The striatum and pain modulation

The aim of this review was to give a general aspect of the sensorial function of the striatum related to pain modulation, which was intensively studied in our laboratory. We analyse the effect of electrical and chemical stimulation of the striatum on the orofacial pain, especially that produced by tooth pulp stimulation of the lower incisors. We demonstrated specific sites within the nucleus which electrical or chemical stimulation produced inhibition of the nociceptive jaw opening reflex. This analgesic action of the striatum was mediated by activation of its dopamine D(2) receptors and transmitted through the indirect pathways of the basal ganglia and the medullary dorsal reticular nucleus (RVM) to the sensorial nuclei of the trigeminal nerve. Its mechanism of action was by inhibition of the nociceptive response of the second order neurons of the nucleus caudalis of the V par.

Quantitative study of salivary secretion in Parkinson's disease

We examined basal and reflex salivary flow rate and composition in 46 patients with Parkinson's disease (PD), both in off and on conditions, compared to 13 age-matched controls without underlying disease or treatment affecting autonomic function. Whole saliva was collected 12 hours after withdrawal of dopaminergic drugs and at the peak of levodopa-induced motor improvement. Twenty-three of the 46 PD patients had received domperidone a week before the study. Basal salivary flow rate was significantly lower in PD patients in the off state compared to controls (P<0.005). Levodopa increased salivary flow rate (P<0.05) both in the domperidone-pretreated and untreated groups. Citric acid stimulated salivary flow rate in both the off and on states in PD patients. This effect was higher in the domperidone-pretreated patients. Salivary concentration of sodium, chloride, and amylase was higher in PD patients than in controls and was not affected by levodopa or domperidone treatment. Levodopa stimulates both basal and reflex salivary flow rate in PD. The mechanism appears to be central, as the effect is not blocked by domperidone. Domperidone may have a peripheral effect that potentiates reflex salivary secretion. Salivary composition is abnormal in PD and is not affected by levodopa treatment.

Inhibition of jaw opening reflex and single neurons in the trigeminal subnucleus caudalis by activation of striatal D2 dopamine receptors

The influence of striatal dopaminergic receptors on the inhibitory action of the striatum on the jaw opening reflex (JOR) was studied in anesthetized rats. Single unit activity was recorded at the subnucleus caudalis of the trigeminal nerve. Dopamine agonists and antagonists were microinjectd into the striatum. The striatal administration of apomorphine inhibits the JOR evoked by dental pulp stimulation. Similar results were observed by microinjections of quinpirole, an agonist of D2 receptors, but not by microinjection of SKF 38393, a D1 agonist. The effect of quinpirole was only inhibited by intrastriatal microinjection of haloperidol, a blocker of D2 receptors and reversed by systemic administration of 1 mg/kg of naloxone. The evoked neuronal responses in subnucleus caudalis, by tooth pulp stimulation, were also suppressed by microinjection of quinpirole into the striatum and reversed by naloxone (1 mg/kg, i.v.). Based on the above results, we conclude that the activation of striatal D2 dopamine receptors is responsible for the inhibition of the JOR possibly by action on the subnucleus caudalis of the trigeminal nerve.

Striatal Inhibition of Nociceptive Responses Evoked in Trigeminal Sensory Neurons by Tooth Pulp Stimulation

The noxious evoked response in trigeminal sensory neurons was studied to address the role of striatum in the control of nociceptive inputs. In urethane-anesthetized rats, the jaw opening reflex (JOR) was produced by suprathreshold stimulation of the tooth pulp and measured as electromyographic response in the digastric muscle, with simultaneous recording of noxious responses in single unit neurons of the spinal trigeminal nucleus pars caudalis (Sp5c). The microinjection of glutamate (80 ηmol/0.5 μl) into striatal JOR inhibitory sites significantly decreased the Aδ and C fiber–mediated–evoked response (53 ± 4.2 and 43.6 ± 6.4% of control value, P < 0.0001) in 92% (31/34) of nociceptive Sp5c neurons. The microinjection of the solvent was ineffective, as was microinjection of glutamate in sites out of the JOR inhibitory ones. In another series of experiments, simultaneous single unit recordings were performed in the motor trigeminal nucleus (Mo5) and the Sp5c nucleus. Microinjection of glutamate decreased the noxious-evoked response in Sp5c and Mo5 neurons in parallel with the JOR, without modifying spontaneous neuronal activity of trigeminal motoneurons ( n = 8 pairs). These results indicate that the striatum could be involved in the modulation of nociceptive inputs and confirm the role of the basal ganglia in the processing of nociceptive information.

Turning behaviour induced by stimulation of the 5-HT receptors in the subthalamic nucleus

The basal ganglia, which receive a rich serotonergic innervation, have been implicated in hyperkinetic and hypokinetic disorders. Moreover, a decrease in subthalamic nucleus (STN) activity has been associated with motor hyperactivity. To address the role of subthalamic serotonergic innervation in its motor function, turning behaviour was studied in rats with stimulation of the subthalamic serotonin (5-HT) receptors by intracerebral microinjections. The intrasubthalamic administration of 5-HT induced dose-dependent contralateral turning behaviour, with a maximal effect at a dose of 2.5 microg in 0.2 microL. Similar results were observed with microinjections of other 5-HT receptor agonists: quipazine (a 5-HT2B/C/3 agonist), MK-212 (a 5-HT2B/C agonist) and m-chlorophenylbiguanidine (a 5-HT3 agonist), while microinjections of 5-HT into the zona incerta or in the previously lesioned STN were ineffective. The effect of 5-HT was blocked by coadministration of the antagonist mianserin. Stimulation of subthalamic 5-HT receptors in animals bearing a lesion of the nigrostriatal pathway did not modify the motor response, which indicates that the dopamine innervation of the nucleus is not involved in this effect. Kainic acid lesion of the substantia nigra pars reticulata (SNr) suppressed the contralateral rotations elicited by stimulation of 5-HT2B/C/3 subthalamic receptors. This suggests a role of the subthalamic-nigral pathway in the turning activity. Furthermore, the partial blockade of glutamatergic receptors in the SNr by the antagonist DNQX increased the contralateral circling elicited by stimulation of 5-HT receptors in the STN. We concluded that the activation of the 5-HT2B/C and 5-HT3 subthalamic receptors elicited contralateral turning behaviour, probably via the subthalamic-nigral pathway.

