Dopamine D1-like receptor activation depolarizes medium spiny neurons of the mouse nucleus accumbens by inhibiting inwardly rectifying K+ currents through a cAMP-dependent protein kinase A-independent mechanism.

Dopamine/cAMP signaling has been reported to mediate behavioral responses related to drug addiction. It also modulates the plasticity and firing properties of medium spiny neurons (MSNs) in the nucleus accumbens (NAc), although the effects of cAMP signaling on the resting membrane potential (RMP) of MSNs has not been specifically defined. In this study, activation of dopamine D1-like receptors (D1Rs) by SKF-38393 elicited membrane depolarization and inward currents in MSNs from the NAc core of 14-17 day-old mice. Similar results were obtained following stimulation of adenylyl cyclase (AC) activity with forskolin or application of exogenous cAMP. Forskolin occluded SKF-38393's effects, thus indicating that D1R action is mediated by AC/cAMP signaling. Accordingly, AC blockade by SQ22536 significantly inhibited the responses to SKF-38393. Effects elicited by D1R stimulation or increased cAMP levels were unaffected by protein kinase A (PKA) or protein kinase C (PKC) blockade and were not mimicked by the Epac agonist, 8CPT-2Me-cAMP. Responses to forskolin were also not significantly modified by cyclic nucleotide-gated (CNG) channel blockade. Forskolin-induced membrane depolarization was associated with increased membrane input resistance. Voltage-clamp experiments revealed that forskolin and SKF-38393 effects were due to inhibition of resting K(+) currents exhibiting inward rectification at hyperpolarized potentials and a reversal potential (around -90 mV) that shifted with the extracellular K(+) concentration. Forskolin and D1R agonist effects were abolished by the inward rectifier K(+) (Kir)-channel blocker, BaCl(2). Collectively, these data suggest that stimulation of postsynaptic D1Rs in MSNs of the NAc core causes membrane depolarization by inhibiting Kir currents. This effect is mediated by AC/cAMP signaling but it is independent on PKA, PKC, Epac and CNG channel activation, suggesting that it may stem from cAMP's direct interaction with Kir channels. D1R/cAMP-mediated excitatory effects may influence the generation of output signals from MSNs by facilitating their transition from the quiescent down-state to the functionally active up-state.

The role of antioxidants in protection from ototoxic drugs.

A number of studies have shown that cisplatin and gentamicin ototoxic effects may result from free radical-mediated damage due to the reduction of antioxidant substances and an increased lipid peroxidation. The authors summarize the results obtained evaluating the auditory and vestibular functions and the inner ear hair cell morphology and survival after administration of antioxidant agents against cisplatin and gentamicin. In the first experiment, albino guinea pigs were treated with gentamicin (100 mg/kg per day, i.m.) alone or gentamicin (100 mg/kg per day, i.m.) plus alpha-tocopherol (100 mg/kg per day, i.m.) for 2 weeks. In a second experiment, albino guinea pigs were injected with cisplatin (2.5 mg/kg per day) or cisplatin (2.5 mg/kg per day) plus tiopronin (300 mg/kg) for 6 days. Electrocochleographic recordings were made from an implanted round window electrode. In all experiments compound action potentials (CAPs) were measured at 2-16 kHz. Changes in cochlear function were characterized as CAP threshold shifts. To evaluate vestibular function, the animals underwent sinusoidal oscillations in the dark about their vertical and longitudinal axes to evoke horizontal and vertical vestibulo-ocular reflexes (VOR). Frequency stimulation parameters ranged from 0.02 to 0.4 Hz and peak-to-peak amplitude was 20 degrees. Morphological changes were analysed by light microscopy and scanning electron microscopy. Both hearing loss and vestibular dysfunction induced by gentamicin were significantly attenuated by alpha-tocopherol. However, tiopronin co-therapy slowed the progression of hearing loss in cisplatin-treated animals and significantly attenuated the final threshold shifts. Cisplatin had little effect on the hair cells of cristae ampullares and maculae. Vestibular function was completely preserved in tiopronin co-treated animals. In conclusion, antioxidants such as alpha-tocopherol or tiopronin interfere with gentamicin and cisplatin damage and this suggests that they may be useful in preventing oto-vestibulotoxicity. Therefore, it is important to develop protective strategies that permit the avoidance of the toxic side effects of these drugs without interfering with their therapeutic effects.

