Development of a monoclonal antibody to immuno-cytochemical analysis of the cellular localization of the peripheral benzodiazepine receptor

We measured dorsal hippocampal activity accompanying sighs and apnea using reflectance imaging and electrophysiologic measures in freely behaving cats. Reflected 660-nm light from a 1-mm2 area of CA1 was captured during sighs and apnea at 25 Hz through a coherent image conduit coupled to a charge coupled device camera. Sighs and apnea frequently coincided with state transitions. Thus, state transitions without apnea or sighs were separately assessed to control for state-related activity changes. All dorsal hippocampal sites showed discrete regions of activation and inactivation during transient respiratory events. Imaged hippocampal activity increased 1-3 s before the enhanced inspiratory effort associated with sighs, and before resumption of breathing after apnea. State transitions lacking sighs and apnea did not elicit analogous optical activity patterns. The suprasylvian cortex, a control for site, showed no significant overall reflectance changes during phasic respiratory events, and no discrete regions of activation or inactivation. Spectral estimates of hippocampal electroencephalographic activity from 0-12 Hz showed significantly increased power at 3-4 Hz rhythmical slow activity before sighs and apnea, and increased 5-6 Hz rhythmical slow activity power during apnea, before resumption of breathing. Imaged activity and broadband hippocampal electroencephalogram power decreased during sighs. We propose that increased hippocampal activity before sigh onset and apnea termination indicates a role for the hippocampus in initiating inspiratory effort during transient respiratory events.     

Naloxone-precipitated changes in biogenic amines and their metabolites in various brain regions of butorphanol-dependent rats

Influence of a naloxone (an opioid receptor antagonist) challenge (5 mg/kg, IP) on levels of biogenic amines and their metabolites in various brain regions of rats infused continuously with butorphanol (a mu/delta/kappa mixed opioid receptor agonist; 26 nmol/microliter/h) or morphine (a mu-opioid receptor agonist; 26 nmol/microliter/h) was investigated using high-performance liquid chromatography with electrochemical detection (HPLC-ED). Naloxone precipitated a withdrawal syndrome and decreased the levels of: dopamine (DA) in the cortex and striatum, 3,4-dihydroxyphenylacetic acid (DOPAC) in the striatum, homovanilic acid (HVA) in the striatum, limbic, midbrain, and pons/medulla regions in butorphanol-dependent rats. However, the levels of norepinephrine (NE), serotonin (5-hydroxytryptamine; 5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) in the regions studied were not affected by naloxone-precipitated withdrawal. In addition, naloxone increased the HVA/DA ratio in the cortex, while this ratio was reduced in the limbic, midbrain, and pons/medulla. The reduction of 5-HIAA/5-HT ratio was also detected in the limbic area. In the animals rendered dependent on morphine, the results obtained were similar to those of butorphanol-dependent rats except for changes of 5-HIAA levels in some brain regions. These results suggest that an alteration of dopaminergic neuron activity following a reduction of DA and its metabolites in specific brain regions (e.g., striatum, limbic, midbrain, and pons/medulla) play an important role in the expression of the opioid withdrawal syndrome.     

Cholinergic modulation of tonic immobility in the rabbit (Oryctolagus cuniculus).

Conducted a study with 13 adult Dutch Belt rabbits to determine the effects of the anticholinergic agent scopolamine and the cholinergic agent physostigmine on tonic immobility in rabbits. Recordings of the EEG activity from cortex and hippocampus were also made before, during, and after each test session. Scopolamine significantly prolonged the response and produced large amplitude slow wave activity in the EEG of both cortex and hippocampus. Physostigmine significantly shortened the duration of immobility and increased rhythmic slow activity in the frequency range of 5.5-9.1 Hz in the hippocampus while producing a desynchronized cortical rhythm. It is suggested that the cortex and hippocampus play a role in modulating tonic immobility duration by inhibiting the brain-stem structures thought to control this response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Proprioceptive consequences of tendon vibration during movement

