Inhibitory effects of the kappa opiate U50,488 in the substantia nigra pars reticulata

Effects of dorsal striatal infusions of R(-)-propylnorapomorphine on kappa-opioid-mediated locomotor activity in the young rat: possible role of the indirect pathway

Stimulation of kappa-opioid receptors in the substantia nigra pars reticulata (SNPR) increases the locomotor activity of young rats: an effect blocked by systemic administration of a D2-like receptor agonist. Based on these initial findings, we proposed that: (a) D2-like receptors in the dorsal striatum are responsible for attenuating kappa-opioid-induced locomotor activity, and (b) the effects of D2-like receptor stimulation are mediated by the indirect pathway, which extends from the dorsal striatum to the SNPR via the globus pallidus (GP) and subthalamic nucleus (STN). To test the first hypothesis, young rats were given a systemic injection (i.p.) of saline or the kappa-opioid receptor agonist (+/-)-trans-U50,488 methanesulfonate salt (U50,488) on postnatal day (PD) 18. Later in the testing session, rats received bilateral infusions of vehicle or the D2-like receptor agonist R(-)-propylnorapomorphine (NPA) into the dorsal striatum, and the ability of NPA to block U50,488-induced locomotor activity was determined. To test the second hypothesis, rats were given sham or bilateral electrolytic lesions of the GP or STN on PD 16. Two days later, saline- and U50,488-induced locomotor activity was measured after systemic (i.p.) administration of vehicle or NPA. As predicted, dorsal striatal infusions of NPA attenuated the U50,488-induced locomotor activity of young rats. Contrary to our expectations, bilateral lesions of the GP or STN did not impair NPA's ability to block U50,488-induced locomotor activity. When considered together, these results suggest that: (a) stimulation of D2-like receptors in the dorsal striatum is sufficient to attenuate the kappa-opioid-mediated locomotor activity of young rats; and (b) the indirect pathway does not mediate the effects of D2-like receptor stimulation in this behavioral model.

Effect of acute and chronic administration of U50,488, a kappa opioid receptor agonist, in 6-OHDA-lesioned rats chronically treated with levodopa

To evaluate the possible involvement of kappa opioid receptor-mediated mechanisms in levodopa-induced motor fluctuations, we have investigated the effects of U50,488, a selective kappa opioid agonist, on levodopa-induced motor alterations in rats with unilateral 6-OHDA lesion. Acute and chronic administration of U50,488 has been studied to evaluate the possible reversion or prevention of these levodopa effects. In a first set of experiments, rats were treated with levodopa (25 mg/kg with benserazide, twice daily, ip) for 22 days and, on Day 23 U50,488 (0.5, 1, or 3 mg/kg, i.p.) was administered immediately before levodopa. In a second set of experiments, rats were treated daily for 22 days with levodopa and U50,488 (1 or 3 mg/kg/day, i.p.). The duration of the rotational behavior induced by chronic levodopa decreased after 22 days (P < 0.05). Acute administration of U50,488 on Day 23 reversed this effect when low doses were administered (P < 0.05). Chronic U50,488 administration did not prevent the shortening in response duration induced by levodopa. Our results demonstrate that the kappa opioid receptor agonist U50,488 reverses but does not prevents levodopa-induced motor alterations in parkinsonian rats. These results suggest a role for kappa opioid receptor-mediated mechanisms in the pathophysiology of levodopa-induced motor response complications. These findings suggest that the stimulation of kappa opioid receptors might confer clinical benefit to parkinsonian patients under levodopa therapy suffering from motor complication syndrome.

