Role of basal ganglia and ectostriatum in the context-dependent properties of the optocollic reflex (OCR) in the pigeon (Columba livia): a lesion study

The possible participation of basal ganglia and associated structures [dorsal striato-pallidum, nucleus spiriformis lateralis (SpL), ectostriatum] in the elaboration of the optocollic reflex (OCR) was investigated by making bilateral chemical lesions (ibotenic acid). Previous data have shown that both the slow and fast phases of the OCR are dependent on the behavioural context. The slow phase velocity (SPV) and the peak velocity of fast phases obtained in non-flying pigeons ('resting condition') were enhanced in pigeons in which a flying posture was experimentally provoked ('flying condition'). Therefore, the effect of lesions was analysed in pigeons standing in the 'resting' or 'flying' condition. In the 'resting' as in the 'flying' condition, all the lesions provoked a decrease in SPV, which augmented with the stimulation velocity. Velocity step stimuli revealed greater OCR deficits than velocity ramp stimuli. Extensive lesions (including the striato-pallidum, ectostriatum and a part of the neostriatum), as well as SpL lesions, provoked a greater SPV decrease over a longer time than lesions restricted to the striato-pallidum or the ectostriatum. The peak velocity of fast phases was only reduced by the 'extensive lesion' in the 'flying condition'. The present data show that the basal ganglia system is involved in the elaboration of optokinetic responses and suggest that, to work in an optimal range, the optokinetic centres need to receive integrated information from basal ganglia in addition to direct visual input.

A new subdivision, marginal division, in the neostriatum of the monkey brain

A new subdivision, the "marginal division" (MrD), was discovered at the caudal border of the striatum and surrounds the rostral edge of the globus pallidus in the rat brain in our previous studies. The neuronal somata of the MrD are mostly fusiform in shape with their long axes lining dorsoventrally. The MrD is more densely filled with substance P (SP)-, Leucine-enkephalin (L-Enk)-, dynorphin B-, neurotensin-, somatostatin- and cholecystokinin (CCK)-immunoreactive fibers and terminal-like structures than the rest of the striatum. The MrD was confirmed in the cat neostriatum as well. The present study intended to explore whether the MrD exists in the monkey neostriatum (putamen) with Nissl, histochemical and immunohistochemical methods. A band of fusiform neurons were obviously identified at the caudomedial edge of the putamen. These neurons lie outside the lateral medullary lamina and indirectly surround the rostrolateral border of the globus pallidus. The abundance of SP-, L-Enk-, neuropeptide Y-, CCK-, dopamine- and serotonin-positive fibers and terminal-like structures with a few positive fusiform neurons accumulating at the caudomedial border of the putamen obviously distinguishes this zone from the rest of neostriatum and globus pallidus. The acetylcholinesterase (AChE) positive and nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) containing fusiform neurons are distinctly visualized in the same zone. The morphological figure and the location of these neurons, and the histochemical and immunohistochemical characteristics of this area coincide well with those of the MrD in the rat and cat striatum. This study thus convincingly identifies the existence of the MrD in the monkey neostriatum. It is fairly asserted that the MrD is a universal structure in the mammalian brain.

Regional and cellular localisation of GABA(A) receptor subunits in the human basal ganglia: An autoradiographic and immunohistochemical study