1. Previous studies have used tendon vibration to investigate kinesthetic illusions in the isometric limb and end point control in the moving limb. These previous studies have shown that vibration distorts the perceptions of static joint angle and movement and causes systematic errors in the end point of movement. In this paper we describe the effects of tendon vibration during movement while human subjects performed a proprioceptively coordinated motor task. In an earlier study we showed that the CNS coordinates this motor task-a movement sequence-with proprioceptive information related to the dynamic position and velocity of the limb. 2. When performing this movement sequence, each subject sat at a table and opened the right hand as the right elbow was passively rotated in the extension direction through a prescribed target angle. Vision of the arm was prevented, and the movement velocity was changed randomly from trial to trial, leaving proprioception as the only useful source of kinematic information with which to perform the task. 3. In randomly occurring trials, vibration was applied to the tendon of the biceps brachii, a muscle that lengthens during elbow extension. In some experiments the timing of tendon vibration was varied with respect to the onset of elbow rotation, and in other experiments the frequency of vibration was varied. In each experiment we compared the accuracy of the subject's response (i.e., the elbow angle at which the subject opened the hand) in trials with tendon vibration with the accuracy in trials without tendon vibration. 4. The effect of tendon vibration depended on the frequency of vibration. When the biceps tendon was vibrated at 20 Hz, subjects opened the hand after the elbow passed through the target angle ("overshooting"). Overshooting is consistent with an underestimate of the actual displacement or velocity of the elbow. Vibration at 30 Hz had little or no effect on the elbow angle at hand opening. Vibration at 40 Hz caused subjects to open the hand before the elbow reached the target angle ("undershooting"). Undershooting is consistent with an overestimate of the actual displacement or velocity of the elbow. The size of the error depended on the velocity of the passively imposed elbow rotation. 5. The effect of tendon vibration also depended on the timing of vibration. If 40-Hz vibration began at the onset of movement, the subject undershot the target. If 40-Hz vibration started 5 s before movement onset and continued throughout the movement, the undershoot error increased in magnitude. However, if 40-Hz vibration started 5 s before movement onset and then stopped at movement onset, the subject overshot the target. When vibration was shut off during movement, a transition occurred from an over-shooting error to an undershooting error at a time that depended on the velocity of elbow rotation. 6. In a separate experiment, subjects were instructed to match either the perceived dynamic position or the perceived velocity of rotation imposed on the right elbow by actively rotating the left elbow. In both matching tasks, tendon vibration produced oppositely directed errors depending on the frequency of vibration. Vibration at 20 Hz produced a perception of decreased elbow velocity and a bias in dynamic position in the flexion direction, and vibration at 40 Hz produced the opposite perceptions. 7. We conclude that muscle spindle afferents, which are activated by tendon vibration, are an important source of the dynamic position and velocity information that the CNS uses to coordinate this movement sequence task. The observed effects of vibration timing and frequency suggest that perceptual changes evoked by vibration cannot be explained by the simple summation of sensory input evoked by movement and by vibration. Rather, the bias in perception produced by vibration appears to be related to the difference between vibration- and movement-evoked activity in muscle spindle afferents.     

Bidirectional processing in the olfactory-limbic axis during olfactory behavior

Field potentials were recorded simultaneously from the olfactory bulb (OB), prepyriform cortex (PPC), entorhinal cortex (EC), and dentate gyrus (DG) of rats trained to respond to appetitively reinforced odors. Preafferent anticipatory events in the beta band (12-35 Hz) suggest transmission from EC to OB before the odorant stimulus. Gamma band (35-120 Hz) power in olfactory regions is significantly reduced during stimulus presentation as compared with high values during preafferent expectation. High coherence of OB and PPC gamma activity during the preodorant control period is interrupted before the stimulus and is followed by increased gamma coherence among OB, EC, and DG. These results suggest that olfactory perceptual processing is bidirectional and covers a wide frequency range.     

Haemodynamic changes in ipsilateral and contralateral fingers caused by acute exposures to hand transmitted vibration

