Activation and lateralization of sensorimotor field for perioral biting reflex by intranigral GABA agonist and by systemic apomorphine in the rat

Behavioral lateralization of mice varying in serotonin transporter genotype

In humans, non-right-handedness is associated with a higher incidence of psychiatric disorders. Since serotonin seems to be involved in both, the development of psychiatric disorders and lateralization, the present study focuses on the effect of the serotonin transporter (5-HTT) gene on behavioral lateralization. For this, we used the 5-HTT knockout mouse model, a well-established animal model for the study of human depression and anxiety disorders. For female mice from all three 5-HTT genotypes (wild type, heterozygous, and homozygous knockout), we repeatedly observed the direction and strength of lateralization of the following four behaviors: grid climbing (GC), food-reaching in an artificial test situation (FRT), self-grooming (SG), and barrier crossing (BC), with the FRT being the standard test for assessing behavioral lateralization in mice. We found no association between behavioral lateralization and 5-HTT genotype. However, in accordance with previous findings, the strength and temporal consistency of lateralization differed between the four behaviors observed. In conclusion, since the 5-HTT genotype did not affect behavioral lateralization in mice, more research on other factors connected with behavioral lateralization and the development of symptoms of psychiatric disorders, such as environmental influences, is needed.

An internal model architecture for novelty detection: implications for cerebellar and collicular roles in sensory processing

The cerebellum is thought to implement internal models for sensory prediction, but details of the underlying circuitry are currently obscure. We therefore investigated a specific example of internal-model based sensory prediction, namely detection of whisker contacts during whisking. Inputs from the vibrissae in rats can be affected by signals generated by whisker movement, a phenomenon also observable in whisking robots. Robot novelty-detection can be improved by adaptive noise-cancellation, in which an adaptive filter learns a forward model of the whisker plant that allows the sensory effects of whisking to be predicted and thus subtracted from the noisy sensory input. However, the forward model only uses information from an efference copy of the whisking commands. Here we show that the addition of sensory information from the whiskers allows the adaptive filter to learn a more complex internal model that performs more robustly than the forward model, particularly when the whisking-induced interference has a periodic structure. We then propose a neural equivalent of the circuitry required for adaptive novelty-detection in the robot, in which the role of the adaptive filter is carried out by the cerebellum, with the comparison of its output (an estimate of the self-induced interference) and the original vibrissal signal occurring in the superior colliculus, a structure noted for its central role in novelty detection. This proposal makes a specific prediction concerning the whisker-related functions of a region in cerebellar cortical zone A₂ that in rats receives climbing fibre input from the superior colliculus (via the inferior olive). This region has not been observed in non-whisking animals such as cats and primates, and its functional role in vibrissal processing has hitherto remained mysterious. Further investigation of this system may throw light on how cerebellar-based internal models could be used in broader sensory, motor and cognitive contexts.

Regulation of the Bcas1 and Baiap3 transcripts in the subthalamic nucleus in mice recovering from MPTP toxicity

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) exposure leads to significant and irreversible damage to dopaminergic neurons in both mice and humans. While MPTP exposure in humans causes permanent symptoms of Parkinson's disease, MPTP treated mice will recover behaviorally over a 3-week period. This mouse specific recovery might be linked to transcriptional changes in the basal ganglia enabling mice to maintain normal motor function in spite of low striatal dopamine levels. Laser microdissection was used to isolate the subthalamic nucleus from mice 7 and 28 days following MPTP exposure. High quality RNA was recovered and expressional analysis was performed on whole mouse genome microarrays. Identified regulated transcripts were validated in a separate batch of animals using quantitative PCR. Two transcripts with a significant regulation from days 7 to 28 in the MPTP treated groups, were identified: the brain specific angiogenesis inhibitor associated protein 3 (Baiap3) and the breast carcinoma amplified sequence 1 (Bcas1). Further studies of the molecular pathways involving these two transcripts may uncover processes in the subthalamic nucleus associated with the behavioral recovery observed after MPTP exposure.

Topographic and functional neuroanatomical study of GABAergic disinhibitory striatum–nigral inputs and inhibitory nigrocollicular pathways: Neural hodology recruiting the substantia nigra, pars reticulata, for the modulation of the neural activity in the inferior colliculus involved with panic-like emotions

Considering the influence of the substantia nigra on mesencephalic neurons involved with fear-induced reactions organized in rostral aspects of the dorsal midbrain, the present work investigated the topographical and functional neuroanatomy of similar influence on caudal division of the corpora quadrigemina, addressing: (a) the neural hodology connecting the neostriatum, the substantia nigra, periaqueductal gray matter and inferior colliculus (IC) neural networks; (b) the influence of the inhibitory neostriatonigral-nigrocollicular GABAergic links on the control of the defensive behavior organized in the IC. The effects of the increase or decrease of activity of nigrocollicular inputs on defensive responses elicited by either electrical or chemical stimulation of the IC were also determined. Electrolytic or chemical lesions of the substantia nigra, pars reticulata (SNpr), decreased the freezing and escape behaviors thresholds elicited by electrical stimulation of the IC, and increased the behavioral responses evoked by the GABAA blockade in the same sites of the mesencephalic tectum (MT) electrically stimulated. These findings were corroborated by similar effects caused by microinjections of the GABAA-receptor agonist muscimol in the SNpr, followed by electrical and chemical stimulations of the IC. The GABAA blockade in the SNpr caused a significant increase in the defensive behavior thresholds elicited by electrical stimulation of the IC and a decrease in the mean incidence of panic-like responses induced by microinjections of bicuculline in the mesencephalic tectum (inferior colliculus). These findings suggest that the substantia nigra receives GABAergic inputs that modulate local and also inhibitory GABAergic outputs toward the IC. In fact, neurotracing experiments with fast blue and iontophoretic microinjections of biotinylated dextran amine either into the inferior colliculus or in the reticular division of the substantia nigra demonstrated a neural link between these structures, as well as between the neostriatum and SNpr.

