Changes in specific binding sites of girisopam after chemical and surgical lesions in the striato-nigral system

Neurotoxin (AMPA)-induced lesions in the caudate nucleus as well as unilateral surgical transection of the striato-nigral pathway strongly depleted the binding of a homophthalazine (formerly called 2,3-benzodiazepines) girisopam (GYKI-51189, EGIS 5810) selectively in the substantia nigra of the rat, ipsilateral to the lesions. In contrast to this, AMPA injections into the substantia nigra failed to effect on girisopam binding to either components of the nigro-striatal system. Data indicate that this homophthalazine may bind to a descending component of the striatum (striato-nigral projecting neurons), or its binding capacity to substantia nigra neurons depends on the integrity of striatal afferent pathways to the substantia nigra.

Diffuse plaques in the cerebellum and corpus striatum in Down's syndrome contain amyloid beta protein (A beta) only in the form of A beta 42(43)

The diffuse amyloid (A beta) plaques of the cerebellum and corpus striatum were examined in 32 patients with Down's syndrome, ranging in age from 9 to 71 years, using the end-specific monoclonal antibodies BA27 and BC05 to detect A beta species terminating at amino acids 40 and 42(43) respectively. When present, the diffuse plaques of both regions contained only A beta 42(43) at all ages. A beta 40 was, however, present along with A beta 42(43) in the few cored plaques that were occasionally present in the Purkinje and molecular cell layers of the cerebellum of some of the more elderly patients. It is concluded that diffuse plaques of the cerebellum and striatum contain only A beta 42(43) and that, in contrast to those of the cerebral cortex, these do not "mature' during their lifetime into A beta 40 containing plaques.

Reinnervation after destruction of the dopaminergic system in the rat nucleus accumbens: a quantitative immunohistochemical analysis

The recurrence of dopamine-immunoreactive (DAi) fibers and the effect of the adrenocorticotrophic hormone (ACTH)-(4-9) analog ORG 2766 on this process were investigated 1, 4, 12 and 24 weeks after a unilateral 6-hydroxydopamine (6-OHDA) lesion in the nucleus accumbens (NAc). DAi fibers were almost completely absent 1 week after the lesion. A gradual increase in DAi fibers throughout the NAc was observed, with subnormal values at 24 weeks. Treatment with ORG 2766 during the first week after the lesion resulted in more DAi fibers 4 weeks after the lesion as compared to placebo treatment, but not 12 and 24 weeks after the lesion. After 6-OHDA lesioning reinnervation of the NAc takes place and this process is transiently facilitated by ORG 2766.

Cocaine withdrawal reduces dopamine transporter binding in the shell of the nucleus accumbens

We have previously shown that withdrawal from repeated, intermittent infusions of cocaine in Lewis rats results in a long-lasting reduction in dopamine transporter levels in the nucleus accumbens. The reduction is dose-dependent, requires multiple injections as well as about a 10-day withdrawal period. In this investigation, we show that the decrease (34%) occurs in the shell rather than in the core of the nucleus accumbens, and that a second cycle of cocaine administration and withdrawal has no additional effect. Also, there were no changes in transporter binding in the caudate putamen, the olfactory tubercle or the ventral tegmental area. These results indicate that the limbic portions of the nucleus accumbens are involved in neurochemical adaptations during withdrawal from cocaine.

Selective sparing of human nucleus accumbens in aging and anoxia

OBJECTIVE

To investigate the effects of aging and anoxia on the nucleus accumbens.

METHODS

The number of neurons in nucleus accumbens and caudate nucleus in 35 patients over 65 and 35 under 65 years, all without neurological or psychiatric disease were counted.

RESULTS

There was no statistically significant difference between the number of neurons in the accumbens in the two groups, but there was a decrease in the number of neurons in the elderly group. There was no reduction in volume of the neuronal nucleoli of the accumbens measured in 12 elderly patients compared to controls. These data suggest a sparing of the accumbens from changes associated with aging. There was relative preservation of the nucleus accumbens in 3 patients with anoxic encephalopathy.