OBJECTIVES: To investigate changes in digital circulation during and after exposure to hand transmitted vibration. By studying two frequencies and two magnitudes of vibration, to investigate the extent to which haemodynamic changes depend on the vibration frequency, the vibration acceleration, and the vibration velocity. METHODS: Finger skin temperature (FST), finger blood flow (FBF), and finger systolic pressure were measured in the fingers of both hands in eight healthy men. Indices of digital vasomotor tone-such as critical closing pressure and vascular resistance-were estimated by pressure-flow curves obtained with different hand heights. With a static load of 10 N, the right hand was exposed for 30 minutes to each of the following root mean squared (rms) acceleration magnitudes and frequencies of vertical vibration: 22 m.s-2 at 31.5 Hz, 22 m.s-2 at 125 Hz, and 87 m.s-2 at 125 Hz. A control condition consisted of exposure to the static load only. The measures of digital circulation and vasomotor tone were taken before exposure to the vibration and the static load, and at 0, 20, 40, and 60 minutes after the end of each exposure. RESULTS: Exposure to static load caused no significant changes in FST, FBF, or indices of vasomotor tone in either the vibrated right middle finger or the non-vibrated left middle finger. In both fingers, exposure to vibration of 125 Hz and 22 m.s-2 produced a greater reduction in FBF and a greater increase in vasomotor tone than did vibration of 31.5 Hz and 22 m.s-2. In the vibrated right finger, exposure to vibration of 125 Hz and 87 m.s-2 provoked an immediate vasodilation which was followed by vasoconstriction during recovery. The non-vibrated left finger showed a significant increase in vasomotor tone throughout the 60 minute period after the end of vibration exposure. CONCLUSIONS: The digital circulatory response to acute vibration depends upon the magnitude and frequency of the vibration stimulus. Vasomotor mechanisms, mediated both centrally and locally, are involved in the reaction of digital vessels to acute vibration. The pattern of the haemodynamic changes in the fingers exposed to the vibration frequencies used in this study do not seem to support the frequency weighting assumed in the current international standard ISO 5349.     

Effect of limbic structure and striatum damage caused by kainic acid on seizure reactions in animals after intracranial injury

It has been established that hippocampus, enthorhinal cortex, amygdala and substantia nigra (pars reticulata) lesions before head injury lead to a decrease of kainic acid-induced behavioral and electrographic seizure expressions. It can be concluded that after head injury the activation of limbic structures excitability due to excitation of "inputs" to these formations takes place. The obtained data indicate the significant role of nucleus caudatus in activation of posttraumatic brain excitatory mechanisms.     

Cocaine alters cerebral metabolism within the ventral striatum and limbic cortex of monkeys

The functional consequences of acute cocaine administration in nonhuman primates were assessed using the quantitative 2-[14C]deoxyglucose method. Local rates of cerebral metabolism were determined after an intravenous infusion of 1.0 mg/kg cocaine or vehicle in six awake cynomolgus monkeys (Macaca fascicularis) trained to sit calmly in a primate chair. Cocaine administration decreased glucose utilization in a discrete set of structures that included both cortical and subcortical portions of the limbic system. Glucose metabolism in the core and shell of the nucleus accumbens was decreased markedly, and smaller decrements were observed in the caudate and anterior putamen. In addition, cocaine administration produced significant decreases in limbic cortex. Metabolism was decreased in orbitofrontal cortex (areas 11, 12o, 13, 13a, 13b), portions of the gyrus rectus including area 25, entorhinal cortex, and parts of the hippocampal formation. The cortical regions in which functional activity was altered provide dense projections to the nucleus accumbens, and the decreased activity in these projections may be responsible in part of the large alterations in functional activity within the ventral striatum. Decreased metabolism also was evident in the anterior nuclear group of the thalamus, raphe nuclei, and locus ceruleus. The acute cerebral metabolic effects of cocaine in the conscious macaque, therefore, were contained primarily within a set of interconnected limbic regions, including ventral prefrontal cortex, medial temporal regions, the ventral striatal complex, and anterior thalamus. The decreased rates of glucose metabolism reported here resemble decrements found using positron emission tomography in humans. In the rat, by contrast, metabolic activity increased and changes were focused in subcortical regions. The present results represent an important expansion of the neural circuitry on which cocaine acts in the monkey as compared with the rat, and this in turn implies that cocaine affects a broader spectra of behaviors in primates than in rodents.     

Effects of exposure to an estrous female on forebrain monoaminergic neurotransmission in the non-copulating male rat

Regional changes in the rate of brain monoamine synthesis were monitored in male rats exposed to, but prevented from physical contact with, an estrous or an ovariectomized female. The in vivo rate of tyrosine and tryptophan hydroxylase activities were estimated by measuring the accumulation of DOPA and 5-HTP following inhibition of cerebral aromatic L-amino acid decarboxylase by means of 3-hydroxybenzylhydrazine (NSD-1015) treatment (100 mg/kg i.p.). 5 min upon NSD-1015 treatment, the males were exposed to an intact estrous female or an ovariectomized female for 20 min before decapitation and brain dissections. Exposure to an estrous female produced an increased rate of tyrosine and tryptophan hydroxylase activity in the medial prefrontal cortex, the dorso-lateral neostriatum and in the ventral neostriatum, in comparison with home-cage controls. By the same comparison, exposure to an ovariectomized female resulted in an increased rate of tyrosine hydroxylase activity in the medial prefrontal cortex, but not in the neostriatal areas, whereas tryptophan hydroxylase activity was unaffected. Finally, exposure to the empty test cage, with no stimulus females present, did not produce any statistically significant changes in the rate of tyrosine or tryptophan hydroxylase activity in any of the brain areas sampled. Taken together with recent findings from this laboratory, the present results demonstrate that the level of sexual motivation brought about by the olfactory, auditory and/or visual stimulation of a receptive female is associated with an increased demand on catecholamine and 5-hydroxytryptamine synthesis in the limbic forebrain of the male rat.(ABSTRACT TRUNCATED AT 250 WORDS)     