The regional and cellular localisation of gamma-aminobutyric acid(A) (GABA(A)) receptors was investigated in the human basal ganglia using receptor autoradiography and immunohistochemical staining for five GABA(A) receptor subunits (alpha(1), alpha(2), alpha(3), beta(2, 3), and gamma(2)) and other neurochemical markers. The results demonstrated that GABA(A) receptors in the striatum showed considerable subunit heterogeneity in their regional distribution and cellular localisation. High densities of GABA(A) receptors in the striosome compartment contained the alpha(2), alpha(3), beta(2, 3), and gamma(2) subunits, and lower densities of receptors in the matrix compartment contained the alpha(1), alpha(2), alpha(3), beta(2,3), and gamma(2) subunits. Also, six different types of neurons were identified in the striatum on the basis of GABA(A) receptor subunit configuration, cellular and dendritic morphology, and chemical neuroanatomy. Three types of alpha(1) subunit immunoreactive neurons were identified: type 1, the most numerous (60%), were medium-sized aspiny neurons that were immunoreactive for parvalbumin and alpha(1), beta(2,3), and gamma(2) subunits; type 2 (38%) were medium-sized to large aspiny neurons immunoreactive for calretinin and alpha(1), alpha(3), beta(2,3), and gamma(2) subunits; and type 3 (2%) were large sparsely spiny neurons immunoreactive for alpha(1), alpha(3), beta(2,3), and gamma(2) subunits. Type 4 neurons were calbindin-positive and immunoreactive for alpha(2), alpha(3), beta(2,3), and gamma(2) subunits. The remaining neurons were immunoreactive for choline acetyltransferase (ChAT) and alpha(3) subunit (type 5) or were neuropeptide Y-positive with no GABA(A) receptor subunit immunoreactivity (type 6). The globus pallidus contained three types of neurons: types 1 and 2 were large neurons and were immunoreactive for alpha(1), alpha(3), beta(2,3), and gamma(2) subunits and for parvalbumin alone (type 1) or for both parvalbumin and calretinin (type 2); type 3 neurons were medium-sized and immunoreactive for calretinin and alpha(1), beta(2, 3), and gamma(2) subunits. These results show that the subunit composition of GABA(A) receptors displays considerable regional and cellular variation in the human striatum but are more homogeneous in the globus pallidus.

Medial prefrontal and neostriatal lesions disrupt performance in an operant delayed alternation task in rats

An operant version of the classical delayed alternation task is presented and applied to evaluate the effects of bilateral prefrontal and striatal lesions in rats. Retractable levers in a conventional operant chamber control discrete trial opportunities for making sequential choice responses to the two sides, and the rats are required to maintain repeated nose poke responses to a central panel during the delay interval, which is randomly varied. The operant task provides measures of the speed and accuracy of response alternation and side bias; analysis at different delay intervals provides an index of the memory demands of accurate performance; and analysis of accuracy depending on the response on preceding trials provides measures of proactive interference and perseveration. Following pretraining in the task contingencies, both striatal and prefrontal lesions induced profound deficits in task accuracy, with no change in side bias and only small changes in movement times. The deficit in the prefrontal lesion group recovered more rapidly, neither group showed any change in sensitivity to proactive interference, while the rats with striatal lesions alone exhibited an increased tendency to perseverate incorrect responses on either side. We conclude that the operant delayed alternation task should assist analysis of fronto-striatal function in rats as well as be useful for the analysis of strategies for fronto-striatal repair.

Absence of striatal volume differences between depressed subjects with no comorbid medical illness and matched comparison subjects

OBJECTIVE

The striatum (caudate and putamen) appears to be important in the pathogenesis of depression. Some studies show smaller than normal striatal structure volumes in depressed subjects. This study compared striatal volumes in depressed and nondepressed women, screened to exclude major cerebrovascular disease risk factors and comorbid medical illness.

METHOD

Caudate and putamen volumes were measured from magnetic resonance imaging scans of 24 depressed women and 24 matched nondepressed comparison subjects.

RESULTS

Caudate and putamen volumes were not significantly different between depressed and nondepressed groups.

CONCLUSIONS

These findings differ from those of previous studies, possibly because of the exclusion of subjects with cerebrovascular risk factors in this study.

Responses of single neurons in the toad's caudal ventral striatum to moving visual stimuli and test of their efferent projection by extracellular antidromic stimulation/recording techniques