CONCLUSIONS

These results show that accumbens was resistant to both aging and anoxia, the mechanism of which is discussed.

Distribution of putative D4 dopamine receptors in postmortem striatum from patients with schizophrenia

The identification of five dopamine receptor subtypes has given the dopamine hypothesis of schizophrenia new life. The D4 receptor is particularly intriguing because it binds clozapine with high affinity. Putative D4 receptors were labeled in postmortem human brain by subtracting the binding of a saturating concentration of 3H-raclopride (6 nM, which labels D2 and D3 receptors) from that labeled by a saturating concentration of [3H]YM 09151-2 (1-1.3 nM, which labels D2, D3, and D4 receptors). In the control brain, putative D4 receptors show a homogenous distribution in striatum and nucleus accumbens. This is also true in schizophrenic brains, although the levels are significantly higher (twofold). These data are inconsistent with mRNA studies that have shown negligible amounts in striatum and accumbens, with modest amounts reported in most of cerebral cortex. These findings suggest that the putative D4 receptors are not synthesized in this region, but are presynaptically localized on striatal afferent terminals. Our findings confirm and extend the report of Seeman et al. (1993). Extension of these findings into the nucleus accumbens is important because of its extensive connections to the limbic system while the putamen is exclusively "motor" striatum.

Dissimilarities between cholinergic and dopaminergic turning elicited by nucleus accumbens stimulation in freely moving rats

Contralateral turning was produced by unilateral injection of carbachol (0.5, 2.5, 5 micrograms) into the nucleus accumbens, but not into the dorsal or ventral striatum. This behaviour was inhibited by muscarinic M1 acetylcholine receptor blockade in the nucleus accumbens, and less effectively by blockade of muscarinic M2 and nicotinic acetylcholine receptors. Unilateral injection of a mixture of the dopamine D1 receptor agonist 1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol (SKF 38393, 5 micrograms) and the dopamine D2 receptor agonist quinpirole (10 micrograms) also produced contralateral turning. The stepping pattern, however, completely differed from that induced by carbachol. The number of carbachol-induced turnings was reduced by dopamine D1 or D2 receptor blockade (8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7-ol (SCH 23390) and l-sulpiride, respectively) in the nucleus accumbens. However, the reduction was due to a change in the turning pattern. Blockade of muscarinic acetylcholine receptors in the nucleus accumbens did not change the contralateral turning induced by unilateral injection of dopamine receptor agonists into the nucleus accumbens. The results demonstrate that there is no functional interaction between the cholinergic and dopaminergic substrates involved, although blockade of the dopamine receptors elicited behavioural deficits that competed with the turning elicited by carbachol. The contralateral turning elicited by carbachol injection into the nucleus accumbens requires an intact dopamine activity at the level of dopamine D1 and D2 receptors in the ipsilateral, but not contralateral, ventrolateral striatum.

Sensitivity of nucleus accumbens neurons in vivo to intoxicating doses of ethanol

The nucleus accumbens septi (NAcc) is considered an important component of the final common pathway involved in the reinforcing properties of ethanol. We studied the effects of intraperitoneal administration of ethanol on spontaneous, glutamate-activated, and fimbria-activated NAcc neurons in acute anesthetized and freely moving unanesthetized rats. Ethanol significantly reduced the firing rate of spontaneous and glutamate-activated NAcc neurons in both electrophysiological preparations. Stimulation of the ipsilateral fimbria evoked single-unit activity in NAcc neurons with two characteristic latencies (early, 7.21 +/- 0.74 msec; late, 18.24 +/- 0.66 msec). Intoxicating doses of ethanol inhibited the recruitment of late, but not of early, fimbria-activated NAcc neurons. These data demonstrate electrophysiological evidence for the existence of neurons in the core region of the NAcc that are sensitive and insensitive to acute systemic ethanol administration.

