Diffusion and clearance of superparamagnetic iron oxide nanoparticles infused into the rat striatum studied by MRI and histochemical techniques.

The purpose of the present study was to investigate, by MRI and histochemical techniques, the diffusion and clearance abilities of superparamagnetic iron oxide nanoparticles (SPION) coated with dextran (Dextran-SPION) and gold (Au-SPION) following their local infusions into the rat brain. In separate groups of anesthetized rats, the Dextran-SPION and Au-SPION were infused at concentrations of 0.01, 0.1, 1 and 5 µg Fe/0.5 µl and at the flow rate of 0.5 µl min(-1) into the left and right striata, respectively. Repetitive T2-weighted spin-echo MRI scans were performed at time intervals of 1, 6, 12, 24, 48, 72 h, and one, two and eight weeks after inoculation. Following infusion of Dextran-SPION (0.1 µg and 1 µg Fe), the maximal distribution volume was observed at about 12-24 h after inoculation and two weeks later the Fe signals were undetectable for the lower dose. On the other hand, Au-SPION remained tightly localized in the closest vicinity of the infusion site as revealed by unchanged MRI signal intensities and strong histochemical staining of Fe(2+) and Fe(3+) ions in the corresponding brain slices. Immunohistochemical staining of astrocytic and microglial reactions revealed that there were no marked differences in GFAP, VIM or OX-42 labeling observed between the nanoparticle types, however the astrocytic reaction was more pronounced in rats receiving nanoparticles compared to the control (aCSF-infused) rats. In conclusion, the present data demonstrate that the viral-sized Dextran-SPION were able to diffuse freely through the interstitial space of the brain being progressively cleared out from the infusion site within two weeks. Thus, Dextran-SPION could be beneficially used in MRI-guided diagnostic applications such as in experimental oncology or as labels and carriers for targeted drug delivery, whereas Au-SPION could be used for labeling and tracking the transplanted stem cells in experimental MRI.

Temporal profile of ultrastructural changes in cortical neurones after a compression lesion.

We studied the occurrence of apoptosis and secondary delayed cell death at various time points in the penumbra zone, which is the target for therapeutic intervention after stroke. A compression lesion was induced in the right sensory motor cortex of rat brains. At 0.5, 1, 3, 6, 12, 24, 48 and 72 h after lesioning, motor functions were evaluated by behavioral tests, and cortical layers IV and V were examined by electron microscopy. Behavioral recovery was observed at 48 h after lesioning. At 0.5-1 h in the lesioned area, the neuropil was expanded and contained affected cells. Apoptotic cells were found between 0.5-72 h, and at 12 h, 47.3 % of the total cell number was apoptotic cells. On the contralateral side, cells showed an enlarged endoplasmic reticulum at 3 h, indicating secondary delayed cell death. Our results show that a compression lesion is a useful model for studying ultrastructural changes in injured cells. The lesion results in the penumbra zone with apoptotic cell death between 0.5-72 h. As secondary delayed cell death occurred on the contralateral side at three hours after lesioning might be the time period during which injured, but still viable, neurons can be targets for acute treatment.

CD8alpha dendritic cells and immune protection from experimental allergic encephalomyelitis.

Dendritic cells (DC) represent a phenotypically heterogeneous population endowed with two important biological functions, immunity and tolerance. Here we report that the injection of splenic CD8alpha(+) DC, derived from rats with experimental allergic encephalomyelitis (EAE), delayed the onset and suppressed the severity of EAE in Lewis rats. This was accompanied by the lack of magnetic resonance imaging (MRI) lesions in the brain and spinal cord and by reduced numbers of inflammatory cells within the central nervous system. Injection of CD8(alpha+) DC inhibited T cell proliferation that may relate to increased interferon (IFN)-gamma and nitric oxide production. Although CD8(+)CD28(-) suppressor T cells, apoptotic cells and co-stimulatory molecules were not altered, CD4(+) T cells expressing interleukin (IL)-10 were augmented in rats receiving CD8alpha(+) DC compared to rats receiving total DC or medium. These results demonstrate that rat splenic CD8alpha(+) DC could provide a cellular basis for a novel, individualized immunotherapy using autologous DC as a complement to conventional therapy in diseases with an autoimmune background such as multiple sclerosis.