The role of antioxidants in protection from ototoxic drugs.

A number of studies have shown that cisplatin and gentamicin ototoxic effects may result from free radical-mediated damage due to the reduction of antioxidant substances and an increased lipid peroxidation. The authors summarize the results obtained evaluating the auditory and vestibular functions and the inner ear hair cell morphology and survival after administration of antioxidant agents against cisplatin and gentamicin. In the first experiment, albino guinea pigs were treated with gentamicin (100 mg/kg per day, i.m.) alone or gentamicin (100 mg/kg per day, i.m.) plus α-tocopherol (100 mg/kg per day, i.m.) for 2 weeks. In a second experiment, albino guinea pigs were injected with cisplatin (2.5 mg/kg per day) or cisplatin (2.5 mg/kg per day) plus tiopronin (300 mg/kg) for 6 days. Electrocochleographic recordings were made from an implanted round window electrode. In all experiments compound action potentials (CAPs) were measured at 2-16 kHz. Changes in cochlear function were characterized as CAP threshold shifts. To evaluate vestibular function, the animals underwent sinusoidal oscillations in the dark about their vertical and longitudinal axes to evoke horizontal and vertical vestibulo-ocular reflexes (VOR). Frequency stimulation parameters ranged from 0.02 to 0.4 Hz and peak-to-peak amplitude was 20°. Morphological changes were analysed by light microscopy and scanning electron microscopy. Both hearing loss and vestibular dysfunction induced by gentamicin were significantly attenuated by α-tocopherol. However, tiopronin co-therapy slowed the progression of hearing loss in cisplatin-treated animals and significantly attenuated the final threshold shifts. Cisplatin had little effect on the hair cells of cristae ampullares and maculae. Vestibular function was completely preserved in tiopronin co-treated animals. In conclusion, antioxidants such as α-tocopherol or tiopronin interfere with gentamicin and cisplatin damage and this suggests that they may be useful in preventing oto-vestibulotoxicity. Therefore, it is important to develop protective strategies that permit the avoidance of the toxic side effects of these drugs without interfering with their therapeutic effects.

Functional role of inducible nitric oxide synthase on mouse colonic motility.

A possible functional role of inducible isoform of nitric oxide synthase (iNOS) was explored in vitro on the motility of mouse distal colon. Using an isotonic - non-isovolumic technique, peristaltic activity and video images of the external wall of colonic segments were recorded before and after addition to the medium of Aminoguanidine (AG) and N-(3-(aminomethyl)benzyl) acetamidine (W1400) [10(-7) M-10(-4) M], two iNOS inhibitors. AG and W1400 induced an hyperexcitability of visceral smooth muscle characterised by an increase of basal tone and spontaneous phasic activity. As a consequence of these effects, the peristaltic activity declined and disappeared at the highest concentrations. These findings indicated a removal of inhibitory action performed by NO synthesised by iNOS in the colonic segment. The implications of results are discussed in term of tonic relaxation of intestinal smooth muscle to allow intraluminal content accommodation.

Eye instability induced by vestibular stimulation in rabbits.

The slow compensatory phases of the vestibulo-ocular reflex (VOR) in the rabbit tend to drift and the drift reverses the direction. This periodic alternating drift (PAD) has two peculiar characteristics: (1) it is induced by sinusoidal vestibular stimulation in naive animals, being evoked immediately after stimulus onset and persisting after the end of stimulation; (2) the peak velocity and period of the drift are dependent on stimulus amplitude. PAD of the rabbit has strong similarities with PAN, a periodic alternating nystagmus observed in humans with cerbellar disorders and in monkeys after nodulo-uvulectomy, although its peak velocity is smaller. It is hypothesized that PAD is due to a slight instability, caused by vestibular stimulation in darkness, of the cerebellar adaptive loop, which exerts a variable gain control on the time constant of the velocity storage integrator.

