Combined toxicity of prenatal bacterial endotoxin exposure and postnatal 6-hydroxydopamine in the adult rat midbrain

We previously reported that injection of the Gram (-) bacteriotoxin, lipopolysaccharide (LPS), into gravid females at embryonic day 10.5 led to the birth of animals with fewer than normal dopamine (DA) neurons when assessed at postnatal days (P) 10 and 21. To determine if these changes continued into adulthood, we have now assessed animals at P120. As part of the previous studies, we also observed that the pro-inflammatory cytokine tumor necrosis factor alpha (TNFalpha) was elevated in the striatum, suggesting that these animals would be more susceptible to subsequent DA neurotoxin exposure. In order to test this hypothesis, we injected (at P99) 6-hydroxydopamine (6OHDA) or saline into animals exposed to LPS or saline prenatally. The results showed that animals exposed to prenatal LPS or postnatal 6OHDA alone had 33% and 46%, respectively, fewer DA neurons than controls, while the two toxins combined produced a less than additive 62% loss. Alterations in striatal DA were similar to, and significantly correlated with (r(2)=0.833) the DA cell losses. Prenatal LPS produced a 31% increase in striatal TNFalpha, and combined exposure with 6OHDA led to an 82% increase. We conclude that prenatal exposure to LPS produces a long-lived THir cell loss that is accompanied by an inflammatory state that leads to further DA neuron loss following subsequent neurotoxin exposure. The results suggest that individuals exposed to LPS prenatally, as might occur had their mother had bacterial vaginosis, would be at increased risk for Parkinson's disease.     

Motor nerve terminal morphologic plasticity induced by small changes in the locomotor activity of the adult rat

The possible existence of plastic changes in the branching pattern and the complexity of silver-impregnated motor nerve terminals was studied in the extensor digitorum longus muscle of adult rats housed in metabolic cages or trained to walk. Results indicate a precise inverse relation between the amount of locomotor activity and the complexity finally attained by the motor nerve terminals.     

Late postnatal changes in rat somatosensory cortex

Summary Temporal and spatial developmental relationships between AChE and GABA-T reactivity in the sensory-motor cortex of rat were evaluated histochemically. Special attention was given to the barrels in layer IV of SmI that stain intensely for both enzymes. In the first and second postnatal weeks very low levels of diffuse GABA-T reactivity are seen in cortex, although cells and neuropil in the neostriatum are already clearly positive neonatally. There is little change until 16–18 days postnatal (dpn), when a steady increase in overall cortical reactivity for GABA-T has begun. In layer IV of SmI cortex, relatively intense foci of GABA-T staining begin to appear then, that overlap the barrel centers. GABA-T reactive non-pyramidal neurons at the periphery of these stained foci have distinctly stained processes that may enter the barrel centers. The intensity of GABA-T staining increases until 28 dpn when adult levels were reached. In contrast, AChE staining in cortex begins to appear at 2–3 dpn with prominent barrel staining seen by 6 dpn. When adult AChE reactivity levels are being achieved throughout all regions of neocortex, between 16–19 dpn, the barrel centers progressively lose demonstrable AChE-staining of their fiber plexus. Hence, the onset of GABA-T staining in the barrels during the third week postnatally coincides with the initiation of the progressive reduction in intensity of AChE staining in the same cortical zones. These observations on GABA-T correlate well with biochemical information on the time course of the maturation of the cortical GABAergic system. We should, therefore, consider the possibility that GABA-T staining may reflect the development of the GABAergic system in neocortex cerebri. The temporal linkage between AChE and GABA-T staining, raises the question of a possible developmental interaction between the non-cholinergic AChE-rich thalamic inputs to somatosensory cortex and the maturation of other more tardily developing components of the barrels in SmI. If the temporal relationship is only coincidental then the data still suggest that an intricate series of sequentially timed events characterize the ontogenesis of neocortical circuitry with relatively major developmental events occurring late in the postnatal period.     