Intraseptal muscarinic ligands and galanin: influence on hippocampal acetylcholine and cognition.

The cholinergic neurons in the septohippocampal projection are implicated in hippocampal functions such as spatial learning and memory. The aim of this study was to examine how septohippocampal cholinergic transmission is modulated by muscarinic inputs and by the neuropeptide galanin, co-localized with acetylcholine (ACh) in septohippocampal cholinergic neurons, and how spatial learning assessed by the Morris water maze test is affected. Muscarinic inputs to the septal area are assumed to be excitatory, whereas galanin is hypothesized to inhibit septohippocampal cholinergic function. To test these hypotheses, compounds were microinjected into the medial septum and hippocampal ACh release was assessed by microdialysis probes in the ventral hippocampus of the rat. Blockade of septal muscarinic transmission by intraseptal scopolamine increased hippocampal ACh release suggesting that septal cholinergic neurons are under tonic inhibition. Stimulation of septal muscarinic receptors by carbachol also increased hippocampal ACh release. Despite this increase, both scopolamine and carbachol tended to impair hippocampus-dependent spatial learning. This finding also suggests a revision of the simplistic notion that an increase in hippocampal ACh may be facilitatory for learning and memory. Galanin infused into the medial septum enhanced hippocampal ACh release and facilitated spatial learning, suggesting that septal galanin, contrary to earlier claims, does not inhibit but excites septohippocampal cholinergic neurons. Galanin receptor stimulation combined with muscarinic blockade in the septal area resulted in an excessive increase of hippocampal ACh release combined with an impairment of spatial learning. This finding suggests that the level of muscarinic activity within the septal area may determine the effects of galanin on hippocampal cognitive functions. In summary, a limited range of cholinergic muscarinic transmission may contribute to optimal hippocampal function, a finding that has important implications for therapeutic approaches in the treatment of disorders of memory function.

Functional recovery after brain lesion--contralateral neuromodulation: an fMRI study.

Behavioral recovery takes place even after permanent damage to the entire brain region normally controlling sensorimotor hind limb function in the rat. In our study, 2 weeks after full behavioral recovery from an experimental unilateral permanent brain damage, the topographic representation of the previous paretic hindlimb was investigated by fMRI. The analysis showed that during electrical stimulation of the previously paretic hindlimb, two normally inactive brain regions were now being activated. One region was the non-damaged contralateral sensori-motor cortex and the other region was located lateral to the lesion. These results suggest that behavioral recovery can be explained by functional reorganization and neuromodulation of the brain.

Analysis of magnetic resonance imaging acoustic noise generated by a 4.7 T experimental system.

High intensity acoustic noise is an undesirable side-effect in magnetic resonance imaging (MRI) that can cause discomfort and hearing loss in patients and may be an impediment in functional MRI (fMRI) studies of the auditory system. Experimental MRI systems with high magnetic field strengths may generate acoustic noise of higher sound pressure levels (SPLs) than conventional 1.0 and 1.5 T clinical systems. We measured the SPL and spectral content of the acoustic noise generated by the Bruker Biospect 47/40 4.7 T experimental MRI system during scanning sequences commonly used in animal testing. Each sequence generated acoustic noise of high SPL, rapid pulse rates, amplitude-modulated pulse envelopes and multi-peaked spectra. The rapid acquisition with enhancement sequence with a 0.25 mm slice thickness generated SPLs of up to 129 dB peak SPL and 130 dB (A). Fourier analysis of the spectral content of the acoustic noise generated by each MRI sequence showed a wide band of acoustic energy with spectral peaks from 0.2-5 kHz. The intense MRI acoustic impulse noise generated by the 4.7 T system may cause masking of stimuli used in fMRI of the auditory cortex, reduce the hearing acuity of experimental animals and present a risk for unprotected human ears.

Cytoprotection does not preserve brain functionality in rats during the acute post-stroke phase despite evidence of non-infarction provided by MRI.