The unilateral 6-OHDA rat model of Parkinson's disease revisited: an electromyographic and behavioural analysis

The characteristic locomotor disturbances of Parkinson's disease (PD) include shuffling gait, short steps and low walking velocity. In this study we investigated features of walking and turning in a rat model of PD caused by unilateral infusion of the neurotoxin 6-hydroxydopamine (6-OHDA). We assessed gait and electromyographic (EMG) patterns of the ankle flexor tibialis anterior and the knee extensor vastus lateralis of the hindlimb, and triceps brachii of the forelimb, during overground locomotion, spontaneous rotation (turning) and apomorphine-induced rotation. When compared with control rats, rats with unilateral dopamine depletion displayed a shuffling gait and short stride lengths. This locomotor pattern was accompanied by prolonged ankle flexor activity on the ipsilateral side, and prolonged activity of knee extensors on the contralateral side. The dopamine depletion also led to enhanced contraversive rotations after an apomorphine challenge. The EMG recordings during drug-induced rotation suggested that hindlimb stepping was a reflective response to an active drive produced by forelimbs. The EMG recordings of the contralateral side during rotation were marked by reduced ankle flexor activity and increased knee extensor activity. Furthermore, EMG recordings indicated that dopamine-agonists induce rotational bias by altering the coupling between ipsi- and contralateral hindlimbs, and between forelimbs. In straight walking, however, the gait of 6-OHDA lesion animals reflected normal, coupled hindlimb stepping as controlled by spinal pattern generators. The data suggest that the unilateral rat model of PD resembles key features of human parkinsonian gait, and that asymmetric descending input may underlie the observed changes in gait patterns.

Gabaergic regulation of the neural organization of fear in the midbrain tectum

In midbrain tectum (MT) structures, such as the dorsal periaqueductal gray (dPAG), the superior colliculus (SC) and the inferior colliculus (IC) GABAergic neurons exert a tonic control on the neural substrates involved in the expression of defensive reactions. In this review, we summarize behavioral, immunohistochemical (brain Fos distribution) and electrophysiological (auditory evoked potentials) data obtained with the reduction of GABA transmission by local injections of a GABA receptor blocker (bicuculline, BIC) or a glutamic acid decarboxylase inhibitor (semicarbazide, SMC) into the MT. Distinct patterns of Fos distribution were obtained following the freezing and escape reactions induced by MT injections of SMC and BIC, respectively. While only the laterodorsal nucleus of the thalamus was labeled after SMC-induced freezing, a widespread increase in Fos expression in the brain occurred after BIC-induced escape. Also, injections of SMC into the IC increased the auditory evoked potentials recorded from this structure. It is suggested that GABAergic mechanisms of MT are also called into play when sensory gating of the MT is activated during different emotional states.

Defense reaction mediated by NMDA mechanisms in the inferior colliculus is modulated by GABAergic nigro-collicular pathways

Electrical stimulation of the inferior colliculus (IC) causes a behavioral activation together with autonomic responses similar to fear reactions to threatening situations. GABAergic mechanisms exert a tonic inhibitory control on the neural substrates of aversion in the IC insofar as local injections of GABA agonists or antagonists inhibit or mimic these defensive behaviors, respectively. Recently, we have shown that systemic injections of the GABA-A receptor agonist muscimol unexpectedly enhanced the freezing and escape responses provoked by gradual increases in the intensity of the electrical stimulation of the IC. Taking into account that the neural circuits mediated by excitatory amino acids (EAA) in the IC may be responsible for the integration of fear states, in the present study we examined whether the defensive behavior induced by local injections of NMDA into the IC is influenced by prior treatment with systemic muscimol and also whether this GABAergic control could be exerted by GABAergic fibers that project to the inferior colliculus from the substantia nigra pars reticulata (SNpr). Rats were implanted with two guide-cannulae aimed at the IC and SNpr through which drug microinfusions with glass micropipette could be made with reduced brain damage. One week after surgery, the animals received either NMDA (7 nmol/0.2 microl) or saline into the IC and were placed into the middle of an enclosure where behavioral responses such as freezing, crossings, jumping, rearing, and turnings could be measured as an indirect index of unconditioned fear. These animals were pretreated either with saline or muscimol (0.5 mg/kg, IP) or with brain injections of saline or muscimol (1 nmol/0.2 ìl into SNpr). NMDA applied into the IC produced a behavioral activation with significant increases in all behavioral measures. IP injections of muscimol or into the SNpr enhanced the defense reaction caused by microinjections of NMDA into the IC. These findings give support to the idea that unconditioned defensive responses generated in the IC may be mediated by NMDA mechanisms. Additionally, a reduction of the inhibitory control exerted by nigrocollicular GABAergic neurons seems to be responsible for the unexpected pro-aversive action of systemic injections of muscimol on the neural substrates of aversion mediated by NMDA in the IC.

The relevance of neuronal substrates of defense in the midbrain tectum to anxiety and stress: empirical and conceptual considerations

The medial hypothalamus, amygdala, and dorsal periaqueductal gray constitute the main neural substrates for the integration of aversive states in the brain. More recently, some regions of the mesencephalon, such as the superior and inferior colliculi have also been proposed as part of this system. In fact, fear-like behaviors often result when these sites are electrically or chemically stimulated. Both the behavioral and autonomic consequences of electrical stimulation of the mesencephalic tectum have been shown to be attenuated by minor tranquilizers, probably through enhancement of gamma-aminobutyric acid (GABA)-mediated neurotransmission, which exerts a tonic inhibitory control on the neural circuits responsible for the so-called defense behavior repertoire. Besides GABA, also 5-hydroxy tryptamine serotonin (5-HT), opioids, neuropeptides, histaminergic and excitatory amino acids have all been implicated in the regulation of anxiety-related behaviors induced by stimulation of midbrain tectum. Efforts have been made to characterize how these neurotransmitters interact with each other in the organization of these reactions to aversive stimulation. In this review, we summarize the evidence linking the brain's defense response systems to the concept of fear-anxiety. Furthermore, a case is made for the consideration of the relevance of this body of data to the search for the physiological underpinnings of depression and its consequences.

Behavioral phenotyping of the MPTP mouse model of Parkinson's disease

In mice, the systemical or intracranial application of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) can lead to severe damage to the nigrostriatal dopaminergic system. This can result in a variety of symptoms concerning motor control resembling those in human Parkinson's disease, such as akinesia, rigidity, tremor, gait and posture disturbances. The aim of this work is to review a variety of behavioral paradigms for these and other symptoms, which have been used to characterize behavioral changes in mice after MPTP treatment. Main results are summarized, and general influential factors as well as potential problems in the experimental procedures are discussed, which should be taken into account when conducting behavioral analyses in mice with parkinsonian symptoms. Since there is reliable evidence (e.g. from strain comparisons) that the susceptibility of the nigrostriatal pathway to neurodegeneration is probably genetically influenced, relevant genes can be expected to be identified in the future. Therefore, the points discussed here will be useful not only for further applications in the MPTP mouse model, but also more generally for the behavioral characterization of future mouse models of PD, e.g. mice with a manipulation of genes relevant to the function of the basal ganglia.