Previous work in anuran amphibians has shown that activity in the caudal ventral striatum correlates with visuomotor activity: orienting responses toward prey fail to occur after striatal lesions. Thus it has been suggested that the striatum influences visually guided behavior. Therefore, the present study investigates visual response properties from neurons recorded in the striatum. Extracellular recordings of 104 single neurons of the cane toad's (Bufo marinus) caudal ventral striatum (STR) reveal five different response properties: resting discharge activity uninfluenced by the visual test stimuli (group STR1, 24.0%); resting discharge activity increased by any moving visual object (STR2, 31.7%); preference to moving compact objects (STR3, 15.4%); preference to certain configurational moving objects (STR4a and b, 13.5%), and resting activity reduced by visual stimuli (STR5, 15.4%). The receptive fields of these neurons encompassed the contralateral (46%) or the entire field of vision (54%). Of the neurons recorded in the striatum, 34% responded to electrical stimuli applied in the rostral diencephalon to the ipsilateral lateral forebrain bundle (LFB) which connects the striatum with the optic tectum (e.g. either directly or via pretectum or tegmentum). Various electrically driven STR neurons (40%) have axons that project caudally through the LFB, which was suggested by their antidromic activation in response to electrical stimuli applied to the LFB in the rostral diencephalon. In the present study, the main striatal output is mediated by 'motion detectors' (STR2) and 'compact object perceivers' (STR3). It is suggested that the caudal ventral striatum is involved in visual attentional processes that allow the translation of perception into action.

Anatomical and functional reconstruction of the nigrostriatal system in vitro: selective innervation of the striatum by dopaminergic neurons

To study development of the nigrostriatal pathway in an in vitro model system, organotypic slices obtained from rat pups (P4) and containing the striatum and the cortex were grown together with apposed embryonic (E13.5) mesencephalic blocks according to the static slice culture method of Stoppini et al. (1991; J. Neurosci. Methods 37:173-182). Under these conditions, mesencephalic dopaminergic (DA) fibers rapidly grow through the slice, preferentially its striatal portion. This innervation provides a true synaptic innervation to the striatum, as shown by the presence of DA terminals on striatal neurons. DA fibers are able to exert a functional influence, as seen by their ability to modulate c-Fos expression in striatal neurons in the same way as in vivo. Thus, blockade, under basal conditions, of the effect of spontaneously released dopamine by the D2 receptor antagonist haloperidol leads to the activation of c-Fos expression in the striatum. Furthermore, stimulation of DA release by amphetamine induces striatal c-Fos expression in a D1 receptor-dependent manner. Next, the mechanisms of the selective striatal innervation were examined. Indeed, DA fibers innervated specifically the striatum, avoiding the cortical portion of the slice. This selectivity seems to be specific for DA neurons; no selectivity could be observed when noradrenergic neurons were substituted for DA neurons. Short-term cocultures in a collagen gel of mesencephalic blocks with striatal blocks failed to reveal any oriented outgrowth of DA fibers from the mesencephalon, suggesting that the selective innervation observed in the organotypic slices results from some contact-dependent, presumably adhesive interactions rather than from the presence of some diffusible substance orienting the growth of DA fibers towards the striatum. On the other hand, DA neurons seeded onto striatal slices did not attach selectively onto the striatal portion of the slice, indicating that the putative specific adhesive interactions governing the selective striatal innervation are not the same as those determining the adhesion of the DA neurons. These results show that cocultures of cortex-striatum and mesencephalic slices result in a system that displays a number of the morphological and functional traits of the normal nigrostriatal system and that can be relied on as a good in vitro model of in vivo development.

Dopamine receptor blockade in the nucleus accumbens inhibits maternal retrieval and licking, but enhances nursing behavior in lactating rats

Maternal behaviors were recorded in rats after a 4-h dam-litter separation and intracranial microinfusion of saline on Day 6 postpartum or cis-flupenthixol (FLU), a dopamine (DA) receptor antagonist, on Days 7-9, within the nucleus accumbens (NA) or dorsomedial striatum (DMS) bilaterally (5, 10, or 20 micro/microL/side), or the lateral ventricle (LV) unilaterally (20 or 40 micro/microL). The number of pups retrieved was inhibited in a dosage-dependent manner by FLU within the NA, but not in other sites. Pup retrieval did not occur within 5 min after 20 microg FLU in five out of nine NA dams; only in these dams did infusions include the shell region of the NA. Duration of pup licking was dose dependently decreased by FLU, the most within the NA, and to a lesser extent within the DMS. Nursing behavior in the kyphotic (upright, dorsally arched) posture, initiated in the absence of pup retrieval by placing the dam over the gathered pups, was not inhibited by intracranial FLU in any site assessed, but rather lasted longer after FLU in NA dams. These various effects of FLU, especially in NA, may be related to modest increases in catalepsy.

