Differences in the regulation of acetylcholine release upon D2 dopamine and N-methyl-D-aspartate receptor activation between the striatal complex of reptiles and the neostriatum of rats

Pain Recognition in Reptiles

Advances in reptile cognitive research would help to (1) better qualify behavioral responses to pain experiences, (2) monitor welfare impacts, and (3) model analgesic studies with ecologically relevant insight to better qualify interventional responses. The focus of future analgesic studies in reptiles require the continued elucidation of the opiate systems and the given variations across taxa in efficacy in nociceptive tests.

Muscarinic, adenosine A(2) and histamine H(3) receptor modulation of haloperidol-induced c-fos expression in the striatum and nucleus accumbens

It is generally believed that haloperidol exerts its motor side effects and therapeutic effects mainly by antagonizing dopamine D(2) receptors in the striatum and the nucleus accumbens, respectively. Several neurotransmitters/modulators, including glutamate, acetylcholine, adenosine and histamine, affect dopaminergic activity in these centers. We have recently shown that N-methyl-D-aspartate receptor-mediated modulation of haloperidol-induced c-fos expression differs in functionally specific regions of the striatum and the nucleus accumbens. In the present study, the entire striatum and the nucleus accumbens were comprehensively examined for the pattern of modulation of haloperidol-induced c-fos expression by adenosine A(2), histamine H(3) and muscarinic receptor antagonists. Blockade of muscarinic and H(3) receptors resulted in a profound suppression of haloperidol-induced c-fos expression in the dorsolateral part of the striatum. In addition, the H(3) receptor antagonist suppressed the effects of haloperidol in the ventrolateral aspect of the striatum and the rostral parts of the medial striatum. Muscarinic receptor antagonists suppressed haloperidol-induced c-fos expression throughout the shell and in the mid-level of the core of the nucleus accumbens while A(2) and H(3) receptor antagonists did not.We found that the muscarinic and H(3) receptor antagonists suppress the induction of c-fos by haloperidol in the dorsolateral aspect of the striatum, an area implicated in the development of extrapyramidal motor symptoms following chronic haloperidol treatment. By contrast, haloperidol-induced c-fos expression in the nucleus accumbens, an area implicated in the therapeutic effects of haloperidol, was suppressed by the muscarinic receptor antagonist, but not by the H(3) receptor antagonist. Therefore we conclude that H(3) receptor modulation may provide a useful therapeutic target in future efforts to minimize neuroleptic-induced motor side effects.

Mammal-like striatal functions in Anolis. I. Distribution of serotonin receptor subtypes, and absence of striosome and matrix organization

Serotonin (5-HT) 5-HT(2A) and 5-HT(2C) receptors are thought to play important roles in the mammalian striatum. As basal ganglia functions in general are thought highly conserved among amniotes, we decided to use in situ autoradiographic methods to determine the occurrence and distribution of pharmacologically mammal-like 5-HT(2A) and 5-HT(2C) receptors in the lizard, Anolis carolinensis, with particular attention to the striatum. We also determined the distributions of 5-HT(1A), 5-HT(1B/D), 5 HT(3), and 5-HT(uptake) receptors for comparison. All 5-HT receptors examined showed pharmacological binding specificity, and forebrain binding density distributions that resembled those reported for mammals. Anolis 5 HT(2A/C) and 5-HT(1A) site distributions were similar in both in vivo and ex vivo binding experiments. 5-HT(2A & C) receptors occur in both high and low affinity states, the former having preferential affinity for (125)I-(+/-)-2,5-dimethoxy-4-iodo-amphetamine hydrochloride ((125)I-DOI). In mammals (125)I-DOI binding shows a patchy density distribution in the striatum, being more dense in striosomes than in surrounding matrix. There was no evidence of any such patchy density of (125)I-DOI binding in the anole striatum, however. As a further indication that anoles do not possess a striosome and matrix striatal organization, neither (3)H-naloxone binding nor histochemical staining for acetylcholinesterase activity (AChE) were patchy. AChE did show a band-like striatal distribution, however, similar to that seen in birds.

