Terry D. Reisine

Neurotoxic action of capsaicin on spinal substance P neurons.

The effects of capsaicin injections into neonatal rats on the ultrastructure of the neonatal dorsal horn and on some biochemical and behavioral parameters in the adult were examined. Electron microscopic observations revealed degeneration and glial engulfment of boutons and umyelinated axons in the dorsal horn 2 and 6 h after neonatal subcutaneous capsaicin injections. Capsaicin treatment had no effect on the activities of glutamic acid decarboxylase and choline acetyltransferase in the dorsal horn. Results of substance P measurements in the CNS showed no effect of capsaicin administration on striatal, hypothalamic or nigral substance P content, whereas substance P levels in the dorsal horn of the spinal cord were reduced by half. The density of [3H]naloxone binding sites in the dorsal horn was significantly reduced, while the affinity was not affected. Capsaicin-treated animals showed significantly increased latencies to respond to a noxious thermal stimulus in both tail-flick and hot-plate tests. The results are discussed in relation to the current concepts of the involvement of substance P and opiate systems in nociception and the potential use of neonatal capsaicin as a selective neurotoxin for the elucidation of the spinal mechanisms of pain.

Neurotransmitter receptor alterations in Parkinson's disease.

Abstract Neurotransmitter receptor binding for GABA, serotonin, cholinergic muscarinic and dopamine receptors and choline acetyltransferase (ChAc) activity were measured in the frontal cortex, caudate nucleus, putamen and globus pallidus from postmortem brains of 10 Parkinsonian patients and 10 controls. No changes in any of these systems were observed in the frontal cortex. In the caudaye nucleus, only the apparent dopamine receptor binding was altered with a significant 30% decrease in the Parkinsonian brain. Both cholinergic muscarinic and serotonin receptor binding were significantly altered in the putamen, the former increasing and the latter decreasing with respect to controls. In addition, ChAc activity was decreased in the putamen. In the globus pallidus, only ChAc activity was significantly changed, decreasing about 60%, with no change in neurotransmitter receptor binding. The results suggest that a progressive loss of dopaminergic receptors in the caudate nucleus may contribute to the decreased response of Parkinsonian patients to L-dopa and dopamine agonist therapy.

Effects of desipramine and yohimbine on α2- and β-adrenoreceptor sensitivity

The effects of yohimbine on desipramine-induced adrenoreceptor alterations were examined in murine limbic forebrain areas. Treatment with both drugs in combination resulted in a significant decrease in [3H]dihydroalprenolol binding, which was not manifest after treatment with either drug alone. Moreover, co-administration of yohimbine was found to accelerate the time course and increase the magnitude of desipramine-induced increases in [3H]clonidine binding. The possible physiologic significance of these findings is discussed along with their pharmacologic implications.

The localization of receptor binding sites in the substantia nigra and striatum of the rat.

Neurotransmitter receptor binding of 5 ligands was examined in the striatum, substantia nigra (SN) and frontal cortex of rats which had received either unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal pathway (NSP) or unilateral kainic acid lesions of the striatum. 6-OHDA lesions of the NSP significantly reduced [3H]dihydroalprenolol ([3H]DHA) and [3H]naloxone ([3H]Nal) binding by 31% and 28% respectively, in the denervated striatum compared to the contralateral side. Scatchard analysis revealed that the alteration in [3H]DHA binding was not due to a change in the affinity of the beta-adrenergic receptor for [3H]DHA. In marked contrast to these changes in the striatum, destruction of the NSP resulted in a significant increase in [3H]DHA and [3H]Nal binding by 44% and 26%, respectively, in the frontal cortex of the lesioned compared to the control side. 6-OHDA lesions in the NSP did not alter striatal receptor binding for [3H]quinuclidinyl benzilate ([3H]QNB), [3H]muscimol ([3H]Mus) or [3H]flunitrazepam ([3H]Flu). Similarily, intrastriatal kainic acid injections did not alter striatal receptor binding for [3H]Nal, [3H]Flu or [3H]Mus. Of the various receptor densities measured in the SN after the above lesions the only alteration observed was a 43% increase in [3H]Flu binding following 6-OHDA lesions of the NSP. Scatchard analysis indicated no change in the affinity of the benzodiazepine receptor for [3H]Flu. 6-OHDA lesions of the NSP did not alter [13H]QNB or [3H]Nal binding in the SN. Striatal kainic acid lesions did not alter nigral [3H]QNB or [3H]Flu binding. The results are discussed in terms of neurotransmitter localization and plasticity within the striatum, SN and frontal cortex.

