Effects of alpha-methyl-p-tyrosine on extracellular dopamine levels in the nucleus accumbens and the dorsal striatum of freely moving rats

Alpha-methyl-p-tyrosine (AMPT) is known to inhibit the formation of dopamine (DA) in the cytosol of dopaminergic neurons and is therefore used to study the role of the cytosolic DA pools. AMPT is usually administered systemically. In the present study, however, the effects of locally infused AMPT on the efflux of DA from the nucleus accumbens and dorsal striatum were analyzed, using in vivo brain microdialysis in unanesthetized rats. The administration of AMPT (100 microM, 4 h) into the nucleus accumbens reduced accumbal DA output to 30% of its baseline level. When it was infused into the dorsal striatum, however, it reduced striatal DA output to 60% of its baseline level. At first sight, these data suggest that the amount of DA available from the AMPT-sensitive pool is larger in the nucleus accumbens than in the striatum. However, this cannot be the case, as the decrease in accumbal and striatal DA efflux induced by systemic administration of AMPT (250 mg/kg given intra-peritoneally) was identical. These results show that local infusion of AMPT is a valuable tool for analyzing the role of AMPT-sensitive pools within a particular brain area, but it cannot be used to compare effects across different brain structures because a fixed dose of AMPT differentially affected the nucleus accumbens and the dorsal striatum.

The non-peptidic delta opioid receptor agonist TAN-67 enhances dopamine efflux in the nucleus accumbens of freely moving rats via a mechanism that involves both glutamate and free radicals

The activation of the delta-opioid receptors in the nucleus accumbens is known to induce a large and rapid increase of accumbal dopamine efflux. (+/-)-TAN-67 (2-methyl-4a(alpha)-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12a(alpha)-octahydro-quinolino[2,3,3,-g]isoquinoline) is a centrally acting non-peptidic delta opioid receptor agent which has recently become available. Interestingly, the (+) enantiomer of TAN-67 induces hyperalgesia in contrast to the (-) enantiomer of TAN-67 that produces profound antinociceptive effects in mice; the latter effects are mediated through delta-1 receptor stimulation. Using the microdialysis technique, the ability of the enantiomers of TAN-67 to alter the release of accumbal dopamine in vivo was analyzed. Like the 25-min infusion of the selective delta-1 opioid receptor agonist (D-[Pen2,5]-enkephalin) DPDPE (50 nM) and the delta-2 opioid receptor agonist deltorphin II (50 nM), the 25-min infusion of both (-)-TAN-67 (25 and 50 nM) and (+)-TAN-67 (25 and 50 nM) into the nucleus accumbens produced a similar transient dose-dependent increase in the accumbal extracellular dopamine level. Naloxone (1 mg/kg i.p., given 25 min prior to the drugs), namely a treatment that is known to inhibit the increase of dopamine induced by DPDPE and deltorphin II, did not affect the transient increase in the accumbal dopamine level produced by infusion of the enantiomers of TAN-67. The DPDPE and deltorphin II-induced increase in accumbal dopamine level, but not that of (-)-TAN-67 and (+)-TAN-67, was eliminated by subsequently perfused tetrodotoxin (2 microM) into the nucleus accumbens. The increase in accumbal dopamine level produced by an infusion of (-)-TAN-67 and (+)-TAN-67 was not altered by a Ca2+-free Ringer's solution. The (-)-TAN-67 and (+)-TAN-67-induced accumbal dopamine efflux was strongly prevented by reserpine (5 mg/kg i.p., given 24 h earlier) or alpha-methyl-para-tyrosine (250 mg/kg i.p., given 2 h earlier). The effects of the enantiomers of TAN-67 on the accumbal dopamine were nullified by combined treatment with reserpine and alpha-methyl-para-tyrosine. The (-)-TAN-induced dopamine efflux was significantly reduced by the N-methyl-D-aspartate (NMDA) receptor antagonists ifenprodil (20 mg/kg i.p., 20 min before) and MK-801 (0.5 mg/kg i.p., 20 min before), respectively. The effects of (-)-TAN-67 on the dopamine efflux were also inhibited by the free radical scavenger N-2-mercaptopropionyl glycine (100 mg/kg i.p., 20 min before). These results show that both enantiomers of TAN-67 enhance the release of reserpine sensitive, vesicular dopamine and alpha-methyl-p-tyrosine sensitive, cytosolic dopamine from dopaminergic nerve terminals in the nucleus accumbens in a way that is independent of neural activity; activation of delta opioid receptors plays no role in these events. All together, the results suggest that (-)-TAN-67 can generate a burst of free radicals that in turn trigger a release of glutamate that ultimately via activation of NMDA receptors enhances the release of dopamine from dopaminergic nerve terminals in the nucleus accumbens.