Afferent and efferent connections of the caudolateral neostriatum in the pigeon (Columba livia): a retro- and anterograde pathway tracing study

The avian caudolateral neostriatum (NCL) was first identified on the basis of its dense dopaminergic innervation. This fact and data from lesion studies have led to the notion that NCL might be the avian equivalent of prefrontal cortex (PFC). A key feature of the PFC is the ability to integrate information from all modalities needed for the generation of motor plans. By using antero- and retrograde pathway tracing techniques, we investigated the organization of sensory afferents to the NCL and the connections with limbic and somatomotor centers in the basal ganglia and archistriatum. Data from all tracing experiments were compared with the distribution of tyrosine-hydroxylase (TH)-immunoreactive fibers, serving as a marker of dopaminergic innervation. The results show that NCL is reciprocally connected with the secondary sensory areas of all modalities and with at least two parasensory areas. Retrograde tracing also demonstrated further afferents from the deep layers of the Wulst and from the frontolateral neostriatum as well as the sources of thalamic input. Efferents of NCL project onto parts of the avian basal ganglia considered to serve somatomotor or limbic functions. Projections to the archistriatum are mainly directed to the somatomotor part of the intermediate archistriatum. In addition, cells in caudal NCL were found to be connected with the ventral and posterior archistriatum, which are considered avian equivalents of mammalian amygdala. All afferents and projection neurons were confined to the plexus of densest TH innervation. Our results show that the NCL is positioned to amalgamate information from all modalities and to exert control over limbic and somatomotor areas. This organization might comprise the neural basis for such complex behaviours as working memory or spatial orientation.

Integration and segregation of limbic cortico-striatal loops at the thalamic level: an experimental tracing study in rats

The frontal lobe and the basal ganglia are involved in a number of parallel, functionally segregated circuits. Information is thought to pass from distinct parts of the (pre)frontal cortex, via the striatum, the pallidum/substantia nigra and the thalamus, back to the premotor/prefrontal cortices. Currently, different views exist as to whether these circuits are to be considered as open or closed loops, as well as to the degree of interconnection between different circuits. The main goal of the present study is to answer some of these questions for the limbic corticostriatal circuits. The latter circuits involve the nucleus accumbens, the ventral pallidum/dorsomedial substantia nigra pars reticulata, the medial parts of the mediodorsal and ventromedial thalamic nuclei and the prefrontal cortex. Within the nucleus accumbens, a core and a shell region are recognized on the basis of anatomical and functional criteria. The shell of the nucleus accumbens projects predominantly to the mediodorsal, the midline and the reticular thalamic nuclei via the ventral pallidum, whereas the core reaches primarily the medial part of the ventromedial thalamic nucleus, the intralaminar and mediodorsal thalamic nuclei via a relay in the dorsomedial substantia nigra pars reticulata. By means of double labeling experiments with injections of anterograde tracers in both the ventral pallidum and the substantia nigra of rats, we were able to demonstrate that circuits involving the shell and the core of the nucleus accumbens remain largely segregated at the level of the thalamus. Only restricted areas of overlap of ventral pallidal and reticular nigral projections occur in the mediodorsal and ventromedial thalamic nuclei, which allows for a limited degree of integration, at the thalamic level, of information passing through the two circuits.

Striatal A2A adenosine receptors differentially regulate spontaneous and K+-evoked glutamate release in vivo in young and aged rats

The effect of the adenosine A2A receptor agonist CGS 21680 on glutamate and aspartate release was investigated in the striatum of young and old rats by microdialysis experiments. CGS 21680 (10 microM) significantly increased glutamate and aspartate spontaneous outflow in young but not in old rats. On the contrary, CGS 21680 induced the same decrease in K+-evoked glutamate outflow in both young and aged rats. A lower dose of CGS 21680 (1 microM) failed to modify either spontaneous or K+-evoked outflow. It is suggested that the opposite effects of the A2A agonist on excitatory amino acid outflow may be respectively mediated by striatal A2A adenosine receptors located on glutamatergic terminals and on the striatal indirect output pathway.