Alterations in dopaminergic receptors in Huntington's disease.

To detect variations in dopaminergic receptors and cholinergic activity in regions of postmortem Huntingtons diseased brains, 3H-spiroperidol binding assays and choline acetyltransferase (ChAc) activities were carried out. A significant reduction in 3H-spiroperidol binding in the caudate nucleus, putamen and frontal cortex of choreic brains was detected which appeared to be due to a decrease in the total number of binding sites rather than to a decrease in affinity of 3H-spiroperidol for the dopaminergic receptor. In choreic brains, there were also significant reductions in ChAc activity in the caudate nucleus and putamen. The decreases of both 3H-spiroperidol binding and ChAc activity in the neostriatum suggest that the dopaminergic receptors are localized postsynaptically on cholinergic interneurons. Dopaminergic receptor alterations in the basal ganglia may be one of the causes of the abnormal motor movements found in HD while alterations of these receptors in the frontal cortex may be associated with the neuronal degeneration found in that area of choreic brains.

Loss of striatal dopaminergic receptors after intrastriatal kainic acid injection

Abstract Lesioning of the rat striatum with kainic acid may provide a useful animal model with which to study Huntingtons Disease since, in both situations, changes in several neurochemical parameters appear similar. In this study, we examined the time course of dopaminergic (DA) and muscarinic cholinergic (MCHOL) receptor alterations after kainic acid injection into the rat striatum. As early as two days after unilateral, intrastriatal injection of kainic acid, most striatal perikaya in the injected area had been destroyed as seen by histological examination. A progressive decrease in the DA and MCHOL receptors continued which was not due to changes in their affinity for their respective receptors. By 48 days after injection, there was about 75% decrease in DA receptors and about a 65% decrease in MCHOL receptors. The DA receptor loss is similar in extent to the reported loss in activity of striatal, dopamine-stimulated adenylate cyclase after kainic acid lesion. The DA and MCHOLreceptor loss is similar to the reported loss of neostriatal DA and MCHOL receptors in Huntingtons Disease.

Effects of combined administration of amphetamine and iprindole on brain adrenergic receptors

Mobley et al. 1° have shown that treatment of rats with amphetamine for 4 days can reduce the sensitivity of the forebrain cyclic AMP generating system to norepinephrine (NE) stimulation. Furthermore, treatment of rats with amphetamine in combination with iprindole, a drug which inhibits the metabolism of amphetamine 4 and increases its brain concentrations in the rat 6 , reduced the time required for this desensitization to 2 days 9. Chronic treatment of rats with antidepressant drugs has also been shown to decrease the sensitivity of the limbic forebrain cAMP generating system to NE stimulation 19, and this effect has been ascribed to a decrease in brain fladrenergic receptor density 1. Therefore, it was of interest to us to determine whether the amphetamine-iprindole effect described above might also be explained by a decrease in brain fl-receptor density, or perhaps an effect on other receptors. Our results reveal that after 3 days of treatment, while amphetamine or iprindole administration alone did not alter cortical fl-adrenergic receptors, the combination of iprindole and amphetamine reduced the density of these receptors. In addition, all 3 drug treatments significantly elevated a2-adrenergic receptor densities but did not affect the properties of al-adrenergic receptors. Groups of 4 Charles River C-D male rats, weighing 230--270 g, were treated twice daily with amphetamine (10 mg/kg i.p.) and once daily with iprindole (25 mg/kg i.p.) for 3 days. Amphetamine and iprindole were administered at 08.30 h and amphetamine again at 16.30 h. Separate groups were treated with each drug alone on the same schedule as in the combination study. A water-injected group served as a control. All rats were sacrificed by decapitation between 08.30 and 09.00 h on the fourth day and the whole brain was rapidly removed and frozen (--20 °C). For receptor binding assays, tissues were prepared in the following manner. The