High-frequency stimulation of the subthalamic nucleus silences subthalamic neurons: a possible cellular mechanism in Parkinson's disease

The subthalamic nucleus participates in the control of movement and is considered a surgical target in the treatment of parkinsonian symptoms. Using the rat brain in vitro slice technique we show that sustained high-frequency (>100 Hz) electrical stimulation (i.e., 'tetanic stimulation') of the nucleus, as used in humans to treat Parkinson's disease, silenced subthalamic neurons. Two main cell types were identified. 'Tonic cells' (68%) showed delayed inward rectification, fired continuously, switched to bursting and stopped firing when strongly depolarized with injected current. Tetanic stimulation of the nucleus induced a steady depolarization (approximately 18 mV) that triggered action potentials at a high rate followed by bursts and finally (approximately 25 s) totally silenced tonic cells. The control tonic activity was recovered rapidly (<10 s) after ending stimulation. 'Phasic cells' (25%) discharged a single initial brief burst of action potentials both when depolarized by prolonged current injection and tetanic stimulation and did not show inward rectification. An infrequent cell type called 'phasic-tonic' (7%) showed a mixed discharge. We suggest that the silencing effect of tetanic stimulation is not a frequency-dependent presynaptic depression and could result from the gradual inactivation of Na+-mediated action potentials. These findings suggest that the remission of parkinsonian symptoms by treatment with high-frequency electrical stimulation of the subthalamic nucleus in humans may primarily reside on its capacity to suppress the action potential activity of subthalamic neurons.

Stimulation of dental pulp with simultaneous recording of the jaw opening reflex in the rat

The processing of nociceptive information in the central nervous system has been analysed in most studies by activation of peripheral nerves. However, the limitation of this method is the simultaneous activation of noxious and inocuous fibers. Nevertheless, the stimulation of the tooth pulp is believed to activate mainly nociceptive fibers which could be the method of choice. On the other hand, the response to nociceptive activation of the dental pulp is easily quantified by the amplitude of the jaw opening reflex, a nocifensive flexion withdrawal reflex. In this protocol we describe a technique to manufacture and implant electrodes in lower incisors of the rat and a method to prepare and insert stainless steel twisted bipolar electrodes to record the electromyographic activity of both digastric muscles, in response to nociceptive dental pulp stimulation. This approach was applied in the study of the analgesic effects of the rat's striatal stimulation.

Pharmacological involvement of the calcium channel blocker flunarizine in dopamine transmission at the striatum

Single intrastriatal microinjections of 25, 50 and 100nmol/microl of flunarizine in normal rats produced a dose-dependent turning behavior toward the injected side when they were challenged with apomorphine (1mg/kg, s.c). This effect was seen at 1, 3 and 7 days following administration of the high dose of flunarizine, but had subsided by 24h after administration of the intermediate dose; the low dose was ineffective. However, intrastriatal injection of the high dose of flunarizine resulted in a local lesion and thereafter this dose was not used. A similar dose-response relationship was determined for nifedipine, an L-type calcium channel antagonist. Injection of this antagonist did not result in apomorphine-elicited rotational behavior, reflecting its lack of antidopaminergic action. Intrastriatal injections of haloperidol (5microg/microl), an antagonist of dopamine D(2) receptors, or the sodium channel blocker lidocaine (40microg/microl), were given in order to compare their effects to those observed with flunarizine. Intracerebral injection of haloperidol produced ipsilateral turning in response to systemic administration of apomorphine given 60min after. The same response was obtained with the injection of apomorphine 10min after the injection of intracerebral lidocaine. This effect was no longer apparent 24h after the microinjection of haloperidol and 60min after the injection of lidocaine. In rats rendered hemiparkinsionian by lesioning the nigrostriatal pathway with 6OHDA, intrastriatal microinjection of flunarizine (50nmol/microl) significantly reduced apomorphine (0.2mg/kg, s.c.)-elicited turning behavior towards the non-lesioned side. These results suggest an antidopaminergic effect of flunarizine mediated by antagonistic action of post-synaptic striatal dopamine receptors. However, an action of the drug on sodium channels may not be ruled out. These studies offer additional supporting evidence for the induction or aggravation of extrapyramidal side-effects in patients receiving flunarizine.

Subthalamic nucleus lesions reduce low frequency oscillatory firing of substantia nigra pars reticulata neurons in a rat model of Parkinson's disease

Single unit recordings performed in animal models of Parkinson's disease revealed that output nuclei neurons display modifications in firing pattern and firing rate, which are supposed to give rise to the clinical manifestations of the illness. We examined the activity pattern of single units from the substantia nigra pars reticulata, the main output nuclei of the rodent basal ganglia, in urethane-anesthetized control and 6-hydroxydopamine-lesioned rats (a widespread model of Parkinson's disease). We further studied the effect of a subthalamic nucleus lesion in both experimental groups. Subthalamic nucleus lesion produces behavioral improvement in animal models of Parkinson's disease, and was expected to reverse the changes induced by 6-hydroxydopamine lesions. A meticulous statistical investigation, which included a non-biased classification of the recorded units by means of cluster analysis, allowed us to identify a low frequency oscillation of firing rate ( approximately 0.9 Hz) occurring in approximately 35% of the units recorded from 6-hydroxydopamine-lesioned rats, as the main feature differentiating 6-hydroxydopamine-lesioned and control rats. Subthalamic nucleus lesions significantly reduced the proportion of oscillatory units in 6-hydroxydopamine-lesioned rats. However, the population of nigral units recorded from rats bearing both lesions still differed significantly from control units. These results suggest that oscillatory activity in the basal ganglia output nuclei may be related to some clinical features of parkinsonism, and suggest a putative mechanism through which therapeutic interventions aimed at modifying subthalamic nucleus function produce clinical benefit in Parkinson's disease.