Structural changes of the gastrointestinal mucosa induced by prostaglandins

Prostaglandins of the E series, which have been proposed as therapeutic agents for the treatment of peptic ulcers and other gastrointestinal diseases, cause hyperplasia of the gastrointestinal mucosa in experimental animals. The changes are most evident in the stomach, especially the antrum, in which the wall is thickened by hyperplasia of surface mucous cells and/or submucosal edema. In rodents, the non-glandular forestomach becomes hyperplastic and hyperkeratotic. Affected stomachs are heavier and may have a larger surface area than control stomachs. Small intestines may be heavier and have a thicker mucosa, with elongation of villi and crypts. Colonic mucosa may exhibit mild hyperplasia at very high dosages. Conflicting data exist as to whether the gastrointestinal mucosal hyperplasia is more related to increased production or decreased loss of epithelial cells.     

Neuroticism and the pupillary response to a brief exposure to noise

'Neurotic' and 'stable' groups (n = 8) were formed by means of the Finnish version of the Eysenck Personality Inventory. Subjects were exposed individually to 80-100 dBA broadband noise. No overt response was made. The dependent variable was the pupil dilation. The louder the noise, the larger the pupil was. At each level of noise intensity, the dilation was largest immediately after the change of intensity. In general, the pupil size decreased in the course of the experiment, indicating habituation. The 'neurotic' subjects displayed the largest relative dilation as a function of noise intensity. Results are discussed in terms of the arousing effects of auditory stimulus intensity.     

Physiological responses induced by 555-min exposure to intermittent noise

Summary Normal medical college students were exposed to noise for 555 min, while the Temporary Threshold Shift (TTS) and changes in the circulatory system were measured. The exposure noise employed was the so-called pink noise of a trapezoidal form. There were two time patterns, A(I) with 1 s of rise-decay time and 1 s of peak level, and A(II) with 500 ms of rise-decay time and 3.5 s of peak level. Thirteen exposure conditions were examined. The noise exposure time of all experiments was 555 min. The following results were obtained. TTS Growth Significant TTS increases were obtained following exposure to intermittent noise of 85 dB(A), intermittent noise of 80 dB(A), and steady state noise of various intensities. The TTS growth observed with steady state noise at 80 dB(A) was significantly greater than that of intermittent noise exposure at 85 dB(A). Moreover, TTS growth observed with steady noise at 82 dB(A) was significantly greater than that with intermittent noise exposure of 85 dB(A). However, the levels of TTS growth observed with steady state noise of 75 dB(A) and steady state noise at 77 dB(A) were almost equal to those of 6 s trapezoidal noise at 80 dB(A) (the “on fraction” being 33%), and 8 s trapezoidal noise at 80 dB(d) (the “on fraction” being 50%). In the above-mentioned experiments, significant increases of TTS growth were observed with various cycle times of trapezoidal noise with peak levels of 85 dB(A) and 80 dB(A), and with four exposure noise conditions of steady state. Under exposure conditions of 75 dB(A), trapezoidal noise with a 6 s cycle time (the “on fraction” being 33%) did not show a significant increase in TTS growth. Changes in the Circulatory System There were no significant differences in systolic and diastolic pressure or pulse rate among the three exposure conditions. The findings on ECG were as follows. Under intermittent noise exposure, decrease in the height of the T wave was observed in all examinees with a depression of the ST segments also being observed in two cases. On exposure to steady state noise, however, slight decrease in the height of the T wave was induced in only two cases, and under control conditions in only one case. Supported by grant from Air Quality Bureau of Jap. Environment Agency in 1979     