Contribution of vesicular and cytosolic dopamine to the increased striatal dopamine efflux elicited by intrastriatal injection of dexamphetamine

Systemic administration of high doses of dexamphetamine induces a dopamine efflux that has its intracellular origin in both the vesicular, reserpine-sensitive dopamine pool and the cytosolic, alpha-methyl-para-tyrosine-sensitive, newly synthesized dopamine pool. It remains unknown whether locally administered dexamphetamine produces similar effects. Using a brain microdialysis technique that is combined with a microinjection needle, the contribution of the vesicular and cytosolic pools to the dopamine efflux induced by striatal injection of dexamphetamine was analyzed in rats. The transient striatal dopamine efflux induced by intrastriatal injection of dexamphetamine (1.0 microg/0.5 microl) was significantly reduced by systemic administration of reserpine (5mg/kg i.p., given 24 h earlier) or alpha-methyl-para-tyrosine (250 mg/kg i.p., given 2 h earlier). The effects of dexamphetamine on the striatal dopamine were nearly nullified by combined treatment with reserpine and alpha-methyl-para-tyrosine. The sum of the amounts of extracellular dopamine that was sensitive to either reserpine or alpha-methyl-para-tyrosine, was far greater than 100%, namely 146.1% of the basal dopamine level and 144.0% of the dexamphetamine-induced dopamine level. The present study indicates that both the vesicular dopamine pool and the cytosolic dopamine pool contribute to the transient increase of striatal dopamine efflux induced by intrastriatal injection of dexamphetamine. This study also suggests that striatally applied dexamphetamine can promote the redistribution of rat striatal dopamine from vesicles to the cytosol in vivo.

Topographical effects of D1-like dopamine receptor agonists on orofacial movements in mice and their differential regulation via oppositional versus synergistic D1-like: D2-like interactions: cautionary observations on SK&F 82958 as an anomalous agent

Using a novel procedure, the regulation of individual topographies of orofacial movement in the mouse by oppositional versus cooperative/synergistic D1-like: D2-like dopamine receptor interactions was studied. The D1-like agonists SK&F 38393 and SK&F 83959 each induced vertical, but not horizontal, jaw movements, together with tongue protrusions and incisor chattering; however, SK&F 82958 induced a different profile which, consistent with other neurochemical and neurophysiological studies, suggests that this agent shows anomalous properties relative to other D1-like agonists. When given alone, the D2-like agonist quinpirole reduced horizontal jaw movements and incisor chattering. On coadministration, both SK&F 38393- and SK&F 83959-induced vertical jaw movements and tongue protrusions were inhibited by quinpirole, while SK&F 82958 again showed an anomalous profile. These findings indicate that, in the mouse, vertical jaw movements and tongue protrusions are regulated by oppositional D1-like: D2-like interactions, and appear to involve a D1-like receptor that is not coupled to adenylyl cyclase, whereas horizontal jaw movements are inhibited by D2-like receptors. Additionally, results obtained using SK&F 82958 as a probe for D1-like mechanisms should be treated with considerable caution until they are confirmed using other D1-like agonists.

Decreased postsynaptic dopaminergic and cholinergic functions in the ventrolateral striatum of spontaneously hypertensive rat

Dopamine and acetylcholine receptor functions in spontaneously hypertensive rats (SHR) and in control progenitor Wistar-Kyoto (WKY) rats were assessed, using dopamine D1-like/D2-like receptor-mediated and acetylcholine receptor-mediated jaw movements as readout parameters. Spontaneous behaviours such as locomotor activity, vacuous chewing, grooming, sniffing and rearing occurred significantly more in SHR than in WKY rats. In the anaesthetised rats, a mixture of SKF 38393 (5 micrograms), a dopamine D1-like receptor agonist, and quinpirole (10 micrograms), a dopamine D2-like receptor agonist, readily produced repetitive jaw movements in WKY rats, but not SHR, when bilaterally injected into the ventrolateral striatum; such injections into the nucleus accumbens shell were ineffective in each strain. Bilateral injections of carbachol (2.5 micrograms each side), an acetylcholine receptor agonist, into the ventrolateral striatum elicited repetitive jaw movements in both SHR and WKY rats, but to a far less degree in SHR. The present study demonstrates that spontaneous behaviours are enhanced in SHR, and that postsynaptic dopamine D1-like/D2-like receptors and acetylcholine receptors in the ventrolateral striatum of SHR are hyposensitive when compared to those of WKY rats.

Masticatory efficiency before and after surgery in oral cancer patients: comparative study of glossectomy, marginal mandibulectomy and segmental mandibulectomy

This study evaluated the effect of oral cancer surgery on masticatory efficiency. Masticatory efficiency was measured using the ATP absorption method. Eating ability was measured using a questionnaire. Two groups were employed as controls: The "normal occlusion group" consisted of subjects who had a complete set of natural maxillary teeth opposed to mandibular teeth, and the "unilateral occlusion group" consisted of subjects who had lost their molar and premolar teeth on one side of the mandible as a result of caries or periodontal diseases. Three treatment groups, each of 6 patients, were studied: a glossectomy group, a marginal mandibulectomy group and a segmental mandibulectomy group. There were no differences in masticatory efficiency between two control groups. Masticatory efficiencies of the three oral cancer treatment groups were lower than in the unilateral occlusion group, even 12 months after surgery. Masticatory efficiency of the glossectomy group was significantly higher 12 months after surgery compared with pre-surgery. Masticatory and eating abilities of the marginal mandibulectomy group and the segmental mandibulectomy were reduced at 3 and 6 months after surgery. The masticatory efficiency 12 months after surgery was higher in the marginal mandibulectomy group than the segmental mandibulectomy group, although the difference was not statistically significant. The self assessed eating ability 12 months after surgery was significantly higher in the marginal mandibulectomy group than the segmental mandibulectomy group. These results suggest that discontinuation of the mandible may lead patients to eat only foods that do not require a substantial amount of chewing. Hence, the quality of life of patients in the marginal mandibulectomy group was considered to be better than that in the segmental mandibulectomy group.