Effects of ibotenic acid lesions of the nucleus accumbens on instrumental action

In a series of studies, we assessed the effects of ibotenic acid lesions of the nucleus accumbens on instrumental performance in hungry rats. Although these lesions were found to generally impair lever press performance for both food pellets and a sucrose solution, they did not affect sensitivity to changes in the incentive value of the outcome induced either by a shift in food deprivation or a shift in the sucrose concentration. Further, these lesions did not affect sensitivity to a change in the instrumental contingency from response-contingent to non-contingent outcome delivery. In contrast, concurrent assessment of food magazine approach responses found that the lesion induced both a deficit in magazine entry and marked insensitivity to shifts in the incentive value of the outcome and to the changed situation that accompanied the change in instrumental contingency. These results are interpreted as suggesting (1) that nucleus accumbens lesions produce a general deficit in affective arousal; and (2) that the influence of affective mechanisms on instrumental performance may be structurally dissociated from the control of performance mediated by the action-outcome relation.

Reversal of hemiparkinsonian syndrome in nonhuman primates by amnion implantation into caudate nucleus

Although recent animal and human experiments suggest that tissue implantation can ameliorate parkinsonism, there is controversy about what mechanism underlies recovery. Secretion of dopamine from the graft seems unlikely to be the sole restorative factor. Regenerative sprouting by the host brain may also underlie behavioral recovery. Fetal amnion and term amnion, which were shown to produce and secrete a factor that supports the outgrowth of neurite processes in vitro, were implanted in hemiparkinsonian monkeys. Fetal amnion implants induced sprouting of dopaminergic fibers from the host brain and behavioral improvement, despite failure of the grafts to survive. Animals implanted with term amnion also had some sprouted dopaminergic fibers and behavioral improvement, but these were limited and were similar to the recovery, in prior experiments using the same primate model of parkinsonism, of animals that received surgical cavitation only. Recovery after central nervous system grafting with fetal amnion, a fetal accessory tissue, does not require secretion of a deficient neurotransmitter(s) from the graft and occurs despite the failure of graft survival. Recovery after cerebral implantation of fetal tissues appears to depend more on the regenerative and recuperative processes of the host brain than on graft replacement of deficient neurotransmitters or development of functional synaptic connections between the graft and the host brain.

Correlated quantitative studies of the neostriatum, nucleus accumbens, substantia nigra, and ventral tegmental area in normal and weaver mutant mice

Normal mice (+/+) and homozygous weaver mutant mice (wv/wv) at 1 year of age were used for three-dimensional computer-aided reconstructions of the nucleus accumbens (NA) and neostriatum (ST) and for quantitative estimations of the total number of medium-sized neurons in the NA and ST, and for the total number of tyrosine hydroxylase (TH)-containing neurons in the ventral tegmental area (VTA) and substantia nigra (SN). The three-dimensional reconstructions showed that the weaver NA and ST are smaller than they are in +/+. Quantitative volumetric measurements of the NA and ST showed wv/wv were smaller than +/+ by nonsignificant differences of 14% and 13%, respectively. The wv/wv group showed statistically significant depletion of neurons in all four structures. On average, NA neurons are reduced by 27%, ST neurons by 22%, VTA-TH neurons by 40%, and SN-TH neurons by 79%. In wv/wv animals, there was a high positive correlation (r = 0.836) between the numbers of SN-TH neurons and ST neurons and a moderate positive correlation (r = 0.534) between the numbers of SN-VTA neurons and NA neurons. The nuclei in TH-containing neurons in wv/wv and +/+ had the same diameters, but in all animals, the SN-TH neurons contained larger nuclei than the VTA-TH neurons. Cytoarchitectonic measurements in control and weaver NA and ST were also similar. In all animals, the NA contains more densely packed neurons with smaller nuclei than those in the ST.

