (M2) and, finally, in pyridylacetic acid (M3) which is excreted with the urine. All these substances are therefore present in the body fluids of subjects treated with betahistine, and thus might have pharmacological effects. The goal of the present study was to investigate whether betahistine or some of its metabolites could exert any effect on vestibular receptors. To this end, the effects of the drugs (10(-7)-10(-2) M) have been examined on frog semicircular canals, an animal model well suited for this purpose. The effects of betahistine and of its metabolites have been evaluated by recording ampullar receptor activity both at rest and during mechanical stimulation of the sensory organ. The results demonstrated that both betahistine and one of its metabolites, the aminoethylpyridine (M1), exert effects quite similar on ampullar receptors; both these substances in fact could reduce greatly ampullar receptor resting discharge but had scanty effects on mechanically-evoked responses. This observation might justify betahistine and possibly M1 anti-vertigo effects. In fact vertigo is normally due to uncontrolled changes in vestibular receptor resting discharge. It is therefore probable that any factor able to reduce vestibular receptor resting firing rate and, in consequence, its variations, may have, as final effect, an anti-vertigo action. The observation that betahistine and M1 have similar effects might be of some clinical interest. In fact, on the basis of our data, the hypothesis may be put forward that the anti-vertigo action of betahistine is at first achieved by betahistine itself and then sustained and prolonged in time by M1.

Regional distribution of calcium currents in frog semicircular canal hair cells

In the present work we studied the regional expression of voltage-dependent Ca channels in hair cells from the frog semicircular canals, employing whole-cell patch-clamp on isolated and in situ hair cells. Although Ca channels are thought to play a major role in afferent transmission, up to now no data were available regarding their distribution in vestibular organs. The problem appears of interest, especially in the light of recent results showing the presence of multiple Ca current components in semicircular canal hair cells. Our data suggest the presence, in all regions of the crista ampullaris, of two classes of cells, one displaying an inactivating Ca current (R1) and one lacking it. In the former cells, Ca current amplitude decreased from the central to the peripheral zone (the maximal currents being observed in the intermediate zone). Only L-type and R2 current components displayed regional differences in expression, whereas the size and properties of R1, although variable among cells, were not regionalized. However, in cells lacking R1, Ca current amplitudes were similar regardless of cell shape and location. The possible contributions of this Ca current distribution to afferent discharge properties are discussed.

Influence of [4Cl-D-Phe6,Leu17]VIP on VIP- and central TRH-induced gastric hyperemia

The specific VIP receptor antagonist, [4Cl-D-Phe6,Leu17]VIP, infused i.v. blocked close-intra-arterial infusion of VIP-induced increase in gastric mucosal blood flow (GMBF, measured by the hydrogen gas clearance), and decrease in mean arterial blood pressure while not influencing basal levels in urethane-anesthetized rats. The thyrotropin-releasing hormone (TRH) stable analog, RX 77368, injected intracisternally (IC, 30 ng) increased GMBF and blood pressure. The VIP antagonist did not significantly reduce the GMBF response to IC RX 77368 while enhancing the rise in blood pressure. These findings indicate that [4Cl-D-Phe6,Leu17]VIP is an antagonist for exogenous VIP-induced gastric hyperemia and hypotension and that VIP modulates the systemic blood pressure response to IC RX 77368 at 30 ng while not playing a primary role in the increase of GMBF.

Role of prostaglandins and nitric oxide in gastrointestinal hyperemia of diabetic rats