In animal models of stroke the promise of a therapy is commonly judged from infarct size measurements, assuming that a reduction in infarct size results in reduction of the functional deficits. We have evaluated the validity of the concept that structural integrity translates into functional integrity during the acute post-stroke period (24 h). Unilateral permanent middle cerebral artery occlusion (pMCAO) in Fischer F344 rats leads to infarcts comprising the ipsilateral striatum and cortical structures, including the somatosensory cortex. Infarct volumes were assessed using magnetic resonance imaging (MRI) methods (T(2), diffusion, perfusion MRI). The functional integrity of the somatosensory cortex was assessed by functional MRI (fMRI) measuring changes in local cerebral blood volume, and by assessing the forelimb grip strength and the beam-walking performance of the animals. Treatment with the calcium antagonist isradipine (2.5 mg/kg injected s.c. immediately after pMCAO) reduced the total infarct size by more than 40% compared to vehicle-injected controls. In particular, the ipsilateral somatosensory cortex appeared normal in diffusion- and T(2)-weighted MRI images. In sham-operated rats simultaneous electrical stimulation of both forepaws led to similar activation of both somatosensory cortices, while in pMCAO animals given vehicle only the contralateral cortex showed an fMRI response. Similarly, in pMCAO rats treated with isradipine, functional activation following bilateral electrical stimulation was only detected in the contralateral somatosensory cortex despite the normal appearance of the ipsilateral cortex in MRI images. Furthermore, fMRI responses to pharmacological stimulation with bicuculline were virtually absent in the ipsilateral somatosensory cortices both in vehicle- and isradipine-treated rats. Finally there was no significant difference between vehicle- and isradipine-treated animals upon the performance of beam-walking test or in forelimb grip strength. It is concluded that during the acute (24 h) post-occlusion period, structural integrity in the somatosensory cortex revealed by MRI does not translate into preservation of function.

Inhalation of low concentrations of toluene induces persistent effects on a learning retention task, beam-walk performance, and cerebrocortical size in the rat.

The organic solvent toluene is widely used in industry. The threshold limit value for extended occupational exposure to toluene is presently set to 200 ppm in the United States. We have investigated the effect of an inhalation exposure of 80 ppm for 4 weeks (6 h/day, 5 days/week), followed by a postexposure period of at least 4 weeks, on behavior and brain features in the rat. Toluene exposure appeared to affect spatial memory, since toluene-exposed rats showed a longer time in the correct quadrant in a Morris swim maze. This effect may indicate that the exposed rats used their praxis strategy longer before they started to look for the platform elsewhere. Toluene-exposed rats showed trends for increases in both locomotion and rearing behaviors and a significantly reduced beam-walk performance. The area of the cerebral cortex, especially the parietal cortex, was decreased by 6-10% in toluene-exposed rats, as shown by magnetic resonance imaging of living rats and autoradiograms of frozen brain sections. The K(D) and B(max) values of the dopamine D(3) agonist [(3)H]PD 128907 were not affected by toluene, as measured in caudate-putamen and subcortical limbic area using biochemical receptor binding assays and in caudate-putamen and islands of Calleja using quantitative receptor autoradiography. Hence, previously demonstrated persistent effects by toluene on the binding characteristics of radioligands binding to both D(2) and D(3) receptors seem to indicate a persistent effect of toluene selectively on dopamine D(2) receptors. Taken together, the present results indicate that exposure to low concentrations of toluene leads to persistent effects on cognitive, neurological, and brain-structural properties in the rat.

Regional brain activation by bicuculline visualized by functional magnetic resonance imaging. Time-resolved assessment of bicuculline-induced changes in local cerebral blood volume using an intravascular contrast agent.