Striatal modulation of the jaw opening reflex

The effect of striatal electrical and chemical conditioning stimulation (L-glutamate 80-160 nmoles/0.5 microl) on the jaw opening reflex (JOR) was studied in Sprague-Dawley male rats anesthetized with urethane. The JOR was evoked by stimulation of the tooth pulp of lower incisors. This response was suppressed by transection of the dental root, which indicates according with the bibliography, a specific activation of the pulp nerves. Three type of responses were obtained on the evoked JOR by conditioning stimulation of the striatum; being the main one the suppression of the reflex elicited by tooth pulp activation. A second type of response was an increase of the tooth-JOR amplitude. This effect was observed more frequently with glutamate stimulation rather than with electrical activation of the striatum. A third response was observed with chemical stimulation but not by electrical stimulation of the striatum. This was a triphasic response which consisted in an increase followed by an inhibition and a late increase of the tooth-JOR amplitude. A biphasic effect, an increase prior to a decrease of the JOR amplitude, was also recorded with a minor frequency. The distribution of effective sites for electrical and chemical stimulation within the striatum are mainly similar located in the rostral aspect of the nucleus, with the inhibitory sites in the middle of the nucleus and intermingled with the excitatory ones. The complex responses (tri/biphasic) were observed ventrally and caudally in the nucleus. On the basis of the results mentioned above, one could assume that the striatum is related to the modulation of the JOR evoked probably by nociceptive stimulation. However, activation of other type of fibers could not be ruled out.

Substantia nigra pars reticulata units in 6-hydroxydopamine-lesioned rats: responses to striatal D2 dopamine receptor stimulation and subthalamic lesions

In order to increase our understanding of Parkinson's disease pathophysiology, we studied the effects of intrastriatally administered selective dopamine receptor agonists on single units from the substantia nigra pars reticulata of 6-hydroxydopamine (6-OHDA)-lesioned rats with or without an additional subthalamic nucleus lesion. Nigral pars reticulata units of 6-OHDA-lesioned rats were classified into two types, showing regular and bursting discharge patterns, respectively ('non-burst' and 'burst' units). Non-burst and burst units showed distinct responses to intrastriatal quinpirole (the former were excited and burst units inhibited). Furthermore, subthalamic nucleus lesions significantly decreased the number of nigral units showing a spontaneous bursting pattern, and reduced the proportion of units that responded to quinpirole. In contrast, subthalamic lesions did not alter the proportion of nigral units that responded to SKF38393, although the lesions changed some response features, e.g. response type and magnitude. Burst analysis showed that quinpirole did not modify the discharge pattern of burst units, whereas SKF38393 produced a shift to regular firing in 62% of the burst units tested. In conjunction, our results support that: (i) the subthalamic nucleus has an important influence on output nuclei firing pattern; (ii) striatal D2 receptors have a strong influence on nigral firing rate, and a less relevant role in controlling firing pattern; (iii) burst and non-burst units differ in their response to selective stimulation of striatal dopamine receptors; (iv) the effects of striatal D2 receptors on nigral units are mainly, though not exclusively, mediated by the subthalamic nucleus; and (v) nigral responses to SKF38393 involve the subthalamic nucleus.

Substantia nigra pars reticulata single unit activity in normal and 60HDA-lesioned rats: effects of intrastriatal apomorphine and subthalamic lesions

The spontaneous activity and the response to intrastriatal application of apomorphine of substantia nigra pars reticulata (SNpr) single units was studied in four experimental groups of rats: (1) normal rats; (2) subthalamic nucleus (STN) lesioned rats; (3) rats bearing a 6-hydroxydopamine (60HDA) lesion; and (4) 60HDA-lesioned animals with an additional STN lesion. Thirty-eight percent of units from 60HDA-lesioned rats showed a bursting pattern of spontaneous activity, which was never found in normal rats. STN lesions had no effect on the spontaneous activity of SNpr units from normal rats, but reduced the percentage of burst units in 60HDA-lesioned animals. Intrastriatal apomorphine produced responses in 62% of SNpr units from normal rats and 85% of units from 60HDA-lesioned animals (P < 0.05). In addition, the modifications in the firing rate and in the coefficient of variation of the interspike intervals induced by intrastriatal apomorphine were significantly greater for the units isolated from 60HDA-lesioned rats. In particular, it was noted that all the burst units responded to apomorphine, showing the highest changes in firing rate and coefficient of variation. However, intrastriatal apomorphine did not always turn the activity of burst units into a more physiological pattern. STN lesions reduced the percentage of units responding to intrastriatal apomorphine in normal rats. In 60HDA-lesioned rats, STN lesions reduced the number of responsive units, and their change in mean firing rate and coefficient of variation. Our results show that the STN participates in the genesis of the bursting pattern of activity of SNpr units in 60HDA-lesioned rats, and that STN lesions can partially revert the abnormal spontaneous and apomorphine-induced responses of SNpr units in these animals.

D1-D2 dopamine receptor interaction: an in vivo single unit electrophysiological study

After intrastriatal administration of selective dopamine receptor agonists only a small percentage of substantia nigra pars reticulata single units showed changes in firing rate (23% after SKF38393 and 17% after quinpirole). After their intrastriatal co-administration, however, or after the application of the non-selective dopamine receptor agonist apomorphine, 72% and 69% of units responded, respectively. This result confirms the participation of the striatum in the phenomenon of D1-D2 receptor interaction, and show that co-activation of both receptor subtypes produced a maximal effect on basal ganglia output nuclei.