Chronic levodopa therapy does not improve skilled reach accuracy or reach range on a pasta matrix reaching task in 6-OHDA dopamine-depleted (hemi-Parkinson analogue) rats

L-dopa therapy reverses some but not all of the motor deficits in human Parkinson patients. Although a number rat analogues of human Parkinson's disease have been developed for evaluating the efficacy of drug therapies, it is not known whether L-dopa has a similar selective action on the motor symptoms in the rat models. To examine the effectiveness of L-dopa in reversing the motor deficits in rats, we administered 6-OHDA unilaterally to produce hemi-Parkinson rats, which were then trained to reach for food using either their impaired (contralateral to the lesion) limb or their good (ipsilateral to the lesion) limb. To assess the skill, accuracy and range of limb movement, rats reached for pasta from a horizontal array of 260 vertically orientated pieces of pasta. The number and location of pasta pieces taken from this matrix was calculated and the qualitative aspects of the reaching movements were rated. The quantitative data on pasta sticks retrieved indicated that forelimb extension and movement radius around the shoulder joint was reduced by 6-OHDA treatment and did not improve after chronic L-dopa treatment. The qualitative analysis showed that grasping patterns, paw movements and body movements impaired by the lesion were also not improved by L-dopa treatment. These findings are the first in the rat to suggest that whereas L-dopa has a general activating effect on the rat's whole-body movements, as displayed in contralateral rotation, its effectiveness does not extend to skilled forelimb movements. The results are discussed in relationship to the idea that the restoration of some skilled movements may require normal synaptic function.

Evidence for a dissociation between MPTP toxicity and tyrosinase activity based on congenic mouse strain susceptibility

The neurotoxicity induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is one of the most valuable available models for investigating critical aspects of human Parkinson's disease. In order to analyze the relevance of pigmentation for MPTP sensitivity, we compared C57Bl/6 wild-type mice with the albino mutant C57Bl/6J-Tyr(c-2J) of the same strain. These animals were treated either with systemic MPTP or with saline and were examined in behavioral tests. Seven days after treatment, the contents of dopamine and other monoamines were determined postmortem in the neostriatum and ventral striatum. Furthermore, the numbers of tyrosine hydroxylase-positive cells were counted in the substantia nigra and ventral tegmental area. Open field testing showed that rearing activity was drastically reduced as an acute effect of MPTP in both wild type and mutants; however, subsequent recovery to control levels was faster in wild-type mice. Nest building also indicated strain-dependent effects, since it was delayed only in mutants treated with MPTP. Neurochemically, MPTP led to severe neostriatal dopamine depletions, which did not differ significantly between wild-type (72.9%) and mutant mice (82.1%). Less severe dopamine depletions were also found in the ventral striatum. Histologically, a loss of tyrosine hydroxylase-labeled cells was observed only in the substantia nigra of both wild-type and mutant mice (13.3 and 21.3%, respectively), but not in the ventral tegmental area. Together, our data do not provide evidence that tyrosinase-deficient mice are less affected by MPTP treatment than the comparable wild type, thus arguing strongly against the hypothesis that enhanced MPTP sensitivity in pigmented mouse strains is caused by tyrosinase activity.

Regulation of rat cortex function by D1 dopamine receptors in the striatum

Interactions between the basal ganglia and the cerebral cortex are critical for normal goal-directed behavior. In the present study, we used immediate-early genes (c-fos, zif 268) as functional markers to investigated how basal ganglia output altered by stimulation/blockade of D1 dopamine receptors in the striatum affects cortical function. Systemic administration of the mixed D1/D2 receptor agonist apomorphine (3 mg/kg) increased immediate-early gene expression in the striatum and throughout most of the cortex. Unilateral intrastriatal infusion of the selective D1 receptor antagonist SCH-23390 (0.5-10 microg) blocked this response bilaterally in striatum and cortex in a dose-dependent manner. Even apparently regionally restricted blockade of striatal D1 receptors attenuated gene expression throughout striatum and cortex in both hemispheres. Intrastriatal administration of the D1 antagonist inhibited apomorphine-induced sniffing/whisking, whereas other motor behaviors were unaffected. To determine whether such changes in cortical gene expression could reflect altered cortical function, we examined the effects of blocking striatal D1 receptors on whisker stimulation-evoked immediate-early gene expression in the sensorimotor cortex. Apomorphine increased sensory stimulation-evoked gene expression in the barrel cortex, and intrastriatal infusion of SCH-23390 attenuated this effect. These results suggest that stimulation of D1 dopamine receptors in the striatum exerts a widespread facilitatory effect on cortical function.

Effects of dopaminergic drugs, occlusal disharmonies, and chronic stress on non-functional masticatory activity in the rat, assessed by incisal attrition

Observational methods and the recording of nonspecific jaw movements or masticatory muscle activity have been used to evaluate oral parafunctional movements in animal models of bruxism. In this study, we have used a new approach in which the non-functional masticatory activity in the rat was assessed by the measurement of incisal attrition, with the aim of investigating the role of diverse factors involved in the etiology of bruxism. We quantified the attrition rate weekly by making superficial notches in the lower incisors and measuring the distances to the incisor edges. Repeated stimulation of the dopaminergic system with apomorphine led to an enhancement of the non-functional masticatory activity (p < 0.0001). The severity of the apomorphine-induced oral behavior was positively correlated (r(s) = 0.69, p < 0.01) with an increase in the incisal attrition rate (20.9%, p < 0.0001). Apomorphine-induced non-functional masticatory activity was strongly enhanced by the placement of an acrylic cap on both lower incisors (306%, p < 0.0001), but not by the cutting of a lower incisor. Repeated cocaine administration also increased the attrition rate (22.5%, p < 0.0001). However, neither chronic blockade of dopaminergic receptors with haloperidol, nor its withdrawal, modified attrition. In addition, since emotional disturbances are considered to be causal factors of bruxism, we tested whether experimental stress might accelerate tooth wear. Exposure to two different chronic stress regimes did not induce significant changes in incisal attrition. Moreover, exposure to chronic stress after the withdrawal of chronic haloperidol treatment did not alter attrition either. These results partially support the role of the central dopaminergic system in bruxism and suggest that stress, in general, may not be a relevant factor in tooth wear.

