Unlesioned Side Research Articles

L-dihydroxyphenylalanine-induced asymmetric changes in striatal uric acid peak: Determination by in vivo electrochemical detection in rats with unilateral nigrostriatal lesions

Rats were unilaterally lesioned with 6-hydroxydopamine to destroy the nigrostriatal pathway. Following injection with 25 mg/kg l-dopa, circling behavior away from the lesioned side was monitored. Concurrently, in vivo electrochemical detection was used to compare changes in striatal extracellular levels of ascorbic acid (Peak 1) and uric acid (Peak 2) on the lesioned and unlesioned sides. Peak 1 changes did not differ, but Peak 2 changed asymmetrically on the two sides. The difference in the changes in Peak 2 was highly correlated with the circling behavior, with the greater increase on the lesioned side.

Direct evidence of acute, massive striatal dopamine release in gerbils with unilateral strokes.

Dopamine release into the extracellular space was measured with in vivo electrochemical detection in the ipsilateral and contralateral striata in Mongolian gerbils that suffered a stroke after acute unilateral carotid artery ligations. A sevenfold increase in the dopamine signal occurred within 15 minutes of carotid ligation in the ischemic side, while the unlesioned side had no significant change. Increased extracellular levels of dopamine persisted throughout the 3-hour recording period. Pretreatment with alpha-methyl-p-tyrosine 6 hours prior to recording significantly attenuated the signal increase. This study is the first direct demonstration of the marked, continuous dopamine release that occurs during acute cerebral ischemia.

Dendritic sprouting and compensatory synaptogenesis in an identified interneuron follow auditory deprivation in a cricket.

We examined the effect of chronic afferent deprivation on an identified interneuron (Int-1) in the auditory system of the Australian field cricket Teleogryllus oceanicus. In normal intact crickets, the auditory afferents from each ear terminate ipsilaterally onto a single Int-1. Each bilaterally paired Int-1 is excited by ultrasound stimulation of its ipsilateral ear but not by the contralateral ear. Unilateral removal of an ear early in postembryonic development deprives the developing Int-1 of ipsilateral auditory innervation. Consequently, the ipsilateral dendrites of the deprived interneuron sprout, grow aberrantly across the ganglionic midline, and terminate specifically in the intact auditory neuropile of the contralateral (unlesioned) side, where they form functional synapses with the contralateral afferents. This unusual compensatory dendritic sprouting restores auditory function to the neuron. Thus, it is demonstrated that the dendritic shape of an identified Int, as well as its synaptic connectivity, is altered as a consequence of chronic sensory deprivation.

Effects of ganglioside GM1 treatment on striatal glucose metabolism, blood flow, and protein phosphorylation of the rat

Effects of ganglioside GM1 administration have been studied in unilaterally partially hemitransected rats on striatal energy metabolism, using the radioactive deoxyglucose (DG) technique, on striatal blood flow, using radiolabelled iodoantipyrine (IAP) as tracer, and on cyclic AMP (cAMP) and Ca2+ induced protein phosphorylation in striatal membranes (P2 fraction). Ganglioside GM1 treatment counteracted the imbalance in striatal energy metabolism, in striatal blood flow, as well as in protein phosphorylation found between the striata of the lesioned and unlesioned side, possibly due to excitatory effects on the lesioned side and inhibitory effects on the unlesioned side. In intact animals, GM1 treatment produced a reduction in cAMP and Ca2+ induced striatal protein phosphorylation. Facilitatory actions of the ganglioside GM1 dominate following a lesion, probably due to its possible function as a modulator of receptors for neuronotrophic factors, leading to restoration of metabolic rate and of cAMP and Ca2+ induced protein phosphorylation in the striatum of the lesioned side. The results emphasize that ganglioside GM1 treatment can restore the metabolism of a partially innervated striatum towards normal, as evaluated both at the level of the entire striatal structure by means of the DG and IAP techniques and at the molecular level by means of studies on the cAMP and Ca2+ induced protein phosphorylation.

Decrease in the number of synapses formed by subcortical inputs to the striate cortex of binocularly deprived cats

The density of synapses was determined from electronmicrographs taken from area 17 of cats binocularly deprived of pattern vision for 6 months and in normally reared litter mates. In each cat the optic radiation was transected on one side 4 days before sacrifice and the density of synapses of subcortical origin was estimated by comparing the density of normal synapses remaining on the lesioned side with the density of synapses on the unlesioned side. In normal animals 36% of the synapses were formed by subcortical afferents, but in the binocularly deprived animals this figure was reduced to only 17%. A decrease found in the total synaptic density in the deprived visual cortex was not statistically significant. Thus, binocular deprivation seems to selectively diminish the subcortical contribution to the synaptic density in the visual cortex.

