The interrelationship between superior colliculus and substantia nigra pars reticulata in programming movements of cats

Dopamine, schizophrenia, mania, and depression: Toward a unified hypothesis of cortico-striatopallido-thalamic function

Considerable evidence from preclinical and clinical investigations implicates disturbances of brain dopamine (DA) function in the pathophysiology of several psychiatric and neurologic disorders. We describe a neural model that may help organize theseindependent experimental observations. Cortical regions classically associated with the limbic system interact with infracortical structures, including the nucleus accumbens, ventral pallidum, and dorsomedial nucleus of the thalamus. In our model, overactivity in forebrain DA systems results in the loss of lateral inhibitory interactions in the nucleus accumbens, causing disinhibition of pallidothalamic efferents; this in turn causes rapid changes and a loss of focused corticothalamic activity in cortical regions controlling cognitive and emotional processes. These effects might be manifested clinically by some symptoms of psychoses. Underactivity of forebrain DA results in excess lateral inhibition in the nucleus accumbens, causing tonic inhibition of pallidothalamic efferents; this perpetuates tonic corticothalamic activity and prevents the initiation of new activity in other critical cortical regions. These effects might be manifested clinically by some symptoms of depression. This model parallels existing explanations for the etiology of several movement disorders, and may lead to testable inferences regarding the neural substrates of specific psychopathologies.

Differential progression of proprioceptive and visual information processing deficits in Parkinson's disease

Indirect evidence suggests that patients with Parkinson's disease (PD) have deficits not only in motor performance, but also in the processing of sensory information. We investigated the role of sensory information processing in PD patients with a broad range of disease severities and in a group of age-matched controls. Subjects were tested in two conditions: pointing to a remembered visual target in complete darkness (DARK) and in the presence of an illuminated frame with a light attached to the index finger (FRAME). Differences in pointing errors in these two conditions reflect the effect of visual feedback on pointing. PD patients showed significantly larger constant and variable errors than controls in the DARK and FRAME condition. The difference of the variable error in the FRAME and DARK condition decreased as a function of the severity of PD. This indicates that any deficits in the processing of proprioceptive information occur already at very mild symptoms of PD, and that deficits in the use of visual feedback develop progressively in later stages of the disease. These results provide a tool for early diagnosis of PD and shed new light on the functional role of the brain structures that are affected in PD.

6-hydroxydopamine lesion in the A8 cell group of cats produces a short-lasting decreased accuracy in goal-directed forepaw-movements

Recently, feline studies have shown that a lesion in the retrorubral area, which includes the dopaminergic A8 cell group, produces motor programming deficits inherent to a hypofunction of the A9 system. A hypofunction in the striatal terminal area of A9 fibers, in turn, is known to produce a hypofunction of its first-order output station, namely the substantia nigra pars reticulata (SNR). The integrity of the SNR allows animals to execute (1) 'postural adjustments that rely on proprioceptive stimuli that originate in body parts at rest' and (2) 'non-externally guided' targeting movements. In view of these considerations, the (dys)function of the SNR of cats with a bilaterally 6-hydroxydopamine lesion of A8 cells in the retrorubral area was tested in an experimental set-up that allows the assessment of changes in these functions. The A8 lesion produced: (a) a short-lasting increase in the number of accurate targeting movements as well as an increase in the time required for the collection of six pellets: these deficits disappeared 4-7 days after the lesion; (b) a long-lasting disappearance of (1) 'postural adjustments that rely on proprioceptive stimuli that originate in body parts at rest' and (2) 'non-externally guided targeting movements'; and (c) a long-lasting display of a new strategy that allowed the lesioned cat to collect its pellets despite of its other deficits. These data led to the conclusion that a lesion of A8 cells even disrupts the function of the SNR, being one of the outputstations of the A8 cell group.

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)

Eye movement-related neurons in the red nucleus

Extracellular unit activity of the parvocellular red nucleus (RN) and spontaneous horizontal eye movements were recorded in adult, nitrous oxide-anesthetized and C1 transected cats. It was found that 7.5% of the neurons of each RN were related to spontaneous horizontal saccadic eye movements. Three types of neurons were observed: (1) bidirectional neurons which increased their frequency of discharge in relation to any horizontal eye movement; (2) unidirectional neurons which altered their frequency of discharge in relation to a horizontal eye movement of a precise direction; and (3) neurons which increased their frequency of discharge in relation to the rapid phase of an horizontal nystagmus. These 3 types of neurons modified their frequency of discharge before the initiation of the eye movement. One pair of oculomotor neurons recorded simultaneously in both RN showed a significant correlation coefficient. These results suggest that the RN may contribute to the preparation or execution of horizontal eye movements.