Mammal-like striatal functions in Anolis. II. Distribution of dopamine D(1) and D(2) receptors, and a laminar pattern of basal ganglia sub-systems

We used in situ autoradiographic ligand binding methods to determine the occurrence and distribution of dopamine D(1) and D(2) receptor sub-types in the anole lizard, Anolis carolinensis. Both were present and exhibited pharmacological specificity characteristics similar to those described for mammals. However, unlike in mammals where in the neostriatum [outside the nucleus accumbens/olfactory tubercle complex (NA/OT)] these receptors exhibit only slight dorsolateral (D(2) high, D(1) low) to ventromedial (D(1 )high, D(2) low) gradients that co mingle extensively, in the anole striatum outside the NA/OT there was a striking laminar pattern, with little if any overlap between D(2) (high in a dorsal band) and D(1) (high ventral to the D(2) band) distributions. As D(1) receptors are related to the direct and D(2) to the indirect basal ganglia (BG) subsystems in mammals, we also determined anole striatal distributions of pre-proenkephalin mRNA, a marker for striatal efferents to the indirect BG subsystem in mammals. Here, too, there was a striking laminar pattern, with pre-proenkephalin mRNA in a band similar to that seen for D(2) receptors. The crisp neuroanatomical separation between these classic BG subsystem markers in Anolis striatum make this species attractive for the study of such systems' functions during behavior.

Catecholamine systems in the brain of vertebrates: new perspectives through a comparative approach

A comparative analysis of catecholaminergic systems in the brain and spinal cord of vertebrates forces to reconsider several aspects of the organization of catecholamine systems. Evidence has been provided for the existence of extensive, putatively catecholaminergic cell groups in the spinal cord, the pretectum, the habenular region, and cortical and subcortical telencephalic areas. Moreover, putatively dopamine- and noradrenaline-accumulating cells have been demonstrated in the hypothalamic periventricular organ of almost every non-mammalian vertebrate studied. In contrast with the classical idea that the evolution of catecholamine systems is marked by an increase in complexity going from anamniotes to amniotes, it is now evident that the brains of anamniotes contain catecholaminergic cell groups, of which the counterparts in amniotes have lost the capacity to produce catecholamines. Moreover, a segmental approach in studying the organization of catecholaminergic systems is advocated. Such an approach has recently led to the conclusion that the chemoarchitecture and connections of the basal ganglia of anamniote and amniote tetrapods are largely comparable. This review has also brought together data about the distribution of receptors and catecholaminergic fibers as well as data about developmental aspects. From these data it has become clear that there is a good match between catecholaminergic fibers and receptors, but, at many places, volume transmission seems to play an important role. Finally, although the available data are still limited, striking differences are observed in the spatiotemporal sequence of appearance of catecholaminergic cell groups, in particular those in the retina and olfactory bulb.

Evolution of the basal ganglia: new perspectives through a comparative approach

The basal ganglia (BG) have received much attention during the last 3 decades mainly because of their clinical relevance. Our understanding of their structure, organisation and function in terms of chemoarchitecture, compartmentalisation, connections and receptor localisation has increased equally. Most of the research has been focused on the mammalian BG, but a considerable number of studies have been carried out in nonmammalian vertebrates, in particular reptiles and birds. The BG of the latter 2 classes of vertebrates, which together with mammals constitute the amniotic vertebrates, have been thoroughly studied by means of tract-tracing and immunohistochemical techniques. The terminology used for amniotic BG structures has frequently been adopted to indicate putative corresponding structures in the brain of anamniotes, i.e. amphibians and fishes, but data for such a comparison were, until recently, almost totally lacking. It has been proposed several times that the occurrence of well developed BG structures probably constitutes a landmark in the anamniote-amniote transition. However, our recent studies of connections, chemoarchitecture and development of the basal forebrain of amphibians have revealed that tetrapod vertebrates share a common pattern of BG organisation. This pattern includes the existence of dorsal and ventral striatopallidal systems, reciprocal connections between the striatopallidal complex and the diencephalic and mesencephalic basal plate (striatonigral and nigrostriatal projections), and descending pathways from the striatopallidal system to the midbrain tectum and reticular formation. The connectional similarities are paralleled by similarities in the distribution of chemical markers of striatal and pallidal structures such as dopamine, substance P and enkephalin, as well as by similarities in development and expression of homeobox genes. On the other hand, a major evolutionary trend is the progressive involvement of the cortex in the processing of the thalamic sensory information relayed to the BG of tetrapods. By using the comparative approach, new insights have been gained with respect to certain features of the BG of vertebrates in general, such as the segmental organisation of the midbrain dopaminergic cell groups, the occurrence of large numbers of dopaminergic cell bodies within the telencephalon itself and the variability in, among others, connectivity and chemoarchitecture. However, the intriguing question whether the basal forebrain organisation of nontetrapods differs essentially from that observed in tetrapods still needs to be answered.