The neostriatum and nucleus accumbens in parkinsonism-dementia complex of Guam: a pathological comparison with Alzheimer's disease and progressive supranuclear palsy

The neostriatum, nucleus accumbens and basal nucleus of Meynert (bnM) in the parkinsonism-dementia complex of Guam (Guam PDC) were examined immunohistologically, ultrastructurally, quantitatively and topographically, and the results were compared with those in Alzheimer's disease (AD) and progressive supranuclear palsy (PSP). Compared to neurologically normal controls, the number of large neurons in Guam PDC was reduced by approximately 70% in the caudate nucleus and putamen and by more than 90% in the nucleus accumbens. The decreased number of large neurons in the neostriatum was significantly correlated to that in the bnM. The remaining large neurons and many of the medium-sized neurons in the neostriatum and nucleus accumbens were immunopositive for tau protein and contained varying amounts of 21- to 25-nm-wide paired helical filaments (PHFs) admixed with straight tubules. Curly fibers and circularly arranged reactive astrocytes were seen in the nucleus accumbens of many PDC patients. Collectively, these findings, which are similar in part to those of AD and differ from those of PSP, suggest that the large neurons in the neostriatum and nucleus accumbens in Guam PDC degenerate through PHF formation, and that extremely severe loss of large neurons in the nucleus accumbens may be linked to marked degeneration of the limbic and ventral tegmental areas and nucleus dorsal raphe.

Dopamine D2 receptor gene expression in rat lines selected for differences in voluntary alcohol consumption

A selective breeding program has led to the establishment of the alcohol-preferring AA (Alko, Alcohol) and alcohol-avoiding ANA (Alko, Nonalcohol) rat lines. To reveal putative baseline differences in dopamine receptor gene expression and dopamine receptor binding profile in the AA and ANA rat lines, we assessed striatal D2 mRNA levels in these two rat lines. Autoradiographical studies on dopamine D1 and D2 receptors in the striatum and nucleus accumbens were also performed with [3H]SCH 23390 and [125I]iodosulpiride/[3H]spiperone, respectively. The baseline differences in D1 or D2 receptor binding and D2 receptor gene expression between AA and ANA rat lines are marginal, and are not likely to play a role in the genetic background of the differential alcohol drinking behavior of these rat lines.

MRI detects acute degeneration of the nigrostriatal dopamine system after MPTP exposure in hemiparkinsonian monkeys

Exposure to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) can cause an acute chemical toxicity resulting in a parkinsonian state in humans and nonhuman primates. We wished to assess whether the toxicity from MPTP is associated with changes on magnetic resonance images of brain structures containing dopamine neuronal processes or with disrupture of the blood-brain barrier. Normal rhesus monkeys and monkeys at various times after being subjected to unilateral intracarotid injection of MPTP (0.4 mg/kg) were studied with magnetic resonance imaging using T1- and T2-weighted spin-echo and gradient-echo sequences. Disrupture of the blood-brain barrier was assessed also with magnetic resonance imaging after administration of gadolinium-diethylenetriamine pentaacetic acid. Parkinsonian symptoms contralateral to the infused carotid usually appeared within 1 day after MPTP exposure, reaching their peak severity by 7 days, when all monkeys showed clear clinical abnormalities. Magnetic resonance imaging changes developed in concomitance with the clinical signs and were characterized by increased signal intensity on T2-weighted images as well as decreased intensity on T1-weighted images of the ipsilateral caudate and putamen. T2 hyperintensity was also present just dorsal to the pars compacta of the substantia nigra, in the region of the proximal nigrostriatal tract. All magnetic resonance imaging changes dissipated in the next 2 weeks. There were no abnormalities at any time in the globus pallidus, nucleus accumbens, and other structures innervated by the mesocorticolimbic dopamine system. After MPTP exposure, there was no evidence of blood-brain barrier disrupture, suggesting that vasogenic edema was an unlikely factor in the production of the observed abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)

N-methyl-D-aspartic acid-induced lesions of the nucleus accumbens and/or ventral pallidum fail to attenuate lateral hypothalamic self-stimulation reward