Turning behavior induced by injections of glutamate receptor antagonists into the substantia nigra of the rat

We have found recently that muscimol microinjections into the subthalamic nucleus produce contralateral turning activity [Murer and Pazo (1993) NeuroReport, 4:1219-1222]. To test the hypothesis that a reduced glutamate action on substantia nigra pars reticulata neurons mediates this turning response, we examined the effect of unilateral intranigral microinjections of the AMPA/kainate receptor antagonist 6,7-dinitro-quinoxaline-2,3-dione (DNQX) and the competitive N-methyl-D-aspartate (NMDA) receptor antagonist DL-2-amino-5-phosphonovaleric acid (AP-5). DNQX and AP-5 both produced a dose-dependent contralateral turning response, while vehicle administration did not induce turning activity. Application of glutamate receptor antagonists at adjacent regions of the mesencephalic tegmentum were also ineffective. Coadministration of NMDA or AMPA significantly reduced the turning response induced by AP-5 or DNQX, respectively. Lesions of the nigrostriatal pathway by 6-hydroxydopamine did not modify the response to DNQX or AP-5 administration into the nigra. However, their behavioral effects were significantly reduced by a lesion of the ipsilateral subthalamic nucleus. Our results show that the blockade of a tonic input acting on AMPA/kainate and NMDA receptors located at the substantia nigra produces contralateral turning behavior. The effect seems to involve pars reticulata cells since this area remains unchanged after destruction of dopaminergic neurons. The subthalamic nucleus seems to be the endogenous source of the agonist acting on the nigral glutamate receptors related to turning behavior.

Defensive behavior induced by stimulation of the ventral striatum in the cat

The behavioral responses induced by electrical stimulation of the ventral striatum were studied in 15 freely moving cats, chronically implanted with multiwire electrodes. Two types of defensive responses could be evoked from the ventral striatum, an arrest response and an escape or flight reaction. Stimulation of the dorsal striatum and the internal capsule induced contralateral head turning and movements of the face or limbs. The number of ventral striatal sites eliciting escape responses increased along the sessions, while their threshold decreased. Lesioning the ventral pallidal region with kainic acid increased significantly the threshold for defensive responses, whereas head turning responses showed no change. The results of this study indicate that the ventral striatum could be part of the neural substrate for defensive behavior, and that the ventral pallidal region plays a role in its mediation.

Turning behavior in rats with unilateral lesions of the subthalamic nucleus: synergism between D1 and D2 receptors

Rats with unilateral kainic acid lesion of the subthalamic nucleus showed a dose dependent rotational response to the lesioned side (ipsilateral) after systemic administration of the non-selective dopaminergic agonist apomorphine. Both D2 and D1 selective antagonists ((-)sulpiride and SCH23390) inhibited the response to apomorphine in these rats. Selective D2 and D1 agonists (quinpirole and SKF38393) were unable to induce turning behavior. However, an ipsilateral circling response was obtained after the simultaneous application of both agonists. The interaction mechanism between dopaminergic receptor subtypes seems to be similar to that of other normosensitive models of turning previously studied (Barone et al., 1986; Robertson and Robertson, 1986; Arnt and Perregard, 1987; Asim et al., 1990; Pazo et al., 1993). It is proposed that the ipsilateral turning response to dopaminergic agonists in rats with subthalamic nucleus lesion results from an impaired behavioral expression of the action of dopaminergic agonists on one side, leading the rats to turn away from the intact hemisphere.

Behavioral responses induced by electrical stimulation of the caudate nucleus in freely moving cats

The caudate nucleus and adjacent structures of 26 freely moving cats were stimulated through multiwire electrodes chronically implanted. Two main effects here observed with trains of pulses of high frequency (100 Hz) and short duration (1 s): (1) contralateral head turning and (2) arrest reaction, which was associated with crouching and escape behavior. The responses follow a certain topographic distribution. Head turning was elicited with the lowest mean threshold in sites located in the internal two-thirds and caudal region of the caudate nucleus, while the arrest reaction was elicited from the ventromedial region of the caudate and adjacent nucleus accumbens. Stimulation of the corpus callosum and internal capsule produces postural instability, ventral flexion of the head and flexion of the contralateral limb. The extra-caudate responses were accompanied by contralateral head turning when the stimulated points were near of the caudate border. Experimental evidence suggested that striatal responses were not due to current spread to adjacent structures or to activation of corticofugal fibers. The head rotation was suppressed following interruption of the ipsilateral striatal outflow by electrolytic lesion of the globus pallidus and adjacent internal capsule. The chemical lesion of the substantia nigra and the ventral pallidum produced a significant increase in the stimulation threshold for head turning and arrest reaction, respectively. These results suggest a topographic arrangement of the responses evoked by electrical stimulation of the caudate nucleus in the cat, which are mediated by the substantia nigra pars reticulata and the ventral pallidum.

Circling behaviour induced by activation of GABAA receptors in the subthalamic nucleus

The behavioural effect of drugs acting on GABAA receptors in the subthalamic region and the entopeduncular nucleus was studied in freely moving cats. Microinjections of muscimol into the zona incerta-Forel's fields produced tilt of the head to the injected site, while injections of bicuculline or picrotoxin produced the same effect but to the opposite side. Microinjections of muscimol into the subthalamic nucleus elicited circling behaviour to the contralateral side, while bicuculline and picrotoxin produced ipsilateral turning. However, when high doses of the antagonists were injected, contralateral circling was observed. Activation or blockade of GABAA receptors into the entopeduncular nucleus was ineffective. These results imply that GABAergic mechanisms in the subthalamic nucleus and the zona incerta-fields of Forel are involved in circling behaviour and vertical head movements, respectively.