Alterations in the benzodiazepine receptor of Huntington's diseased human brain

Benzodiazepines (BDZs) are a class of drugs that are widely prescribed for their anxiolytic, anticonvulsant, hypnotic and muscle relaxant properties 10. Recent studies have shown that BDZs bind to cell surface receptors in the central nervous system (CNS)7,12,x3. These reports suggest that there may be substances in the brain which normally interact with the BDZ receptor. Several studies have attempted to determine whether BDZ receptors are localized on glial or neuronal cells. Braestrup et al. 1, have found that destruction of neuronal cell bodies in the substantia nigra with kainic acid results in a reduction in BDZ receptor density in this area. Braestrup et al.1, 2 have also found that in cell cultures of astroglia, there are no BDZ receptors although other neurotransmitter receptors are present. These studies suggest that BDZ receptors in the CNS might be associated with neuronal membranes. Another line of research into the understanding of the location of BDZ receptors in the CNS is the use of postmortem brain tissue from patients dying of neurological disorders. In Huntingtons disease (HD), there is selective loss of small interneurons in the basal ganglia as well as widespread neuronal destruction in the cerebral cortex 4. There is no depletion of glial cell population in these brain areas but rather a proliferation. Several studies have correlated the decrease in various neurotransmitter receptor densities in the basal ganglia and frontal cortex of HD brains with the neuronal degeneration in these regions4,11, ~n. To this end, we have monitored BDZ receptors in several regions of HD brains to provide further support for the hypothesis that there is a partial population of BDZ receptors on neuronal cell membranes in the brain. Postmortem brain tissue from 5 adult patients (average age 62 ~: 3 years) diagnosed as having Huntingtons Disease (adult-onset type) were used in this study.

Localization of dopamine receptors in rat brain

Recently, several lesioning techniques have been developed which selectively destroy various neuronal elements. 6-Hydroxydopamine (6-OHDA), has been demonstrated to preferentially destroy catecholamine-containing neurons 22. Injection of 6OHDA in the lateral hypothalamic area near the substantia nigra (SN), causes degeneration of the nigrostriatal dopamine pathway (NSP). Kainic acid (KA), a neurotoxin, is believed to destroy neuronal cell bodies near the site of injection, while sparing adjacent axons or terminals 4. Both neurotoxins have been extensively employed in order to better understand the mechanisms underlying neurotransmission in the brain. It has been suggested that there are multiple classes of dopamine (DA) receptors in the brain 12. Kebabian et al. 11, have proposed that an adenylate cyclase linked receptor is one type of DA receptor. Others have indicated that neuroleptics interact with yet another type of DA receptor 14. It is also possible that different types of DA receptors are located preand postsynaptic at DA synapses 28. We have demonstrated that the neuroleptic, spiroperidol, binds to dopamine receptors in both the striatum and SN (refs. 5-7). In order to determine the neuronal localization of the DA receptor as labeled by spiroperidol we have performed 6-OHDA and KA lesions in the NSP and striatum, respectively, and have monitored alterations in [aH]spiroperidol binding in both the striatum and SN. In additional experiments, [SH]serotonin binding was determined in order to correlate the alterations in [3H]spiroperidol binding with changes in serotonin receptor density. A total of 65 male Wistar rats weighing about 300 g were employed in the present study. All surgery was conducted in a stereotaxic apparatus (Kopf) while the animals were under Nembutal anesthesia. Unilateral 6-OHDA lesions of the NSP were achieved by injections of 2.0 #1 of a physiological saline solution containing 4 /~g/2/~1 6-OHDA and 0.3 mg/ml ascorbic acid at the co-ordinates AP +4.4, ML + 1.8 and DV 2.5, according to the atlas of KSnig and Klippe118. These animals were injected intraperitoneally with desipramine HCI (25 mg/kg) 30 min before 6-OHDA

Inhibition of in vivo 3H-spiperone binding by the proposed antipsychotic des-try1-γ-endorphin

The proposed antipsychotic neuropeptide des-tyrosine1-gamma-endorphin (DT gamma E, beta LPH62,77) inhibits in vivo 3H-spiperone binding in the hypothalamus, corpus striatum and mesolimbic areas of rat brain. The neuroleptic drug haloperidol produces similar effects in these areas as well as in frontal cortex, but is considerably more potent than DT gamma E. Correspondingly, haloperidol produces postural and motor abnormalities not seen with DY gamma E. These data together with the results from previous in vitro studies suggest DT gamma E might act indirectly, having a selective neuroleptic-like action at 3H-spiperone binding sites.