Dynorphin regulates D1 dopamine receptor-mediated responses in the striatum: relative contributions of pre- and postsynaptic mechanisms in dorsal and ventral striatum demonstrated by altered immediate-early gene induction

Dynorphin, an endogenous kappa opioid receptor ligand, acts in the striatum to regulate the response of striatonigral neurons to D1 dopamine receptor stimulation. We investigated the relative contributions of both presynaptic kappa receptors on dopamine terminals and postsynaptic kappa receptors on striatal neurons by analyzing opioid regulation of D1 effects in the absence of presynaptic kappa receptors, after 6-hydroxydopamine depletion of striatal dopamine. D1-receptor-mediated immediate-early gene induction was measured by using in situ hybridization histochemistry. First, repeated treatment with the D1-receptor agonist SKF-38393 (2 mg/kg/day, 3-14 days) was used to increase dynorphin levels in rats with dopamine depletions. In the nucleus accumbens, increased dynorphin expression was accompanied by reduced induction of the immediate-early genes c-fos and zif 268 by SKF-38393. In contrast, in dorsal/lateral aspects of the dopamine-depleted striatum, this D1 response was sustained despite a large increase in dynorphin expression. These results are consistent with a requirement of dopamine terminals (presynaptic kappa receptors) for the inhibitory action of dynorphin in the dorsal/lateral striatum, but not in the ventral striatum. Second, the kappa receptor agonist spiradoline (1-10 mg/kg) reduced c-fos and zif 268 induction by SKF-39393 (2.5 mg/kg) preferentially in ventral parts of the dopamine-depleted striatum, which contain higher levels of kappa receptor mRNA and binding. These results also indicate that postsynaptic kappa receptors contribute to the inhibition of the D1 response at least in the ventral striatum. Together, these results indicate that dynorphin in the striatum functions to regulate dopamine input to striatonigral neurons, acting at both pre- and postsynaptic sites, and that the relative contributions of these mechanisms differ between dorsal and ventral striatal regions.

Effects of kappa receptor agonists on D1 and D2 dopamine agonist and antagonist-induced behaviors

Striatal dynorphin-containing neurons receive dopaminergic inputs from the substantia nigra pars compacta and project primarily to the substantia nigra pars reticulata and entopeduncular nucleus. These neurons mainly express dopamine (DA) D1 receptors and thus dynorphin system stimulation might be expected largely to influence D1 receptor agonist or antagonist effects on motor function. It is well known the interaction existing between DA D1 and D2 drugs in the induction of behavioral effects. However, the effects of dynorphin on selective D1 and D2 DA agonist and antagonist-induced behaviors have not yet been investigated. Administration of the kappa agonists spiradoline (0.5, 1 and 5 mg/kg) or U50,488H (1, 10 and 25 mg/kg) decreased non-stereotyped grooming induced by the selective D1 agonist SKF38393. This effect was inhibited by the non-selective opioid receptor antagonist naloxone (20 mg/kg) and by the selective kappa antagonist nor-binaltorphimine (nor-BNI, 20 mg/kg). Stereotypies induced by the selective D2 agonist quinpirole were decreased by spiradoline (1 and 5 mg/kg) and by U50,488H (1, 10 and 25 mg/kg), while jerking movements of a type associated with increased D2 receptor and decreased D1 receptor stimulation emerged. Kappa agonist effects were inhibited by the prior administration of SKF38393 (10 mg/kg); these inhibitory effects were blocked by prior administration of the D1 antagonist SCH23390 (5 mg/kg). Naloxone reversed the effects of both kappa agonists on quinpirole-induced stereotypies. Kappa agonists increased D1 antagonist-induced catalepsy, but had no effect on D2 antagonist-induced catalepsy. Naloxone and nor-BNI inhibited this effect. These results suggest that the motoric effects of D1 receptor antagonists in part reflect stimulation of striatal dynorphin containing efferents.