The dorsocaudal neostriatum of the domestic chick: a structure serving higher associative functions

The dorsocaudal neostriatal (dNC) complex consists of at least three functionally distinct subregions and is part of an 'imprinting' pathway, which interconnects several forebrain regions that are known to be involved in juvenile learning. Based on its anatomical features, at least one subregion of the dNC complex, the neostriatum dorsocaudale (Ndc) may be considered as the equivalent of the mammalian polysensory association cortices. Several lines of evidence point to a role for this forebrain region in learning and memory formation. After auditory or visual imprinting changes of stimulus-evoked metabolic activities and of synaptic densities have been measured in the Ndc. Pharmacological behavioral studies revealed that the activation of NMDA receptors plays a critical role during this learning process and that NMDA receptor activation is required for the associated metabolic and synaptic changes. In addition to glutamatergic afferents, anatomical studies revealed a massive input from monoaminergic and peptidergic pathways into the dNC complex, suggesting a modulatory role for these systems during imprinting. The results presented here together with data from other avian species support the view that the dNc complex, and in particular the Ndc, plays an important role in juvenile and adult learning.

Double anterograde tracing of outputs from adjacent "barrel columns" of rat somatosensory cortex. Neostriatal projection patterns and terminal ultrastructure

The sensory input to the neostriatum from groups of cortical cells related to individual facial vibrissae has been investigated at both light- and electron-microscopic resolution. The purpose of the study was to establish the extent to which corticostriatal input maintains the anatomical coding of spatial information that is present in cortex. A double anterograde tracing method was used to identify the output projections from groups of adjacent neurons in different barrel columns, so that the anatomical relationships between two groups could be studied throughout their length. Adjacent whiskers are represented in adjoining cortical barrels and an examination of corticostriatal projections from these reveals two patterns of projection. In one, the anatomical topography is partially preserved; the barrels are represented in adjoining, discrete, areas of the somatosensory neostriatum. In the second projection pattern, the neostriatal innervation is diffuse and adjacent barrels are represented in overlapping regions of the neostriatum. Moreover, the fibres are thinner, have smaller boutons, and are present in both the ipsilateral and contralateral neostriatum. The two systems also enter the neostriatal neuropile separately. The discrete topographic system enters the adjacent neostriatum as collaterals which leave the descending corticofugal fibres at right angles, while the diffuse system enters directly from the corpus callosum at an acute angle. Examination of the neostriatal terminal fields by correlated light and electron microscopy, shows that characteristic axospinous terminals on spiny neurons are made by both groups of cortical fibres, although they differ in their size and morphology. It is concluded that at least two corticostriatal pathways arise from the barrel cortex. One connection maintains some of the anatomical code implicit in the barrel pattern of primary somatosensory cortex, but another, more diffuse, system is overlaid upon it which may carry different information from this complex area of cortex.

Differential alterations in basal and D-amphetamine-induced behavioural pattern following 6-OHDA or ibotenic acid lesions into the dorsal striatum

It is well known that the corpus striatum is related to the sterotyped activation induced by several psychostimulants. In this study we analyzed the effects of 6-OHDA, in comparison with those of ibotenic acid lesions, into the dorsal striatum, on the behavioural pattern induced by saline or D-amphetamine treatment. A computerized technique for recording the animal motor activity was developed in order to define in a detailed way the behavioural profile in lesioned and sham-operated rats induced by the saline or D-amphetamine treatment. A 6-OHDA lesion into the dorsal striatum modified the basal behavioural pattern which was mainly characterized by reduced motor activation while ibotenic acid lesion affected the structure of the basal behavioral pattern. D-Amphetamine administration in 6-OHDA lesioned rats induced a behavioural stimulation, but a decreased motor and stereotyped activation was observed compared to the sham-operated animals treated with D-amphetamine. In contrast, D-amphetamine administration in the ibotenic acid-lesioned rats induced a motor and stereotyped activity which was not reduced compared to that seen after D-amphetamine treatment in sham-operated rats. These results suggest that these two types of lesion induced differential effects on the behavioural pattern either after saline or after D-amphetamine administration. Dopaminergic neurotransmission in the dorsal striatum plays a permissive role on the emergence of the behavioural responses, while the dorsal striatum circuitry plays a crucial role on the organization of the behavioural pattern. In addition, dopaminergic activity in this structure serves a primary control in the D-amphetamine-elicited motor activation or stereotypy, while the striatal structure is involved in the shaping of the D-amphetamine behavioural pattern.

