Involvement of the substantia innominata/ventral pallidum complex in transmitting forelimb muscular rigidity evoked from the nucleus accumbens in rats

Lateral preoptic and ventral pallidal roles in locomotion and other movements

The lateral preoptic area (LPO) and ventral pallidum (VP) are structurally and functionally distinct territories in the subcommissural basal forebrain. It was recently shown that unilateral infusion of the GABAA receptor antagonist, bicuculline, into the LPO strongly invigorates exploratory locomotion, whereas bicuculline infused unilaterally into the VP has a negligible locomotor effect, but when infused bilaterally, produces vigorous, abnormal pivoting and gnawing movements and compulsive ingestion. This study was done to further characterize these responses. We observed that bilateral LPO infusions of bicuculline activate exploratory locomotion only slightly more potently than unilateral infusions and that unilateral and bilateral LPO injections of the GABAA receptor agonist muscimol potently suppress basal locomotion, but only modestly inhibit locomotion invigorated by amphetamine. In contrast, unilateral infusions of muscimol into the VP affect basal and amphetamine-elicited locomotion negligibly, but bilateral VP muscimol infusions profoundly suppress both. Locomotor activation elicited from the LPO by bicuculline was inhibited modestly and profoundly by blockade of dopamine D2 and D1 receptors, respectively, but was not entirely abolished even under combined blockade of dopamine D1 and D2 receptors. That is, infusing the LPO with bic caused instances of near normal, even if sporadic, invigoration of locomotion in the presence of saturating dopamine receptor blockade, indicating that LPO can stimulate locomotion in the absence of dopamine signaling. Pivoting following bilateral VP bicuculline infusions was unaffected by dopamine D2 receptor blockade, but was completely suppressed by D1 receptor blockade. The present results are discussed in a context of neuroanatomical and functional organization underlying exploratory locomotion and adaptive movements.

Spiraling dopaminergic circuitry from the ventral striatum to dorsal striatum is an effective feed-forward loop

Central dopamine systems are key players in the cerebral organization of behavior and in various neurological and psychiatric diseases. We demonstrate the presence of a neurochemical feed-forward loop characterized by region-specific changes in dopamine efflux in serially connected striatal regions, providing evidence in favor of the existence of so-called spiraling striato-nigro-striatal connections. Using in vivo microdialysis of rats, we show that simultaneous stimulation of dopamine D1 and D2 receptors in the accumbal shell decreased dorsal striatal dopamine efflux via a direct or indirect feed-forward loop involving shell, core, ventrolateral and dorsal part of the striatum: simultaneous stimulation of dopamine D1 and D2 receptors in the shell decreased dopamine efflux in the core; flupenthixol-induced inhibition of dopamine D1 and D2 receptors in the core increased dopamine efflux in the ventrolateral part of the striatum, and simultaneous stimulation of dopamine D1 and D2 receptors in the ventrolateral part of the striatum decreased dopamine efflux in the dorsal part of the striatum. Finally, simultaneous stimulation of dopamine D1 and D2 receptors in the shell decreased dopamine efflux in the dorsal part of the striatum. Thus, distinct striatal regions act also in series, providing a better understanding of the neural mechanisms underlying dopamine-dependent behaviors and the progression of dopamine-dependent disorders such as depression, schizophrenia, attention deficit hyperactivity disorder (ADHD), and addiction.

Switching to cue-directed behavior: specific for ventral striatal dopamine but not ventral pallidum/substantia innominata gaba as revealed by a swimming-test procedure in rats

In this study it was investigated whether ventral striatal dopamine-induced changes in switching to cue-directed behavioral patterns were funnelled via the rostral areas of the ventral pallidum/substantia innominata (VP/SI) complex and, if so, whether changes in switching to cue-directed behavioral patterns could be elicited in the VP/SI complex by manipulating GABAergic activity. To this end rats were bilaterally equipped with cannulae directed at the ventral striatum and/or rostral VP/SI complex and subjected to a swimming-test procedure for 6 min. Injections of the dopamine-releasing agent d-amphetamine (10 microg/0.5 microl per side) enhanced the number of different cue-directed behavioral patterns while they had no effect upon the number of different non-cue-directed behavioral patterns in line with previous studies (Life Sci - 1989 1697). This increase was attenuated by a low dose of the GABAa agonist muscimol (1 ng/0.5 microl) into the rostral VP/SI complex. This dose of muscimol when injected alone into the rostral VP/SI complex had no effect upon the number of different cue-directed behavioral patterns. Only the lowest dose of the GABAa antagonist bicuculline (10-25 ng/0.5 microl per side) into the rostral VP/SI complex slightly, and in a non-d-amphetamine-like manner, increased the number of different cue-directed behavioral patterns while none of the doses had an effect on the number of different non-cue-directed behavioral patterns. Both injections of d-amphetamine into the ventral striatum and injections of bicuculline into the rostral VP/SI complex strongly increased motor activity in the 10-min period preceding the swimming test. We conclude from the data that switching to cue-directed behavioral patterns is sensitive to manipulations with the dopaminergic activity in the ventral striatum but not with the GABAergic activity in the VP/SI complex although the VP/SI transmits it to other brain structures. In contrast motor activity is sensitive to manipulations with both ventral striatal dopamine and rostral VP/SI complex GABA.