The aim of the study was to characterize the gastric and mesenteric vascular changes induced by diabetes and the implication of endothelial [nitric oxide (NO) and prostaglandins] and humoral (glucagon) factors in such changes. Diabetes was induced in rats by a single streptozotocin injection. Four weeks later, gastric mucosa, left gastric artery, and superior mesenteric artery blood flows were measured using hydrogen gas clearance and perivascular ultrasonic flowmeter techniques, respectively, in anesthetized and fasted diabetic and control rats. Blood pressure, hematocrit, blood volume, and blood viscosity were also measured. Left gastric (41 +/- 6 vs. 25 +/- 4 ml.min-1.100 g-1) and superior mesenteric artery blood flows (83 +/- 8 vs. 65 +/- 4 ml.min-1.100 g-1) were significantly higher in diabetic than in control rats. The increased blood flow in the left gastric artery was distributed to a hypertrophic mucosa in diabetic rats; therefore, the blood flow per 100 g tissue in the gastric mucosa was not significantly different in diabetic compared with control rats. Pretreatment with indomethacin reduced both increase gastric and mesenteric flows of the diabetic rats to the same levels as in control rats. NG-nitro-L-arginine methyl ester decreased gastric blood flow in a dose-dependent manner and to a similar extent in diabetic and control rats. In contrast, an increased sensitivity to the higher doses of the NO inhibitor was observed in the mesenteric vascular bed of diabetic rats. Glucagon reduction achieved by somatostatin infusion did not influence either gastric or mesenteric blood flow in diabetic rats. In summary, the present study revealed an increase in gastric and mesenteric arterial blood flows in streptozotocin-induced diabetic rats. The gastrointestinal hyperemia seems to be due, at least in part, to the increased demand of a hypertrophic mucosa and is mediated primarily by endogenous prostaglandins. Increased vascular sensitivity to NO may also contribute to the mesenteric vasodilation.

Glucose-induced islet hyperemia is mediated by nitric oxide

PURPOSE

To determine whether hyperglycemia affects pancreatic islet microcirculation in vivo and whether nitric oxide is a mediator.

METHODS

Islet blood flow was measured before and after infusion of glucose during in vivo microscopy of mouse pancreatic islet. The pancreas of male BALB/c mice was exteriorized and viewed under the microscope utilizing monochromatic transmitted light. The carotid artery and tail vein were cannulated and systemic blood pressure was monitored continuously. Under fluorescent light, a 0.02 mL bolus of 2% fluorescein isothyocyanate (FITC-albumin) was injected intra-arterially and the first pulse of FITC-albumin through an islet capillary was videorecorded. Following equilibration, either glucose or normal saline 300 mg/g of body weight was given intravenously. Five minutes later, a second bolus was given and the second pulse was videorecorded. The study was repeated in the presence of N omega-nitro-L-arginine methyl ester (L-NAME). The FITC-albumin bolus mean transit time (TT) and observed cross time (OCT) through the islet were calculated using slow-motion video analysis of the recorded images.

RESULTS

Infusion of glucose resulted in a significant increase in islet blood flow with no change in systemic blood pressure: baseline TT was 20 +/- 1.3 pixel/0.03 sec and baseline OCT was 0.6 +/- 0.04 seconds; during hyperglycemia, TT was 16.1 +/- 1 pixel/0.03 sec, and OCT was 0.48 +/- 0.03 seconds (n = 11, P < 0.05 versus basal via paired t-test). Continuous infusion of L-NAME negated the effect of hyperglycemia on islet blood flow: baseline TT was 20 +/- 1.8 pixel/0.03 sec and OCT was and 0.6 +/- 0.05 seconds; during hyperglycemia, TT was 20 +/- 1.1 pixel/0.03 sec and OCT was 0.6 +/- 0.33 seconds (n = 10; P < 0.05 versus glucose via unpaired t-test).

D2 dopamine receptor TaqI A alleles in medically ill alcoholic and nonalcoholic patients

The prevalence of TaqI A alleles of the D2 dopamine receptor (DRD2) gene was examined in two subgroups of medically ill nonalcoholics (more prevalent and less prevalent substance users, MPSU and LPSU, respectively) and in two subgroups of medically ill alcoholics (more severe and less severe alcoholics, MSA and LSA, respectively). The prevalence of the A1 allele in the 80 nonalcoholic and 73 alcoholic patients was 30.0% and 52.1%, respectively (P = 0.009). In the four subgroups of these patients, the prevalence of this allele was: LPSU = 18.2%, MPSU = 34.5%, LSA = 44.4% and MSA = 58.3%. Linear trend analysis showed that as the use of substances and severity of alcoholism increase, so does A1 prevalence (P = 0.001). Specific, subgroup comparisons showed A1 prevalence in MSA to be about 3-fold (P = 0.007) and 1.5-fold (P = 0.04) higher than in LPSU and MPSU subgroups, respectively. Similarly, in a combined analysis of independent studies, A1 prevalence in MSA was higher when compared to LSA (P < 5 x 10(-3), MPSU (P < 10(-4) and LPSU (P < 10(-8) subgroups. There was virtually no difference in the prevalence of the A1 allele between LSA and MPSU subgroups. None of the specific medical or neuropsychiatric complications of alcoholism was associated with the A1 allele. In conclusion, the severity of alcohol dependence in alcoholics and of substance use behaviors in controls are important variables in DRD2 allelic association. The present report and converging lines of evidence suggest that the DRD2 locus could represent a prominent gene risk factor for susceptibility to severe alcoholism. However, other genes and environmental factors, when combined, still play the larger role.