Loss of dopamine D2 receptors in Alzheimer's disease with parkinsonism but not Parkinson's or Alzheimer's disease

A significant proportion of patients with Alzheimer's disease (AD) exhibit extrapyramidal features that are referred to as parkinsonism (AD/Park) to distinguish the clinical and pathological features that differ from Parkinson's disease (PD). Previous results from this laboratory have shown that, although the presynaptic components of the dopamine (DA) system are markedly affected in AD/Park, the pathology is not similar to PD (Murray et al. 1995; Joyce et al. 1997). In the present study, we determined whether the parkinsonian symptoms in AD/Park might also reflect changes in numbers of postsynaptic DA receptors. We analyzed the binding of [125I]epidepride biding to DA D2/D3 receptors and [3H]SCH 23390 to D1 receptors by autoradiography in the striatum of six patients with PD, nine patients with AD, seven patients with AD/Park, and 14 neurologically intact control subjects. D2 receptors were reduced in the caudate and putamen of the AD/Park group (by 42 and 27% of controls, respectively) but not reduced in AD or PD. D1 receptors were elevated by 36% in the putamen of the PD group. Dopamine receptor changes are, therefore, not similar in PD, AD, and AD/Park. The elevation in D1 receptors in PD may contribute to the unwanted side effects of L-dopa treatment. The loss of D2 receptors in AD/Park, not observed in AD lacking overt parkinsonian symptomatology, may contribute to the presence of parkinsonian features and lack of responsiveness to L-dopa.

Progesterone facilitates the acquisition of avoidance learning and protects against subcortical neuronal death following prefrontal cortex ablation in the rat

Following a cortical injury, neurons in areas near and connected to the site of injury begin to degenerate. The observed neuronal death may contribute to the severity of the observed behavioral impairments. The purpose of the present study was to examine if progesterone, a hormone known for its effectiveness at reducing cerebral edema, could protect against secondary neuronal death and facilitate the acquisition of an avoidance learning task in an ablation model of cortical injury. Rats served as sham controls or received bilateral ablation of the medial prefrontal cortex followed by a 10-day regimen of progesterone (4 mg/kg) or oil vehicle (1 ml/kg) beginning 1 h after cortical lesions. Progesterone-treated lesion rats showed a significant facilitation of avoidance learning compared to oil-treated lesion controls. In addition, progesterone-treated lesion animals did not differ from either progesterone- or oil-treated sham controls in avoidance learning. Anatomical analysis revealed that progesterone treatment decreased the amount of neuronal death seen in the striatum and the mediodorsal nucleus of the thalamus. The findings are consistent with the notion that progesterone is an effective neuroprotective agent and suggest that the hormone can reduce the behavioral impairments associated with frontal cortical ablation injury.

Selective deficits in reversal learning after neostriatum caudolaterale lesions in pigeons: possible behavioral equivalencies to the mammalian prefrontal system

The neostriatum caudolaterale (NCL) of birds is thought to be equivalent to the mammalian prefrontal cortex (PFC) due to its dense dopaminergic innervation, its associative structure, and its importance for cognitive tasks which are known to be affected in mammals with prefrontal lesions. The aim of the present study was to analyze the functional importance of the NCL and its main thalamic afferent structure, the n. dorsolateralis posterior thalami (DLP), in reversal and go/no-go tasks, two behavioral procedures which are often used to assess mammalian prefrontal functions. Using a multiple regression analysis in which structure-specific lesion extents are correlated with different postoperative behavioral measures, the specific contribution of the relevant structures were differentiated from the neighbouring areas CDL (area corticoidea dorsolateralis) and NC (neostriatum caudale). The analyses showed a highly significant contribution of the NCL to reversal but not to go/no-go or to visual discrimination performance, while all other structures under analysis had no impact on any behavioral measure. These results underline the specific contribution of the pigeons' NCL on a subset of cognitive tasks which are known to be affected by prefrontal lesions in mammals.