Neural mediation of nursing and related maternal behaviors

Nursing is the behavioral concomitant of lactation and the most generalizable maternal behavior across mammals. In lactating rats nursing often occurs in the kyphotic (upright crouched) posture; like the neuroendocrine determinants of milk synthesis and release, kyphosis requires suckling by the young. The dam's active pronurturant behaviors, such as retrieval and licking of pups, requires perioral somatosensory stimulation, which is often a precursor of kyphosis as well, and is inhibited by suckling. The sequential nature of maternal behaviors and the dissociations in their somatosensory regulation are critical to understanding their neural mediation, as exemplified by our recent work in lactating rats. We found that the caudal lateral and ventrolateral midbrain periaqueductal gray (cPAGl,vl) is a sensorimotor integration site for the kyphotic nursing posture. Destruction of the cPAGl,vl, or increased activity of the inhibitory neurotransmitter GABA within it, severely reduced kyphosis, increased nursing in more atypical postures, and had little or no effect on pronurturance. Various forebrain sites are known to mediate retrieval and licking of pups. Inhibition of dopaminergic activity in the nucleus accumbens of dams via microinfusions of a mixed D1/D2 dopamine receptor antagonist, cis-flupenthixol (FLU), dose-dependently reduced these active behaviors, while increasing nursing duration. Retrieval was inhibited, however, only by infusions of FLU that included the nucleus accumbens shell, which is reciprocally connected with other sites implicated in retrieval of pups. Thus, maternal behavior is not a unitary process but rather a complex category consisting of sequential behavioral components that have their own sensory and neural determinants.

GABA(A) agents injected into the ventral pallidum differentially affect dopaminergic pivoting and cholinergic circling elicited from the shell of the nucleus accumbens

The ability of GABA(A) receptors in the ventral pallidum to modulate shell-specific behavior was studied. Injections of the non-selective acetylcholine receptor agonist, carbachol (5 microg), into the shell of the nucleus accumbens elicited contraversive circling, namely turning marked by normal stepping; in contrast, injections of a mixture of dopamine D(1) (SKF 38393, 5 microg) and D(2) (quinpirole, 10 microg) receptor agonists into this brain structure elicited contraversive pivoting, namely turning marked by abnormal hindlimb stepping. Unilateral injections of the GABA(A) receptor agonist muscimol (10, 25 and 50 ng) into the ventral pallidum dose-dependently mimicked shell-specific circling, especially when given at a level +8.6mm anterior to the interaural line; this effect was GABA(A) receptor specific, because it was prevented by the GABA(A) receptor antagonist bicuculline (150 ng). Unilateral pallidal injections of a dose of muscimol that was ineffective per se (10 ng) abolished contraversive pivoting elicited by shell injections of dopamine receptor agonists; instead, it elicited moderate ipsiversive pivoting. Pallidal injections of bicuculline (150 ng) replaced the contraversive pivoting elicited by dopamine receptor agonist with ipsiversive circling. In contrast, unilateral pallidal injections of 10 ng muscimol (anterior +8.6mm level) suppressed the contraversive circling elicited by shell injections of carbachol; instead, it elicited moderate ipsiversive pivoting. Pallidal injections of bicuculline (150 ng) produced short-lasting ipsiversive circling that was followed by contraversive pivoting. We conclude that the ventromedial portion of the ventral pallidum contains GABA(A) receptors that are crucial for the transmission of information from the shell of the nucleus accumbens via the ventral pallidum towards other brain structures; this holds especially for information about shell-specific circling elicited by carbachol. The same portion of the ventral pallidum also contains GABA(A) receptors that control the transfer of information from the nucleus accumbens towards structures outside the ventral pallidum; this holds especially for information about shell-specific pivoting elicited by dopaminergic agonists.