Effects of lesions of amygdaloid nuclei and substantia nigra on aversive responses induced by electrical stimulation of the inferior colliculus

Stimulation of the central nucleus of the inferior colliculus causes defensive behavior. In this work we examined the influence of lesions of brain structures involved in the expression of fear, such as periaqueductal gray matter, amygdala, and substantia nigra pars reticulata (SNpr), on these aversive responses. Thus, rats were implanted with an electrode in the central nucleus of the inferior colliculus, for the determination of the thresholds of alertness, freezing, and escape responses. Each rat also bore a cannula implanted in the periaqueductal, amygdala or Snpr for injection of the neurotoxin N-methyl-D-aspartate (8 micrograms/0.8 microliters). The data obtained show that lesion of the central nucleus of the amygdala increases the thresholds of aversive responses whereas lesion of the basolateral complex decreases the threshold of these responses. Lesion of the Snpr increased the aversive consequences of the electrical stimulation of the inferior colliculus whereas periaqueductal gray lesions, either dorsal or ventral regions, did not change these responses. From the evidences obtained in this work, it is suggested that the expression of the defensive behavior induced by activation of the neural substrates of the inferior colliculus does not seem to depend on the integrity of the periaqueductal gray. On the contrary, the basolateral complex inhibits and the central nucleus amplifies the aversive responses integrated in the inferior colliculus. Furthermore, SNpr seems also to be an important motor output for the defensive behavior induced by stimulation of the inferior colliculus, in agreement with what has been suggested for other brain structures implicated in the expression of fear.

Impairments and compensatory adjustments in spontaneous movement after unilateral dopamine depletion in rats

Rats with unilateral dopamine (DA) depletions (hemi-Parkinson rats) display directional biases in their locomotion in spontaneous and drug induced tests. These biases have been explained as being due either to changed responsiveness to sensory stimulation, changes in motor ability, or to central changes, but as yet their basis is not fully understood. The purpose of the present experiment is to examine the posture of immobility and the posture and strategies of locomotion in rats with unilateral DA depletions. The rats are found to display impairments in their bad limbs (contralateral-to-lesion limbs) in adjusting posture and moving. They compensate by supporting themselves mainly on their good hindlimb, using the bad hindlimb and tail for balance and by disproportionately relying upon their good limbs to turn and to walk. Thus, their center of gravity is shifted to the good side and movement is preferentially directed toward the good side, in part to maintain equilibrium and in part to remove weight from the bad limbs so that they can enter the swing phase of the stepping cycle. It is proposed that the bad limbs may be unable to apply force to adjust posture and produce movement. These results provide a basis for predicting the movements that the animals will use in various situations and they expand the test repertoire this hemi-Parkinson model provides for studying recovery processes after loss of dopamine.

Role of the nucleus accumbens and the striatum in the production of turning behaviour in intact rats

Recent knowledge of the mechanisms underlying turning or circling behaviour in intact rats is reviewed. Most interest has been directed towards the striatum because of the classical hypothesis that turning behaviour results from lateral differences in the activity of the bilateral nigrostriatal pathway. However, the assumption that asymmetrical activation of the striatum is a necessary condition for dopamine-dependent turning behaviour has been questioned by several studies showing that unilateral injection of amphetamine or dopamine receptor agonists into the nucleus accumbens, a target of the mesolimbic dopaminergic system, also produces reliable circling away from the side of injection. Apart from discussing differences in stepping patterns of turning and discussing the role of the dopamine D1/D2 receptor interaction, the present survey focuses attention upon the two-component hypothesis, especially in relation to our recent studies in which activities of dopamine D1 and D2 receptors in the striatum and the nucleus accumbens have been manipulated separately in intact rats. It is hypothesized that turning behaviour is produced by asymmetry within nucleus accumbens circuits which involve neuronal connections from the nucleus accumbens to the A9 cell area, which in turn projects to the ventrolateral striatum that determines the direction of turning.

GABAergic nigro-collicular pathways modulate the defensive behaviour elicited by midbrain tectum stimulation

Midbrain tectum (MT) structures such as the dorsal periaqueductal gray matter and deep layers of superior colliculus are well-known for the organization and generation of defensive behaviour. Electrical stimulation or microinjection of GABA antagonists into these structures produce aversive behaviour. In order to determine whether the nigrocollicular GABAergic fibers exert some control over this behaviour, rats bearing neurochemical lesions with kainic acid in the substantia nigra, pars reticulata (SNpr) and compacta (SNpc), were submitted to MT microinjections of bicuculline or electrical stimulation at aversive thresholds. The same procedure was carried out after enhancement or inhibition of GABAergic transmission in SNpr through microinjections of muscimol or bicuculline, respectively. Animals with SNpr neurochemical lesion exhibited a significant decrease in the aversive thresholds and an increase in the responsiveness to bicuculline microinjections. An opposite effect was observed following microinjections of bicuculline into the SNpr. The enhancement of the GABAergic transmission into the SNpr following microinjection of muscimol mimicked the effects produced by the lesion with kainic acid. These results suggest an inhibitory control of GABAergic fibers from the substantia nigra, pars reticulata, on aversive behaviour induced by midbrain stimulation.

Unilateral lesion in the tuberomammillary nucleus region: behavioral asymmetries and effects of histamine precursor

The subnuclei of tuberomammillary nucleus are located in the posterior part of the hypothalamus adjacent to the basolateral surface of the mammillary bodies. The neurons of this nucleus innervate extensive parts of the brain with several transmitters, particularly with histamine. In fact, they represent the only source of histaminergic projections in the brain. The present study deals with the effects of a lesion in this region on behavior. Unilateral electrolytic direct current (DC) lesions in the tuberomammillary nucleus led to an asymmetry in thigmotactic scanning; i.e., at 11 days, but not 1 day postlesion, the rats scanned the walls of an open field more with the vibrissae contralateral to the lesion than with those of the ipsilateral side. Furthermore, they emitted more ipsiversive than contraversive wide angle turns. The behavioral asymmetries are, in general, opposite in direction to those induced by lesion of the neighboring lateral hypothalamus and substantia nigra, indicating that they are specific to the tuberomammillary region destroyed. Application of the histamine precursor histidine led to a compensation of these asymmetries, suggesting that the tuberomammillary's histaminergic efferents are functionally related to the lesion-induced behavioral effects.