On the origin of dopamine and its metabolite in predominantly noradrenergic innervated brain areas

The origin of dopamine (DA) and its metabolite in predominantly noradrenergic brain areas was investigated in rats with a unilateral electrolytic lesion of the locus coeruleus. Using the unlesioned side as a control, levels of DA, noradrenaline (NA), and the DA metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), were measured in lateral hippocampus, cerebellum, frontal cortex, occipital cortex, brainstem and striatum. Lesion of the locus coeruleus decreased brain NA levels in those regions innervated by this nucleus, but had no effect on levels of DA and DOPAC in any of the regions studied. It is concluded that even in regions of very low DA concentration, DA and DOPAC probably originate from dopaminergic neurons rather than via NA formation in noradrenergic neurons.

Localization and quantitation of dynorphin B in the rat hippocampus

The present study measures the content of dynorphin B in the rat hippocampus, and localizes the dynorphins within the intrinsic hippocampal neuronal circuitry. The level of dynorphin B, which is representative of the prodynorphin-derived peptides, was markedly depleted by intrahippocampal injection of colchice, which destroyed the great majority of the hippocampal granule cells and the associated mossy fiber pathway. The hippocampus contralateral to the injection demonstrated a slight, non-significant rise in dynorphin B levels after colchicine. Entorhinal cortical lesions ablating the perforant pathway input to the hippocampus did not significantly alter dynorphin B levels in the hippocampus. Unilateral fimbrial transection caused a small but significant increase in dynorphin B on the side of the lesion relative to the unlesioned side, but neither side was significantly different from control.

Replication and differentiation of olfactory receptor neurons following axotomy in the adult hamster: a morphometric analysis of postnatal neurogenesis.

Regeneration of olfactory receptor neurons following unilateral olfactory nerve section was studied in Syrian golden hamsters by morphometric procedures. Characteristic structural and histochemical features of olfactory receptor neurons were compared on the sectioned and intact sides of the nasal septum at 6, 12, 18, 33, and 130 days following axotomy. The parameters measured were epithelial thickness and the numbers of nuclei, hematoxylin-staining olfactory vesicles, olfactory marker protein (OMP)-containing neuronal perikarya, and OMP-containing olfactory vesicles. The olfactory receptor neuron population was severely depleted 6 days after axotomy. In the succeeding 12-day period there was an initially rapid, then slower return of receptor neuron numbers. Though the regenerating olfactory epithelium appeared normal by gross inspection 33 days after the lesion, morphometric analysis revealed a substantial increase in the number of olfactory receptor neurons between 33 and 130 days postlesion. At our longest survival interval, all quantitative parameters had returned to 91-99% of control values. The numbers of OMP-containing perikarya and olfactory vesicles on the sectioned side were unchanged between the sixth and 12th postlesion days, thus suggesting that neural turnover was depressed for several days following surgery. Marker protein developed in newly formed receptor neurons between 6 and 12 days after the formation of the olfactory vesicle. Consequently, the ratio between OMP-containing olfactory vesicles and hematoxylin-staining vesicles (O/H) was used as an index of neural differentiation. The O/H ratio on the sectioned side was minimal 12 days following axotomy when stem-cell division was well under way but OMP antigenicity had not yet been expressed in newly formed neurons. At 33 days postlesion, O/H ratios were slightly but significantly greater than the control value, reflecting a degree of synchrony in the regenerating receptor neuron population. The average O/H ratio on the unlesioned side was 0.667. This value, together with our other observations, was used to derive an estimate of the life span of hamster olfactory receptor neurons, approximately 25-35 days.

Voltammetric carbon paste electrodes monitor uric acid and not 5-HIAA at the 5-hydroxyindole potential in the rat brain

Changes in the height of peak 2 obtained using linear sweep voltammetry and carbon paste electrodes chronically implanted in discrete brain regions of the unrestrained rat were measured under a variety of conditions; in the past this peak has been attributed to the oxidation of 5-hydroxyindoleacetic acid (5-HIAA). Unilateral 5,7-dihydroxytryptamine (5,7-DHT) lesions of the medial forebrain bundle reduced the 5-HIAA content of the striatum and hippocampus to 10% of the unlesioned side, but did not alter the height of peak 2 recorded in these regions. In contrast, microinfusion of uricase beside striatial electrodes reduced the height of peak 2 by 96%; systemic amphetamine-induced increases in the height of the peak were also prevented by this enzyme. These results indicate that uric acid, and not 5-HIAA, is mainly responsible for peak 2, and that changes in the height of this peak reflect changes in the extracellular concentration of uric acid.