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.

Dopamine D1- and D2-dependent catalepsy in the rat requires functional NMDA receptors in the corpus striatum, nucleus accumbens and substantia nigra pars reticulata

This study investigated the anticataleptic activity of MK-801 versus the D1 antagonist SCH 23390 and the D2 antagonist raclopride, using the horizontal bar test in the rat. MK-801, 0.2 mg/kg i.p., strongly opposed the cataleptogenic actions of SCH 23390 and raclopride administered systemically (1 and 3 mg/kg i.p., respectively), or directly into the corpus striatum (CS) or nucleus accumbens (NAc; 1 and 10 microg, respectively). Conversely, intraCS and intraNAc pretreatment with MK-801 (10 microg) markedly attenuated the cataleptic response to a systemic injection of SCH 23390 or raclopride. In the latter experiments the anticataleptic effect of MK-801 was pronounced and sustained (> 2 h), except with intraCS MK-801 versus raclopride, where it was initially profound but only short-lived (15 min). Stereotaxic injection of MK-801 (1 microg) into the substantia nigra pars reticulata (SNr) prevented catalepsy developing to either dopamine D1 or D2 receptor antagonism. These results indicate there must be unimpeded glutamate neurotransmission in the CS and NAc before catalepsy can develop fully to D1 and D2 dopamine receptor blockade in these structures. The weaker glutamate-D2 interaction in the CS than in the NAc may be related to differences in the N-methyl-D-aspartate receptor subpopulations in these nuclei. Finally, the ability of intranigral MK-801 to diminish both D1- and D2-dependent catalepsy suggests the SNr acts as a common output pathway for the expression of both forms of catalepsy in the rat.

Modifications in glutamatergic transmission after dopamine depletion of the nucleus accumbens. A combined in vivo/in vitro electrophysiological study in the rat

The interaction between the glutamatergic and dopaminergic input in the nucleus accumbens was examined by studying the effects of dopamine depletion of the nucleus accumbens on the local field potentials, and the L-glutamate elicited responses of the nucleus accumbens in anaesthetized rats in vivo. A characteristic field potential in the nucleus accumbens is evoked by electrical stimulation of the fornix/fimbria fibres, with a monosynaptic positive peak at 10 ms (P10). Rats were unilaterally injected with 6-hydroxydopamine in the nucleus accumbens. The contralateral accumbens was sham lesioned. The rats were divided into short-term and long-term survival groups of one to two weeks and 24 weeks, respectively. In the short-term group, a striking increase (up to three times) of the amplitude of the P10 components, at the site of the lesion, compared with the sham lesioned contralateral accumbens and untreated rats, was found. The long-term group could still display a slight increase although on average this was not significantly different from controls. In the short-term group, at the centre of the lesion, the paired-pulse facilitation ratio was significantly smaller than at the more ventral, less denervated, border of the accumbens. These differences were no longer visible in the long-term group. Single-unit activity of the accumbens, elicited by the iontophoretical application of L-glutamate showed, in controls, a maximal firing frequency ranging from 5 to 40 Hz (mean 25 Hz), whereas in the short-term group more than 50% of the accumbens neurons fired with higher frequencies, reaching up to 90 Hz (mean 55 Hz). In the long-term group the firing frequency varied from 5 to 60 Hz (mean 41 Hz). No changes in threshold ejection glutamate current were found for both lesioned groups. In control rats the L-glutamate elicited responses of six cells tested could be suppressed by dopamine whereas in lesioned rats three of the six cells tested were unresponsive to dopamine. Intracellular recordings of accumbens cells in slices in 6-hydroxydopamine and sham lesioned rats, showed no significant changes in the intrinsic membrane properties, e.g. resting membrane potential, input resistance, spike threshold, action potential amplitude or duration. We conclude that dopamine denervation leads to an increase of excitability of the principal accumbens neurons. This is reflected by the increase of the firing frequency of these cells and of the amplitude of the evoked field potentials. The former is more likely of postsynaptic origin whereas the latter may also have a presynaptic contribution. These effects cannot be attributed to changes in intrinsic membrane properties of the cells.