Inhibition of peristaltic activity by cannabinoids in the isolated distal colon of mouse.

The effects of the cannabinoid receptor agonist Win 55,212-2 and of the competitive cannabinoid receptor antagonist SR 141716A on the electrically-evoked peristalsis of isolated distal colon of mouse were studied. Intraluminal pressure, longitudinal displacement, ejected fluid volume and changes in morphology of external intestinal wall were simultaneously recorded in the pre-drug period and in presence of Win 55,212-2 alone or in combination with SR 141716A. In the pre-drug period (control), peristaltic activity was characterised by regular, monophasic waves and the intraluminal content propelled towards anterograde (oro-aboral) direction with a propulsion velocity of 1.25 +/- 0.1 mm x s(-1). Pressure and shortening waves showed a peak amplitude of 2.44 +/- 0.32 kPa and 1.8 +/- 0.72 mm, respectively. The mean amount of fluid volume ejected during each contraction was 80 +/- 12.6 microl. The addition of Win 55,212-2 [10(-7)-10(-4) M] to the organ bath determined a dose-related attenuation of peristaltic activity consequent to the decrease of circular and longitudinal muscle strength. The decrease of contractile activity was followed by dose-dependent decrease of the amount of fluid ejected during peristalsis. The effects of Win 55,212-2 [10(-7)-10(-5) M] were prevented by SR 141716A, indicating the presence of cannabinoid CB1 receptors in the mouse distal colon. SR 141716A alone enhanced both tonic and phasic motor activities in the colonic longitudinal smooth muscle, suggesting that CB1 receptor antagonists could act either through antagonising the effect of endogenous CB1 receptor agonist or by an agonist effect on these receptors. The present results further support the hypothesis that cannabinoids perform a neuromodulatory role in various tracts of gastrointestinal system and first demonstrate their action also in the distal colon of rodents.

Functional recovery after extra-ocular muscle deafferentation in the rabbit.

The present research analysed on chronic animals the functional recovery of eye motility after impairment of the proprioceptive input at the level of the semilunar ganglion. The horizontal vestibulo-ocular reflex (HVOR) was recorded in normal pigmented rabbits before and after a partial electrolytic lesion of the semilunar ganglion. The recordings were repeated daily for 8-10 days to evaluate the recovery. Immediately after the lesion, as previously observed, HVOR slow phases were unaffected, while quick phases (QPs) showed a reduction in peak velocity and a deviation of trajectories from the horizontal plane. QP peak velocity was almost completely restored within 3-5 days, while trajectory deviation was not corrected during the observation period. Furthermore, in some animals, the variability of trajectories showed, starting from days 3-5, a progressive increase that led to a greater spatial disorganization. A process of lesion-induced plasticity takes place. but only the velocity of QPs can be recovered rapidly, while the QP trajectory impairment does not appear to be compensated substantially, which underlines a determinant role in the control of QP spatial orientation exerted by EOM proprioceptive signals.

Characterization of Ca(2+)-channels responsible for K(+)-evoked [(3)H]noradrenaline release from rat brain cortex synaptosomes and their response to amyotrophic lateral sclerosis IgGs.