Membrane-associated molecules guide limbic and nonlimbic thalamocortical projections

Membrane-associated signals expressed in restricted domains of the developing cerebral cortex may mediate axon target recognition during the establishment of thalamocortical projections, which form in a highly precise manner during development. To test this hypothesis, we first analyzed the outgrowth of thalamic explants from limbic and nonlimbic nuclei on membrane substrates prepared from limbic cortex and neocortex. The results show that different thalamic fiber populations are able to discriminate between membrane substrates prepared from target and nontarget cortical regions. A candidate molecule that could mediate selective choice in the thalamocortical system is the limbic system-associated membrane protein (LAMP), which is an early marker of cortical and subcortical limbic regions (Pimenta et al.,1995) that can promote outgrowth of limbic axons. Limbic thalamic and cortical axons showed preferences for recombinant LAMP (rLAMP) in a stripe assay. Incubation of cortical membranes with an antibody against LAMP prevented the ability of limbic thalamic fibers to distinguish between membranes from limbic cortex and neocortex. Strikingly, nonlimbic thalamic fibers also responded to LAMP, but in contrast to limbic thalamic fibers, rLAMP inhibited branch formation and acted as a repulsive axonal guidance signal for nonlimbic thalamic axons. The present studies indicate that LAMP fulfills a role as a selective guidance cue in the developing thalamocortical system.     

Physician awareness of prescription drug costs: a missing element of drug advertising and promotion

The effects of high-dose ketamine on the c-fos protein (c-Fos) expression were investigated in rat by an immunohistochemical technique. The administration of 100 mg/kg ketamine i.p. induced seizure-like activity (limbic seizure). No c-Fos immunoreactivity was observed in hippocampus, piriform cortex and amygdala, while it was observed in neocortex and thalamus. These findings disagree with the reports that ketamine depresses the neuronal function of the neocortex and thalamus, while it stimulates the limbic system.     

The effect of starvation of lipid peroxidation in synaptosomal and mitochondrial factions of various brain structures

Content of lipid hydroperoxides (LHP) and malonic dialdehyde (MDA) was measured in homogenates of rat brain cortex (limbic, sensomotor and orbital cortex) and subcortex brain structures (hypothalamus, medulla oblongata, and midbrain) and in their synaptosomal and mitochondrial fractions within various periods of starvation 1, 2, 3, 5 and 7 days. Lipid peroxidation was shown to intensify distinctly in the brain regions studied especially in the sensomotor cortex only after relatively long-term starvation during 5-7 days. The rate of lipid peroxidation was considerably higher in mitochondrial fractions of these brain structures studied than in the synaptosomes; high contents of LHP and MDA was found in mitochondria. Activation of lipid peroxidation appears to be distinctly responsible for impairment of the structure and functional components of nervous cells occurring during long-term starvation.     

The effect of white and filtered noise on contrast detection thresholds

The influence of high-frequency microstimulation (HFMS) of one of the hemispheres on the parameters of spontaneous gamma-oscillations in the neural network containing callosal cells of the motor cortex of both hemispheres. There were three modes in the background oscillation periods distribution, which corresponded to the frequencies 40-60, 70-100, and 100-200 Hz. These oscillation frequencies were also revealed after the HFMS in neural interactions of the cells, which were active before the HFMS; the frequency 40-60 Hz, which dominated before the HFMS, became even more pronounced. The same three groups of oscillation frequencies were found in the activity of cells which became active after the HFMS. The expression of oscillations, the number of oscillatory interactions, as well as the number of neuronal pairs with additional synchronization decreased after the HFMS, which suggests a decrease in synchronization. Taking into account the results of simulation experiments that the frequency of gamma-oscillations is determined by the strength of inhibitory and excitatory input, we suggest that the long-term posttetanic modifications in the efficacy of synaptic inputs of the neurons of both hemispheres underlie the observed posttetanic changes.     