Control of turning behavior under apomorphine by sensory input from the face

It has been shown that peripheral manipulation of sensory input by removal of vibrissae on one side of the rat's face induces turning behavior which is directed towards the contralateral vibrissae-intact side, under the influence of the dopamine receptor agonist apomorphine. In the present experiment, we examined whether rats under apomorphine turn towards the side with more sensory input, or simply away from the manipulated side. Thus, an experimental manipulation was designed to increase sensory input. Sensory stimulation was applied by attaching a clip into the fur on one side of the face. Rats injected with apomorphine in doses of 0.5-5.0 mg/kg (but not with 0.05 mg/kg or vehicle) exhibited turning behavior towards the side of the clip. This sensory stimulation was also found to influence spontaneous behavioral asymmetries. These results show that an imbalance in sensory input is sufficient to produce turning under apomorphine.

Lateralized changes in behavior and striatal dopamine release following unilateral tactile stimulation of the perioral region: a microdialysis study

Intracranial microdialysis was used to measure dopamine (DA) release in the ventrolateral neostriatum of freely moving rats before and after unilateral tactile stimulation was applied to the orofacial region. Several behavioral parameters which have been linked to changes in nigrostriatal DA transmission (scanning, or snout contact with the walls of the observation chamber, turning and locomotion) were measured as well. Orofacial stimulation was followed by an asymmetrical increase in DA release with concentrations of transmitter higher in the neostriatum ipsilateral to the side of stimulation. Asymmetrical scanning behavior was observed during the time period when DA release was asymmetric, with rats favoring use of the side of the face contralateral to increased DA release. Increases in the DA metabolites DOPAC and HVA were found in the striatum ipsilateral to stimulation, but were delayed 40 min following the increase in DA.

Trigeminal-basal ganglia interaction: control of sensory-motor gating and positive reinforcement

Functional interactions between the basal ganglia and the perioral area were analyzed by means of electrical brain stimulation in the rat. The first experiment showed that unilateral stimulation of the substantia nigra sensitized the contralateral perioral area for a biting reflex upon its tactile stimulation. This biting reflex consists of lip withdrawal, orienting towards and biting into the stimulus source. The same sites in the substantia nigra also produced electrical self-stimulation using bar-pressing as the operant. A positive correlation was found between threshold currents for biting and for self-stimulation. However, the current levels necessary for reinforcement were considerably higher than those to facilitate the biting reflex. In the second experiment, it was found that manipulation of the perioral area by unilateral vibrissae removal reduced the rate of electrical self-stimulation in the substantia nigra. This effect was lateralized, depended on time after vibrissae removal, and could be reversed by systemic injections of the dopamine receptor agonist apomorphine. These results, which provide evidence for a reciprocal interaction between the basal ganglia and the perioral area, are discussed with respect to mechanisms of sensory-motor gating, motivation and reinforcement.

The basal ganglia-orofacial system: studies on neurobehavioral plasticity and sensory-motor tuning

We have employed the unilateral removal of the vibrissae as a tool to examine ensuing behavioral changes in relation to concomitant changes in the central nervous system. In this paper we review a series of studies showing that unilateral removal of the vibrissae leads to behavioral asymmetries (e.g., in thigmotactic scanning) from which rats recover over time. Time-related to these behavioral changes we found neuronal alterations in striatal afferents, that is, in uncrossed and crossed projections from the substantia nigra and the tuberomammillary nucleus. The involvement of dopaminergic mechanisms was indicated by results showing that dopaminergic agonists can induce asymmetries in thigmotactic scanning and turning; the direction of these asymmetries was also dependent on time after vibrissae removal. Furthermore, it was shown that endogenous preferential use of one vibrissae side in thigmotactic scanning interacts with the expression of spontaneous and drug-induced behavioral asymmetries exhibited after unilateral vibrissae removal. Neurochemical studies indicated that both unilateral vibrissae removal and unilateral perioral stimulation can have lateralized effects on biogenic amines in the brain. Finally, using electrical stimulation of the substantia nigra, evidence was found for a lateralized and bidirectional interaction between basal ganglia and the orofacial systems, indicating an involvement in mechanisms of motivation and particular stimulation. These results are important from several perspectives. One, they indicate functional links between the orofacial systems and the basal ganglia. Two, they raise the possibility that unilateral removal of the vibrissae can serve as a model (a) to investigate the dynamics of recovery of function after CNS insults, in general, and specifically, (b) to study neuronal plasticity in the nigrostriatal and tuberomammillary-striatal pathways, and (c) to investigate the neuropharmacology of catecholamine systems in the brain.

Further studies of the effects of intranigral morphine on behavioral responses to noxious stimuli

Bilateral intranigral microinjection of morphine produces dose-related and naloxone reversible analgesic-like effects on the hot-plate and tail-flick tests. The main objectives of the present studies were to further characterize the analgesic-like effects of intranigral morphine, to determine whether these effects were related to a general impairment of sensory or motor function, and to assess their anatomical specificity. The principal findings are: (1) intranigral morphine (10 micrograms) suppresses pain-related behavior without altering responses to a variety of non-noxious auditory, visual, and somatic stimuli, and without producing motor impairment; (2) movement of injector needles approximately 1 mm rostral, dorsal, or medial to the active nigral site significantly reduces the analgesic-like effect of morphine on the tail-flick test; and (3) electrolytic lesions confined to the nigra significantly reduced the analgesic-like effect of morphine on the hot-plate test. It is concluded that the analgesic-like effects of intranigral morphine are mediated by the substantia nigra and that these effects are specifically related to pain.

Relation between motor asymmetry and direction of rotational behaviour under amphetamine and apomorphine in rats with unilateral degeneration of the nigrostriatal dopamine system

The study examines whether in rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra, the direction of amphetamine- and apomorphine-induced rotations is determined by a bias to step more frequently with one hindleg. Results show that there is a strong asymmetry in usage of hindlegs under apomorphine but a weak one under amphetamine. Moreover, under apomorphine, virtually all steps are backward. Under amphetamine, however, steps are directed both backward and forward, although backward steps are relatively more prevalent when striatal dopamine depletion is nearly total. The different styles of rotation reflect the activation of pure turning under apomorphine, and turning combined with forward progression under amphetamine. It is suggested that presence of forward progression during turning depends on the capacity to modulate striatal activation. Moreover, the different styles of rotation are inconsistent with the hypothesis that a bias in leg usage sets the direction of turning. Instead, it seems that unilateral striatal activation sets the directionality of turning, independent of any hindlimb motor asymmetries.