Behavioral correlates of a progressive dysfunctioning of the deeper layers of the colliculus superior: effects of picrotoxin

Intracaudate injections of relatively high doses of apomorphine produce a regression in motor behavior of cats collecting food pellets in a treadmill design (25). It has been hypothesized that this regression is partly due to functional disturbances in brain regions receiving (in) directly striatal output signals. In view of this hypothesis it was investigated whether experimentally induced changes in GABAergic activity within the deeper layers of the colliculus superior, which is a second order output station of the caudate nucleus, are also able to elicit a regression in motor behavior. Therefore, motor behavior of cats was tested in the treadmill paradigm before and after intracollicular injections of the GABA antagonist picrotoxin. Picrotoxin produced dose-dependently a regression in motor behavior which was comparable to that elicited by intrastriatally injected apomorphine. The noted effects were GABA-specific since muscimol attenuated the picrotoxin-induced regression. The present data are discussed in view of a model for a hierarchical organization of the brain.

Effects of intrastriatal apomorphine on changes in switching behaviour induced by the glutamate agonist AMPA injected into the cat caudate nucleus

Bilateral intracaudate application of the glutamate agonist DL-alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA), viz. an agonist of quisqualate receptors, is known to produce the following effects in cats that had to climb on a small wooden bar and, subsequently, to switch to distinct patterns: it produces increases in switching from one pattern to another pattern (1) and it induces limb deficits, i.e. unilateral deficient placing of the fore- and/or hindlimb. In the present study, the effect of stimulating striatal dopamine receptors on behavioural changes induced by intracaudate injections of AMPA was investigated. Therefore, the dopamine agonist apomorphine was injected into the caudate nucleus 5 min before the striatal injection of 1.0 micrograms AMPA. AMPA-induced increases in switching behaviour were prevented by 0.6 micrograms, but not 0.3 micrograms, apomorphine. In contrast, AMPA-induced limb deficits were not prevented by pretreatment of apomorphine. In view of the notion that the dopaminergic caudate nucleus, its output station the substantia nigra, pars reticulata and the nigral output station the deeper layers of the colliculus superior are essential for switching behaviour, but not for the display of disturbances like AMPA-induced limb deficits, the present data strongly suggest that only AMPA-induced changes in switching, but not AMPA-induced limb deficits, are mediated by the caudato-nigro-collicular circuitry. The glutamate receptor-selectivity of the modulatory action of dopamine is discussed.

Search after neurobiological profile of individual-specific features of Wistar rats

The first part of this study demonstrates that the bimodal shape of variation in "fleeing" and "nonfleeing" or "freezing" rats of an outbred strain of Wistar rats forms part of an overall biomodal variation in behavioural responses to injections of agents, which selectively alter, or reflect, the noradrenergic or dopaminergic activity in the ventral striatum, and dopaminergic activity in the dorsal striatum, the GABA-ergic activity in the substantia nigra, pars reticulata, and the GABA-ergic activity in the deeper layers of the superior colliculus. It is concluded that the "fleeing" and "nonfleeing" rats, each of them marked by their own trans-situational consistency in pharmacological and behavioural responses, represent the two fundamentally different types of individuals which normally exist in unselected populations of rodents. The second part of this study demonstrates that the pharmacogenetic selection of apomorphine-susceptible (APO-SUS) and apomorphine-unsusceptible (APO-UNSUS) rats, i.e., one individual-specific feature of the overall bimodal variation for pharmacological responses in our outbred strain of rats, is a valid tool to disperse the above-mentioned individual-specific features as far as possible. First, these lines allowed us to prove that the overall bimodal shape of variation in pharmacological and behavioral responses of individual outbred rats is in part genetically determined. Second, these lines allowed us to prove that a bimodal variation in neurochemical features of the circuitry, in which the ventral striatum is embedded, underlies the overall bimodal variation in pharmacological and behavioural responses. Third, these lines allowed us to demonstrate that a fundamental difference in organizing behaviour with the help of external and internal information has to be considered as a common factor giving rise to the individual differentiation found in the present study. Given the notion that this individual differentiation appears to be valid across lines, substrains and strains of rats, the present study lays the foundation for understanding at least a part of the physiological basis underlying differences between the two fundamentally different types of individuals existing in normal populations of rodents.