The selectivity of sexual responses to song displays: effects of partial chemical lesion of the HVC in female canaries

By stimulating female canaries with computer edited songs, we investigated the involvement of the caudal nucleus of the ventral hyperstriatum or high vocal center (HVC) in the selectivity of sexual responsiveness to different kinds of conspecific songs. Due to the fact that the types of conspecific song phrases act as relevant cues to give song its sexual potency, we compared courtship responses to two conspecific songs, highly sexually-stimulating and weakly sexually-stimulating song, before and after the partial ibotenate lesion of the HVC. Sexual responses to heterospecific song were also tested. Copulation solicitation displays were used as an index of female responses. The partial chemical lesions of the HVC whatever the HVC portion damaged affected female bird behavior; they responded more strongly to weakly sexually-stimulating song and to heterospecific song than before the lesions. However, the conspecific sexually attractive song continued to elicit the highest level of sexual displays. None of the control birds ever altered their pattern of responses to the three song types. The results suggest that the HVC is part of the neural network engaged in the control of sexual preferences to conspecific song displays.

Effects of intrastriatal cannabinoids on rotational behavior in rats: interactions with the dopaminergic system

The effect of unilateral intrastriatal cannabinoid receptor stimulation on rotational behavior in rats was explored. The potent cannabinoid agonist CP 55,940 (5 microg/0.5 microl) induced contralateral turning when microinjected unilaterally into the striatum. The D2 dopamine agonist quinpirole reversed this contralateral rotation but failed to affect motor behavior on its own. Finally, the D1 dopamine agonist SKF 82958 inhibited movement when administered into the striatum and this inhibition was reversed by co-administration of the cannabinoid agonist. Surprisingly, microinjections of the cannabinoid agonist into the striatum induced movement through activation of the striatonigral pathway and/or inhibition of the striatopallidal pathway, while the D1 dopamine agonist produced the opposite effect.

Stimulation of the neostriatum induces jaw-opener muscle activity, but not jaw-closer muscle activity: an electromyographic study in the rat

Microstimulation was carried out at 36 sites in the dorsal striatum in lightly anesthetized rats. Only at two sites, microstimulation of 40 microA induced a considerable EMG activity in the jaw-opener (anterior digastric muscle). No activity was evoked in the jaw-closers (masseter and temporalis muscles). The effective sites were confirmed to be localized in a small central region of the striatum at a level corresponding to the caudal end of the anterior commissure. The effect was ascribed to excitation of a small cluster of striatal neurons, rather than to antidromic activation of cerebral cortical neurons through their axons within the striatum. (1) The effect was abolished after destruction of neurons in the striatal region by injecting kainic acid. (2) The effect was not influenced by ablation of the neocortex. (3) Microinjection of kainic acid into the striatal region also induced the similar muscle activity in the jaw-opener, but not in the jaw-closers.

D1 dopamine receptors and the reversal of isolation-induced behaviors in mice

In a previous study, it was demonstrated that the high rates of social reactivity exhibited by isolated male mice in a dyadic encounter were mediated, at least in part, by an increased sensitivity of the D1 dopamine receptors. The present research was guided by the hypothesis that the behavioral effects of isolation are reversible, and that changes in dopaminergic function support this reversibility. To this end, mice selectively bred for high and low levels of aggression were reared in isolation from weaning (21 days) to puberty (45 days), at which point they were either assigned to groups or left in isolation until day 69. By comparison to the continuous isolation condition, mice that eventually formed groups exhibited significantly less reactivity in a dyadic test conducted on day 69, showed a reduced response to dihydrexidine (DHX), and a decreased density of D1 dopamine receptors. This experiment provided evidence for the plasticity of the neurobiological system supporting reactive responses, and confirmed the view that its functional organization is open to experientially-induced changes.