D1 and D2 receptors and circling behavior in rats with unilateral lesion of the entopeduncular nucleus

The role of D1 and D2 striatal dopamine receptors on circling behavior was studied in a normosensitive model obtained by unilateral kainic acid lesion of the entopeduncular nucleus. In this model, the sensitivity of striatal dopamine receptors was preserved, because kainic acid destroyed the neurons of the entopeduncular nucleus and left undamage the fibers of passage and axon terminals. Systemic administration of SKF 38393 to these animals fails to induce circling activity. In contrast, administration of quinpirole elicited rotation toward the lesioned side, which was increased by concurrent injection of SKF 38393. This behavior was inhibited by pretreatment with either a specific D1 (SCH 23390) or D2 (-sulpiride) antagonist. The apomorphine also induced ipsilateral circling that was abolished by pretreatment with D1 or D2 antagonists. The above results suggest that coactivation of both D1 and D2 striatal dopamine receptors are necessary to induce rotation in this normosensitive model.

Spontaneous and evoked activity of the caudate neurons to central and peripheral stimuli after brain lesions

The involvement of the cerebral cortex, commissural fibers and thalamus on caudate-caudate relations was studied in locally anesthetized, paralysed and artificially ventilated cats. This type of experimental preparation was necessary since a complete suppression of spontaneous and evoked activity is produced by subanesthetic doses of general anesthesia. Two types of caudate action potentials were encountered on the basis of their waveform characteristics: biphasic and triphasic spikes, the former being the largest population (80%). These waveforms were independent of the microelectrode resistance and the distance to recorded neurons. However, their responses were very similar to both central and peripheral stimuli. Caudate stimulation depressed the spontaneous discharges of the majority of the responsive units recorded within the opposite nucleus, while striatal neurons were activated by stimulation of the contralateral cortex. Decortication, thalamic lesion (motor nuclei and massa intermedia) and section of the corpus callosum decrease the firing rates of caudate neurons with biphasic spikes, while the discharges of the neurons with triphasic action potentials remained unchanged. Bilateral ablation of the cerebral cortex decreased the responsiveness of striatal neurons to contralateral nucleus and sciatic nerve and reduced the number of spontaneously active cells per recording tract. Section of the commissural fibers also depressed the caudate responses to the contralateral nucleus, and to the opposite precruciate cortex, although thalamic lesion did not affect the responsiveness of caudate cells to both central and peripheral stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the mesopontine area in the circling behavior induced by apomorphine in rats bearing unilateral lesion of the entopeduncular nucleus

The role of the mesopontine area and superior colliculus in turning behavior induced by systemic administration of apomorphine was studied in rats bearing a unilateral entopeduncular lesion. Bilateral electrolytic damage of the superior colliculus resulted in an enhancement of the ipsilateral circling response to apomorphine, perhaps as a consequence of an increased locomotor drive in such animals. Bilateral electrolytic lesions of the mesopontine area decreased apomorphine-induced turning in entopeduncular rats, while a bilateral kainic acid lesion of the same region was ineffective. It was concluded that the pedunculopontine nucleus and adjacent reticular formation are not an essential link for the striopallidal complex output mediating circling in this model. Fibers running through this region could be implicated in the expression of the behavior under study. Since a unilateral electrolytic lesion of the mesopontine area contralateral to the damaged entopeduncular nucleus reduced drug-induced turning, we propose that an uncrossed pathway from the intact striopallidal complex mediates circling in our rats.

Effects of central and peripheral inputs on single pineal cell activity in the rat

The influences exerted by central and peripheral afferents to the pineal gland have been studied in rats anesthetized with urethane (1.2 g/kg, i.p.). Spontaneous action potentials arising from the pinealocytes were recorded by means of glass micropipettes filled with 3 M NaCl containing a dye. The electrical stimulation of suprachiasmatic nucleus, superior cervical ganglia, sciatic nerve and retina evoked discharge changes in a significant number of pineal cells. However, a relatively higher proportion of pinealocytes failed to respond to these afferents. Three types of responses could be observed. Inhibitions were the predominant response patterns to suprachiasmatic nucleus, superior cervical ganglia and sciatic nerve, while excitations were mainly elicited following photic stimulation, whereas the remaining evoked activity was biphasic responses, which were observed in a small number of cells after stimulation of suprachiasmatic nucleus, superior cervical ganglia and retina. These data confirm some previous neural inputs to the pineal and demonstrate the existence of a modulatory effect of the suprachiasmatic nucleus on pinealocyte discharges as well as somatosensory afferents to the gland by way of the sciatic nerve.

Responses elicited by species-specific models in the cichlid Crenicichla lepidota (Heckel)

Species recognition by the cichlid fish C. lepidota was studied by measuring species-specific aggressive behavior toward either live conspecifics (control) or toward different two-dimensional models. A plain fish-shaped model elicited aggressive behavior, but the responses were mostly absent when the model was a rectangle. Adding heavy stripes to the fish-shaped form increased the responses, which were further enhanced by adding a spot. Comparable aggressive responses were also induced by adding spots and eye to dummies with thin stripes. We conclude that in our experimental conditions, fish-like shape and contrast seem to be of great significance for recognition of conspecifics in the cichlid C. lepidota (Heckel).

Automatic temperature controller for maintaining body temperature in experimental animals

A system for autoregulation of body temperature of large and small animals is described. The device uses the IC AD590 as a temperature transducer. It operates on the basis of continuous regulation of the heating current, and does not emit transients which interfere with electrical recordings. A panel meter shows either the rectal temperature of the animal or the current flow to the blanket.