Effects of hemivibrissotomy in the rat: time-dependent asymmetries in turning and biogenic amines induced by apomorphine

Behavioral and neurochemical changes accompanying unilateral removal of vibrissae were investigated in the rat. Rats were tested either 4 hours or 10 days after hemivibrissotomy. A systemic injection of apomorphine (0.5 mg/kg) induced turning behavior towards the intact vibrissae side in rats tested 4 hours after hemivibrissotomy. Compared to these animals, apomorphine induced more turning towards the side of vibrissae removal and less turning towards the intact side in animals tested 10 days after vibrissae removal. This reversal is suggestive of time-dependent changes in dopamine receptor sensitivity. Analysis of biogenic amines (dopamine, norepinephrine, serotonin) in the hemispheres ipsi- and contralateral to the side of vibrissae removal revealed evidence for neurochemical changes in apomorphine- and amphetamine-treated rats. Lateralized and bilateral differences were found in the neostriatum, septum and ventral mesencephalon, which were dependent on the side and duration of hemivibrissotomy. These results are discussed with respect to the behavioral and neural analogy between hemivibrissotomy and unilateral 6-hydroxydopamine lesions of the nigrostrial system.

Asymmetries in crossed and uncrossed nigrostriatal projections dependent on duration of unilateral removal of vibrissae in rats

The influence of unilateral removal of vibrissae on the crossed and uncrossed nigrostriatal projections was examined with the horseradish peroxidase tract tracing technique. Hemivibrissotomy mainly affected the projections arising from the rostral part of the substantia nigra. One to three days after clipping the vibrissae, rats were found to have more labeled neurons in the crossed projection to the caudate-putamen (CPU) on the same side as vibrissae removal than in the crossed projection to the CPU opposite to vibrissae removal. A reversed asymmetry was seen in rats examined 4-20 days after vibrissae removal. These animals had more labeled cells in the crossed and uncrossed projections terminating in the CPU opposite to the shaved side, i.e. in the hemisphere deprived of vibrissal sensory input. This time-course of neural alterations is similar to that of the recovery from behavioral asymmetries seen after hemivibrissotomy. Similar time-dependent alterations in the nigrostriatal projection had been found after unilateral injection of 6-OHDA into the substantia nigra.

Event or emergency? Two response systems in the mammalian superior colliculus

Recent studies of the effects of stimulating the superior colliculus (SC) in rodents suggest that this structure mediates at least two classes of response to novel sensory stimuli. One class contains the familiar orienting response, together with movements resembling tracking or pursuit, and appears appropriate for undefined sensory 'events'. The second class contains defensive movements such as avoidance or flight, together with cardiovascular changes, that would be appropriate for a sudden emergency such as the appearance of a predator, or of an object on collision course. The two response systems appear to depend on separate output projections, and are probably subject to different sensory and forebrain influences. These findings (1) suggest an explanation for the complex anatomical organization of the SC, with multiple output pathways differentially accessed by a very wide variety of inputs, (2) emphasize the similarities between the SC and the optic tectum in non-mammalian species, and (3) suggest that the SC may be useful as a model for studying both the sensory control of defensive responses, and how intelligent decisions can be taken about relatively simple sensory inputs.

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.

Lateralized wall-facing versus turning as measures of behavioral asymmetries and recovery of function after injection of 6-hydroxydopamine into the substantia nigra

The tendency of a rat to approach the wall of an open-field and to travel along the perimeter of the field (termed as "peritaxis" or "wall-facing") is affected by unilateral removal of the vibrissae. Peritaxis is lateralized by hemivibrissotomy. The finding that the dopamine agonist apomorphine reversed the direction of wall-facing asymmetry after 10 days of vibrissae removal suggested a link between this sensorimotor asymmetry and dopamine transmission. The present experiment examined the influence of a unilateral injection of 6-hydroxydopamine into the substantia nigra on peritaxis and compared this behavioral measure with turning behavior as an index of lesion-induced sensorimotor asymmetries and of recovery of function. The lesion of the substantia nigra reduced wall-facing with the side contralateral to the lesion to near-zero values. During the first week after the injection animals with incomplete dopamine depletion recovered from this asymmetry. The changes in wall-facing behavior were paralleled by turning asymmetries. Wall-facing was at least as sensitive to application of amphetamine and apomorphine as turning behavior. We concluded that lateralized wall-facing, or peritaxis, can serve as a useful index of dysfunction in the nigrostriatal dopamine system and the influence of catecholaminergic drugs. Wall-facing can also serve as a measure of recovery of function.

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.

Apomorphine reverses direction of asymmetry in facial scanning after 10 days of unilateral vibrissae removal in rat: vibrissotomy-induced denervation supersensitivity?

Sensorimotor asymmetries of hemivibrissotomized rats were investigated in an open field. To examine possible behavioral plasticity after unilateral removal of the vibrissae, we compared two groups of rats which had experienced the sensory imbalance for different durations. One group was shaved on one side of the face daily for 10 days before behavioral testing (group 10-Days). The other group was first shaved 4 h prior to the behavioral testing and was sham-shaved for the preceding 10 days (group 4-H). On day 11, the undrugged behavior was examined, and then, one hour later, the behavior induced by apomorphine (0.75 mg/kg, s.c.) was analyzed. In the undrugged state both groups tended to scan the walls of the enclosure with the vibrissae side of the face. After injection of apomorphine, the 4-H group also scanned the walls preferentially with the vibrissae side. In contrast, the 10-Days group reversed the scanning asymmetry under the influence of this drug. That is, animals in this latter group now preferred to scan the walls with the shaved side of the face. These findings are suggestive of a plasticity in dopamine transmission subsequent to unilateral removal of vibrissae. The reversal in direction of asymmetry under apomorphine of the 10-Days group is reminiscent of the apomorphine-induced reversal in sensorimotor asymmetries found after unilateral 6-hydroxydopamine lesion of the substantia nigra, which has been attributed to dopamine receptor supersensitivity.