Neuropeptide Y and dynorphin-immunoreactive large dense-core vesicles are strategically localized for presynaptic modulation in the hippocampal formation and substantia nigra

Neuropeptide Y (NPY) and dynorphin elicit regionally selective presynaptic modulation in the hippocampal formation and the pars reticulata of the substantia nigra, respectively. We examined potential anatomical substrates for their presynaptic modulation by determining the distribution and size of large (80-120 nm) dense-core vesicles (DCVs), organelles previously shown to be immunoreactive for each peptide. Throughout the hippocampal formation, NPY-immunoreactive DCVs were located primarily in axon terminals and were more sparingly distributed in dendrites. In comparison with other portions of the hippocampal formation, NPY-labeled DCVs were most abundant in axons and terminals of the CA1 region. The DCVs in the CA1 region of the hippocampus also more frequently had larger mean cross-sectional diameters when located along portions of the terminal in contact with unlabeled axons. In both the CA1 region of the hippocampus and the dentate gyrus, NPY-labeled DCVs in contact with portions of the axonal membrane apposed to astrocytes also were larger than those located more centrally in the axon terminal. Dynorphin-immunoreactive DCVs in axon terminals of the substantia nigra were significantly larger when found near portions of the axonal membrane in contact not only with other axons and astrocytic processes, but also occasionally with postsynaptic dendrites. The parallels between diameters of DCVs and known selectivity of NPY for presynaptic modulation in the CA1 region of the hippocampus suggest a direct correlation between the size and distribution of immunoreactive DCVs and their sites of exocytotic release.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of the basal ganglia in nociception and pain

The involvement of the basal ganglia in motor functions has been well studied. Recent neurophysiological, clinical and behavioral experiments indicate that the basal ganglia also process non-noxious and noxious somatosensory information. However, the functional significance of somatosensory information processing within the basal ganglia is not well understood. This review explores the role of the striatum, globus pallidus and substantia nigra in nociceptive sensorimotor integration and suggests several roles of these basal ganglia structures in nociception and pain. Electrophysiological experiments have detailed the non-nociceptive and nociceptive response properties of basal ganglia neurons. Most studies agree that some neurons within the basal ganglia encode stimulus intensity. However, these neurons do not appear to encode stimulus location since the receptive fields of these cells are large. Many basal ganglia neurons responsive to somatosensory stimulation are activated exclusively or differentially by noxious stimulation. Indirect techniques used to measure neuronal activity (i.e., positron emission tomography and 2-deoxyglucose methods) also indicate that the basal ganglia are activated differentially by noxious stimulation. Neuroanatomical experiments suggest several pathways by which nociceptive information may reach the basal ganglia. Neuroanatomical studies have also indicated that the basal ganglia are rich in many different neuroactive chemicals that may be involved in the modulation of nociceptive information. Microinjection of opiates, dopamine and gamma-aminobutyric acid (GABA) into the basal ganglia have varied effects on pain behavior. Administration of these neurochemicals into the basal ganglia affects supraspinal pain behaviors more consistently than spinal reflexive behaviors. The reduction of pain behavior following electrical stimulation of the substantia nigra and caudate nucleus provides additional evidence for a role of the basal ganglia in pain modulation. Some patients with basal ganglia disease (e.g., Parkinson's disease, Huntington's disease) have alterations in pain sensation in addition to motor abnormalities. Frequently, these patients have intermittent pain that is difficult to localize. Collectively, these data suggest that the basal ganglia may be involved in the (1) sensory-discriminative dimension of pain, (2) affective dimension of pain, (3) cognitive dimension of pain, (4) modulation of nociceptive information and (5) sensory gating of nociceptive information to higher motor areas. Further experiments that correlate neuronal discharge activity with stimulus intensity and escape behavior in operantly conditioned animals are necessary to fully understand how the basal ganglia are involved in nociceptive sensorimotor integration.

Electrophysiological effects of cholecystokinin on neurons in rat substantia nigra pars reticulata

The electrophysiological effects of carboxyterminal fragments of cholecystokinin (CCK) on neurons in the dorsal substantia nigra pars reticulata (SNr) were evaluated in anesthetized rats. Microiontophoretic administration of sulfated CCK octapeptide (CCK-8S, agonist for CCK-A and CCK-B receptors) and the selective CCK-B receptor agonists, CCK-4 and unsulfated CCK-8, inhibited the firing rates of a subpopulation of SNr neurons. This effect appears to be mediated by CCK-B receptors.