Immunological paralysis induced by brief exposure of cells to protein antigens

The paralysing effect of brief exposure to antigen has been studied in a system in which cells were exposed and then tested by challenge immunization after transfer into syngeneic unresponsive mice. Bovine and human serum albumins (BSA and HSA) were used chiefly, but lysozyme was also tested. Irradiation and paralysis on their own had drawbacks as methods of procuring unresponsive hosts, and worked best in combination. The response measured in the hosts as antigen binding capacity (ABC) was found to be proportional to the number of reactive cells transferred. Lymph node cells and blood leucocytes proved more active than spleen cells. Cells did not become paralysed immediately upon exposure to high concentrations of antigen; blood leucocytes required approximately 2 hours in vivo exposure, and cells from lymphoid organs approximately 24 hours. The effectiveness of 24 hours exposure depended on antigen dose. Tentative measurements of the time taken for antigen to diffuse through the organs suggested that this delay would not account for the difference in timing between cells of different anatomical origin. Exposure in vitro was not found repeatably effective in inducing paralysis. The conclusion was drawn that paralysis is induced by the direct action of antigen on lymphocytes, but that the cells may undergo some further step of differentiation before induction is complete.     

Electroencephalographic changes induced by prolonged exposure to sound

Summary Marked changes of cerebral electrical activity were observed to be induced by intense noise. In animals, high frequency oscillations appeared, and at certain times regular waves appeared in various cortical areas. In man, a depression of the alpha-rhythm, the appearance of a marked beta-rhythm, spike potentials, and a regular rhythm were observed. It is suggested that these changes are produced by activation of the reticular formation of the brain stem brought about by the action of intense sound stimulation.(Presented by Active Member AMN SSSR P. S. Kupalov) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 54, No. 7, pp. 11–13, July, 1962     

Central and peripheral benzodiazepine ligands prevent mitochondrial damage induced by noise exposure in the rat myocardium: An ultrastructural study

Noise represents an environmental stress factor affecting several organs and apparatuses, including the cardiovascular system. In experimental animals undergoing noise exposure, subcellular myocardial changes have been reported, especially at the mitochondrial level. In previous studies we found that diazepam, acting at both central and peripheral benzodiazepine receptors, prevented the onset of this myocardial damage. In the present study, we investigated the specific role played by central and/or peripheral benzodiazepine receptors in preventing noise‐induced myocardial alterations. In particular, the effect of clonazepam as a selective ligand for central sites, in comparison with the efficacy of ligands selective for peripheral sites, such as Ro 5–4864 and PK‐11195, was evaluated. Rats were pretreated with the test drugs 30 min before exposure to noise for 6 or 12 hr and then sacrificed. After fixing, samples of right atrium and ventricle were taken and processed for either transmission or scanning electron microscopy. After 6 hr of noise exposure, only the atrium exhibited significant mitochondrial alterations, whereas after 12 hr both atrium and ventricle were damaged. As expected, diazepam prevented noise‐induced mitochondrial injury at both 6 and 12 hr. By contrast, clonazepam was effective only after 6 hr. The peripheral ligand PK‐11195 attenuated mitochondrial damage at both 6 and 12 hr, whereas Ro 5–4864 was effective only after 12 hr. In the present study, we confirm that noise exposure induces mitochondrial damage in the rat myocardium. Drugs acting at both central and peripheral benzodiazepine receptors significantly prevent this damage. Differences in the amount and in the duration of the protective effect might depend on variability in the potency and in the pharmacokinetics of the specific drugs. Anat Rec 255:334–341, 1999. © 1999 Wiley‐Liss, Inc.     

The orienting response to brief auditory stimuli in preweanling and adult rats

The cardiac orienting response to brief auditory stimuli was measured in preweanling and adult rats. The eliciting stimulus varied in duration (2 or 10 s) and complexity (continuous or pulsing). Stimulus complexity affected response magnitude with the pulsing stimulus eliciting a larger response than the continuous stimulus. Stimulus duration affected response persistence but only when a pulsing stimulus was used. In contrast to recent research with stimuli of much longer duration, age did not significantly affect any aspect of the cardiac response to the novel auditory stimuli in the present study. These results are discussed in terms of (1) the effects of stimulus duration on the heart-rate component of the orienting response and (2) two-stage models of attention.© 1994 John Wiley & Sons, Inc.     