The correlated blanching of synaptic bodies and reduction in afferent firing rates caused by transmitter-depleting agents in the frog semicircular canal

Synaptic bodies (SBs) associated with rings of synaptic vesicles and well-defined, pre- and post-synaptic membrane structures are indicators of maturity in most hair cell-afferent nerve junctions. The role of the SBs remains elusive despite several experiments showing that they may be involved in storage of neurotransmitter. Our results demonstrate that SBs of the adult posterior semicircular canal (SCC) cristae hair cells become less electron dense following incubation of the SCC with the transmitter-depleting drug tetrabenazine (TBZ). Objective quantification and comparison of the densities of the SBs in untreated and TBZ-treated frog SCC demonstrated that TBZ significantly decreased the electron density of SBs. This reduction in electron density was accompanied by a reduction in firing rates of afferent fibers innervating the posterior SCC. A second transmitter-depleting drug, guanethidine, previously shown to reduce the electron density of hair cell SBs, also reduced the firing rates of afferent fibers innervating the posterior SCC. In contrast, the electron density of dense granules (DG), similar in size and shape to synaptic bodies (SB) in hair cells, did not change after incubation in TBZ, thus indicating that granules and SBs are not similar in regard to their electron density. The role of SBs in synaptic transmission and the transmitter, if any, stored in the SBs remain unknown. Nonetheless, the association of the lessening of electron density with a reduction in afferent firing rate provides impetus for the further investigation of the SB's role in neurotransmission.

Role of nitric oxide in gastric hyperemia induced by central vagal stimulation

The effects of N omega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthesis, on the vagal cholinergic increase in gastric mucosal blood flow (GMBF) and acid secretion induced by intracisternal injection of the thyrotropin-releasing hormone (TRH) analogue, RX 77368, were studied. GMBF and acid secretion were measured simultaneously by the hydrogen gas clearance technique and titration of gastric perfusate in urethan-anesthetized rats. RX 77368 (30 ng) injected intracisternally stimulated gastric acid secretion and GMBF for 90 and 180 min respectively. GMBF was increased from basal 63 +/- 4 to 166 +/- 14 ml.min-1.100 g-1 at 60 min postinjection. L-NAME (3 mg/kg) injected intravenously 15 min before RX 77368 completely prevented the increase in GMBF induced by the TRH analogue, whereas the acid response was not modified. The effect of L-NAME was reversed by L-arginine but not by the stereoisomer D-arginine. These results show that the increase in GMBF, but not the stimulation of acid secretion, induced by central vagal activation is mediated through a product of L-arginine-NO pathway.

In vivo microscopy of rat skeletal muscle after ischemia using labelled neutrophils (PMN)

Neutrophils (PMN) have been implicated as mediators of the "no-reflow" phenomenon seen in skeletal muscle during reperfusion after ischemia. In order to evaluate the PMN contribution to the changes seen in the microcirculation of skeletal muscle after ischemia, we evaluated PMN velocity using in vivo microscopy in a rat model. After the induction of anesthesia, the right iliac and femoral arteries were isolated. The right anterior tibialis muscle was exposed in situ, covered with a plexiglass disc, and perfused with Kreb's solution. Fluorescein-labeled bovine albumin was given intravenously, which identified the capillaries under microscopic magnification as viewed on the video screen. Acridine orange was then administered intravenously, which selectively fluoresced the PMN. The right iliac and femoral arteries were clamped for ischemia intervals of 5, 10, 15, 20, 25, and 30 min. Acridine orange was given immediately after the arteries were unclamped, after 30 min of reperfusion and after 60 min of reperfusion. PMN velocity was determined by the distance traveled by the PMN over time using the videotape and frame-by-frame review. Results demonstrated no change in PMN velocity (mm/sec) after 5 min of ischemia. After 10, 15, and 20 min of ischemia, PMN velocity initially slowed and then recovered, which was not statistically significant. After 25 min of ischemia, PMN velocity decreased significantly, which persisted (P < 0.05 compared to 5-min ischemia by ANOVA). No flow was seen after 30 min of ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclic AMP modulates sensory-neural communication at the vestibular end organ