Chronic intraventricular injections of nerve growth factor elevate hippocampal choline acetyltransferase activity in adult rats with partial septo-hippocampal lesions

Nerve growth factor (NGF) was injected intraventricularly during 4 weeks into adult rats with unilateral partial lessions of the cholinergic septo-hippocampal pathway. On the lesioned side, NGF treatment elevated choline acetyltransferase (ChAT) activity up to 60% above the activity measured on the lesioned side of cytochrome c-treated controls. On the unlesioned side, NGF treatment increased ChAT activity only to an insignificant degree. ChAT activity in the septum of NGF-treated animals was increased by 60% as compared to controls. The NGF-induced increases on the lesioned side and in the septum were not accompanied by elevations in acetylcholinesterate (AChE) activity. Furthermore, histochemical analysis revealed no difference in AChE staining pattern or intensity between NGF-treated and control animals. The lack of effect on AChE strongly suggests that the increases in ChAT activity in hippocampus and septum, are due to an elevation of ChAT activity within cholinergic neurpns surviving the lesion rather than to a promotion of sprouting of cholinergic fibers.

Monosialoganglioside internal ester stimulates the dopaminergic reinnervation of the striatum after unilateral hemitransection in rat

The effects of the administration of GM1 monosialoganglioside internal ester, AGF2, on the dopaminergic reinnervation of the striatum in rats with unilateral hemitransection has been studied. AGF2 increases the apparent Vmax and the density of tyrosine-hydroxylase-positive nerve terminals in the striatum of the lesioned side, without modification of the tyrosine-hydroxylase activity in the unlesioned side. AGF2, at lower doses, is more active than its parent natural molecule GM1. AGF2 has a larger half-life and a higher distribution volume than GM1, and undergoes a slow hydrolysis in the serum releasing the original natural compound GM1. Mannitol and dexamethazone, often used to prevent swelling of the brain after injury, or isoaxonine, proposed to stimulate neurite growth are unable to reproduce the effects of AGF2 on the recovery of striatal tyrosine-hydroxylase activity after hemitransection. The data are compatible with the view that AGF2, through its conversion into GM1, facilitates the collateral sprouting of the nigro-striatal dopaminergic neurons.

Hyperalgesia and the reduction of monoamines resulting from lesions of the dorsolateral funiculus

Unilateral lesions of the dorsolateral funiculus (DLF) in the rat resulted in unilateral hyperalgesia as revealed by a hindpaw withdrawal test to heat. Larger lesions invloving the dorsal column and ventrolateral quadrant did not cause hyperalgesia. The levels of 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), noradrenaline (NA) and dopamine (DA) were measured in the lumbar dorsal quadrant using high performance liquid chromatography (HPLC). In hyperalgesic animals DLF lesions caused an ipsilateral reduction of all the amines and a contralateral reduction of 5-HT and NA. This suggests that serotonergic and noradrenergic axons in the DLF give a contralateral innervation. A correlation was sought between the reduction of amine level and the degree of hyperalgesia shown by individual rats on lesioned and unlesioned sides of the cord. No consistent correlation was found with any of the amines.

Multifocal brain sites for apomorphine-induced circling and other stereotyped motor behaviour in the 6-hydroxydopamine-lesioned rat

Rats pretreated with 6-hydroxydopamine (6-OHDA, 8μg in 4 μl) in one medial forebrain bundle exhibited an assortment of stereotyped activities and pronounced circling towards the unlesioned side when apomorphine was administered either subcutaneously (0.5 mg/kg), or by discrete stereotaxic injection (5 μg in 0.2 μl) into the caudate nucleus, nucleus accumbens, amygdala, lateral habenula, ventromedial thalamus, substantia nigra zona reticulata, periaqueductal grey or superior colliculus (but not a variety of other areas) ipsilateral to the lesion. These rotational responses were absent in unlesioned animals and, where tested, were attenuated by intraperitoneal haloperidol (0.5 mg/kg). It is suggested that multiple brain sites become sensitive to apomorphine following dopamine depletion by 6-OHDA.