GABAA and GABAB receptors in the nucleus accumbens shell differentially modulate dopamine and acetylcholine receptor-mediated turning behaviour

The ability of GABAA and GABAB receptors in the shell of the nucleus accumbens to modulate distinct types of turning behaviour was investigated in freely moving rats, using the unilateral injection technique. The GABAA receptor agonist muscimol and the GABAA receptor antagonist bicuculline did not produce turning behaviour; the same holds for the GABAB agonist baclofen and the GABAB antagonist 2-hydroxysaclofen. A mixture of the dopamine D1 receptor agonist SKF 38393 and the dopamine D(2/3) receptor agonist quinpirole has been found to elicit contraversive pivoting, when injected into the shell. This pivoting was dose-dependently inhibited by muscimol, and the inhibitory effect of muscimol was antagonised by bicuculline. Pivoting was also dose-dependently inhibited by baclofen; however, 2-hydroxysaclofen did not antagonise the inhibitory effect. The acetylcholine receptor agonist carbachol has been found to elicit contraversive circling, when injected into the shell. This carbachol-induced circling was inhibited by baclofen, and 2-hydroxysaclofen antagonised the inhibitory effect. Carbachol-induced circling was also partially inhibited by muscimol; however, the inhibitory effect of muscimol was not antagonised by bicuculline. It is concluded that mesolimbic GABAA receptors exert an inhibitory control on dopamine-dependent pivoting that can be elicited from the shell of the nucleus accumbens, and that GABAB receptors exert an inhibitory control on acetylcholine-dependent circling that can be elicited from the shell of the nucleus accumbens. This data extends the earlier reported findings that the neurochemical substrate in the shell of the nucleus accumbens that mediates dopamine-dependent pivoting is fundamentally different from the shell substrate that mediates acetylcholine-dependent circling.

Role of mu- and delta-opioid receptors in the nucleus accumbens in turning behaviour of rats

The role of mu-, delta1- and delta2-opioid receptors in the nucleus accumbens in pivoting was investigated in freely moving rats. Unilateral injections of the mu-opioid receptor agonist, [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO, 1 and 2 microg) and the delta2-opioid receptor agonist, deltorphin II (1 and 2 microg), but not the delta1-opioid receptor agonist, [D-Pen(2,5)]-enkephalin (DPDPE, 1-4 microg), into the shell or the core of the nucleus accumbens significantly induced contraversive pivoting. The pivoting induced by DAMGO (2 microg) and deltorphin II (2 microg) was inhibited significantly by the mu-opioid receptor antagonist, D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Phe-Thr-NH2 (CTOP, 0.1 and 1 microg), and the delta2-opioid receptor antagonist, naltriben (NTB, 0.1 and 1 mg/kg, i.p.), respectively. The DAMGO (2 microg)- or deltorphin II (2 microg)-induced pivoting was also inhibited significantly by co-administration of the dopamine D1/D2 receptor antagonist, cis(Z)-flupentixol (1 and 10 microg). The pivoting induced by unilateral injections of a mixture of dopamine D1 (SKF 38393, 5 microg) and D2 (quinpirole, 10 microg) receptor agonists into the shell was significantly inhibited by cis(Z)-flupentixol (1 and 10 microg) or NTB (1 and 3 mg/kg, i.p.), but not CTOP (1 microg) or delta1-opioid receptor antagonist, (E)-7-benzylidenenaltrexone (1 mg/kg, i.p.). The contraversive pivoting elicited by the cholinergic agonist, carbachol (5 microg), into the core was inhibited by co-administration of the muscarinic M1 antagonist, pirenzepine (1 microg), but not cis(Z)-flupentixol (1 microg). The results suggest that unilateral activation of mu- or delta2-opioid, but not delta1-opioid, receptors in the core and/or shell of the nucleus accumbens elicits contraversive pivoting that requires intact dopamine D1/D2 receptors in the shell, but not intact muscarinic M1 mechanism in the core. The study also shows that delta2-opioid, but not mu- and delta1-opioid, receptors in the core and/or shell modulate the shell-specific, dopamine D1/D2 receptor mechanisms involved in the production of pivoting.

Deltorphin II enhances extracellular levels of dopamine in the nucleus accumbens via opioid receptor-independent mechanisms

The effects of the delta2-opioid receptor agonist, deltorphin II, on extracellular levels of dopamine in the rat nucleus accumbens were investigated in awake animals by in vivo brain microdialysis. In agreement with previous studies, perfusion of deltorphin II (50.0 nmol) into the nucleus accumbens significantly increased the extracellular amount of accumbal dopamine. The effect of deltorphin II (50.0 nmol) was not altered by the selective delta2-opioid receptor antagonist, naltriben (1.5 nmol), which alone did not significantly affect the basal levels of dopamine. Selective antagonists of neither the mu-opioid receptors, D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Phe-Thr-NH2 (0.15 nmol), nor the delta1-opioid receptors, (E)-7-benzylidenenaltrexone tartrate (0.15 nmol), failed to significantly alter the effects of deltorphin II. The nonselective opioid receptor antagonist, naloxone (0.75 and 1.5 nmol), which alone did not significantly affect the basal levels of dopamine, also failed to affect the effects of deltorphin II. Moreover, under the condition that the sodium channel blocker, tetrodotoxin (0.1 nmol), was perfused continuously into the nucleus accumbens, the deltorphin II-induced increase in extracellular levels of dopamine was reduced by 72%. These results suggest that deltorphin II enhances extracellular dopamine in the nucleus accumbens via opioid receptor-independent, tetrodotoxin-sensitive mechanisms.