Adenosine 3':5'-cyclic phosphate (cAMP) is a second messenger that plays an important role in mediating neuronal interactions in many systems. A possible role for cAMP in sensorineural communication at the vestibular end organ was studied. The putative roles for cAMP action investigated here were: the ability of cAMP to act as the second messenger for the efferent transmitter, acetylcholine, and the possible involvement of cAMP in modulating spontaneous or mechanically-evoked afferent nerve firing. Levels of cAMP were increased pharmacologically with forskolin, 3-isobutyl-1-methyl xanthine (IBMX) and dibutyryl cAMP. Changes in multiunit afferent nerve firing measured from the ampullar nerve of the semicircular canal, and the transepithelial potential measured across the neuroepithelium of the semicircular canal were recorded. At selected doses, all drugs produced a similar increase in spontaneous multiunit afferent nerve firing with a concomitant decrease in the transepithelial potential. Mechanically-evoked hair cell activity and the response to exogenously applied acetylcholine were unaffected by these drugs. We are suggesting that the excitatory aspects of the acetylcholine response are not mediated via a cAMP-dependent mechanism. However, cAMP does play an important role in modulating spontaneous afferent nerve firing in the semicircular canal. The finding that spontaneous afferent nerve firing can be biochemically modulated without altering mechanically-induced afferent firing is novel and deserves further investigation.

Use of the Million Clinical Multiaxial Inventory in evaluating patients with severe tinnitus

The Million Clinical Multiaxial Inventory (MCMI) was evaluated as a diagnostic tool for personality disorder among 41 patients with severe tinnitus. Nearly 70 percent of the subjects demonstrated a personality disorder. Nearly half of the patients fell into one of two categories; dependent/submissive or the narcissistic category. Other important features include a high incidence (24%) of severe anxiety. One-third of the patients had a complaint tendency but 50 percent had a denial problem. We have found the MCMI to be easy to administer and evaluate and it provides the clinician with useful information. We believe that more routine use of this or similar instruments would improve the treatment outcome of tinnitus sufferers by bringing into focus the important psychological factors found in each patient.

Predictable and unpredictable shock stimulates gastric contractility and causes mucosal injury in rats

The effects of tailshock on gastric contractility and lesions were investigated in rats exposed to 100 1-mA tailshocks while confined inside plastic tubes. A light preceded each shock in one group and was randomly presented with respect to shock in the other. Following the session, animals were given 3 hr of rest before being sacrificed. Contractility of the corpus of the stomach was measured by means of chronically implanted extraluminal force transducers. Contractility was measured in 10-min blocks and analyzed by computer. Lesions were quantified by inspection; quantitative histology was performed on corpus and antrum sections. Signaled (n = 13) and unsignaled (n = 17) shock stimulated high-amplitude gastric contractions in fasted rats, which continued for 2 hr after the shock session. Cumulative contractile activity (1.5-hr shock plus 2-hr rest) in shocked animals was twice that in restrained and unrestrained control animals (n = 19, p less than .05), and contractile activity had a 30%-40% greater average amplitude than after a meal. Compared with unrestrained controls, shocked rats had visibly more mucosal injury (2.2 +/- 0.5 mm2 vs. 0.1 +/- 0 mm2). Larger cumulative contractile activity was associated with a larger area of erosions (r = .36, p less than .05). Frequency and duration of contractions did not distinguish between shocked and unshocked groups. We conclude that in rats, signaled and unsignaled tailshock stimulates persistent, high-amplitude gastric contractions and is associated with injury of the mucosa of the stomach.