Functional magnetic resonance imaging (fMRI) has been applied to study rat focal brain activation induced by intravenous administration of the GABA(A) antagonist bicuculline. Using magnetite nanoparticles as a blood pool contrast agent, local changes in cerebral blood volume (CBV) were assessed with high temporal (10 s) and spatial (0.35 x 0.6 mm(2)) resolutions. Upon infusion of the bicuculline region-specific increases in CBV have been observed, suggesting CBV to reflect brain activity. During the first 2 min, the signal increases were predominant in the cortex, followed by increases in other brain areas, such as the caudate putamen, thalamus and cerebellum. Ten minutes after the start of infusion, a dominant response was observed in the thalamus, while in the caudate putamen a biphasic response pattern was seen. The magnitude of the signal responses in all brain regions was dependent on the dose of bicuculline and, in general, matched the known distribution of GABA(A) binding sites. This study suggests that pharmacological fMRI, displaying brain function at the highly specific level of drug-receptor interaction, should foster our understanding of normal and pathological brain function.

Magnetic resonance imaging of the membranous labyrinth during in vivo gadolinium (Gd-DTPA-BMA) uptake in the normal and lesioned cochlea.

MRI with a T1 contrast agent was used to investigate the normal and noise-damaged cochlea. The time course and distribution of the in vivo uptake of the gadodiamide chelate bound paramagnetic Gd ion (GdDTPA-BMA) throughout the membranous labyrinth of normal and impulse noise-damaged guinea pig cochleae were measured by MRI at 4.7T. Simultaneous signal enhancement of the basal, medial and apical scala tympani (ST) and scala vestibuli (SV) was observed within 10 min following i.v. injection, reaching maximum levels at around 100 min. ANOVA and post hoc paired t-tests showed statistically significant differences in the levels and rates of Gd uptake-enhancement between the scalae. The ST revealed the most rapid and extensive enhancement throughout the period of active Gd uptake, while the SV showed comparatively slower and less enhancement, and the intact scala media (SM) indicated insignificant enhancement. The in vivo Gd penetration and enhancement of the membranous SM increased significantly in the noise-damaged cochlea, suggesting lesioning of the cochlear membranes.

Magnetic resonance imaging of the cochlea, spiral ganglia and eighth nerve of the guinea pig.

The membranous labyrinth of the guinea pig cochlea and retrocochlear neural structures were investigated by magnetic resonance imaging (MRI) using an experimental system with a field strength of 4.7T and a single turn surface coil 25 mm in diameter, or standard resonators of 34 or 70 mm in diameter and gradient field strengths of 950 mTm and 200 mTm. High-resolution 2-D and 3-D images of 0.3-1.0 mm slice thickness were acquired by a rapid acquisition with relaxation enhancement (RARE) sequence and a standard multi-echo technique. Structural and dimensional aspects of the cochlea were resolved in vitro and in vivo down to <50 microm, showing the scala vestibule, scala media, scala tympani, spiral ganglia and the cochlear (eighth) nerve. In vivo perfusions with the gadodiamide (GdDTPA-BMA) chelate-bound paramagnetic gadolinium ion resulted in dynamic temporal enhancement of the scala vestibule and scala tympani, but did not penetrate the scala media.

Distribution and kinetics of galanin infused into the ventral hippocampus of the rat: relationship to spatial learning.

A recent study has shown that ventral hippocampal galanin plays a role in spatial learning and that it has an inhibitory effect on basal acetylcholine release [Ogren S. O. et al. (1996) Neuroscience 75, 1127-1140]. The present studies were designed to compare the in vivo tissue distribution and kinetics of infused galanin (porcine) with the temporal effect of galanin on spatial learning in the rat. Daily bilateral microinfusions of galanin (1.5 nmol/side for five days) via chronic cannulae placed in the ventral hippocampus produced a significant impairment of acquisition of the spatial task when infused 20 min, but not 5 or 60 min, before the daily training session. No overall impairment of memory retention (examined 24 h after the last training session) was observed in the galanin-treated rats. These results indicate that galanin given in the ventral hippocampus produces a time-dependent effect on acquisition. Using an antibody to porcine galanin and immunohistochemistry, galanin infused in the ventral hippocampus was found to be distributed mainly within the ventral part of the hippocampus and around the infusion site. The infused galanin was rapidly cleared from the extracellular space between 5 and 20 min after infusion. Five minutes after infusion of galanin, a number of cells in the ventral hippocampus, both within and outside the zone of extracellularly located galanin, showed a positive galanin-like immunoreactivity. These cells appear morphologically to be medium-sized neurons with a similar position as cells showing neuropeptide Y-like immunoreactivity. At 20 and 60 min after infusion of galanin, no cells with detectable levels of galanin-like immunoreactivity could be seen. These results indicate that the temporal kinetics and distribution of infused galanin are of major importance for its behavioural effect in the ventral hippocampus. The rapid clearance of the infused galanin and its internalization by neuronal endocytotic mechanisms may be important for its effect on cognition.