GABA(A) receptors in the nucleus accumbens core modulate turning behavior induced by dopamine receptor stimulation

The role of GABA(A) and GABA(B) receptors in the core of the nucleus accumbens in turning behavior of rats was investigated. Unilateral injections into the core of the nucleus accumbens of the GABA(A) receptor agonist (muscimol, 50 ng) and antagonist (bicuculline, 200 ng), and the GABA(B) receptor agonist (baclofen, 100 ng) and antagonist (2-hydroxysaclofen, 2 microg) did not produce turning behavior. In rats pretreated with unilateral injections of the dopamine D1-like/D2-like receptor antagonist, cis(Z)-flupentixol (10 microg), into the ventrolateral striatum and saline into the nucleus accumbens core of contralateral side, systemic injection of a mixture of dopamine D1-like (SKF 38393, 3 mg/kg) and D2-like (quinpirole, 1 mg/kg) receptor agonists has been found to elicit contraversive pivoting, namely pivoting away from the side of the core injection. This dopamine D1-like/D2-like receptor-mediated pivoting was significantly inhibited by injections into the core of the nucleus accumbens of muscimol (50 ng), but not bicuculline (200 ng). In contrast, the dopamine D1-like/D2-like receptor-mediated pivoting was suppressed by either baclofen (100 ng) or 2-hydroxysaclofen (2 microg) injected into the nucleus accumbens core. It is therefore concluded that neither GABA(A) nor GABA(B) receptor stimulation in the core of the nucleus accumbens produces turning behavior, and that GABA(A), but not GABA(B), receptors in the nucleus accumbens core may modulate dopamine D1-like/D2-like receptor-mediated pivoting.

Evidence that angiotensin II enhances apomorphine-induced jaw movements via AT1 receptors in the ventrolateral striatum: Studies by magnet-sensing system in freely moving rats

The role of angiotensin AT(1) receptors in the ventrolateral striatum in modulating apomorphine-induced jaw movements was studied using a magnet-sensing system combined with an intracerebral drug microinjection technique in freely moving rats. Bilateral injections of angiotensin II (1 and 2 micro g/0.2 micro l in each side) into the ventrolateral striatum, which alone did not significantly elicit jaw movements, dose-dependently enhanced apomorphine (1 mg/kg i.v.)-induced repetitive jaw movements. The enhancement of apomorphine-induced jaw movements by angiotensin II (2 micro g) was dose-dependently antagonized by the angiotensin AT(1) receptor antagonist losartan (15 and 30 mg/kg i.p.), given 3 h before, while losartan (30 mg/kg i.p.) alone did not significantly affect the apomorphine (1 mg/kg)-induced jaw movements. These results indicate that angiotensin II enhances apomorphine-induced jaw movements via stimulation of angiotensin AT(1) receptors located in the ventrolateral striatum.

Gabaa receptors in the pedunculopontine tegmental nucleus play a crucial role in rat shell-specific dopamine-mediated, but not shell-specific acetylcholine-mediated, turning behaviour

The role of GABA(A) receptors in the pedunculopontine tegmental nucleus in turning behaviour of rats was studied. Unilateral injection of the GABA(A) receptor agonist, muscimol (25-100 ng), into the pedunculopontine tegmental nucleus dose-dependently produced contraversive pivoting, namely tight head-to-tail turning marked by abnormal hindlimb backward stepping. This effect was GABA(A) receptor specific, since it was prevented by the GABA(A) receptor antagonist, bicuculline (50 ng), which alone did not elicit turning behaviour. Unilateral injection of a mixture of dopamine D(1) ((+/-)-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol [SKF 38393], 5 microg) and D(2) (quinpirole, 10 microg) receptor agonists into the nucleus accumbens shell has been found to elicit contraversive pivoting, whilst unilateral injection of the acetylcholine receptor agonist (carbachol, 5 microg) into the same site is known to elicit contraversive circling, namely turning marked by normal stepping. The pivoting induced by a mixture of SKF 38393 (5 microg) and quinpirole (10 microg) injected into the nucleus accumbens shell was significantly inhibited by bicuculline (50 ng) injected into the pedunculopontine tegmental nucleus, whereas muscimol (25 ng) had no effect. Neither muscimol (25 ng) nor bicuculline (50 ng) modulated the contraversive circling induced by carbachol (5 microg) injected into the nucleus accumbens shell. It is therefore concluded that unilateral stimulation of GABA(A) receptors in the pedunculopontine tegmental nucleus can elicit contraversive pivoting and that the pedunculopontine tegmental nucleus is one of the output stations of the accumbens region that mediates shell-specific, dopaminergic pivoting, but not of the accumbens region that mediates shell-specific, cholinergic circling.