Local as well as remote functional and metabolic changes after focal ischemia in cats

Behavior and limb placing ability were analyzed acutely and subacutely (up to 21 days) following unilateral occlusion of the middle cerebral artery (MCA) in cats. Immediately following occlusion, all tested cats started to display a sequence of different behaviors, characteristic for 1) an ipsilateral inhibition of dopaminergic activity in the caudate nucleus (CN); 2) an inhibition of GABAergic activity in the reticular substantia nigra (SNR); 3) a stimulation of GABA receptors in the deeper layers of the colliculus superior (CSDL) (starting-time of these phases: about 4, 12 and 25 min, respectively). The latter behavior was also present subacutely. In addition, unilateral orofacial dyskinetic movements were observed acutely as well as subacutely. Contralateral limb placing was deficient in all cats 60 min postocclusion; it was at least partly restored subacutely. Twenty-one days after the occlusion, [14C]-2-D-deoxyglucose uptake was relatively reduced in the ipsilateral CN (especially in its posterior part), the ipsilateral SNR and the ipsilateral CSDL. The anterior CN appeared to be less affected than the posterior CN. Metabolism was relatively reduced in the sensorimotor cortex only in part of the tested cats. The data show that unilateral MCA occlusion produces consistent functional changes in all structures studied apart from the sensorimotor cortex, viz. the CN, the SNR and the CSDL.

Interconnections between substantia nigra reticulata and medullary reticular formation

Injections of wheat germ agglutinin-HRP into the medullary reticular formation (MRf) or the substantia nigra reticulata (SNr) revealed the presence of reciprocating fiber connections between the two areas. Large injections in the MRf demonstrated the existence of labeled neurons in the lateral portions of the SNr. Isolated injections into the parvocellular nuclei of the MRf resulted in the presence of terminal fields in the SNr particularly its lateral portions. Injections in the SNr resulted in the presence of labeled cells in the parvocellular nuclei. The significance of these findings is discussed in terms of oro-facial dyskinesias.

Effect of intracaudate haloperidol and apomorphine on switching motor patterns upon current behaviour of cats

Previous studies using various experimental set-ups, have shown that the dopaminergic activity in the caudate nucleus (CN) is involved in the organism's ability to switch from one motor or behavioural program to another without the help of external stimuli (switching arbitrarily). The main purpose of the present study was to investigate how arbitrarily switching motor patterns manifests itself in an 'open field situation'. Therefore, the effects of CN application of haloperidol (12.5 micrograms/5 microliter) and apomorphine (0.6 micrograms/5 microliter) were analyzed on the ability to switch from one motor program to any other program in cats habituated to an observation cage. Application of haloperidol decreased switching. In addition the number of distinct motor patterns declined after injecting haloperidol into the CN. The haloperidol-induced effect, however, was not selectively restricted to any particular motor pattern. Switching from one motor pattern to another increased after CN injection of apomorphine. Moreover, the number of distinct motor patterns increased after CN injection of apomorphine. However, the effect of CN application of apomorphine was not selectively restricted to any particular motor pattern. Since previous studies have demonstrated that various expressions of dopaminergic CN activity are funnelled through the deeper layers of the superior colliculus (dl-SC), it was hypothesized that switching induced by CN application of apomorphine may also be channelled through the dl-SC. Therefore the effect of dl-SC-injected muscimol (75 ng/1 microliter) was analyzed on the ability to switch motor programs in cats pretreated with apomorphine. Injection of muscimol into the dl-SC reduced both the number of distinct motor patterns and the number of switchings in cats pretreated with apomorphine.

Effect of increasing doses of intracaudate haloperidol upon motor expressions that require an intact substantia nigra pars reticulata and/or superior colliculus in cats

In the present study it was investigated whether intracaudate (CN) injections of increasing doses of haloperidol progressively affect movements that require the integrity of the substantia nigra pars reticulata (SNR) and/or the deeper layers of the superior colliculus (dl-SC) in cats. Therefore, cats were trained to walk from one side of a narrow bar to the other side both under full light and under stroboscopic illumination (2 flashes/s). Previously it has been shown that this set-up is useful for assessing changes in the execution of dl-SC and SNR-related non-externally guided targeting movements. Moreover, cats were trained to step out of a startbox on a rotating cylinder which, according to previous studies, also implies the execution of a dl-SC- and SNR-related non-externally guided targeting movement. CN application of 25 micrograms/5 microliters haloperidol, but not CN injection of 12.5 micrograms/5 microliters haloperidol or apomorphine (0.6 micrograms/5 microliters), reduced the occurrence of these dl-SC- and SNR-related targeting movements. Dl-SC injection of picrotoxin (100 ng/0.5 microliter) did not restore the haloperidol (25 micrograms/5 microliter) induced decrement in the occurrence of these targeting movements. In addition, CN application of 25 micrograms/5 microliter haloperidol, but not 12.5 micrograms/5 microliter haloperidol, reduced the feline ability to execute SNR-specific limb movements while crossing a revolving cylinder. The present results show that only a severe but not a moderate inhibition of dopamine receptors within the CN affects motor expressions characteristic of the SNR and/or dl-SC.