The contribution of the different Ca(2+)-channel subtypes to the K(+)-evoked [(3)H]noradrenaline release from rat cerebral cortex synaptosomes has been investigated. In the same experimental model, it was also verified whether the calcium-mediated neurotransmitter release is influenced by IgGs purified from sera of seven patients affected by sporadic amyotrophic lateral sclerosis. Synaptosome treatment with 3.0 microM nifedipine or 2.0 microM calciseptine, which block L-type channels, slightly decreased [(3)H]noradrenaline release, the reduction being 7 and 13% of the control values, respectively. The blockade of N-type Ca(2+)-channels with omega-conotoxin-GVIA (0.001-1.0 microM) induced a concentration-dependent reduction of the neurotransmitter release, with maximum effect of 34%. omega-Agatoxin-IVA failed to significantly affect the studied release, which was instead markedly reduced by omega-conotoxin-MVIIC. After the blockade of N-type channels with maximal concentrations of omega-conotoxin-GVIA, 3.0 microM omega-conotoxin-MVIIC reduced the release by 58%. Synaptosome treatment with amyotrophic lateral sclerosis IgGs enhanced the K(+)-evoked [(3)H]noradrenaline release, which was mostly mediated by P/Q- and N-type Ca(2+)-channels. The increase induced by pathologic IgGs (0.2 mg/ml) ranged from 11 to 62% for the different patients, and it was concentration-dependent. The basal release was instead unaffected by IgG treatment. The results of the present study suggest that the K(+)-evoked [(3)H]noradrenaline release from brain cortex synaptosomes is mainly mediated by activation of P/Q- and N-type Ca(2+)-channels. Autoantibodies present in the sera of patients affected by sporadic amyotrophic lateral sclerosis may interact with these channels by producing an increased calcium influx, with consequent enhancement of the neurotransmitter release. Preliminary results of the present study have been published in abstract form (Martire et al., 1997, Pharmacol. Res. 35:9).

Mechanical properties of smooth muscle portal vein in normal and dystrophin-deficient (mdx) mice.

Mechanical properties of the vascular smooth muscle from normal and dystrophin-deficient (mdx) mice were examined. Changes in resting and developed tensions in response to stretch were recorded in isolated portal vein. The vascular segments were elongated in 5 % increments of the 'in situ' length (Lr) up to 1.30Lr. The resting length-tension curves in male mdxmice were similar to normal mice, while a marked decrease in the slope of the curve was noted in female mdx mice. These findings were not affected by atropine, phentolamine, tetrodotoxin or [Ca2+] in the surrounding media. At Lr, the tension of isolated portal vein was characterized by spontaneous synchronized uniform force waves in normal mouse. In contrast, in mdxmouse portal veins an irregular motor pattern characterized by desynchronized force waves with a decrease of amplitude and an increase in frequency was recorded. Extension of the length of the portal vein segment did not increase the spontaneous phasic activity developed in female mdx mice although this was noted with male mdx mice and normal mice. Experiments with chemical depolarizing agents indicated that spontaneous myogenic excitation activated the great majority of vascular smooth muscle cells in normal mouse portal vein, whereas in mdx mice only a reduced number of these cells were excited suggesting that in the mdx mouse the intercellular electronic coupling is altered. In conclusion this study provides the first description of the mechanical activities of portal vein longitudinal muscle and shows that in mdx mice the motor activity is severely disrupted.

Auditory steady-state responses to click trains from the rat temporal cortex.

In order to investigate the mechanisms underlying the generation of steady-state responses (SSRs), auditory evoked potentials elicited by click trains presented at several stimulation rates (30, 40, 50, 60 Hz) were recorded in 7 awake rats by means of epidural electrodes placed over the temporal cortex. Mean amplitude-rate function calculated on the recorded responses appeared almost flat and showed the maximum value at 50 Hz, while mean phases showed a linear increase when increasing the stimulation rate. In each rat, predictions of the recorded responses at 30, 40, 50 and 60 Hz were synthesized by superimposing middle-latency auditory evoked potentials (MAEPs) at suitable time intervals at each rate. Mean amplitudes calculated on the predicted curves decreased linearly when increasing the stimulation rate and appeared higher in comparison to those obtained from the recorded SSRs. Predicted phases showed a linear increase when increasing the stimulation rate and were leading with respect to corresponding phase values calculated for recorded SSRs. Our findings indicate that the MAEP superimposition mechanism does not adequately predict the generation of temporal recorded SSRs in rats. This was explained by admitting that phenomena related to the recovery cycle and, to a lesser extent, to rate-dependent facilitating effects come into play.

Nitric oxide regenerates the normal colonic peristaltic activity in mdx dystrophic mouse.