Rostrocaudal subregional differences in the response of enkephalin, dynorphin and substance P synthesis in rat nucleus accumbens to dopamine depletion

Quantitative in situ hybridization histochemistry was used to examine the effects of unilateral 6-hydroxydopamine lesions of the ascending dopaminergic fibres on levels of mRNA encoding the neuropeptides enkephalin, dynorphin and substance P in subregions of the nucleus accumbens. The nucleus accumbens was divided into quadrants and changes in mRNA were measured along the rostrocaudal extent of the nucleus. Two weeks after the lesion an increase was found in enkephalin mRNA in the lesioned side compared to the non-lesioned side, whereas a decrease was observed for dynorphin and substance P mRNA. The changes in mRNA levels differed from quadrant to quadrant and were not uniformly distributed along the rostrocaudal axis. Both types of changes, i.e. increase and decrease, were much higher in rostral parts of the nucleus than in caudal parts, indicating regional differences in the effects of blockade of the dopaminergic neurotransmission. The lesion-induced increases and decreases in mRNA levels occurred in both the shell and the core subregions of the nucleus accumbens and were not specifically related to either of these areas. Factors are discussed that may contribute to the rostrocaudal gradient in the changes of enkephalin, substance P and dynorphin mRNA levels. On the basis of their afferent and efferent connections, the rostral and caudal parts of the nucleus accumbens are considered to be involved in different functions. The present results suggest that dopamine depletion may affect these functions in a differential manner.

Role of neostriatum and nucleus accumbens in stepping induced by apomorphine and dexamphetamine

Systemic administration of apomorphine and dexamphetamine are known to produce circling in rats by changing the functioning of hindlimb stepping and forelimb stepping, respectively. In the present study intracranial injections of the dopamine antagonist sulpiride were used to study the involvement of the neostriatum and nucleus accumbens in these effects. It was found that injections of sulpiride into the neostriatum, but not the nucleus accumbens, dose-dependently (1-20 ng) reduced the number of apomorphine-induced hindlimb doublets without affecting the dexamphetamine-induced forelimb crossing steps. On the other hand, it was found that injections into the nucleus accumbens, but not the neostriatum, reduced the number of dexamphetamine-induced forelimb crossing steps without affecting the apomorphine-induced hindlimb doublets. This effect was not dose-dependent. The data suggest that the neostriatum, but not the nucleus accumbens, is primarily involved in the apomorphine-induced changes in hindlimb stepping, and that the nucleus accumbens, but not the neostriatum, is primarily involved in the dexamphetamine-induced changes in forelimb stepping.

Motor activity and the GABAA-receptor in the ventral pallidum/substantia innominata complex

The present study deals with the role of the gamma-aminobutyric acid-A (GABAA) receptor in motor activity in the rostral part of the ventral pallidum/substantia innominata complex. Both the specific GABAA antagonist bicuculline (25-100 ng/0.5 microliter) and the GABAA agonist muscimol (25 ng/0.5 microliter) enhanced motor activity. It was moreover found that bicuculline (50-100 ng) dose-dependently attenuated the activity induced by muscimol (25 ng). Conversely, muscimol (25 ng) attenuated the bicuculline (25-50 ng) induced activity. These data thus show that both stimulation and blockade of GABAA receptors within the area under study enhance motor activity.

Subregions of the caudate nucleus and their in- and output channels in oro-facial dyskinesia: a behavioural and retrograde tracing study in the cat

Previous studies have shown that the feline caudate nucleus contains DPI-sensitive (caput nuclei caudati, anterodorsal part; r-CRM) and DPI-insensitive (caput nuclei caudati, rostromedial part; CRM) regions. Stimulation of dopamine receptors within the r-CRM by dopamine or DPI are known to elicit oro-facial dyskinesia (OFD), i.e. a syndrome of tic-like contractions of the facial muscles in combination with tongue protrusions. OFD is also elicited from the sub-commissural part of the globus pallidus (scGP), a first order output station of the r-CRM, but not from the CRM. On the basis of these data it has been hypothesized that (1) OFD is a specific feature of the r-CRM, but not the CRM; (2) effects elicited from the r-CRM are funneled via the scGP, and that (3) r-CRM and CRM are differentially innervated. Cats were bilaterally equipped with cannulas directed at the CRM or r-CRM and scGP. Following recovery from the operation the cats received bilateral injections of DPI into CRM (5 micrograms/5 microliter) or r-CRM (5 and 10 micrograms/5 microliter), the latter in combination with muscimol (50 and 100 ng/1 microliter) into the scGP or its solvent. Subsequently, behaviour was analyzed. OFD, quantified in number of tongue protrusions, was only elicited from the r-CRM, but not from the CRM confirming previously reported data in this respect. Furthermore the effect varied according to the dose used. The OFD elicited from the r-CRM was found to be blocked at the level of the scGP by local injections of muscimol, a GABA agonist.(ABSTRACT TRUNCATED AT 250 WORDS)