Movements of cats on a rotating cylinder: role of the substantia nigra pars reticulata and the deeper layers of the superior colliculus

Recently it has been shown that the substantia nigra pars reticulata (SNR) is required for adjusting the body position. In this study the role of the SNR in the execution of movements was investigated. Therefore, the effects of bilateral SNR injections of picrotoxin (500 ng/0.5 microliter) and muscimol (200 ng/1 microliter) were investigated on movements of cats which were trained to cross a rotating cylinder. SNR injection of picrotoxin suppressed the movements that were executed by cats injected with distilled water (0.5 microliter), i.e. 'normal movements'. While crossing the rotating cylinder, picrotoxin-injected cats mainly executed movements that almost never occurred in distilled water treated cats. Picrotoxin-injected cats executed 'special movements', i.e. forward locomotion in which the hindlimbs were affected, and 'counter-movements'. While executing the latter movements no forward locomotion occurred at all; the cats solely executed lateral fore- and hindlimb movements opposite to the direction in which the cylinder rotated. SNR application of muscimol enhanced the execution of 'normal movements'. Since the SNR sends information to the deeper layers of the superior colliculus (dl-SC) via GABAergic fibers, it was also investigated whether pharmacological stimulation (muscimol) and inhibition (picrotoxin) of the GABAergic dl-SC activity affected these movements on the rotating cylinder: no changes were observed after injecting otherwise effective doses of muscimol (75 ng/1 microliter) and picrotoxin (100 ng/0.5 microliter). In order to compare the function of the SNR and dl-SC in programming a different type of movements, the effects of GABAergic agents in the dl-SC (picrotoxin 100 ng/0.5 microliter and muscimol 75 ng/1 microliter) and the SNR (picrotoxin 500 ng/0.5 microliter and muscimol 200 ng/1 microliter) were investigated on the feline ability to execute goal-directed movements in an experimental set-up that prevented the occurrence of targeting movements which were continuously guided by external, i.e. auditory, visual, tactile and olfactory stimuli. For that purpose cats were trained to step out of a startbox on a rotating cylinder, i.e. the target. Dl-SC injection of muscimol or SNR application of picrotoxin prevented the cats from stepping out of the startbox on the rotating cylinder. In contrast, cats injected with muscimol into the SNR or picrotoxin into the dl-SC stepped out of the startbox, although dl-SC application of picrotoxin elicited forelimb misplacements: frequently the cats placed their forelimbs alongside of, but not on the cylinder when trying to leave the startbox.(ABSTRACT TRUNCATED AT 400 WORDS)

The interrelationship between superior colliculus and substantia nigra pars reticulata in programming movements of cats: a follow-up

The present feline study deals with the execution of targeting movements which can be elicited either by injection of picrotoxin into the deeper layers of the superior colliculus (dl-SC) or by application of muscimol into the substantia nigra pars reticulata (SNR), and suppressed either by dl-SC injection of muscimol or by SNR application of picrotoxin: the movements under discussion are the so-called non-externally guided targeting movements, i.e. targeting movements that are elicited but not continuously guided by external (visual, auditory, olfactory and tactile) stimuli. In this study we investigated whether the integrity of the SNR is required for the execution of these targeting movements elicited from the dl-SC. Cats were trained, therefore, to walk from one side of a narrow bar to the other side under stroboscopic illumination (2 flashes/s). The animals received bilateral injections both into the SNR (solvent 0.5 microliter or picrotoxin 500 ng/0.5 microliter) and into the dl-SC (solvent 0.5 microliter or picrotoxin 50-100 ng/0.5 microliter). Injections of picrotoxin into the dl-SC did not evoke non-externally guided targeting movements in case picrotoxin was also injected into the SNR. It is concluded that the integrity of the SNR is required for the execution of non-externally guided targeting movements elicited from the dl-SC. Besides, we investigated whether freezing, i.e., an SNR-specific effect, which can be evoked by injection of picrotoxin into this area, is funnelled through the dl-SC. Therefore, the behaviour of cats which had received bilateral injections both into the SNR (solvent 0.5 microliter or picrotoxin 500 ng/0.5 microliter) and into the dl-SC (solvent 0.5 microliter or picrotoxin 50-100 ng/0.5 microliter) was analysed. Application of picrotoxin into the dl-SC did not suppress the occurrence of freezing, elicited by SNR injection of picrotoxin. It is concluded that the SNR-specific freezing is not channelled through the dl-SC.