We demonstrated in vitro that the colonic peristaltic activity is modified in dystrophin-deficient mdx mouse indicating a defect in the enteric nervous system (ENS). Since nitric oxide (NO) has been proposed as a putative inhibitory mediator of ENS, here we have examined the effects of both L-Arginine (L-Arg) and Nomega-nitro-L-arginine methyl ester (L-NAME) on the peristaltic activity of mdx mouse distal colon. The motor pattern of colonic segment showed irregular peristaltic waves. L-Arg (10(-7) - 10(-5) M) induced the peristaltic activity to slow down. At a concentration of 10(-5) M, L-Arg produced hypomotility, characterised by a decrease in amplitude, frequency and ejected fluid volume. Conversely, L-NAME elicited hypermotility, this effect being reversed once again by the subsequent addition of L-Arg. Interestingly the addition of 10(-5) M L-Arg to the organ bath led to the normal progression, in an oral to aboral direction, of 90% of the peristaltic waves. This last result strongly suggests that exogenous application of L-Arg restores the integrative circuits of the ENS responsible for programming and co-ordinating peristaltic activity in the distal colon of mdx mouse.

In vitro excitatory actions of corticotropin-releasing factor on rat colonic motility.

Corticotropin-releasing factor (CRF) has been shown to affect gastrointestinal functions, however, a direct effect of CRF on the intestine has not been demonstrated. To determine the direct effect of CRF and its antagonist alpha-helical-CRF9-41 (alpha-h-CRF) on the enteric nervous system, we studied the action of these substances on electrical and mechanical parameters of peristaltic activity on isolated distal colon of the rat. The effects of CRF were evaluated in vitro on rat isolated colonic segments in which intraluminal pressure, longitudinal displacement, ejected fluid volume and extracellular electrical activity were simultaneously recorded during colonic peristaltic reflex. The addition of CRF (10(-10) - 10(-8) M) to the bath fluid provoked a concentration-dependent increase of both mechanical and electrical peristaltic activity. The CRF-receptor antagonist alpha-h-CRF dose-dependently (10(-10) - 10(-7) M) induced a decrease of the colonic mechanical and electrical activity and prevented (10(-8) - 10(-6) M) CRF (10(-8) M) maximal effects. These results indicate: (a) CRF can exert its effects on colon functions by a direct action, (b) a specific CRF-receptor is present in the rat colon. Indeed, CRF effects are antagonized by the specific CRF antagonist alpha-h-CRF, (c) the fact the alpha-h-CRF displays an activity on its own reveals that colonic functions are controlled by an endogenous CRF tonic activity.

Inhibition of nitric oxide synthase prevents magnesium-free-induced epileptiform activity in guinea-pig piriform cortex neurones in vitro.

The effects of N-nitro-L-arginine methyl ester (L-NAME), a nitric oxide (NO) synthase inhibitor, were examined on Mg2+-free-induced epileptiform activity, in guinea-pig piriform cortex slices in vitro. L-NAME (0.1-1 mM) had no effect on neuronal membrane properties or electrically-evoked postsynaptic potentials (PSPs). In contrast, during superfusion of the slices with Mg2+-free solution neurones exhibited spontaneous and stimulus-evoked epileptiform potentials that were suppressed in the presence of L-NAME (100 microM) or the selective NMDA receptor antagonist DL-APV (100 microM). The inhibitory effects induced by L-NAME were reversibly reduced by L-arginine (1 mM), but not D-arginine (1 mM), the latter drug not being a substrate for NO formation. It was concluded that L-NAME can suppress epileptiform activity induced by Mg2+-free exposure primarily through a decrease in presynaptic transmitter release, although additional actions on the NMDA-receptor complex were also considered.

Sympathetic control of skeletal muscle function: possible co-operation between noradrenaline and neuropeptide Y in rabbit jaw muscles.