Prefrontal, accumbal [shell] and ventral striatal mechanisms in jaw movements and non-cyclase-coupled dopamine D1-like receptors

The effect on jaw movements of intracerebral injections of the dopamine D1-like receptor agents SK&F 83959 (3-methyl-6-chloro-7,8-dihydroxy-1-[3-methylphenyl]-2,3,4,5-tetrahydro-1H-3-benzazepine), SK&F 38393 ([R]-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine) and SCH 23390 ([R]-3-methyl-7-chloro-8-hydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine) and of injections of the dopamine D2-like receptor agonist quinpirole into the ventrolateral striatum, accumbens shell or prefrontal cortex were studied. SK&F 38393 and SK&F 83959 injected into the ventrolateral striatum synergised with i.v. quinpirole; in the shell of accumbens, SK&F 38393 evidenced weaker synergism with quinpirole, while SK&F 83959 did not synergise with it; neither agent synergised with quinpirole in the prefrontal cortex. Co-injection of SCH 23390 or SK&F 83959 into the prefrontal cortex antagonised jaw movements induced by injection of SK&F 83959 into the ventrolateral striatum in combination with i.v. quinpirole. Injection of SK&F 83959 + quinpirole into the ventrolateral striatum, but not into the accumbens shell, resulted in synergism. These findings indicate a primary, but not exclusive, role for ventral striatal, non-cyclase-coupled dopamine D1-like receptors in the induction of jaw movements. These processes appear to require tonic activity of prefrontal cyclase-linked dopamine D1A [and/or D1B] receptors.

Altered pre- and postsynaptic dopamine receptor functions in spontaneously hypertensive rat: an animal model of attention-deficit hyperactivity disorder

Dopamine receptor function in spontaneously hypertensive rats (SHR) and in control progenitor Wistar-Kyoto (WKY) rats was assessed from their dopamine D1-like/D2-like receptor-mediated jaw movements and dopamine release from the nucleus accumbens and from the ventrolateral striatum measured by an in vivo microdialysis technique. Spontaneous locomotor activity and rearing were significantly higher in SHR than in WKY rats. Co-administration of SKF 38393 (1.0, 2.0 and 3.0 mg/kg), a dopamine D1-like receptor agonist, and quinpirole (1.0 mg/kg), a dopamine D2-like receptor agonist, produced repetitive jaw movements in WKY rats in a dose-dependent manner. However, this synergism was not evident in SHR. Basal dopamine levels in both the nucleus accumbens and the ventrolateral striatum were lower in SHR than WKY rats, though the levels of dopamine were lower in the nucleus accumbens than the ventrolateral striatum in both strains. After infusion of quinpirole (100 microM for 180 min) the dopamine levels in both regions were reduced. In the nucleus accumbens, the quinpirole-mediated reduction of dopamine release at 40 min and 60 min after infusion was larger in SHR than WKY rats, whereas this difference between the SHR and WKY rats was small in the ventrolateral striatum. The present study therefore suggests that, when compared to WKY rats, postsynaptic dopamine D1-like/D2-like receptors in the SHR are hyposensitive, while presynaptic dopamine D2-like receptors located particularly in the nucleus accumbens are hypersensitive.

The superior colliculus contains a discrete region involved in the control of jaw movements: role of GABAA receptors

The role of GABA(A) receptors in the superior colliculus in the production of rat repetitive jaw movements was examined, as this nucleus receives tonic GABAergic inhibitory inputs from the dorsolateral part of the substantia nigra pars reticulata and the entopeduncular nucleus. Both regions are also connected with the ventrolateral striatum where stimulation of either dopamine or acetylcholine receptors has been found to elicit distinct types of jaw movements in rats. The GABA(A) receptor antagonist bicuculline (50 and 150 ng/0.2 microl per side) dose-dependently produced repetitive jaw movements only when injected bilaterally into a circumscribed region (A 3.0) of the lateral deeper layers of the superior colliculus; this region is known to receive input predominantly from the dorsolateral part of the substantia nigra pars reticulata. The effects of bicuculline were GABA(A) receptor specific because the effects were abolished by muscimol, a GABA(A) receptor agonist, given into the same site. The bicuculline-induced jaw movements differed qualitatively from those elicited by injection of a mixture of (+/-)-6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol (SKF 82958; 5 microg) and quinpirole (10 microg), agonist at dopamine D1 and D2 receptors, respectively, or carbachol (2.5 microg), an acetylcholine receptor agonist, into the ventrolateral striatum. Nevertheless, injection of muscimol into the lateral deeper layers of the superior colliculus (A 3.0) inhibited jaw movements evoked by the dopamine D1/D2 receptor stimulation. Conversely, the jaw movements evoked by acetylcholine receptor stimulation were enhanced by injection of muscimol into the superior colliculus. In conclusion, GABA(A) receptor blockade in a circumscribed region (A 3.0) of the lateral deeper layers of the superior colliculus elicits characteristic repetitive jaw movements, and the GABA(A) receptors in that region modulate the dopamine D1/D2 receptor-mediated and acetylcholine receptor-mediated jaw movements in an opposite manner.