Changes in pancreatic exocrine secretion after repeated haloperidol administration

The effect of repeated administration of haloperidol on the pancreatic secretion was studied in urethane-anesthetized Swiss mice. Haloperidol (2 mg/kg) injected daily i.p. for 7 days, increase the volume and protein content of the basal pancreatic juice significantly. This secretory activity was partially blocked by i.p. injection of atropine (5 mg/kg), both in control and treated animals. The volume of the secretory response to bethanechol, a cholinergic agonist, was decreased by haloperidol without any change in amylase release. From these findings it is concluded that repeated haloperidol treatment produces an increase of basal pancreatic secretion, which is probably the result of changes in the sensitivity of dopamine receptors of the gland.

Increase of muscarinic cholinergic receptors in the rat submandibular glands after parasympathectomy and repeated administration of haloperidol

1. The mechanisms of the supersensitivity to cholinergic drugs after chronic haloperidol was studied in normal and parasympathectomized submandibular glands of the rats. 2. Both parasympathectomy and haloperidol treatment for 7 days (2 mg/kg/day, i.p.) increased the sialogogue response of the glands to methacholine, a cholinomimetic drug. 3. Both denervation and haloperidol administration induce up-regulation of the muscarinic receptors as expressed per gram of the tissue. 4. Haloperidol causes no further increase in sensitivity than denervation alone. 5. These data demonstrate that secretory supersensitivity to cholinergic drugs in the rat submandibular glands, after chronic haloperidol and parasympathectomy is related to an increase in muscarinic cholinergic receptors.

Central and peripheral modulation of spontaneous neuronal activity in the caudate nucleus

The modulatory action of the caudate on the neural activity of the contralateral nucleus was studied in locally anesthetized, paralysed and artificially ventilated cats. This type of preparation was necessary because of a complete suppression of spontaneous spike activity after subanesthetic doses of general anesthesia. Two types of caudate action potential were characterized according to their waveform: biphasic and triphasic spikes, with a predominance of the former. These waveforms appeared to be independent of recording distance; however, their responses were similar to both central and peripheral stimuli. Caudate stimulation modified the spontaneous activity of the majority of the single units recorded within the opposite nucleus. This effect was mainly inhibitory and keeps up certain somatotopic distribution in the rostrocaudal extent of the nucleus. Kainic lesion of the site of stimulation suppressed the responses in the contralateral caudate nucleus, whereas the responses to substantia nigra and precruciate cortex remained unaltered. On the other hand, stimulation of the precruciate cortex opposite to the recording sites always excited the caudate neurons. The responses evoked by stimulation of ipsilateral substantia nigra and of contralateral sciatic nerve followed a similar pattern to those elicited by caudate stimuli. These results suggest a mostly inhibitory effect of the caudate on neuronal activity within the opposite nucleus, which is reinforced by the action of central and peripheral somatosensory inputs.

Selective increase of alpha 1-adrenoceptors and muscarinic cholinergic receptors in rat cerebral cortex after chronic haloperidol

The effect of chronic administration of haloperidol on alpha 1-, alpha 2-, and beta-adrenoceptors, cholinergic muscarinic, GABAA and benzodiazepine receptors in the cerebral cortex of the rat was investigated. Doses of 0.3 and 2 mg/kg of haloperidol during 7 days increased markedly the density of alpha 1-adrenoceptors without changes in affinity. The alpha 2- and beta-adrenoceptors were not modified after neuroleptic administration. The number of muscarinic receptors were also increased after haloperidol treatment (2 mg/kg/day). However, the GABAA and benzodiazepine binding sites remained unchanged. In the brainstem an increment in the alpha 1-, but not the beta-adrenoceptors was observed. The well known increase in the dopamine receptors in the striatum was confirmed. These observations demonstrate a multireceptor effect of haloperidol in the cerebral cortex.

Spinal cord substrate of the turning behavior induced by unilateral lesion of the entopeduncular nucleus

The neural pathways in the spinal cord mediating circling behavior in animals with unilateral kainic acid lesion of the entopeduncular nucleus were studied in rats. The circling activity toward the lesioned side was indiced by i.p. administration of apomorphine (3 mg/kg). Section of the lateral funiculus ipsilateral to the lesioned entopeduncular nucleus, reduced significantly the rate of drug induced rotations. The above was a common lesion of ventrolateral and dorsolateral transections of the cervical spinal cord. However, the latter transection was more effective than the former to block the circling. On the other hand, lesion of the contralateral spinal cord fails to modify turning behavior. These findings suggest that crossed fibers descending in the dorsolateral quadrant directly from the basal ganglia or mediating synaptic relay in the lower brainstem may be the anatomical substrate of the circling produced by striatal stimulation.

Effect of chronic administration of haloperidol on secretory response mediated by cholinergic receptors in rat submandibular glands

Administration of haloperidol influences peripheral non-dopaminergic receptors. The sialagogue response of the submandibular glands of the rats to methacholine was enhanced by chronic administration of haloperidol. The binding of [3H]QNB to muscarinic receptors in the submandibular glands was not changed by chronic haloperidol. The supersensitivity of postsynaptic cholinergic receptors to drugs in haloperidol treated rats is not related to changes in the number or affinity of such receptors. This paper confirmed the sialagogue supersensitivity to adrenergic drugs related to an increase in alpha 1-adrenoceptors in the submandibular glands of haloperidol injected rats.

The sialagogue response of striatal dopamine receptors to L-dopa is not influenced by castration or chronic estrogen treatment

The secretory response of salivary glands to L-dopa, elicited by stimulation of dopamine receptors in the striatum and the circling behavior induced by apomorphine in animals bearing a unilateral kainic lesion of the entopeduncular nucleus, was studied in intact and ovariectomized female rats. Castration did not modify the sialagogue response to L-dopa, while the turning behavior was significantly increased. Daily administration of 17-beta-estradiol benzoate during 7 days to ovariectomized rats decreased the circling activity to the level of intact female rats, while the salivary secretion to L-dopa was unaffected. The above findings suggest that the sialagogue response induced by L-dopa may be due to the interaction of this agonist with D1 striatal receptors, whose activity is not influenced by estrogens. However, we cannot rule out any possible alteration in the metabolism and/or presynaptic conversion of L-dopa to dopamine by estrogen treatment. The changes in turning behavior may be attributed to an antidopaminergic effect of estrogens and/or, like L-dopa, to modifications in the metabolism of apomorphine induced by the hormone.