Presynaptic muscarinic receptors on dopaminergic terminals in the nucleus accumbens

Levels of muscarinic receptors were measured in the nucleus accumbens of rat following 0.8 μg 6-hydroxydopamine or vehicle injections (0.2 μl) into the ventral tegmental area to investigate whether the dopaminergic terminals destroyed by this procedure bear muscarinic receptors. Dopamine levels in the nucleus accumbens ipsilateral to the injection of 6-hydroxydopamine were substantially reduced by 83% as compared to the unlesioned side after 7 days. Significant decreases in the specific binding of [ 3H]N-methylscopolamine of 9 and 15% were also seen in the nucleus accumbens ipsilateral to the lesion after 7 and 14 days respectively. The class of muscarinic receptor depleted by the lesion was further investigated using [ 3H]oxotremorine-M to label the ‘super high’ affinity binding sites. The percentage occupancy of total muscarinic receptors by [ 3H]oxotremorine-M was significantly decreased by lesion e.g. 23% after 7 days, indicating a selective loss of ‘super high’ affinity binding sites. The lesion caused no change in the affinity constant for the muscarinic antagonist, propylbenzilylcholine. Studies of the binding of the agonists carbachol and oxotremorine-M by competition with [ 3H]propylbenzilylcholine showed little change in the concentrations of affinity constants of the ‘high’ and ‘low’ affinity binding sites with the 6-hydroxydopamine lesion.

Inhibition by apomorphine of the potassium-evoked release of [3H]-gamma-aminobutyric acid from the rat substantia nigra in vitro.

1 The spontaneous and potassium-evoked release of tritium from the rat substantia nigra prelabelled with [(3)H]-gamma-aminobutyric acid [(3)H]-GABA were assessed in vitro under conditions of superfusion.2 Kainic acid lesions performed in the right caudate nucleus resulted in a 70% reduction in the ability of the homolateral nigral cells to take up and retain [(3)H]-GABA when compared with the unlesioned side. The potassium-evoked release of [(3)H]-GABA remained proportional to the radioactivity retained in the tissue suggesting that the nigral GABA neurones that survived kainic acid treatment were still functional.3 The spontaneous outflow of [(3)H]-GABA was significantly increased by exposure to different concentrations of exogenous GABA (10 to 1000 muM) when amino-oxyacetic acid was present in the incubation medium.4 Apomorphine in concentrations ranging from 1 to 30 muM inhibited the calcium-dependent release of [(3)H]-GABA induced by 1 min exposure to 30 mM K(+). These concentrations of apomorphine did not affect the spontaneous outflow of radioactivity. In vivo administration of haloperidol 0.2 mg/kg antagonized the in vitro inhibition by apomorphine of the K(+)-evoked release of [(3)H]-GABA.5 The results obtained with apomorphine and haloperidol suggest the presence of presynaptic dopamine-like inhibitory receptors in gabaergic nerve terminals.6 Dopamine in concentrations ranging up to 300 muM did not modify either the spontaneous or the K(+)-evoked release of [(3)H]-GABA from the substantia nigra. These concentrations of dopamine effectively displaced [(3)H]-dopamine recently taken up into the substantia nigra.7 Our results do not support the view that dendritic release of dopamine from the substantia nigra might be involved in the physiological modulation of the spontaneous or the stimulation-evoked release of GABA.

Increased activity of ornithine decarboxylase in goldfish following optic nerve crush.

Ornithine decarboxylase (ODC) activity increased in goldfish retina, brain, and kidney several days following unilateral intraorbital optic nerve crush. Activity in both retinas followed a similar time course, an elevation being first detectable 3 days following crush, maximal on day 5 and returning to control levels by day 7. Increases were significantly higher in the retina on the lesioned side than in control retina. If one eye was surgically removed, a more prolonged elevation of ODC activity was seen in the remaining eye than was observed in control retinas following contralateral nerve crush. Sham operation or behavioral stress secondary to aversive electrical shock did not lead to significant increases in ODC activity in brain or retina. Explants of retinas whose optic nerve had been crushed 10--14 days prior to explantation, as well as those derived from the unlesioned side, showed increases in ODC activity following addition of beta-NGF to the medium. The response was greater in post-crush retinas than in control retinas. These results taken together suggest an increased responsiveness of the regenerating retina to stimuli that lead to increased ODC activity. While the nature of the in vivo signal(s) may be complex, it is inferred that degenerative changes in the distal stump play a significant role.