Role of the cholinergic systems of the dorsal and ventral striatum of the rat brain in controlling learned movements

Comparative studies were performed of the effects of injections of a cholinergic agonist (carbachol) and antagonist (scopolamine) into the ventral and dorsal striatum on the performance of a learned movement involving prolonged maintenance of extension of the forelimb in rats. Doses of carbachol (0.03-3.00 micrograms) into the ventral striatum were accompanied by increases in the numbers of movements with prolonged maintenance of extension with application of pressure against an obstacle, with a simultaneous decrease in the percentage of rapid nonreinforced movements (by an average of 18.8%). Injections into the dorsal striatum disrupted slow movements which were not reinforced during training, on a background of stable performance of the learned reflex. Doses of scopolamine (0.3-3.0 micrograms) into both the dorsal and ventral parts of the striatum produced increases (by 22.7 +/- 8.2% and 68.9 +/- 14.3%) in the numbers of rapid nonreinforced movements typical of the repertoire of untrained animals. These data led to the suggestion that the cholinergic system of the ventral striatum is involved in the maintenance of forelimb muscle tone in rats during the performance of movements in which pressure is applied to an obstacle. The cholinergic system of the dorsal striatum does not have this property, but plays a significant role in the process of learning new sensory-controlled movements.

Organization of the dorsocaudal neostriatal complex: a retrograde and anterograde tracing study in the domestic chick with special emphasis on pathways relevant to imprinting

In the forebrain of domestic chicks, a network of distinct regions is crucially involved in auditory and visual filial imprinting. Among these areas, a distinct part of the dorsocaudal neostriatal complex (dNC complex), termed neostriatum dorsocaudale (Ndc), was recently discovered by its enhanced metabolic activity during the presentation of auditory and visual imprinting stimuli. Since there is evidence that the dNC complex consists of several distinct functional subareas, we investigated the neural connections of different parts of the dNC complex by retro- and anterograde pathway tracing. Special emphasis was put on the connections of the dNC complex with other imprinting relevant regions in the rostral telencephalon, such as the mediorostral neostriatum/hyperstriatum ventrale (MNH) and the intermediate and medial part of the hyperstriatum ventrale (IMHV). By anterograde and multiple retrograde pathway tracing, we found that the dNC complex may at least be subdivided into three major constituents. The most medial part of the dNC complex, termed neostriatum dorsale (Nd), is characterized by strong reciprocal connections with the neostriatal part of the MNH and by its auditory related inputs, including those from the output layers L1 and L3 of field L, and the shell region of the thalamic n. ovoidalis. The Ndc, which occupies the central aspects of the dNC complex, is mainly characterized by reciprocal connections with the ectostriatal belt (Ep) and the adjacent neostriatum (N). Furthermore, Nd and Ndc receive strong thalamic input from the n. dorsolateralis posterior (DLP), both project to the IMHV, and both are reciprocally connected with the archistriatum intermedium (AI). The most lateral aspect of the dNC complex, termed Ndl, is characterized by afferents from the neostriatum frontale, pars trigeminalis (NFT), and by the lack of a thalamic input. Results indicate that the dNC complex comprises distinct subregions, which are characterized by their specific afferents from parasensory areas of different sensory modalities. These different subregions may be integral components of a general pattern of sensory processing in the avian telencephalon. The strong interconnections between Nd, Ndc, and MNH as well as IMHV may constitute essential parts of auditory and visual imprinting circuits.

Descending auditory pathways in the adult male zebra finch (Taeniopygia guttata)

Here, we examine the connectivity of two previously identified telencephalic stations of the auditory system of adult zebra finches, the neostriatal "shelf" that underlies the high vocal center (HVC) and the archistriatal "cup" adjacent to the robust nucleus of the archistriatum (RA). We used different kinds of neuroanatomical tracers to visualize the projections from the shelf to the HVC. In addition, we show that the shelf projects to the cup and that the cup projects to thalamic, midbrain, and pontine nuclei of the ascending auditory pathway. Our observations extend to songbirds anatomical features that are found in the auditory pathways of a nonoscine bird, the pigeon (Wild et al. [1993] J. Comp. Neurol. 337:32-62), and we suggest that the descending auditory projections found in mammals may also be a general property of the avian brain. Finally, we show that the oscine song control system is closely apposed to auditory pathways at many levels. Our observations may help in understanding the evolution and organization of networks for vocal communication and vocal learning in songbirds.