Chronic haloperidol causes increase in salivary response and alpha 1-adrenoceptors in submandibular gland of the rat

The effect of chronic haloperidol on the receptor-secretion coupling of the submandibular glands of the rat was studied. After injection of 2 mg/kg haloperidol daily for 7 days, the dose-response curve to L-noradrenaline was displaced to the left, with lowering of the threshold and enhancement of the maximal response. This was accompanied by a 73% increase in alpha 1-adrenoceptors in the glands. The effect was selective, since no changes were observed in alpha 2- and beta-adrenoceptors.

Salivary secretion induced by L-DOPA in haloperidol-treated rats

The effect of chronic haloperidol treatment on salivary secretion induced by L-dopa, was studied in male Sprague-Dawley rats. Dose-response relationships for L-dopa, obtained 24 h after haloperidol treatment, showed that salivary secretion was greater in rats that had been injected with haloperidol (2 mg/kg/day, i.p.) for 7 days than in controls. The threshold doses requirements were significantly reduced in that group. Pretreatment with carbidopa suppressed the salivary secretion produced by L-dopa in haloperidol-treated and control rats whose glands had been denervated. The secretory response in innervated glands was higher in haloperidol-treated animals than in controls. Haloperidol treatment also increased salivation induced by L-noradrenaline as determined by dose-response relationships. This was associated with a decrease in the threshold doses requirement. In controls and in rats chronically treated with haloperidol, the salivary responses to L-noradrenaline were temporarily depressed by 80-90% by a prior acute injection of haloperidol (2 mg/kg, i.v.) presumably acting as an alpha blocker. A similar reduction was observed after acute treatment with phentolamine (3 mg/kg, i.v.). The data obtained in this study, i.e. that chronic administration of haloperidol increases the salivary response to L-dopa and L-noradrenaline, suggests that such an affect could be due to the development of supersensitivity of striatal dopamine receptors as well as of peripheral alpha-adrenergic receptors.

Cholinergic mechanisms within the caudate nucleus mediate changes in blood pressure

Microinjections of 10 micrograms of carbachol into the caudate nucleus induced changes in the blood pressure of cats anesthetized locally, paralyzed and artificially respired. These responses were dependent on the site of injection. Carbachol, microinjected at rostral levels of the caudate nucleus, elicited pressor responses while a decrease in blood pressure was observed following injections at caudal levels. Both of these effects were blocked by prior microinjection of atropine. Microinjections of carbachol outside the caudate did not affect the resting blood pressure. However, injections of carbachol into the lateral ventricle always produced pressor responses independent of the site of injection along the antero-posterior extension of the ventricle. On the other hand, microinjections of dopamine (20 micrograms) into the caudate nucleus failed to modify blood pressure. From this study, it is concluded that within the caudate nucleus there are two different muscarinic mechanisms, which when activated, mediate changes in blood pressure, possibly through the sympathetic nervous system.

Changes in multiunit activity of nigral neurons induced by cholinergic and dopaminergic stimulation of the caudate nucleus

The effects of stimulation of the caudate cholinergic and dopaminergic receptors on multiunit activity in the ipsilateral substantia nigra were studied in cats locally anesthetized, paralyzed and artificially respired. Cholinergic stimulation by intracaudate microinjections of 10 micrograms of carbachol diminished multiunit activity by 36% in the ventral substantia nigra (SN) and increased activity by 48% in the dorsal SN. This effect was abolished after electrolytic lesion of the ipsilateral striatonigral pathway. Opposite responses were observed following intracaudate administration of 20 micrograms of dopamine or 20 micrograms of D-amphetamine. Multiunit activity in the ventral SN increased by 36% and 34%, respectively, while the activity in the dorsal SN was reduced by 56% and 53%, respectively. Similar results were obtained in response to systemic administration of D-amphetamine. Extracaudate microinjections of carbachol and dopamine left multiunit activity in the SN unaffected. In conclusion, our results indicate an opposite action of caudate cholinergic and dopaminergic receptors on multiunit activity in the SN of the cat.

Somatotopic organization of caudate-caudate relationships in the cat

Experiments were carried out on cats locally anesthetized and paralyzed with Flaxedil. Stimulation of the caudate nucleus and the sciatic nerve evoked biphasic positive-negative field potentials in the contralateral nucleus with mean latencies of 16.1 +/- 1.8 msec and 18.1 +/- 1.6 msec, and peak to peak amplitudes of 185.5 +/- 19.8 microV and 236.9 +/- 11.5 microV, respectively. A mediolateral distribution was observed in the caudate connections. The medial and lateral halves of one nucleus project to medial and lateral halves of the contralateral caudate, respectively. However, maximum amplitude responses were grouped in the middle-external two-thirds of the caudate. No responses could be evoked in the caudate tail by stimulation of any part of the opposite nucleus. On the other hand, the somatic afferents are distributed to all levels of the caudate nucleus. Although the largest responses were recorded in the same areas where the highest potentials were evoked by contralateral caudate stimulation. It is concluded that, in the cat, a topographic organization of the caudate-caudate relations exist in the mediolateral axis of the nucleus, and that its middle regions could be the primary receptive fields for caudate and somatic afferents.