Perinatal asphyxia induces long-term changes in dopamine D1, D2, and D3 receptor binding in the rat brain.

We have investigated the long-term effects of 15-16 min or 19-20 min of perinatal asphyxia on D1, D2, and D3 receptors (analyzed by quantitative autoradiography) in the mesotelencephalic dopamine systems of the 4-week-old rat. Perinatal asphyxia reduced D1 antagonist binding ([3H]SCH 23390 in the presence of ketanserine) in the accumbens nucleus, the olfactory tubercle, and the substantia nigra and increased D1 agonist binding ([3H]dopamine in the presence of spiperone) in the accumbens nucleus and the olfactory tubercle. No changes in D2 antagonist binding ([123]iodosulpride) were found, whereas D2 agonist binding ([3H]N-propylnorapomorphine, [3H]NPA) was reduced in the posterior part of the caudate-putamen, and following 19-20 min of asphyxia it was also reduced in the accumbens nucleus. D3 agonist binding (R/S-(+/-)-2-(N,N-di[2,3(n)-3H] propylamino)-7-hydroxy-1,2,3,4-tetrahydronaphthalene, [3H]7-OH-DPAT) was increased in the anterior part of the caudate-putamen following 15-16 min but not 19-20 min of asphyxia. The results indicate that perinatal asphyxia reduced the number of D1 receptors and increased D1 agonist affinity in the accumbens nucleus and the olfactory tubercle and reduced the number of D1 receptors in the substantia nigra. The number of D2 receptors was unchanged by asphyxia, whereas the D2 agonist affinity was reduced in the caudate-putamen and in the accumbens nucleus. D3 agonist binding was increased in the caudate-putamen selectively following 15-16 min of asphyxia. In conclusion, asphyxia during birth induces long-term changes in the binding characteristics of dopamine receptors in the mesotelencephalic dopamine systems, which may contribute to previously reported behavioral changes.

Endothelin-1 induced lesions of the frontoparietal cortex of the rat. A possible model of focal cortical ischemia.

Endothelin-1 (ET-1) was unilaterally applied onto the surface of the dorsal frontoparietal cortex of the rat. Cortical blood flow measurements using laser-Doppler flowmetry demonstrated dose-dependent reductions of frontoparietal cortical blood flow. Histological analysis demonstrated dose-related lesions and the time course was followed using MRI. The lesions appear to be associated with a large penumbra area indicated by morphological characteristics. Thus, cortical surface exposure to ET-1 may produce graded lesions of the frontoparietal cortex related to local ischemia.

Perinatal asphyxia-induced changes in rat brain tyrosine hydroxylase-immunoreactive cell body number: effects of nicotine treatment.

Perinatal asphyxia (15-22 min) was induced to male Sprague-Dawley rat pups during the last day of gestation and the surviving pups were sacrificed at 4 weeks of age. Brain sections were stained for tyrosine hydroxylase immunoreactivity and Cresyl violet. With increasing duration of perinatal asphyxia a reduction in the number of tyrosine hydroxylase immunoreactive (TH-IR) nerve cell bodies was found in the locus ceruleus, probably reflecting an increased death of noradrenaline nerve cell bodies. In contrast, perinatal asphyxia (15-20 min) resulted in an increased number of TH-IR nerve cell bodies in the A9 (zona compacta of the substantia nigra) and the A10 (ventral tegmental area) regions of the mesencephalon, probably reflecting an increased survival of dopamine nerve cell bodies. Perinatal asphyxia for longer than 20 min periods reduced the number of TH-IR cell bodies in the 4 week old rat, even below those found in control animals, indicating that when asphyxia is induced for a period leading to almost 100% mortality, a long-term reduction of the number of mesencephalic dopamine neurons is produced. It has previously been shown that a 4 week postnatal nicotine (0.2 micromol/kg per h) treatment counteracts the asphyxia-induced increase in TH-IR cell body number in the substantia nigra and ventral tegmental area. Such nicotine treatment did not influence the reduction in TH-IR cell bodies in the locus ceruleus following 15-20 min of perinatal asphyxia.