Role of AMPA and NMDA receptors in the nucleus accumbens shell in turning behaviour of rats: interaction with dopamine receptors

The role of AMPA and NMDA receptors in the shell of the nucleus accumbens in turning behaviour of rats was investigated. Unilateral injection of the AMPA receptor agonist, AMPA (0.25, 0.4, 0.5 and 1 microg), into the shell of the nucleus accumbens dose-dependently produced contraversive pivoting, namely tight head-to-tail turning marked by abnormal hindlimb backward stepping, while injection of AMPA (0.5 microg) into the core produced only a marginal effect. This shell-specific AMPA effect was dose-dependently inhibited by the AMPA receptor antagonist, NBQX (1 and 10 ng), which alone did not produce turning behaviour. The AMPA-induced pivoting was also dose-dependently inhibited by the non-competitive NMDA receptor antagonist, MK-801 (0.1 and 0.5 microg). Neither MK-801 (0.1, 0.5 and 5 microg) nor the NMDA receptor agonist, NMDA (0.5 and 1 microg), injected unilaterally into the shell, produced turning behaviour. Unilateral injection of a mixture of dopamine D(1) (SKF 38393, 5 microg) and D(2) (quinpirole, 10 microg) receptor agonists into the shell has been found to elicit contraversive pivoting. The dopamine D(1)/D(2) receptor antagonist, cis-(Z)-flupentixol (1 and 10 microg), injected into the shell, in doses known to block dopamine D(1)/D(2) receptor-mediated pivoting, also significantly inhibited AMPA (0.5 microg)-induced pivoting. Moreover, both NBQX (1 and 10 ng) and MK-801 (0.1 and 0.5 microg), injected into the shell, significantly inhibited dopamine D(1)/D(2) receptor-mediated pivoting. It is therefore concluded that unilateral stimulation of AMPA receptors in the shell of the nucleus accumbens can elicit contraversive pivoting, and that both AMPA and dopamine D(1)/D(2) receptors play a critical role in shell-specific pivoting in contrast to NMDA receptors that at best play only a modulatory role.

Comparative phenotypic resolution of spontaneous, D2-like and D1-like agonist-induced orofacial movement topographies in congenic mutants with dopamine D2 vs. D3 receptor ?knockout?

Using a novel system, the role of D2-like dopamine receptors in distinct topographies of orofacial movement was assessed in mutant mice with congenic D2 vs. D3 receptor knockout, and compared with findings in D1A mutants. Under spontaneous conditions, D2 mutants evidenced increased vertical jaw movements and unaltered horizontal jaw movements, with reductions in tongue protrusions and incisor chattering; in D3 mutants, only incisor chattering was reduced. Given previous evidence that D1A mutants show reduced horizontal but not vertical jaw movements, this indicates that apparent oppositional D1-like:D2-like interactions in the regulation of composited jaw movements may in fact reflect the independent actions of D2 receptors to inhibit vertical jaw movements and of D1A receptors to facilitate horizontal jaw movements. Effects of the D2-like agonist RU 24213 to exert greater reduction in horizontal than in vertical jaw movements were not altered prominently in either D2 or D3 mutants. The D1-like agonists A 68930 and SK&F 83959 induced vertical jaw movements, tongue protrusions, and incisor chattering; induction of tongue protrusions by A 68930 was reduced in D2 mutants. D2 receptors exert topographically specific regulation of orofacial movements in a manner distinct from their D1A counterparts, while D3 receptors exert only minor regulation of such movements.

Measurement of dopamine receptor-mediated jaw movements by a magnet-sensing system in freely moving rats

This study tested a system for monitoring jaw movements in freely moving rats. A Hall-effect transducer was fixed to the skull in order to sense voltage changes induced by variations in the position of a magnet fixed to the mandible. By measuring dopamine receptor-mediated jaw movements, this system produces data comparable to that obtained using a light-sensitive transducer system in anesthetized rats, while also measuring the vertical component of jaw movements in freely moving rats. In combination with conventional visual observation, this system may provide a useful tool for assessing movements of the orofacial region during spontaneous and drug-evoked behavior.

Tyrosine-induced release of dopamine is under inhibitory control of presynaptic dopamine D2 and, probably, D3 receptors in the dorsal striatum, but not in the nucleus accumbens