The role of the caudate-putamen nucleus in salivary secretion induced by L-DOPA

Experiments were performed in rats of the Wistar strain anesthetized with alpha-chloralose (100 mg/kg). Electrolytic lesion of either components of the striopallidal complex (corpus striatum, globus pallidus or entopeduncular nucleus) reduced the sensory response to L-DOPA in the contralateral submaxillary glands. Damage to other neural structures, directly or indirectly related to the striopallidal system, left the salivary response unaffected. These structures were: substantia nigra, cerebral cortex, ventromedial and center median-parafascicular thalamic nuclei, nucleus accumbens and posterior hypothalamic areas, including the medial forebrain bundle and lateral habenular nucleus. However, lesions placed in H1-H2 fields of Forel and reticular formation, lateral to the periaqueductal gray, reduced the salivary response in the contralateral glands. This effect was similar to that observed in animals with lesions of the striopallidal complex. From this study, it is concluded that the striatum is the target area for the central effect of L-DOPA on salivary secretion, by activation of pathways descending through the fields of Forel and mesencephalic reticular formation to the contralateral lower brain stem.

Study of the neural basis of circling behavior induced by L-dopa in lesioned entopeduncular cats

Experiments were carried out in cats bearing unilateral electrolytic lesion of the entopeduncular nucleus. The animals were tested for circling 1-2 weeks after surgery. Postoperatively the cats displayed transient spontaneous ipsiversive turning. The administration i.p. of L-DOPA (80 mg/kg) plus CarbiDOPA (30 mg/kg), suspended in 10% Tween 80, induced rotational behavior toward the lesioned side. This effect began about 26 min after drug administration and reached its maximum 40-110 min after the injection. Electrolytic lesions placed in the superior colliculus, strionigral pathway or pedunculopontine nucleus, contralateral to the lesioned entopeduncular nucleus did not modify the circling behavior induced by L-DOPA. Similar results were observed following unilateral lesion of the sensorimotor cortex or the VL thalamic nucleus. These results suggest that the circus movements induced by L-DOPA, in animals with unilateral lesion of the entopeduncular nucleus, is not mediated by the classic outflow of the striopallidal system.

Electrophysiological study of evoked electrical activity in the pineal gland

Experiments were carried out in rats, unanesthetized, paralyzed and artificially respirated. The electrical activity from the pineal gland was recorded with bipolar electrodes. Field potentials were evoked in the pineal after peripheral (photic and sciatic nerve) and central (septal area, habenular complex and optic tract) stimulations. In general these potentials were biphasic with the exception of that evoked by the sciatic nerve and optic tract, which exhibited a complex response and a triphasic field potential, respectively. Bilateral sympathectomy did not modify the pineal evoked responses, but when the pineal stalk was sectioned all the responses were immediately suppressed after the lesion. On the basis of the above experimental data one could conclude that the bulk of the inputs to the pineal gland come through its stalk. At the present, the physiological significance of these findings is not clear.

Studies on the mechanisms of L-dopa-induced salivary secretion

Systemic administration of L-dopa and dopamine elicited a marked and sustained secretory response in the rat's submaxillary glands. These effects were blocked by pretreatment with phentolamine plus propranolol. Acute unilateral sympathectomy (decentralization or denervation) reduced the response to L-dopa by about 41-48%. But it left unchanged the secretory response to dopamine. Chemical sympathectomy by hexamethonium caused a similar reduction (45%) in the secretory response to L-dopa while parasympathectomy was unable to modify the salivary secretion caused by L-dopa or dopamine. Pretreatment with haloperidol reduced the salivary secretion to L-dopa in normal animals (unoperated glands), while the response to dopamine was unaffected. On the other hand, haloperidol did not alter the salivary response to L-dopa in animals with surgical sympathectomy (denervation) as compared to the same animals treated with L-dopa alone. From this study we conclude that the salivary secretion induced by L-dopa is mediated by both central and peripheral mechanisms. Dopaminergic receptors may be involved in the central effect and alpha- and beta-receptors in the peripheral response.

Electrophysiological evidence for the existence of caudate-caudate connections

Experiments were performed in cats unanesthetized and paralyzed with Flaxedil. The stimulation of the right caudate elicited in the contralateral nucleus, biphasic positive-negative field potentials with latencies between 11-20 msec and peak to peak amplitudes of 132-216 microv. These were the shortest latencies and the highest amplitudes for those potentials evoked by stimulation of the symmetrical positions to recording electrode. However, no responses could be evoked in the caudate tail by stimulation of any part of the opposite nucleus. Lesions of cerebral cortex (sensorimotor cortex or hemidecortication) and thalamus (center median-parafascicular complex and massa intermedia) left the evoked responses in the caudate nucleus unchanged. However, the evoked potentials were suppressed by section of the corpus callosum. Our results suggest direct connections between both caudates, through the corpus callosum.

Effects of melatonin on spontaneous and evoked neuronal activity in the mesencephalic reticular formation

The acute effects of melatonin on the spontaneous activity of single cells in the mesencephalic reticular formation were studied in 40 male rats unanesthetized and immobilized with Flaxedil. One hundred and ten neurons were explored. Only 64 modified their spontaneous activity after the intravenous administration of melatonin. This response consisted of an increase in neural firing (6 neurons), decrease (55 neurons) and biphasic response of decrease and increase (3 neurons). When the effect of melatonin on the evoked activity in the mesencephalic neurons by peripheral stimulation (sciatic and photic) was checked an increase of the number of neurons that showed inhibitory responses to photic stimulation was found. No changes in blood pressure and EEG were observed at the doses of melatonin used (200, 400 and 600 micrograms/100 g of body weight). However, with doses of 600 micrograms a tendency toward synchronization was seen in the EEG. The present observations indicate an inhibitory effect of melatonin on the spontaneous neuronal activity of the mesencephalic reticular formation. This effect may contribute to the changes in the sleep-wakefulness cycle and anticonvulsant action attributed to this hormone.