The role of opioid mechanisms in the anorectic effects of stimulants: U50,488H enhances amphetamine inhibition of free feeding in rats

The influences of the kappa-opiate agonist U50,488H (U50; 4 mg/kg IP), the neuroleptic haloperidol (HAL; 0.3 mg/kg IP), and MK-801 (0.2 mg/kg IP), a noncompetitive antagonist for NMDA receptors, were compared on the effects of nine days of d-amphetamine (AMPH) treatment (3 mg/kg IP) on food and water intake and urine output. AMPH prevented feeding stimulation produced by U50 during the first 2 h, whereas U50 inhibited the hyperphagic phase that rats showed between 2 and 5 h after AMPH administration. Tolerance did not develop to the first 2-h suppression of feeding; in contrast, the late hyperphagic phase slowly recovered across the nine days of treatment. Combined administration of the two drugs barely affected water intake but considerably increased urine output. Unlike U50, HAL left the late hyperphagic response to AMPH unchanged and delayed the development of hyperdipsia. In our study MK-801 had one effect only: It significantly reduced amphetamine diuresis. These results suggest that by inhibiting the late hyperphagic response U50 enhances the anorectic effects of AMPH, but that dopamine probably has no direct role in this interaction.

Effects of sigma ligands on rat cerebellar Purkinje neuron firing: an iontophoretic study

The electrophysiological responses of rat cerebellar Purkinje neurons to selective sigma ligands applied iontophoretically was examined in urethane anesthetized male Sprague-Dawley rats. 1,3-Di-o-tolylguanidine (DTG), dextrallorphan (DEX), (+)-pentazocine((+)-PENT), (+)-3-(3-Hydroxyphenyl)-N-propylpiperidine ((+)-3-PPP), and the novel diamine BD1008, were ejected from multibarrel pipettes onto individual Purkinje cells. In some neurons, cell firing was inhibited following ejections of all compounds. These inhibitory effects were dose dependent and occurred without changes in spike amplitude or duration, thus ruling out local anesthetic effects as a mechanism. (+)-3-PPP and DEX increased firing rate in 27% and 14% (n = 15, n = 14, respectively) of cells studied. The results of this study indicate that sigma ligands significantly alter the spontaneous firing of Purkinje neurons, consistent with previous work suggesting motor effects of sigma ligands via the rubro-cerebellar circuitry.

Cellular substrates for interactions between dynorphin terminals and dopamine dendrites in rat ventral tegmental area and substantia nigra

Dynorphin and other kappa opioid agonists are thought to elicit aversive actions and changes in motor activity through direct or indirect modulation of dopamine neurons in ventral tegmental area (VTA) and substantia nigra (SN), respectively. We comparatively examined the immunoperoxidase localization of anti-dynorphin A antiserum in sections through the VTA and SN of adult rat brain to assess whether there were common or differential distributions of this opioid peptide relative to the dopamine neurons. We also more directly examined the relationship between dynorphin terminals and dopamine neurons in VTA and SN by combining immunoperoxidase labeling of rabbit dynorphin antiserum and immunogold-silver detection of mouse antibodies against tyrosine hydroxylase (TH) in single sections through the VTA and SN. Light microscopy showed dynorphin-like immunoreactivity (DY-LI) in varicose processes. These were relatively sparse in VTA and were unevenly distributed in the SN, with little labeling in the pars compacta (pcSN) and the highest density of DY-LI in the medial and lateral pars reticulata (prSN). Electron microscopy established that the regional differences were attributed to differences in density (number/unit area) of immunoreactive profiles. The profiles containing DY-LI were designated as axon terminals based on having diameters greater than 0.1 micron, few microtubules and many synaptic vesicles. In both the VTA and SN, the dynorphin-labeled terminals contained primarily small (35-40 nm) clear vesicles. These vesicles were rimmed with peroxidase immunoreactivity and were often seen clustered above axodendritic synapses. These synaptic specializations were usually symmetric; however a few asymmetric densities also were formed by immunoreactive terminals in both VTA and SN. Additionally, most of the dynorphin-labeled terminals contained 1-2, but occasionally 7 or more intensely peroxidase positive dense core vesicles (DCVs). Approximately 60% of the DCVs were located near axolemmal surfaces. The axolemmal surfaces contacted by immunoreactive DCVs were more often apposed to dendrites in the VTA; while in the SN other axon terminals were the most commonly apposed neuronal profiles. In both regions, a substantial proportion of the plasmalemmal surface in contact with the labeled DCVs was apposed to astrocytic processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Opioid receptors in midbrain dopaminergic regions of the rat. II. Kappa and delta receptor autoradiography