Stimulation of dopamine D2-like receptors decreases extracellular dopamine in the dorsal striatum and the nucleus accumbens. It is unknown whether the role of these receptors differs from that of dopamine D3 receptors. It is also unknown to what extent the role of these two types of receptors varies across both structures. Using microdialysis, we therefore investigated whether intracerebrally administered quinpirole, a dopamine D2-like receptor agonist, and PD 128907, (S(+)-(4aR,10bR)-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]-benzopyrano[4,3-b]-1,4-oxazin-9-ol, a dopamine D3 receptor preferring agonist, differentially alter the tyrosine-induced increase of extracellular dopamine in the dorsal striatum and the nucleus accumbens, respectively. Perfusion of tyrosine (100 microM) into the dorsal striatum and the nucleus accumbens enhanced extracellular dopamine in a physiological manner in both areas. Infusion of the Na(+) channel blocker tetrodotoxin (2 microM) suppressed the enhanced level of dopamine derived from exogenous tyrosine in both brain areas. Infusion of the dopamine D2-like receptor agonist quinpirole at a concentration (1 nM), which alone did not affect basal extracellular dopamine, reduced tyrosine-enhanced extracellular dopamine when infused into the dorsal striatum, but not into the nucleus accumbens; the preferential dopamine D3 receptor agonist, PD 128907, had similar effects. Haloperidol, a dopamine D2-like receptor antagonist, given systemically at a dose, which alone did not significantly affect basal dopamine levels (10 nmol/kg i.p.), enhanced extracellular dopamine derived from exogenous tyrosine. This haloperidol treatment antagonized only the quinpirole-induced, but not the PD 128907-induced reduction in dopamine levels seen in tyrosine-treated rats. The results show that extracellular dopamine derived from exogenous tyrosine is under inhibitory control of presynaptic dopamine D2-like receptors in the dorsal striatum, but not in the nucleus accumbens; to what extent the same holds for dopamine D3 receptors remains to be proven. Future studies are required to elucidate whether the noted difference is absolute or not.

Dopaminergic and cholinergic stimulation of the ventrolateral striatum elicit rat jaw movements that are funnelled via distinct efferents

It has been reported that two distinct types of jaw movements can be elicited by bilateral injections of drugs into the ventrolateral striatum: (1) dopamine receptor-mediated jaw movements that are elicited by a mixture of (+/-)-6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol (SKF 82958; 5 microg) and quinpirole (10 microg), and (2) acetylcholine receptor-mediated jaw movements that are elicited by carbachol (2.5 microg). In the present study, electromyographic analysis was used to characterise these movements: the dopamine receptor-mediated jaw movements were marked by a dominant digastric activity during jaw opening and a dominant masseter activity during jaw closing (digastric/masseter type), whereas the acetylcholine receptor-mediated jaw movements were marked by a dominant digastric activity during jaw opening without any significant change in masseter activity during jaw closing (digastric type). The main goal was to (in)validate the hypothesis that these two types of jaw movements are funnelled via distinct gamma-aminobutyric acid (GABA)ergic output channels. Bilateral injections of both muscimol (25 and 50 ng/0.2 microl per side) and bicuculline (50 and 150 ng/0.2 microl per side) into the ventral pallidum, entopeduncular nucleus or dorsolateral part of the substantia nigra pars reticulata essentially inhibited dopamine receptor-mediated jaw movements to various degrees. In contrast, acetylcholine receptor-mediated jaw movements were inhibited by muscimol given into the entopeduncular nucleus and dorsolateral part of the substantia nigra pars reticulata, whereas these movements were enhanced by bicuculline. The acetylcholine receptor-mediated jaw movements were not affected by muscimol injections into the ventral pallidum, but were inhibited by bicuculline injections. Studies on such injections into the ventral pallidum, entopeduncular nucleus or dorsolateral part of the substantia nigra pars reticulata of naive rats revealed that jaw movements of the digastric/masseter type were elicited either by muscimol injections into the dorsolateral part of the substantia nigra pars reticulata or by combined injections of muscimol and bicuculline into the entopeduncular nucleus, and that jaw movements of the digastric type were elicited only by combined injections of muscimol and bicuculline into the entopeduncular nucleus. Together, the data allow the conclusion that dopamine receptor-mediated and acetylcholine receptor-mediated jaw movements are two distinct types of jaw movements that are funnelled via separate GABAergic output channels. It is suggested that the three different profiles of responses to GABAergic drugs in animals showing either dopamine receptor-mediated or acetylcholine receptor-mediated jaw movements reflect the involvement of three distinct types of output neurons of the striatum, namely: type I neurons with collateralised axons to the ventral pallidum, entopeduncular nucleus and dorsolateral part of the substantia nigra pars reticulata, mediating the dopamine receptor-mediated jaw movements; type II neurons with collateralised axons to the globus pallidus that, in turn, project to the entopeduncular nucleus and the dorsolateral part of the substantia nigra pars reticulata, mediating directly the acetylcholine receptor-mediated jaw movements; and type III neurons with a single axon to the ventral pallidum, mediating indirectly the acetylcholine receptor-mediated movements. It is evident that future studies are required to provide direct evidence in favour of the latter hypothesis.

Phenotypic resolution of spontaneous and D1-like agonist-induced orofacial movement topographies in congenic dopamine D1A receptor 'knockout' mice

A novel system was used to assess the role of D(1)-like dopamine receptors in distinct topographies of orofacial movements in mice with congenic D(1A) receptor knockout. Under spontaneous conditions, vertical jaw movements in wild-types declined with time at a rate that was reduced in D(1A) mutants, while horizontal jaw movements emerged progressively in wild-types but not in D(1A) mutants; tongue protrusions were absent in D(1A) mutants, while incisor chattering was initially reduced in D(1A) mutants but rose subsequently to reach the level of wild-types. D(1A) receptors exert a topographically specific role in regulating individual spontaneous orofacial movements, and these involve interactions with psychomotor processes which 'sculpt' behavioural change over time. The anomalous D(1)-like agonist SK&F 83959, which fails to stimulate, and indeed inhibits the stimulation of adenylyl cyclase induced by dopamine, readily stimulated vertical jaw movements, tongue protrusions and incisor chattering, and these response topographies were absent in D(1A) mutants. These results suggest that D(1A) receptors may exert some form of permissive role over orofacial topographies initiated via a novel, putative D(1)-like site not linked to adenylyl cyclase, or that some D(1A) receptors might be coupled to a transduction system other than adenylyl cyclase.