Head and body movements produced by electrical stimulation of superior colliculus in rats: effects of interruption of crossed tectoreticulospinal pathway

Stimulation of the superior colliculus in rats produces movements of the head and body that resemble either orientation and approach towards a contralateral stimulus, or avoidance of, or escape from, such a stimulus. A variety of evidence indicates that the crossed descending pathway, which runs in the contralateral predorsal bundle to the pontomedullary reticular formation and the spinal cord, is involved in orienting movements. The nature of this involvement was investigated, by assessing the effects on tectally-elicited movements of midbrain knife-cuts intended to section the pathway as it crosses midline in the dorsal tegmental decussation. As expected, ipsilateral movements resembling avoidance or escape were little affected by dorsal tegmental decussation section, whereas contralateral circling movements of the body were almost abolished. However, contralateral movements of the head in response to electrical stimulation were not eliminated, nor were orienting head movements to visual or tactile stimuli. There was some suggestion that section of the dorsal tegmental decussation increased the latency of head movements from electrical stimulation at lateral sites, and decreased the accuracy of orienting movements to sensory stimuli. These results support the view that the crossed tectoreticulospinal system is concerned with approach rather than avoidance movements. However, it appears that other, as yet unidentified, tectal efferent systems are also involved in orienting head movements. It is possible that this division of labour may reflect functional differences between various kinds of apparently similar orienting responses. One suggestion is that the tectoreticulospinal system is concerned less in open-loop orienting responses (that are initiated but not subsequently guided by sensory stimuli), than in following or pursuit movements.

Neuronal plasticity in the nigrostriatal system of the rat after unilateral removal of vibrissae

The vibrissae of rats were shaved from one side of the face daily for 10 days. To see whether or not this treatment had an effect on crossed and uncrossed striatal afferent connections from the midbrain, the tract tracer horseradish peroxidase was applied to the caudate-putamen on day 11. When the tracer was deposited on the side opposite the vibrissae removal, more labeled cells were found in the contralateral substantia nigra than when it was applied on the same side as the vibrissae removal, or placed in animals with intact vibrissae. Unilateral removal of vibrissae did not affect uptake of the tracer by the cells which give rise to the homolateral nigrostriatal projections. These changes in HRP labeling in the crossed projection from the substantia nigra were seen after 10 days of unilateral removal of the vibrissae; i.e., at a time when the animals have had opportunity to learn to compensate for vibrissotomy-induced behavioral asymmetries.

Substance P in the human brain

The distribution of substance P immunoreactive sites was investigated by immunoenzymatic methods in a large series of paraffin embedded human brain sections from the collection assembled by Oscar and Cécile Vogt several decades ago, as well as from more recent post-mortem material. These studies demonstrated that substance P immunoreactivity was preserved in archival material permitting a detailed account of the localization of immunoreactive cell bodies, fibre networks and tracts in the human brain. Previous observations made on experimental animals and man were confirmed and extended. Additionally, substance P immunoreactive cell bodies were seen in most cortical areas and novel features were noted in the distribution of substance P-containing elements in the tuberal region, corpus striatum, substantia nigra (particularly in relationship to blood vessels) and in association with melanin-containing cells. Reconstruction of some substance P pathways was attempted by the analysis of semi-serial sections in more than one plane. Immunocytochemistry, in combination with image analysis, enabled some measurements of the differential concentrations of substance P immunoreactive material to be made and allowed a close correlation of this with defined anatomical landmarks or enkephalin immunoreactive sites.

Caudate neuronal activity in cats during head turning: selectivity for sensory-triggered movements

Units were recorded extracellularly from the caudate nucleus (CN) of cats during movement. The majority of CN units fired during sensory-triggered movements rather than movements in general. However, sensory stimulation was a necessary but not a sufficient condition for CN unit responding; stimuli caused unit responses only when movements were evoked. Additionally, only movements triggered by particular stimuli were associated with unit responding. These unit responses were not sensory because neural activity changes were associated with movement onset rather than stimulus presentation. These data are in accord with recent suggestions of a sensory-based motor function for the basal ganglia.

Behavioral effects of microinjections of SR 95103, a new GABA-A antagonist, into the medial hypothalamus or the mesencephalic central gray

The behavioral effects of unilateral microinjections of SR 95103, a new GABA-A receptor antagonist, into periventricular structures were studied. When injected into the medial hypothalamus (MH) or into the dorsal part of the mesencephalic central gray (CG), SR 95103 produced a dose-dependent behavioral activation together with jumps. However, the characteristics of this behavioral activation differed according to whether SR 95103 was injected into the MH or into the CG. The behavioral activation was found to be attenuated by pretreatment with THIP, a GABA receptor agonist. When injected into the CG or into the deep layers of the superior colliculus, SR 95103 proved to affect the rat's reactivity to tactile stimuli as evidenced by ipsilateral 'neglect' combined with contralateral hyperreactivity expressed as withdrawal reactions and jumping. Similar results were obtained following microinjections of bicuculline methiodide at the same sites. These data confirm that in both the MH and the CG, GABA-A receptors are involved in the neural control of the generation and/or expression of aversive effects. The data further suggest that at the level of the CG and the deep layers of the superior colliculus, GABA is also involved in the gating of sensory information towards the substrate underlying the generation of such aversive effects.

A consideration of sensory factors involved in motor functions of the basal ganglia

There is a sizeable literature concerning basal ganglia (BG) functioning that is based on data from experiments employing a method of analysis that is traditionally used with other motor areas. A brief review of this literature is presented and the following conclusion is reached: as compared to the success of traditional methodologies in elucidating the workings of other motor systems, their use in BG investigations has proven disappointing. A possible reason for the shortcomings of traditional analyses in BG research is discussed. The remainder of this review concerns an alternative approach to the study of the BG that follows from consideration of a variety of clinical and experimental findings. The literature suggests that sensory aspects of BG functioning must be taken into account to fully appreciate the role of this system in motor control. A review of the literature concerning the latter suggests two points: The BG function as sensory analyzer for motor systems. That is, the BG convert sensory data from a form that is receptor oriented to a form that is relevant for guiding movement. The BG ultimately affect movement by gating sensory inputs into other motor areas rather than by directly affecting these areas. This sensory-based model of BG functioning explains a number of apparent discrepancies in the literature. In addition, seemingly anomalous findings are reconciled with the overwhelming evidence that the BG are a motor system. In particular, the suggestions of a BG role in attention and cognition are viewed as being intrinsic rather than orthogonal to the role of the BG in movement.