Stimulation of the cervical sympathetic nerve at 10/s increases by 12.9 +/- 0.7% peak tension of maximal twitches in the directly stimulated jaw muscles and markedly depresses (41.6 +/- 1.3%) the tonic vibration reflex (TVR) elicited in the same muscles by vibration of the mandible. Both effects are not significantly influenced by administration of beta-adrenoceptor antagonists. When both alpha- and beta-adrenergic receptors are blocked, sympathetic stimulation induces a very small increase in twitch tension (3.8 +/- 0.7%), while no detectable change in the TVR is observed. Close arterial injection of alpha 1-adrenoceptor agonist phenylephrine mimics the effects induced by sympathetic stimulation on twitch tension and TVR, dose-dependently. The noradrenaline co-transmitter neuropeptide Y also produces a long-lasting, dose-dependent increase in the twitch tension which is unaffected by blockade of adrenergic receptors as well as of the neuromuscular junctions. Contribution of neuropeptide Y to the sympathetically-induced reduction of the stretch reflex is not clearly demonstrated. These data suggest that co-operation between noradrenaline and neuropeptide Y may be effective in determining sympathetic modulation of skeletal muscle function.

Possible modulation of auditory middle latency responses by nitric oxide in the inferior colliculus of anaesthetized rats.

Nitric oxide (NO) is a short-lived radical species endowed with intercellular signalling functions in the mammalian brain. In the present study we have investigated the effects of focal injection into one inferior colliculus of N omega-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, on the acoustic middle latency responses (MLRs) evoked by click stimuli and recorded from the auditory cortex in anaesthetized rats. Microinfusion of L-NAME (1.0 mM) did not alter the latency of MLRs nor did it affect the evoked brain stem responses (ABRs). By contrast, L-NAME reduced P1a-N1 amplitude of MLRs by 51.7 +/- 6.6% (mean +/- SEM; n = 5) and almost complete recovery to background amplitude was obtained 15-25 min after treatment. The less active isomer, D-NAME (1.0 mM; n = 5), failed to produce consistent effects on the evoked MLRs. A higher concentration of L-NAME (5.0 mM; n = 5) yielded a 69.0 +/- 13.3% inhibition whereas maximum inhibition produced by 0.5 mM (n = 3) L-NAME was approximately equal to 10% of control value. The inhibitory effect typically evoked by 1.0 mM L-NAME was prevented by treating rats with L-arginine (5.0 mM; n = 5), the endogenous precursor of NO synthesis. Reduction of MLR amplitude was also obtained in rats receiving intracollicular injection of dizocilpine (MK801; 1.0 microM) and LY274614 (1.0 mM), two selective N-methyl-D-aspartate (NMDA) receptor antagonists. In conclusion, the present data support a role for intracollicular NO in the processing and transmission of the acoustic input to the auditory cortex in the rat.

Analysis of peristaltic reflex in young mdx dystrophic mice.

Experiments have been carried out in isolated distal colon of young normal and mdx dystrophic mice, the animal homologous of Duchenne muscular dystrophy. Intraluminal pressure, longitudinal displacement, ejected fluid volume and changes in morphology during peristaltic events were recorded. In both male and female normal animals, pressure waves were observed to be generally regular in shape, amplitude (14.19 +/- 2.45 (SD) cm H2O), frequency (54.00 +/- 10.78 h-1) and duration (31.12 +/- 3.47 s). The propulsive activity resulted in orthograde transport of intraluminal content. Mdx mice exhibited great changes in relation to sex, since clear and more marked dysfunctions were recorded in female mice. In male mdx animals, an increase of intraluminal pressure (22%) and ejected fluid volume (38%) were recorded. In females, a remarkable significant (P < 0.001) increase (78%) of intraluminal pressure was observed. Simultaneous anterograde and retrograde propulsive activity also occurred. Localized annular constrictions in proximal, central and distal portions of colonic segment were observed. The implications of the results are discussed in terms of injury of myogenic and nervous pathways controlling mdx colonic smooth muscle.

Generation of human auditory steady-state responses (SSRs). I: Stimulus rate effects.