Involvement of laminin binding integrins and laminin-5 in branching morphogenesis of the ureteric bud during kidney development

Branching morphogenesis of the ureteric bud (UB) [induced by the metanephric mesenchyme (MM)] is necessary for normal kidney development. The role of integrins in this complex developmental process is not well understood. However, the recent advent of in vitro model systems to study branching of UB cells and isolated UB tissue makes possible a more detailed analysis of the integrins involved. We detected integrin subunits alpha3, alpha6, beta1, and beta4 in both the UB and cells derived from the early UB. Blocking the function of each of these integrin subunits individually markedly inhibited branching morphogenesis in cell culture models. However, inhibiting individual integrin function with blocking antibodies in whole kidney and isolated UB culture only partially inhibited UB branching morphogenesis, suggesting that, in these more complex in vitro systems, multiple integrins are involved in the branching program. In whole organ and isolated bud culture, marked retardation of UB branching was observed only when both alpha3 and alpha6 integrin subunits were inhibited. The alpha6 integrin subunit can be expressed as both alpha6beta1 and alpha6beta4, and both of these beta subunits are important for UB branching morphogenesis in both cell and organ culture. Furthermore, laminin-5, a common ligand for integrins alpha3beta1 and alpha6beta4, was detected in the developing UB and shown to be required for normal UB branching morphogenesis in whole embryonic kidney organ culture as well as isolated UB culture. Together, these data from UB cell culture, organ culture, and isolated UB culture models indicate that both integrin alpha3 and alpha6 subunits play a direct role in UB branching morphogenesis, as opposed to being modulators of the inductive effects of mesenchyme on UB development. Furthermore the data are consistent with a role for laminin-5, acting through its alpha3beta1 and/or alpha6beta4 integrin receptors, in UB branching during nephrogenesis. These data may help to partially explain the renal phenotype seen in integrin alpha3 and alpha3/alpha6 subunit-deficient animals.

Cooperative interactions of laminin 5 gamma2 chain, matrix metalloproteinase-2, and membrane type-1-matrix/metalloproteinase are required for mimicry of embryonic vasculogenesis by aggressive melanoma

Vasculogenic mimicry describes a process where aggressive tumor cells in three-dimensional matrices mimic embryonic vasculogenesis by forming extracellular matrix (ECM)-rich, patterned tubular networks. Microarray gene chip analyses revealed significant increases in the expression of laminin 5 (Ln-5, gamma2 chain) and matrix metalloproteinases (MMP)-1, -2, -9, and MT1-MMP (MMP-14) in aggressive compared with poorly aggressive melanoma cells. These components colocalized with developing patterned networks and antisense oligonucleotides to the Ln-5 gamma2 chain (but not sense oligonucleotides), and antibodies to MMP-2 or MT1-MMP (but not MMP-9) inhibited the formation of these networks. Cultures which did not receive antibodies to either MMPs-2 or -14 contained the Ln-5 gamma2 chain promigratory cleavage fragments. Poorly aggressive melanoma cells seeded on collagen I matrices preconditioned by the aggressive cells formed tubular networks along the Ln-5 gamma2 chain-enriched tracks deposited by the aggressive cells. These results suggest that increased expression of MMP-2 and MT1-MMP, along with matrix deposition of the Ln-5 gamma2 chain and/or its cleavage fragments, are required for vasculogenic mimicry by aggressive melanoma cells. Furthermore, the apparent recapitulation of laminin-rich, patterned networks observed in aggressive melanoma patients' tissue sections by aggressive melanoma tumor cells in three-dimensional culture may also serve as a model to help identify specific molecular targets which could function as templates for the coordinated migration of aggressive tumor cells and their proteolytic remodeling of the ECM and may have profound implications for the development of novel therapies directed at the ECM to alter tumor progression.

The LG3 module of laminin-5 harbors a binding site for integrin alpha3beta1 that promotes cell adhesion, spreading, and migration

Laminins are a family of extracellular matrix glycoproteins involved in cell adhesion and migration. A major obstacle to understanding their structure-function relationships is the lack of small laminin domains capable of replicating integrin-binding, cell-adhesive, and migratory functions of the intact molecule. Here, we show that the recombinant LG3 (rLG3) module (26 kDa) of laminin-5 (Ln-5) alpha(3) chain replicated key Ln-5 activities. rLG3 but not rLG1 or rLG2 supported cell adhesion and migration of at least two distinct cell lines, in an integrin alpha(3)beta(1)-dependent manner. Cell adhesion to rLG3 was regulated by divalent cations and accompanied by cell spreading and tyrosine phosphorylation of FAK focal adhesion kinase. The integrin binding activity of rLG3 was confirmed by rLG3 affinity chromatography of detergent cell lysates, which resulted in specific purification of integrin alpha(3)beta(1). To our knowledge, this is the first report directly demonstrating that a recombinant laminin LG module is an active domain capable of supporting integrin-dependent cell adhesion and migration.