Effects of perinatal asphyxia on the mesostriatal/mesolimbic dopamine system of neonatal and 4-week-old male rats.

The present study was undertaken in order to study the effects of perinatal asphyxia on tyrosine hydroxylase (TH) activity, dopamine levels and turnover, and dopamine metabolites (3,4-dihydroxyphenylacetic acid, DOPAC, homovanillic acid, HVA, and 3-methoxytyramine, 3-MT, analyzed by high-performance liquid chromatography, HPLC) measured in the basal ganglia of the 20- to 40-min-old newborn and 4-week-old male rat. Asphyxia was induced in pups by placing the fetuses, still in their uterus horns removed by hysterectomy from pregnant rats at full term, in a 37 degrees C water bath for 15-16 min or 19-20 min. Following asphyxia, the uterus horns were opened, and the pups were removed and stimulated to breathe. A 100% and 50-80% pup survival was obtained following 15-16 min and 19-20 min of asphyxia, respectively. Acute changes were studied in brains from newborn pups 20-40 min after delivery, and long-term changes were studied in brains from 4-week-old rats. No changes in TH-activity could be observed in the substantia nigra/ventral tegmental area (SN/VTA), the striatum, or the accumbens nucleus/olfactory tubercle (ACC/TUB), in the newborn or the 4-week-old rat. In the newborn rat, 19-20 min of asphyxia increased (as compared to controls) dopamine levels in the SN/VTA to 136 +/- 14% and in the ACC/TUB to 160 +/- 10%, indicating an increased synthesis and/or release of dopamine. DO-PAC levels were increased in the SN/VTA to 150 +/- 14% and in the ACC/TUB to 151 +/- 10%, and HVA levels were increased to 152 +/- 16% in the striatum and to 117 +/- 4% in the ACC/TUB. Following 15-16 min of asphyxia, dopamine levels were increased to 130 +/- 12% in the ACC/TUB, and DOPAC levels were increased to 135 +/- 6% and 130 +/- 12% in the SN/VTA and the ACC/TUB, respectively. This suggests that the increased dopamine levels may preferably reflect an increased release of dopamine following perinatal asphyxia. In the 4-week-old rat, dopamine levels were decreased in the SN/VTA to 71 +/- 4%, in the striatum to 52 +/- 8%, and in the ACC/TUB to 53 +/- 7%, following 19-20 min of perinatal asphyxia as compared to controls. No changes were observed in DOPAC, HVA, or 3-MT levels, indicating that the reduced dopamine levels reflect a reduced dopamine synthesis following perinatal asphyxia. A decrease in dopamine utilization was observed in the striatum to 15 +/- 8% and in the ACC/TUB to 9 +/- 13% following 19-20 min of perinatal asphyxia as compared to controls. This indicates that perinatal asphyxia produced long-lasting reductions in activity in the mesostriatal/mesolimbic dopamine systems in the 4-week-old rat.

Dopaminergic transmission in the rat retina: evidence for volume transmission.