Developmental changes in hyperexcitability of CA1 pyramidal neurons induced by repeated brief episodes of hypoxia in the rat hippocampal slices

We have previously demonstrated that repeated exposure of adult rat hippocampal slices to brief episodes of hypoxia induce a sustained decrease in the threshold of stimulus-evoked population spike discharges in CA1 pyramidal neurons [O. Godukhin, A. Savin, S. Kalemenev, S. Levin, Neuronal hyperexcitability induced by repeated brief episodes of hypoxia in rat hippocampal slices: involvement of ionotropic glutamate receptors and L-type Ca2+ channels, Neuropharmacology 42 (2002) 459-466, S.V. Kalemenev, A.V. Savin, S.G. Levin, O.V. Godukhin, Long-term potentiation and epileptiform activity induced by brief hypoxic episodes in CA1 area of the rat hippocampal slices. Russ. Physiol. J. 86 (2000) 1676-1681]. In the present study, using the above-mentioned in vitro model of epileptogenesis, we compared the developmental changes in hypoxia-induced hyperexcitability of CA1 neuronal network in the rat hippocampal slices prepared from three age rat groups: postnatal days (P) 13-14 (young), P60-70 (adult) and P600-650 (old). Furthermore, we were interested in learning about an age dependence of the hypoxia-induced changes in the efficacies of glutamatergic transmission and paired-pulse inhibition in CA3-CA1 synapses that may underlie ontogenetic differences in seizure susceptibility in hippocampal network. The principal results of this work are summarized as follow. In comparison with P60-70 hippocampal slices, CA1 pyramidal neurons in P13-14 and P600-650 slices showed intrinsically (without repeated brief hypoxa) an increased propensity to generate epileptiform stimulus-evoked population spike discharges. However, in contrast to adult and old animals, repeated brief episodes of hypoxia are incapable to induce a sustained decrease in the threshold of stimulus-evoked population spike discharges in CA1 pyramidal neurons of hippocampal slices prepared from of P13-14 rats, though they transform paired-pulse inhibition to paired-pulse facilitation and induce hypoxic LTP in CA3-CA1 synapses. The role of some other factors in the developmental changes in hyperexcitability of CA1 pyramidal neurons in response to repeated brief episodes of hypoxia is discussed.     

Somatostatin and leu-enkephalin in the rat auditory brainstem during fetal and postnatal development

A transient expression of the neuropeptide somatostatin has been described in several brain areas during early ontogeny and several opioid peptides, such as leu-enkephalin, have also been found in the brain at this stage in development. It is therefore believed that somatostatin and leu-enkephalin may play a role in neural maturation. The aim of the present study was to describe the spatiotemporal pattern of somatostain and leu-enkephalin immunoreactivity in the auditory brainstem nuclei of the developing rat and to correlate it with other developmental events. In order to achieve this goal, we applied peroxidase-antiperoxidase immunocytochemistry to rat brains between embryonic day (E) 17 and adulthood. Somatostatin immunoreactivity (SIR) was found in all nuclei of the auditory brainstem, yet it was temporally restricted in most nuclei. SIR appeared prenatally and reached maximum levels around postnatal day (P) 7, when great numbers of immunoreactive neurons were present in the ventral cochlear nucleus (VCN) and in the lateral lemniscus. At that time relatively low numbers of cells were labeled in the dorsal cochlear nucleus, the lateral superior olive (LSO), and the inferior colliculus (IC). During the same period, when somata in the VCN were somatostatin-immunoreactive (SIR), a dense network of labeled fibers was also present in the LSO, the medial superior olive (MSO), and the medial nucleus of the trapezoid body (MNTB). As these nuclei receive direct input from VCN neurons, and as the distribution and morphology of the somatostatinergic fibers in the superior olivary complex (SOC) was like that of axons from VCN neurons, these findings suggest a transient somatostatinergic connection within the auditory system. Aside from the LSO, MSO, and MNTB, labeled fibers were found to a smaller extent in all other auditory brainstem nuclei. After P7, the SIR decreased and only a few immunoreactive elements were found in the adult auditory brainstem nuclei, indicating that somatostatin is transiently expressed in the rat auditory brainstem. Leu-enkephalin immunoreactivity showed a lower number and weaker intensity of labeled structures as compared to SIR, with E18 being the earliest day at which labeled fibers appeared in the SOC. At birth, immunoreactive fibers were also present in the cochlear nuclear complex and in the IC. Leu-enkephalin immunoreactive somata were found only after P12 in the CN and after P16 in the IC. Leu-enkephalin immunoreactivity was not transient, but increased progressively with age until about P21, when the adult levels were reached. Our results demonstrate somatostatinergic and leu-enkephalinergic inputs onto auditory brainstem neurons during perinatal life, i.e., during a period when the processes of synapse maturation occur. It is thus likely that both neuropeptides may influence the development of synaptic connections in the auditory brainstem.     