Auditory evoked responses were recorded in 16 normally hearing subjects in order to investigate the mechanisms underlying the generation of the 40 Hz steady-state response (SSR). In the first part of our study, auditory potentials were evoked by 0.1 ms clicks presented at 105 dB p.e. SPL with repetition rates of 7.9 (to obtain middle latency response, MLR), 20, 30, 40, 50, 60 Hz. In each subject predictions of the responses recorded at stimulus repetition rates of 30, 40, 50, 60 Hz were synthesized by superimposing MLRs at suitable time intervals. The calculated mean amplitude/rate and phase/rate functions behaved similarly for the recorded and predicted curves, showing the highest amplitude at 40 Hz and a linear increase of phase values when increasing the stimulus rate. Nevertheless the synthetic curves closely predicted amplitude and phase values of the recorded responses only at 40 Hz. At frequencies below 40 Hz, the mean amplitude of the predicted curve was lower than that of the recorded one while at frequencies above 40 Hz the mean amplitude was higher. Predicted phase values were found lagging at 30 Hz, and leading at 50 Hz and 60 Hz in comparison to phase values calculated on the recorded responses. Our findings suggest that a model based on the linear addition of transient MLRs is not able to adequately predict steady-state responses at stimulus rates other than at 40 Hz. Other mechanisms related to the recovery cycle of the activated system come into play in the steady-state response generation causing a decrease in amplitude and an increase in phase lag when increasing the stimulus repetition rate.

Vestibular projections to hypothalamic supraoptic and paraventricular nuclei.

The effects of electrical stimulation of the eighth nerve and caloric stimulation of the labyrinth were tested on the spontaneous or evoked electrical activity of single neurons located in the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei. It was found that these neurons responded to both kinds of stimulation. In particular, the neurons of the SON showed a predominant response pattern characterized by a sequence of excitation-inhibition, whereas the neurons of the PVN showed different patterns of response with various combinations of inhibition and excitation sequences. The latencies of these neuronal responses to the electrically induced eight nerve volleys were compatible only with a polysynaptic connection. The possible pathways involved in this vestibulo-hypothalamic relation as well as their functional role are discussed.

[The definition of a reference protocol for the clinical study of vertigo drugs]. / Definizione di un protocollo quadro per lo studio clinico di farmaci antivertiginosi.

The aim of this paper is to define the problems that arise in the clinical evaluation of drugs for the treatment of vertigo. Among these are the objective criteria used in defining vertigo and those used in evaluating efficacy of the drugs. The resulting protocol for a clinical study of vestibular drugs is a document that clarifies the debated points in the field, and above all furnishes guidelines for establishing uniformity in clinical studies. This, therefore, may become the reference protocol in Italy for clinical evaluations of drugs for the treatment of vertigo.

Penicillin-induced paroxysmal activity in brainstem neurons.

The spontaneous electrical activity of single mesencephalic and bulbar neurons was recorded in hemispherectomized rats, following topical application of the GABA-antagonist penicillin-G on the mesencephalon or on the rhombencephalon, to investigate whether these structures could develop a specific penicillin paroxysmal activity independently of the upper structures. Twenty minutes following penicillin-G, the mesencephalic neurons developed paroxysmal activity characterized by a significant increase in the spontaneous electrical activity, the appearance of multiunit activity and, frequently, phasic activity with rhythmical outbursts. The paroxysmal activity at bulbar level appeared later than that observed in the mesencephalon and was characterized by a significant increase of the spontaneous firing rate of the neurons, single short bursts and sometimes rhythmical outbursts. The bulbar outbursts always discharged at lower frequency than those at the mesencephalic level. Following a midcollicular transection the paroxysmal bulbar activity abruptly disappeared. This phenomenon might be explained by a loss of facilitation from superior structures on the bulbar neurons which in roditors show a poor GABA-receptor distribution. In other words, penicillin alone, due to the scarcity of GABA receptors, might not be sufficient to induce paroxysmal activity in bulbar neurons but the simultaneous presence of both the superior facilitation and the drug might enhance neuronal excitability to a critical level. However, the diffusion of the drug upwards to the mesencephalon, with consequent activation of a system allowing the downward propagation of paroxysmal activity, cannot be excluded. In conclusion, while the mesencephalic neurons demonstrate a proper ability to develop penicillin paroxysmal discharge, the bulbar neurons must be sustained by intact connections with upper structures to be able to do so.