Opiates and opioid peptides are known to influence the dopaminergic (DA) neurons in the midbrain. The purpose of this study was to map and quantify the density of kappa and delta opioid receptor subtypes in the retrorubral field, substantia nigra, and ventral tegmental area and related nuclei, which contain DA nuclei A8, A9, and A10, respectively. Sections through the rostral-caudal extent of the rat midbrain were stained with an antibody against tyrosine hydroxylase, as a DA cell marker, and comparable sections were processed for in vitro receptor autoradiography using the kappa-selective ligand, U-69593, and the delta-selective ligand, D-Pen2, D-Pen5-enkephalin. In general, both kappa and delta ligands exhibited low levels of specific binding in regions occupied by the midbrain DA neurons. Kappa binding (4-8 fmol/mg tissue) was high throughout the rostral-caudal extent of the substantia nigra, in rostral portions of the ventral tegmental area, and in the nucleus paranigralis; low binding occurred in the retrorubral field and central linear nucleus raphe. Delta binding (6-18 fmol/mg tissue) was high in the caudal portion of the substantia nigra pars reticulata, and in the medial terminal nucleus of the accessory optic system (a region previously shown to contain DA dendrites). The kappa and delta receptor binding is heterogeneously distributed in regions occupied by midbrain dopaminergic neurons, and several fold lower than the binding of mu opioid receptors in the same brain regions.

Neurotransmitter regulation of dopamine neurons in the ventral tegmental area

Over the last 10 years there has been important progress towards understanding how neurotransmitters regulate dopaminergic output. Reasonable estimates can be made of the synaptic arrangement of afferents to dopamine and non-dopamine cells in the ventral tegmental area (VTA). These models are derived from correlative findings using a variety of techniques. In addition to improved lesioning and pathway-tracing techniques, the capacity to measure mRNA in situ allows the localization of transmitters and receptors to neurons and/or axon terminals in the VTA. The application of intracellular electrophysiology to VTA tissue slices has permitted great strides towards understanding the influence of transmitters on dopamine cell function, as well as towards elucidating relative synaptic organization. Finally, the advent of in vivo dialysis has verified the effects of transmitters on dopamine and gamma-aminobutyric acid transmission in the VTA. Although reasonable estimates can be made of a single transmitter's actions under largely pharmacological conditions, our knowledge of how transmitters work in concert in the VTA to regulate the functional state of dopamine cells is only just emerging. The fact that individual transmitters can have seemingly opposite effects on dopaminergic function demonstrates that the actions of neurotransmitters in the VTA are, to some extent, state-dependent. Thus, different transmitters perform similar functions or the same transmitter may perform opposing functions when environmental circumstances are altered. Understanding the dynamic range of a transmitter's action and how this couples in concert with other transmitters to modulate dopamine neurons in the VTA is essential to defining the role of dopamine cells in the etiology and maintenance of neuropsychiatric disorders. Further, it will permit a more rational exploration of drugs possessing utility in treating disorders involving dopamine transmission.