Monkeys with combined amygdalo-hippocampal lesions succeed in object discrimination learning despite 24-hour intertrial intervals.

14 rhesus monkeys, including 3 who had undergone amygdalo-hippocampal lesions before participating in a previous visual learning study, were trained on object-discrimination trials that were separated by 24 hrs to test the hypothesis that the 24-hr interval would prevent Ss with limbic lesions from learning. It is noted in previous research that monkeys with combined amygdalo-hippocampal removal show severe impairments on visual-memory tasks after delays of 1–2 min, yet they learn visual-discrimination habits nearly as quickly as normal monkeys with intertrial intervals of the same duration. Results of the present study indicate that, as long as the lesions did not encroach on the inferior temporal cortex, operated Ss could acquire concurrent sets of 20 object-discrimination habits at the same rate as unoperated Ss in an average of approximately 10 trials/set. Findings suggest that learning and retention processes are divisible into a mechanism for memory formation that is dependent on the limbic system and a mechanism for habit formation that is not. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of amygdaloid kindling on [3H]dopamine and [14C]acetylcholine release from rat prefrontal cortex and striatal slices

The involvement of the dopaminergic (DA) systems in the control of limbic kindled seizures is ill defined. The effects of kindling on DA activity may have been overlooked in the past, because of its subtle unilateral occurrence and/or the variance of the endogenous imbalance of DA activity in normal animals. In the present study rats were screened for their endogenous DA imbalance using amphetamine-induced rotational behaviour. Electrical or sham kindling was applied in the hemisphere with the higher endogenous DA activity. Sections of the bilateral prefrontal cortex and dorsal and ventral striatum were dissected either 2 hours or 21 days after the final seizure and the electrically stimulated release of [3H]DA and [14C]acetylcholine (ACh) determined. Release was also measured in the presence of quinpirole or sulpiride to assess the activity of pre- and postsynaptic DA D2-receptors. Long-term effects of kindling consisted of facilitation of ACh release in the ventral striatum contralateral to the kindled amygdala and bilateral depression of DA release in the prefrontal cortex. Kindling therefore produced area specific changes in neurotransmitter systems giving rise to increased pro-convulsive cholinergic activity in the ventral striatum and decreased anti-convulsive dopaminergic activity in the prefrontal cortex.     

Postnatal development of low [Mg2+] oscillations in neocortex

One form of rhythmic activity intrinsic to neocortex can be induced in slices of adult somatosensory cortex by lowering [Mg2+]o to unblock N-methyl--aspartate (NMDA) receptors. It has been suggested that a population of intrinsically burst-firing (IB) neurons that are unique to cortical layer 5 may play a role in the rhythmic activity seen under these conditions. Whole cell patch-clamp and field-potential recordings in slices of somatosensory cortex from neonatal rats were used to study the development of IB cells and the development of 0 [Mg2+] oscillations. IB cells were not encountered before postnatal day 12 (P12) in layer 5, but from P13 to P19 an increasing proportion of cells had IB properties. Recordings from cells at P7, P17, and P19 in 0 [Mg2+] indicate that dramatic changes occur postnatally in 0 [Mg2+]-induced activity. At P7, cells largely showed trains of single action potentials. In contrast, at P19, cells showed organized bursts of rhythmic activity lasting 0.5-5 s separated by periods of relative quiescence. Cells recorded at P17 were found to have less organized rhythmic activity than cells from P19 cortex. Field-potential recordings in 0 [Mg2+] made at P7 showed infrequent and slowly occurring field depolarizations, whereas field-potential recordings at P19 consisted of spontaneous bursts of 4-12 Hz oscillations identical to those observed in the adult. Application of NE, which inhibits burst-firing of layer 5 IB cells, significantly altered the discharge pattern of 0 [Mg2+] oscillations at P19. These data suggest that the maturation of one type of rhythmic network activity intrinsic to neocortex is influenced by the development of the membrane properties of a single cell type.     