Acute and long-lasting changes in extracellular-matrix chondroitin-sulphate proteoglycans induced by injection of chondroitinase ABC in the adult rat brain

Lattice-like perineuronal accumulations of extracellular-matrix proteoglycans have been shown to develop during postnatal maturation and to persist throughout life as perineuronal nets (PNs) in many brain regions. However, the dynamics of their reorganization in adults are as yet unknown. The aim of the present study was to examine the capability of PNs for reconstitution after experimental destruction and to search for possible consequences of extracellular-matrix degradation for neurons and glial cells. The changes were induced by single intracortical injections of Proteus vulgaris chondroitinase ABC and studied after postinjection periods of 1 day to 5 months. The N-acetylgalactosamine-binding Wisteria floribunda agglutinin (WFA), an antibody against chondroitin-sulphate proteoglycans, three antibodies recognizing initial chondroitin or chondroitin-sulphate moieties (’stubs’) of proteoglycan core proteins, an antibody against the hyaluronan-binding protein component of versican, and biotinylated hyaluronectin, which binds to hyaluronan, were used as cytochemical markers. One day postinjection, the WFA-binding sites and hyaluronan were shown to be almost completely removed within a circumscribed digestion zone. The staining of different core-protein components revealed only fragments of PNs. These changes were found to be partly compensated 4 weeks after injection of chondroitinase ABC. After 8 and 12 weeks postinjection, the cytochemical and structural characteristics as well as the area-specific distribution patterns of PNs were progressively reconstituted. At 5 months postinjection, they could not be distinguished from those in untreated tissue. In contrast to such transient changes, a diffuse chondroitin-sulphate proteoglycan immunoreactivity persisted in the neuropil. Loss of neurons or alterations of their structure as well as reactions of glial cells were not observed. We conclude from this study that PNs, enzymatically destroyed in the adult rat brain, can be completely reconstituted, but the restoration of their extracellular-matrix components needs several months. Received: 16 December 1997 / Accepted: 17 February 1998     

Central and peripheral benzodiazepine ligands prevent mitochondrial damage induced by noise exposure in the rat myocardium: an ultrastructural study.