Supersensitivity of nigral serotonin receptors and rat rotational behaviour

Direct injections of 5-hydroxytryptamine (5-HT) into the corpus striatum (CS) and substantia nigra (SN) after unilateral 5,7-dihydroxytryptamine (5,7-DHT) of the dorsal raphe nucleus (DRN), resulted in a significant dose-related contralateral turning behaviour in SN-injected but not in CS-injected animals. Receptor binding studies in these animals revealed a 3 fold increase in [ 3H]5-HT binding sites (B max) and a similar increase in affinity constant (K D) in the SN from the lesioned side when compared with the unlesioned side. There was no change in binding characteristics in the CS of DRN-lesioned animals. The data presented would confirm our previous findings that nigral 5-HT receptors become supersensitive after denervation of the DRN-SN pathway.

Cross-tolerance of dopamine metabolism to baclofen, gamma-butyrolactone and HA-966 in the striatum and olfactory tubercle of the rat.

Abstract Rats received 7 daily injections with baclofen (40 mg/kg), GBL (750 mg/kg) or HA-966 (100 mg/kg). Dopamine (DA) was measured in the striatum and olfactory tubercle (OT) of rats, sacrificed 0.5 h or 1 h after the last injection. Marked tolerance and cross-tolerance for the DA-elevating effect of these drugs was seen in the striatum, but not in OT. When on day 7 a unilateral lesion of the nigrostriatal pathway was made, also some tolerance to the DA increase in the striatum on the lesioned side was seen in HA-966-pretreated rats, but it was small compared to the tolerance after an additional drug administration in non-lesioned animals. A low dose of apomorphine (0.25 mg/kg, i.p.) had no effect on DA, dihydroxyphenylacetic acid DOPAC) or homovanillic acid (HVA) levels in the lesioned striata, whether the rats had been pretreated for 6 days with HA-966 or not. However, this dose of apomorphine had a significantly more lowering effect on striatal DOPAC and HVA levels on the unlesioned side of HA-966 pretreated rats. The results show that tolerance develops to the increase of DA synthesis, which is possibly receptor-mediated. This tolerance develops more readily in the striatum than in the olfactory tubercle.

Diminished decarboxylation of l-dopa in rat striatum after intrastriatal injections of kainic acid

Injection of kainic acid into rat striatum reduced striatal DOPA decarboxylase activity by 20% as compared with that in control unlesioned sides. After administration of L-DOPA, concentrations of dopamine (but not DOPA) were lower (by 33%) in lesioned than in control striata indicating decreased in vivo formation of dopamine from exogenous DOPA after kainate lesions. These findings suggest that in the rat, a significant part of striatal DOPA decarboxylase activity i·s localized in neurons originating within the striatum (interneurons and/or efferents) whose perikaria are selectively destroyed by kainic acid.

POTENTIATION OF RESPONSES TO MONOAMINES BY ANTIDEPRESSANTS AFTER DESTRUCTION OF MONOAMINE AFFERENTS

1 Stereotaxic lesioning and microiontophoretic techniques were used to study the effects of lesions of the medial forebrain bundle (MFB) on the potentiation by antidepressant drugs of responses to monoamines of cortical neurones.2 Active uptake of noradrenaline (NA) and 5 hydroxytryptamine (5-HT) by synaptosomes from the motor and somatosensory cortex was reduced to approximately 20%, 10 to 14 days following lesion of the MFB in rats.3 Unilateral lesions of the MFB caused changes in responsiveness of neurones to NA and 5-HT, applied by iontophoresis, in the cortex ipsilateral to the lesion. Excitatory responses to both amines were observed less frequently and depression was the predominant response. Excitatory responses on the lesioned side were significantly smaller than on the unlesioned side, but the size of depressant responses was unaltered.4 Viloxazine strongly potentiated responses of cortical neurones to NA and 5-HT on both sides of the brain of MFB-lesioned rats. There were no significant differences in the potentiation of responses to monoamines on the lesioned or unlesioned sides of the brain.5 Desipramine potentiated responses to NA of neurones in the cortex ipsilateral to MFB lesions.6 Chlorimipramine potentiated responses to 5-HT of neurones in the cortex ipsilateral to MFB lesions.7 It is concluded that antidepressants can potentiate responses to monoamines despite a profound reduction in presynaptic terminals. The potentiation is unlikely to be the result of blockade of monoamine uptake into presynaptic terminals, and is probably a postsynaptic effect of the antidepressant drugs.