The study was designed to determine whether dopaminergic neurotransmission in the retina can operate via volume transmission. In double immunolabelling experiments, a mismatch as well as a match was demonstrated in the rat retina between tyrosine hydroxylase (TH) and dopamine (DA) immunoreactive (ir) terminals and cell bodies and dopamine D2 receptor-like ir cell bodies and processes. The match regions were located in the inner nuclear and plexiform layers (D2 ir cell bodies plus processes). The mismatch regions were located in the ganglion cell layer, the outer plexiform layer, and the outer segment of the photoreceptor layer, where very few TH ir terminals can be found in relation to the D2 like ir processes. In similar experiments analyzing D1 receptor like ir processes versus TH ir nerve terminals, mainly a mismatch in their distribution could be demonstrated, with the D1 like ir processes present in the outer plexiform layer and the outer segment where a mismatch in D2 like receptors also exists. The demonstration of a mismatch between the localization of the TH terminal plexus and the dopamine D2 and D1 receptor subtypes in the outer plexiform layer, the outer segment and the ganglion cell layer (only D2 immunoreactivity (IR)) suggests that dopamine, mainly from the inner plexiform layer, may reach the D2 and D1 mismatch receptors via diffusion in the extracellular space. After injecting dopamine into the corpus vitreum, dopamine diffuses through the retina, and strong catecholamine (CA) fluorescence appears in the entire inner plexiform layer and the entire outer plexiform layer, representing the match and mismatch DA receptor areas, respectively. The DA is probably bound to D1 and D2 receptors in both plexiform layers, since the DA receptor antagonist chlorpromazine fully blocks the appearance of the DA fluorescence, while only a partial blockade is found after haloperidol treatment which mainly blocks D2 receptors. These results indicate that the amacrine and/or interplexiform DA cells, with sparse branches in the outer plexiform layer, can operate via volume transmission in the rat retina to influence the outer plexiform layer and the outer segment, as well as other layers of the rat retina such as the ganglion cell layer.

Nicotine treatment counteracts perinatal asphyxia-induced changes in the mesostriatal/limbic dopamine systems and in motor behaviour in the four-week-old male rat.

In the present study, the effects of nicotine treatment on the changes induced by perinatal asphyxia in exploratory and D-amphetamine-induced behaviour, and in the number of brain tyrosine hydroxylase-immunoreactive nerve cell bodies were investigated in four-week-old male rats. Asphyxia was induced in pups by placing the fetuses, still in their uterus horns removed by hysterectomy from full-term pregnant rats, in a 37 degrees C water bath for 15-16 min or 19-20 min. Surviving male pups were treated with nicotine via suckling from surrogate mothers implanted subcutaneously with Alzet minipumps containing nicotine (0.2 mumol/kg per h) for four weeks. The minipumps implanted in the mothers of sham-treated animals contained saline only. After treatment, exploratory behaviour and D-amphetamine-induced behaviour was analysed in a computerized "activity" box. After the behavioural experiments, the rats were taken for tyrosine hydroxylase immunohistochemistry, and the total number of tyrosine hydroxylase immunoreactive cell bodies were counted in the A9 and A10 regions of the substantia nigra and the ventral tegmental area, respectively. Nicotine serum levels were measured using gas chromatography in selected asphyctic and control pups at different periods after delivery. During the exploratory phase, in saline-nurtured rats, 15-16 min of asphyxia slightly increased (approximately 25%) locomotion, motility and rearing. In contrast, 19-20 min of asphyxia reduced the locomotion and rearing by approximately 50%, as compared to controls. An increase in amphetamine-induced behaviours was observed after 15-16 min, but not after 19-20 min of asphyxia, as compared to controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Long distance pathways of diffusion for dextran along fibre bundles in brain. Relevance for volume transmission.

Texas Red-labelled dextran with a mol. wt of 3000 g mol-1, a marker for the extracellular space, was injected unilaterally into the neostriatum of adult rats (0.3-30 micrograms microliter-1) and its distribution evaluated 1 min to 5 h later. Diffusion in the neuropil was observed with clearance starting after 30 min. After 10-15 min strong labelling along the myelinated fibre bundles was observed in the entire neostriatum. After about 20 min the labelling along the fibres reached into the corpus callosum and the overlaying deep layers of the cerebral cortex. A marked cellular uptake and accumulation of labelled dextran was found in putative perivascular pericytes. Thus, in the living brain preferential extracellular fluid pathways for diffusion exist, especially along fibre bundles, which allow the exchange of chemical signals between two distant regions. These may represent extracellular fluid pathways for volume transmission.