Noise represents an environmental stress factor affecting several organs and apparatuses, including the cardiovascular system. In experimental animals undergoing noise exposure, subcellular myocardial changes have been reported, especially at the mitochondrial level. In previous studies we found that diazepam, acting at both central and peripheral benzodiazepine receptors, prevented the onset of this myocardial damage. In the present study, we investigated the specific role played by central and/or peripheral benzodiazepine receptors in preventing noise-induced myocardial alterations. In particular, the effect of clonazepam as a selective ligand for central sites, in comparison with the efficacy of ligands selective for peripheral sites, such as Ro 5-4864 and PK-11195, was evaluated. Rats were pretreated with the test drugs 30 min before exposure to noise for 6 or 12 hr and then sacrificed. After fixing, samples of right atrium and ventricle were taken and processed for either transmission or scanning electron microscopy. After 6 hr of noise exposure, only the atrium exhibited significant mitochondrial alterations, whereas after 12 hr both atrium and ventricle were damaged. As expected, diazepam prevented noise-induced mitochondrial injury at both 6 and 12 hr. By contrast, clonazepam was effective only after 6 hr. The peripheral ligand PK-11195 attenuated mitochondrial damage at both 6 and 12 hr, whereas Ro 5-4864 was effective only after 12 hr. In the present study, we confirm that noise exposure induces mitochondrial damage in the rat myocardium. Drugs acting at both central and peripheral benzodiazepine receptors significantly prevent this damage. Differences in the amount and in the duration of the protective effect might depend on variability in the potency and in the pharmacokinetics of the specific drugs.     

Gene expression profiles in the rat central nervous system induced by JP-8 jet fuel vapor exposure

Jet propulsion fuel-8 (JP-8) is the predominant fuel for military land vehicles and aircraft used in the US and NATO. Occupational exposure to jet fuel in military personnel has raised concern for the health risk associated with such exposure in the Department of Defense. Clinical studies of humans chronically exposed to jet fuel have suggested both neurotoxicity and neurobehavioral deficits. We utilized rat neurobiology U34 array to measure gene expression changes in whole brain tissue of rats exposed repeatedly to JP-8, under conditions that simulated possible occupational exposure (6 h/day for 91 days) to JP-8 vapor at 250, 500, and 1000 mg/m(3), respectively. Our studies revealed that the gene expression changes of exposure groups can be divided into two main categories according to their functions: (1). neurotransmitter signaling pathways; and (2). stress response. The implications of these gene expression changes are discussed.     

Mechanoelectrical transduction assisted by Brownian motion: a role for noise in the auditory system

The organs of the vestibular, auditory and lateral line systems rely on a common strategy for the stimulation of their primary receptors, the hair cells: stimuli induce shear between hair cell epithelia and accessory structures to which hair bundles, the hair cells' mechanosensitive organelles, are attached. The inner hair cells of the cochlea, whose hair bundles are not attached to the overlying tectorial membrane, are a notable exception. Because their hair bundles are not restrained, they undergo significant Brownian motion, a characteristic traditionally thought to blunt the sensitivity of hearing. Contrary to this view, the work reported here indicates that Brownian motion of the hair bundle serves to enhance the sensitivity of mechanoelectrical transduction.     

Age-related GABAA receptor changes in rat auditory cortex

Auditory cortex (AI) shows age-related decreases in pre-synaptic markers for gamma-aminobutyric acid (GABA) and degraded AI neuronal response properties. Previous studies find age-related increases in spontaneous and driven activity, decreased spectral and directional sensitivity, and impaired novelty detection. The present study examined expression of GABA_A receptor (GABA_AR) subunit message, protein, and quantitative GABA_AR binding in young, middle-aged, and aged rat AI, with comparisons with adjoining parietal cortex. Significant loss of GABA_AR α₁ subunit message across AI layers was observed in middle-aged and aged rats and α₁ subunit protein levels declined in layers II and III. Age-related increases in GABA_AR α₃ subunit message and protein levels were observed in certain AI layers. GABA_AR subunits, including β₁, β₂, γ₁, γ_2s, and γ_2L, primarily, but not exclusively, showed age-related declines at the message and protein levels. The ability of GABA to modulate [³H]t-butylbicycloorthobenzoate binding in the chloride channel showed age-related decreases in peak binding and changes in desensitization kinetics. Collectively, age-related changes in GABA_AR subunit composition would alter the magnitude and temporal properties of inhibitory synaptic transmission and could underpin observed age-related functional changes seen in the elderly.