Predictable and unpredictable shock stimulates gastric contractility and causes mucosal injury in rats

The effects of tailshock on gastric contractility and lesions were investigated in rats exposed to 100 1-mA tailshocks while confined inside plastic tubes. A light preceded each shock in one group and was randomly presented with respect to shock in the other. Following the session, animals were given 3 hr of rest before being sacrificed. Contractility of the corpus of the stomach was measured by means of chronically implanted extraluminal force transducers. Contractility was measured in 10-min blocks and analyzed by computer. Lesions were quantified by inspection; quantitative histology was performed on corpus and antrum sections. Signaled (n = 13) and unsignaled (n = 17) shock stimulated high-amplitude gastric contractions in fasted rats, which continued for 2 hr after the shock session. Cumulative contractile activity (1.5-hr shock plus 2-hr rest) in shocked animals was twice that in restrained and unrestrained control animals (n = 19, p less than .05), and contractile activity had a 30%-40% greater average amplitude than after a meal. Compared with unrestrained controls, shocked rats had visibly more mucosal injury (2.2 +/- 0.5 mm2 vs. 0.1 +/- 0 mm2). Larger cumulative contractile activity was associated with a larger area of erosions (r = .36, p less than .05). Frequency and duration of contractions did not distinguish between shocked and unshocked groups. We conclude that in rats, signaled and unsignaled tailshock stimulates persistent, high-amplitude gastric contractions and is associated with injury of the mucosa of the stomach.

Cytochalasin D suppresses sound evoked potentials in the guinea pig cochlea

Cytochalasin D (CD), an inhibitor of actin polymerization, was perfused through the guinea pig cochlea while monitoring various cochlear potentials. CD (10(-7)-10(-5) M) reduced the magnitude of the compound action potential of the cochlear nerve and the summating potential, and increased N1 latency. The cochlear microphonic potential was the least sensitive potential with only a slight effect being observed at 10(-5) M. The results are consistent with the hypothesis that actin has a role in cochlear function.

Cimetidine and ranitidine protect against cold restraint-induced ulceration in rat by suppressing gastric acid secretion

The effect of the H2-receptor antagonists cimetidine and ranitidine on pentagastrin-stimulated gastric acid secretion in anesthetized rats, and gastric mucosal lesion formation and gastric motility in unanesthetized cold-restrained rats was studied. Both cimetidine and ranitidine suppressed pentagastrin-stimulated gastric secretion in a dose-dependent fashion. Cold restraint-induced lesion formation was not prevented with doses of both agents that inhibited acid secretion by 75%. Doses which suppressed pentagastrin-stimulated acid secretion more than 90% significantly prevented the development of gastric mucosal lesions produced by cold restraint. Doses of both H2 blockers which demonstrated significant suppression of lesion formation had no effect on cold restraint-stimulated gastric contractility. We conclude that cimetidine and ranitidine suppress cold restraint-induced lesion formation by suppressing acid secretion and not by suppressing gastric contractility.

Amino acid content of guinea pig perilymph collected under conditions of quiet or sound stimulation

With the cochlear aqueducts blocked, guinea pig cochleas were perfused with artificial perilymph. The collected perfusates were treated with 5-(dimethylamino)-1-naphthalenesulfonyl chloride (dansyl-Cl). The derivatized constituents were analyzed by high- performance liquid chromatography using fluorometric detection. The concentration of none of the compounds measured, including the putative transmitters glutamate and aspartate, was found to increase in the perfusate in response to sound stimulation. These results do not support the suggestion that one of these compounds might be primary afferent transmitter of audition.

A simple, sensitive method for the quantitation of kanamycin in tissue and biological fluids

A method is described for the quantitative determination of kanamycin in blood, urine, cochlear perilymph and kidney. The method is simple, involving only protein precipitation, chromatographic separation and fluorometric determination following reaction with fluorescamine. The method is sensitive, determining as little as 80--100 ng/ml of kanamycin. The method is reliable, recovering better than 90% of the kanamycin added to the fluids and tissues mentioned. It is also less cumbersome and less expensive than other methods currently used.