Effects of intracerebroventricularly administered mu-, delta- and kappa-opioid agonists on locomotor activity of the guinea pig and the pharmacology of the locomotor response to U50,488H

The effects of intracerebroventricular administration of morphine, the selective mu-agonist DAMGO, the delta-agonist DPDPE, the kappa-preferring peptide dynorphin A(1-13) and the kappa-agonist U50,488H on locomotor behaviour in the guinea pig were investigated. Morphine (total dose = 0.01, 0.1, 1, 10, 200 nmol), DAMGO and DPDPE (total dose = 0.1, 1, 10, 100 nmol of each) produced piloerection and sedation, indicating that the responses of guinea pigs to mu- and delta-opioid agonists differed from those of rats and mice. In contrast, U50,488H (total dose = 10, 100 nmol) and dynorphin A(1-13) (total dose = 100 nmol) produced increased locomotor activity which was attenuated by pretreatment with naloxone and norbinaltorphimine, thus confirming the involvement of kappa-opioid receptors. Furthermore, pretreatment with spantide, baclofen, muscimol, bicuculline, MK-801, raclopride and atropine also inhibited the U50,488H-induced locomotor activity, suggesting the involvement of GABA, dopamine, excitatory amino acids, substance P and acetylcholine in this response.

Involvement of the nigrotectal and nigrothalamic pathways in kappa opioid-induced circling

The relationship between kappa opioid-induced movement and output stations of the substantia nigra pars reticulata (SNpr) was examined using the rodent circling model. Contralateral rotation produced by intranigral microinjection of the kappa opiate U50,488 was lower in animals with ibotenic acid lesions of either the ipsilateral ventromedial thalamus or superior colliculus than in control animals without lesions. These results suggest that endogenous kappa opioids in the SNpr may influence movement through actions on the nigrothalamic and nigrotectal pathways. In contrast, animals with ipsilateral lesions of the striatum showed an increase in circling relative to controls, possibly due to kappa receptor supersensitivity in the SNpr.

The kappa-opioid receptor agonist spiradoline differentially alters the rotational response to dopamine D1 and D2 agonists

The effect of the selective kappa-opioid agonist, spiradoline, on rotational behavior induced by a dopamine D1 or D2 agonist was examined in rats with a unilateral 6-hydroxydopamine lesion of the nigrostriatal pathway. Spiradoline reduced the rotational response to the D1 agonist SKF 38393 in a dose-dependent manner. Spiradoline had no effect on the total number of turns elicited by the D2 agonist quinpirole, but did alter the pattern of quinpirole-induced rotation at the highest dose tested. By itself, spiradoline did not have any obvious effects on motor behavior and did not cause rotation in either the ipsilateral or contralateral direction. These data suggest that kappa receptor stimulation, possibly mediated by the endogenous agonist dynorphin under physiological conditions, may function to dampen striatal output through the D1 receptor-regulated striatonigral pathway.

Striatonigral projection neurons: a retrograde labeling study of the percentages that contain substance P or enkephalin in pigeons

Two largely separate populations of neuropeptide-containing striatonigral projection neurons have been distinguished in pigeons, one population whose neurons contain substance P (SP) and dynorphin (DYN) and a second population whose neurons contain enkephalin (ENK) (Reiner, '86a; Anderson and Reiner, '90a). In the present study, we investigated the abundance of these two types of neurons relative to all striatonigral projection neurons by combining retrograde labeling by the fluorescent dye fluorogold with immunofluorescence labeling for SP and ENK. Pigeons received large intranigral injections of fluorogold to retrogradely label the striatonigral projection neurons, and several days later they were treated with colchicine (32 hours before transcardial perfusion). Adjacent series of sections through the basal ganglia were labeled for SP and ENK using immunofluorescence techniques. The tissue was examined using fluorescence microscopy and the percentages of retrogradely labeled neurons containing either SP or ENK were quantified. We found that 85-95% of the fluorogold-labeled striatonigral neurons were SP+, whereas only 1-4% were ENK+. Thus the majority of striatonigral projection neurons in pigeons appear to contain SP, whereas a small percentage contain ENK. Only a small percentage of striatonigral neurons did not contain either. Since striatal projection neurons also contain GABA (Reiner, '86b), the present results suggest that a high percentage of striatonigral projection neurons coexpress SP, DYN and GABA, whereas a small fraction coexpress ENK and GABA. The available data are consistent with the conclusion that this is true in reptilian and mammalian species as well.