Experimental study of fracture surface roughness on rocks with crack velocity

In experimental animals, administration of 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy) leads to extensive, but incomplete, loss of 5-hydroxytryptamine (5-HT) innervation in the brain. Here, we report the effects of MDMA on 5-HT neuronal function measured in the rat in vivo using electrophysiological and microdialysis techniques. Two weeks after administration of an established neurotoxic regimen of MDMA (20 mg/kg s.c., twice daily for 4 days) we found; 1) no change in either the density or the firing activity of 5-HT neurons in the dorsal raphé nucleus; 2) no change in basal extracellular 5-HT in either the frontal cortex or the hippocampus, although extracellular 5-hydroxyindoleacetic acid was reduced by about 50% in both regions; and 3) no change in the amount of 5-HT released in the hippocampus in response to electrical stimulation (5 Hz) of either the dorsal or medial raphé nucleus, but a marked reduction in the amount of 5-HT released in the frontal cortex after electrical stimulation of the dorsal raphé nucleus. In summary, although MDMA causes marked 5-HT neurotoxicity, our data suggest that 5-HT cell firing is unchanged and, furthermore, that 5-HT release is maintained in some (but not all) forebrain regions even in response to physiological levels of stimulation.     

Delayed development of spontaneous seizures and prolonged convulsive state in rats after massed stimulation of the anterior piriform cortex

We studied the short- and long-term epileptogenic effects of massed stimulation (MS) of the piriform cortex. Sprague-Dawley rats with electrodes implanted bilaterally in the anterior piriform cortex and the dorsal and ventral hippocampi underwent MS: electrical stimulation of the left piriform cortex every 5 min for 6 h (afterdischarge threshold, 60 Hz, 1 ms, 1 s). Animals were retested (5 stimulations) 3-4 times later at different time points to check for the kindled state. Our data showed that MS resulted in delayed development of severe epilepsy. The interval between MS and the first appearance of convulsive response (2 weeks) was characterized by deep refractoriness to seizure (silent period). Unexpectedly, dramatic seizure activity occurred 4-7 weeks after MS. This was manifested by (1) generalized tonic-clonic convulsions with multiple failings, which were elicited repeatedly during retest; (2) frequent progression of elicited generalized convulsions into a prolonged (> 8 min) postictal convulsive state expressed mainly by continuous partial seizures and even new bouts of generalized seizures, and (3) development of mild spontaneous seizures. We found that epileptiform activity predominated in the ventral hippocampus. Mossy fiber sprouting was also most pronounced in this area. We propose that the MS resulted in formation of pathological circuits which involve both piriform cortex and ventral hippocampus and lead to severe epilepsy.     

Blood pressure measurement. Criteria employed in scientific articles published in Brazilian journals]

OBJECT: To investigate whether hand-arm vibration and noise have a combined effect on temporary threshold shift (TTS) of hearing among healthy subjects. METHOD AND DESIGN: Nineteen healthy subjects with an average age of 25.7 (SD 7.7) years were exposed to vibration (30 m/s2, 60 Hz), noise [90 dB(A)] and both, respectively. The subject's right hand was placed on the plate of a vibrator and the right ear exposed to noise via headphones. Subjects were exposed to vibration and/or noise for 3 min and after a 1-min pause the exposure was repeated five times. Hearing thresholds at 1, 4 and 6 kHz were measured during the time periods before, between (during pauses) and after exposure. RESULTS: Exposure to vibration alone caused almost no hearing threshold changes at every frequency tested. But exposure to noise or a combination of vibration and noise caused a significant increase in TTSs at 4 and 6 kHz. Moreover, exposure to a combination of vibration and noise caused significantly higher TTSs than exposure to noise at 4 and 6 kHz. CONCLUSION: The present results demonstrate the combined effects of hand-arm vibration and noise can enhance exposure to hand-arm vibration and noise can enhance the TTS of hearing more than noise exposure, though hand-arm vibration alone may hardly affect TTS.     

Influence of vertical vibration on heart rate of pigs

Pigs with a body weight between 15 and 20 kg were vibrated in the vertical direction for 1 h at 2, 8, and 18 Hz, in combination with root mean square (RMS) acceleration magnitudes of 1 or 3 m/s2. Welfare and stress were quantified by comparing heart rate characteristics during a control period (2200 to 0600) before vibration exposure and during vibration (1000 to 1100). The level of maximum heart rate and number of ventricular ectopic beats during vibration at 2 and 8 Hz in combination with a RMS acceleration of 3 m/s2 indicated a larger fear response than at 1 m/s2. Isocomfort contours based on mean heart rate during vibration showed the greatest specific sensitivity of the pigs to vibration at a frequency of 8 and 18 Hz, especially in combination with a RMS acceleration of 3 m/s2. During transport, RMS acceleration should be less than 3 m/s2 to protect pigs' welfare. Pigs were more sensitive to acceleration than to frequencies within the range of treatments in this investigation. Although the response of the pigs in this experiment fit within the model concept for adult humans and for domestic fowl, changes in heart rate are dependent on body weight.