Feeding induced by injections of muscimol into the substantia nigra of rats: unaffected by haloperidol but abolished by large lesions of the superior colliculus

Intense activation of central dopamine systems has been associated with oral stereotyped behaviour, whereas less intense stimulation of these systems can increase feeding in non-deprived animals. There are several lines of evidence which suggest that the gamma-aminobutyric acid-containing striatonigral and nigrotectal projections are essential pathways mediating dopamine-related oral stereotypy. The present series of experiments was conducted to examine whether the same output route also mediates dopamine-related feeding. In the first experiment it was shown that bilateral injections of a sub-stereotypic dose of muscimol (0.05 nM) into the substantia nigra increased feeding of non-deprived rats. In Experiment II the feeding response was further characterised by demonstrating that food intake was initially suppressed for 30 min after which it was potentiated for 90 min. In Experiment III it was shown that a single dose of haloperidol (0.4 mg/kg), which was adequate to suppress overall food intake, was ineffective in preventing the increase in feeding produced by intranigral muscimol (0.05 nM). In contrast, it was demonstrated in Experiment IV that large lesions of the superior colliculus completely abolished the muscimol-induced increase in feeding. These results suggest that the striatonigral and nigrotectal projections may be important efferent pathways for both the oral stereotypy and the feeding responses linked with central dopamine transmission.

Dissociation of stimulation-bound feeding and apomorphine-induced gnawing by lesions of superior colliculus

The intense stereotyped gnawing induced by high doses of apomorphine is almost abolished by large bilateral lesions of the superior colliculus. It has been argued that the feeding produced by electrical stimulation of the lateral hypothalamic area is closely related to dopamine-mediated oral stereotypies; if so, it might be expected that lesions of the superior colliculus would also disrupt stimulation-bound feeding. Feeding was obtained from 14 hypothalamic electrodes in 8 hooded Lister rats. Subsequent electrolytic lesions of the superior colliculus had no overall effect on this behaviour from 13 of the 14 electrodes, even though the lesions reduced the gnawing induced by 8-20 mg/kg apomorphine to less than 10% of its preoperative intensity. It is concluded that stimulation-bound feeding and apomorphine-induced gnawing are not dependent on identical neural circuitry, and therefore stimulation-bound feeding is probably not mediated by the nigrotectal pathway.

Unilateral injection of GABA agonists in the superior colliculus: asymmetry to tactile stimulation

A unilateral microinjection of each one of three different GABA agonists (Muscimol: 1.4 nmoles; Baclofen: 0.8 nmole; THIP: 10.7 nmoles) into the superior colliculus was found to result in a reversible asymmetry in the rat's responsiveness to tactile stimulation. The rat was hyporeactive to stimulations applied contralaterally and hyperreactive to stimulations applied ipsilaterally to the infusion site. Furthermore, the rat showed ipsiversive turning in response to tactile stimulation applied either ipsi- or contralaterally to the infusion site. The results are discussed in relation with motor and sensory asymmetry produced by unilateral manipulations affecting the striato-nigro tectal system.

Posture-independent sensorimotor analysis of inter-hemispheric receptor asymmetries in neostriatum

Nigrostriatal dopaminergic neurons are thought to be critically important for somato-sensorimotor behavior. Following unilateral irreversible elimination of these neurons, an animal shows an ipsiversive postural bias and permanently fails to orient its head toward tactile stimuli placed on the contralateral side of the body. In response to apomorphine, a dopamine agonist, these rats display contraversive circling. This effect is thought to reflect denervation-induced proliferation of dopamine receptors in the ipsilateral striatum. We have developed a sensitive procedure that measures sensorimotor function independent of postural and circling biases. We record the latencies to remove small pieces of adhesive stimuli placed onto the snout or radial surface of the forelimbs. The stimuli are placed symmetrically and simultaneously, which is analogous to tactile-extinction procedures used clinically. In the first study we found that rats with unilateral 6-hydroxydopamine (6-OHDA)-induced lesions of the nigrostriatal pathway showed a contralateral sensorimotor bias in response to doses of apomorphine below those necessary to produce contraversive circling. In a second study, unilateral striatal microinjections of kainic acid (KA) were used to destroy the neurons on which the postsynaptic dopaminergic receptors of the nigrostriatal system are contained. Compared to 6-OHDA, KA produced unexpected results in standard orientation tests. None of the KA-treated rats showed contralateral neglect, and some even showed ipsilateral deficits. However, the standard orientation tests are confounded by postural asymmetries, which were irregular in the KA-treated group. Using again the posture-independent sensorimotor procedure, we found that all KA-treated rats, like the 6-OHDA-treated rats, uniformly displayed ipsilateral sensorimotor biases. Sensorimotor function relating to inter-striatal asymmetries may be more specifically assessed with the bilateral-adhesive tests.

A quantitative analysis of stereotyped gnawing induced by apomorphine

An apparatus was designed and constructed to enable a quantitative analysis of the stereotyped gnawing produced by the dopamine agonist apomorphine. Using this apparatus it was discovered that increasing the subcutaneous dose of apomorphine increased (1) the number of animals that gnawed, and (2) the duration of gnawing in those animals that gnawed at all doses. Other aspects of apomorphine-induced gnawing, in particular the latency to respond and the frequency and duration of individual gnaws, were relatively unaffected. Likely properties of the system responsible for the organization of sterotyped gnawing are discussed.

Lateralized loss of biting attack-patterned reflexes following induction of contralateral sensory neglect in the cat: a possible role for the striatum in centrally elicited aggressive behaviour

A syndrome of "contralateral sensory neglect' was induced by hypothalamic knife cuts in 6 of 10 cats in which quiet biting attack behaviour could be elicited by lateral hypothalamic stimulation. The contralateral sensory neglect in the 6 affected cats was accompanied by a loss on the "neglected' side of the body of the patterned reflexes which mediate positioning of the head to bite and the jaw-opening component of biting. As a result, when these cats were stimulated in the lateral hypothalamus, although they continued to approach and even make tactile contact with the rat, they generally failed to bite it. Analysis of the histological and behavioural data suggested that damage to the nigrostriatal and/or striato/pallidonigral fibre systems provided the likely basis for both the induction of the contralateral sensory neglect and the lateralized patterned reflex loss. It was suggested, with respect to these specific patterned reflex components of the attack, that an important contribution may be made by the striatum.