The role of ventral striatum in the maintenance and transmission of a hypothalamic intracranial self-stimulation (ICSS) reward signal was investigated using the rate-frequency multiple-curve shift paradigm. The excitotoxin N-methyl-D-aspartic acid (NMDA) was bilaterally administered into the nucleus accumbens (15 micrograms per side), the ventral pallidum (15 micrograms per side) or the juncture between the two structures (20 micrograms per side) creating three lesion groups. Both the nucleus accumbens (NAC) lesion group and the ventral pallidum (VP) lesion group displayed substantial NMDA-induced damage which was generally restricted to the intended limbic structure. The NMDA lesions in the third group displayed extensive damage to both the NAC and VP, as intended, but also typically diffused into adjacent medial structures. NMDA-induced lesions in all groups caused a suppression in motor/performance activity at all currents tested. Contrary to motor effects, reward efficacy was relatively unaffected for the NAC and VP groups. The lack of reward effects may be due to plasticity of neuronal systems and redundancy of circuit connections. However, this explanation is questionable given the fact that NMDA lesions which encompassed both the NAC and VP had little effect on reward efficacy. The above data suggests that the nucleus accumbens and the ventral pallidum are not critical for ICSS rewards stimulation and that hypothalamic ICSS reward signals are processed downstream from these limbic structures.

Chronic morphine impairs axoplasmic transport in the rat mesolimbic dopamine system

Chronic morphine has been shown to decrease levels of neurofilaments (NFs) in the ventral tegmental area (VTA), which plays a critical role in the rewarding properties of morphine and other drugs of abuse. Since decreased levels of NFs are closely associated with a decrease in slow axonal transport, we studied the effect of chronic morphine on axonal transport in the VTA-nucleus accumbens (NAc) pathway. Chronic morphine decreased axonal transport from the VTA to the NAc by 50%. Chronic morphine did not alter axonal transport from the locus coeruleus to several of its projection areas, consistent with the lack of effect of chronic morphine on NFs in this brain region.

Leucotomized schizophrenics lose neurons in the mediodorsal thalamic nucleus

It has previously been shown that chronic schizophrenic patients have a 40-50% reduction in the total number of nerve and glia cells in the mediodorsal thalamic nucleus and the nucleus accumbens compared with controls, while the total neuron and glia number is the same in the two groups in the ventral pallidum. Using new stereological cell counting methods, neuron and glia cell numbers were estimated in the mediodorsal thalamic nucleus, the ventro-medial part of nucleus accumbens and the ventral pallidum in nine brains from leucotomized schizophrenics. This number was compared with counts from control cases and chronic schizophrenics without leucotomy. The results showed that the total number of nerve cells in the mediodorsal thalamic nucleus was statistically significantly reduced from 1.08 x 10(6) in chronic schizophrenics to 0.88 x 10(6) in leucotomized schizophrenics. Total neuron number was statistically significantly reduced in the ventro-medial part of the nucleus accumbens in schizophrenics without further reduction in leucotomized schizophrenics. The total neuron number in ventral pallidum was normal. With frontal leucotomy it is possible to investigate the consequences of disconnection of the prefrontal cortex to central regions in the human brain. The mediodorsal nucleus of thalamus represents a major efferent projection to the prefrontal cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of 6-hydroxydopamine lesions of the nucleus accumbens and the mesolimbic dopamine system on oral self-administration of ethanol in the rat

Rats readily learn to self-administer ethanol using a procedure where ethanol is introduced in the presence of a sweetener. After gradual removal of the sweetener, sufficient quantities of ethanol are self-administered in non fluid-, non food-deprived rats to produce reliable blood ethanol concentrations. Previous studies using this self-administration model have shown that dopamine receptor antagonists injected systemically or directly into the terminal regions of the mesolimbic dopamine system decrease lever pressing for ethanol, suggesting an important role for dopamine in ethanol reinforcement. The purpose of the present study was to test the hypothesis that the mesolimbic dopamine system is a critical substrate for ethanol reinforcement. Results of this study show that 6-hydroxydopamine (6-OHDA)-induced lesions of the mesolimbic dopamine system, sufficient to produce a 93% depletion of dopamine in the nucleus accumbens, an 85% depletion in the olfactory tubercle, an 82% depletion in the frontal cortex and a 78% depletion in the amygdala, failed to alter ethanol self-administration as measured by the total lever presses. However, the 6-OHDA lesion rats showed an altered pattern of responding for ethanol: an increase in the slope of the regression line of cumulative responses vs. time and an increase in the frequency of responding at inter-response intervals of 4-6 and 6-8 s post 6-OHDA lesion; suggesting that this lesion produced a subtle change in motor or attentional function. The results of this study indicate that while the mesolimbic dopamine system may contribute to the reinforcing actions of ethanol, it is not critical for maintaining ethanol reinforcement.

Reevaluation of the two-component hypothesis for turning behaviour by manipulating activities in the striatum and the nucleus accumbens of intact rats

The role of dopamine D1 and D2 receptor stimulation in the production of turning behaviour in rats was studied. In rats pretreated with unilateral injections of the non-selective dopamine D1/D2 receptor antagonist, cis(Z)-flupentixol (10 micrograms/0.5 microliter), into the ventral striatum, quinpirole (1, 3, 5, 10 mg/kg i.p.), a selective dopamine D2 receptor agonist, induced dose-dependent turning behaviour, while SKF 38393 (1, 3, 5, 10 mg/kg i.p.), a selective dopamine D1 receptor agonist, did not. The effect of the two drugs together was much greater than the effect of quinpirole alone and was reduced by additional blockade of dopamine D1/D2 receptors in either the ipsilateral or contralateral nucleus accumbens. The role of the nucleus accumbens in turning behaviour was determined from the effects of unilateral injections of SKF 38393 and quinpirole into the nucleus accumbens. The results show that unilateral injections of a mixture of the two drugs (SKF 38393 5 micrograms + quinpirole 10 micrograms/0.5 microliter) into the nucleus accumbens produced turning while injections of single drugs did not. Turning was abolished by the blockade of dopamine D1/D2 receptors in the ipsilateral but not contralateral ventral striatum. Turning was also reduced by the blockade of the contralateral nucleus accumbens. Moreover, turning was not produced by injections of the drug mixture into the dorsal or ventral striatum.

Regionally selective deficits in uptake sites for glutamate and gamma-aminobutyric acid in the basal ganglia in schizophrenia

In a post-mortem study of schizophrenic and control subjects, the sodium-dependent binding of D-[3H]aspartate and [3H]nipecotic acid were used to investigate uptake sites of glutamate and gamma-aminobutyric acid (GABA), respectively, in subcortical brain regions. Binding to the glutamate uptake site was substantially reduced in both the putamen and lateral pallidum of the schizophrenic subjects. Binding to the GABA uptake site was substantially reduced in the putamen; smaller reductions were apparent in the caudate nucleus and lateral pallidum. The results suggest that glutamatergic and GABAergic mechanisms in the basal ganglia are abnormal in schizophrenia. These abnormalities could be relevant to the development of psychosis but could also relate to the spectrum of mild motor disturbances often described in the disease.

BEHAVIOURAL ANALYSIS OF UNILATERAL MONOAMINE DEPLETION IN THE MARMOSET

Unilateral stereotaxic injections of 6-hydroxydopamine (6-OHDA) into the nigrostriatal bundle of marmosets (Callithrix jacchus) produced substantial losses of tyrosine hydroxylase immunoreactive neurons from the substantia nigra, and mean dopamine (DA) depletions of 98-99% in the caudate nucleus, putamen and nucleus accumbens, and of 91-97% in frontal cortex, on the side of the lesion. Noradrenaline (NA) and 5-hydroxytryptamine (5-HT) levels were also affected. Behavioural tests conducted pre-operatively and at regular intervals during the 6 mths following surgery revealed persistent deficits in the lesioned marmosets as a group compared with sham-lesioned controls, although individual marmosets sometimes recovered or showed no initial deficit on some tests. The main behavioural effects of the lesion were as follows: (i) an increase in the time spent with the head positioned ipsilaterally with respect to the rest of the body; (ii) ipsilateral spontaneous and amphetamine-induced rotation, although occasional intermittent periods of contralateral rotation and head biases were also recorded; (iii) contralateral apomorphine-induced rotation; (iv) reduced spontaneous activity; (v) ipsilateral hand preference on a conveyor belt task, although hand skill (measured as percentage errors when the speed of the belt was increased) was not affected; (vi) neglect of contralateral stimuli, both at the conveyor belt where lesioned monkeys often failed to respond on trials on which apple pieces arrived from the contralateral side, and on a test of sensorimotor neglect in which adhesive labels were placed around both feet. Comparisons of biochemical measures of the lesion with behavioural scores in individual monkeys suggest that DA depletions in excess of 95% are essential for long-term behavioural deficits.

The effects of excitotoxic lesions of the nucleus accumbens on a matching to position task

The effects of bilateral ibotenic acid lesions of the nucleus accumbens in the rat were examined on a delayed matching to position task. The lesion induced a stable delay-dependent performance deficit suggestive of a short-term memory problem. Following analysis of the impaired performance on trials with long delays, using measures akin to signal detection indices, the deficit was interpreted as being largely due to the intrusion of a side-dependent response bias. Low-dose amphetamine (0.75 mg/kg) produced a similar disruption in the sham-operated rats, both in terms of accuracy impairment and degree of strategical bias. As well as mimicking the effects of low-dose amphetamine in sham-operated rats, the lesion also protected against the disruptive effects of the drug at low doses. Whilst exhibiting no performance deficit when the matching schedule lacked a delay component, the lesioned rats were very significantly impaired in switching their response strategies when exposed to a series of reversals. In addition, the lesioned rats were remarkably resistant to an extinction procedure. Both these findings indicate that the lesioned rats were unable to exhibit flexibility in their response patterns. These results, taken together with those of the delayed matching procedure, imply that one of the functions of the intact nucleus accumbens is to inhibit habitual responding under conditions of non-reward and low stimulus control, possibly via its connections to the dorsal striatal system.

Suppression of noradrenergic innervation compensates for behavioral deficits induced by lesion of dopaminergic terminals in the lateral septum

Spontaneous alternation which is disrupted by lesion of septal dopaminergic (DA) afferents was chosen as a behavioral marker for the study of functional interactions between DA and noradrenergic (NA) innervation of the lateral septum. Three groups of rats were studied: a solvent group which received only vehicle injection, and two lesioned groups, one with DA lesion and the second with simultaneous DA + NA lesion of the septal innervation. DA lesion was produced by infusing 6-hydroxydopamine (6-OHDA) into the lateral septum after pretreatment with desmethylimipramine (DMI) injected intraperitoneally. The DA + NA lesion was produced by infusing 6-OHDA without DMI pretreatment. The lesion of DA innervation alone led to a disturbance of alternation behavior in a Y-maze, but performance was not affected by the combined DA + NA lesion. The group with septal DA lesion was then injected with 6-OHDA into the pedunculus cerebellaris superior (PCS) in order to destroy NA efferents from the locus coeruleus. The two other groups were sham-operated. After post-operative recovery, the rats were retested for spontaneous alternation. The rats with the PCS NA lesion subsequent to the DA septal lesion displayed normal alternation behavior. Their performance was not different from that of animals with both NA and DA lesions in the septum. Thus the NA lesion appears to prevent the alternation deficits induced by the DA septal lesion, and also abolishes the deficits induced by the prior DA lesions. These results may have therapeutic implications.