The synaptic framework for chemical signaling in nucleus accumbens

Our knowledge of the organization of the nucleus accumbens has been greatly advanced in the last two decades, but only now are we beginning to understand the complex neural circuitry that underlies the mix of behaviors attributed to this nucleus. Superimposed on the neurochemically defined territories of the shell and core are four or more conduits for information flow. Each of these behaviorally relevant pathways can be characterized by the spatial distribution of inputs to its central unit: the GABAergic projection neuron, a spiny cell that also contains the opioid peptides, enkephalin or dynorphin. In this review, current models of accumbal circuits will be examined and, with the aid of recent anatomical findings, further extended to shed light on how functionally diverse information is processed in this nucleus. However complex, accumbal wiring is not fixed, and, as we will show, psychostimulants, dopamine-deleting lesions, and chronic blockade of dopaminergic receptors can alter the anatomical substrate, synaptology, and neurotrophic factors that govern circuits through the shell and core.

Nucleus accumbens in the lizard Psammodromus algirus: chemoarchitecture and cortical afferent connections

To better understand the organization and evolution of the basal ganglia of vertebrates, in the present study we have analyzed the chemoarchitecture and the cortical input to the nucleus accumbens in the lacertid lizard Psammodromus algirus. The nucleus accumbens contains many gamma-aminobutyric acid (GABA)-positive neurons and calbindin-positive neurons, the majority of which may be spiny projection neurons, and a few dispersed neuropeptide Y-positive neurons that likely represent aspiny interneurons. The nucleus accumbens contains two chemoarchitectonically different fields: a rostromedial field that stains heavily for substance P, dopamine, GABA(A) receptor, and a caudolateral field that stains only lightly to moderately for them, appearing more similar to the adjacent striatum. Injections of biotinylated dextran amine were placed in either the medial, dorsomedial, or dorsal cortices of Psammodromus. The medial and the dorsal cortices project heavily to the rostromedial field of the accumbens, whereas they project lightly to moderately to the caudolateral field. Cortical terminals make asymmetric, presumably excitatory, synaptic contacts with distal dendrites and the head of spines. Our results indicate that the hippocampal-like projection to the nucleus accumbens is similar between mammals and reptiles in that cortical terminals make mainly excitatory synapses on spiny, putatively projection neurons. However, our results and results from previous investigations indicate that important differences exist between the nucleus accumbens of mammals and reptiles regarding local modulatory interactions between cortical, dopaminergic, and cholinergic elements, which suggest that the reptilian nucleus accumbens may be as a whole comparable to the shell of the mammalian nucleus accumbens.

Distribution of choline acetyltransferase immunoreactivity in the brain of anuran (Rana perezi, Xenopus laevis) and urodele (Pleurodeles waltl) amphibians

Because our knowledge of cholinergic systems in the brains of amphibians is limited, the present study aimed to provide detailed information on the distribution of cholinergic cell bodies and fibers as revealed by immunohistochemistry with antibodies directed against the enzyme choline acetyltransferase (ChAT). To determine general and derived features of the cholinergic systems within the class of Amphibia, both anuran (Rana perezi, Xenopus laevis) and urodele (Pleurodeles waltl) amphibians were studied. Distinct groups of ChAT-immunoreactive cell bodies were observed in the basal telencephalon, hypothalamus, habenula, isthmic nucleus, isthmic reticular formation, cranial nerve motor nuclei, and spinal cord. Prominent plexuses of cholinergic fibers were found in the olfactory bulb, pallium, basal telencephalon, ventral thalamus, tectum, and nucleus interpeduncularis. Comparison of these results with those obtained in other vertebrates, including a segmental approach to correlate cell populations, reveals that the cholinergic systems in amphibians share many features with amniotes. Thus, cholinergic pedunculopontine and laterodorsal tegmental nuclei could be identified in the amphibian brain. The finding of weakly immunoreactive cells in the striatum of Rana, which is in contrast with the condition found in Xenopus, Pleurodeles, and other anamniotes studied so far, has revived the notion that basal ganglia organization is more preserved during evolution than previously thought.

Synaptic relationships of enkephalinergic and cholinergic neurons in the nucleus accumbens of the rat

Leucine5-enkephalin- and choline acetyltransferase-containing, presumably cholinergic, neurons revealed by dual label immunocytochemistry were found in the shell and core of the rat nucleus accumbens. The perikarya, dendrites and boutons of cholinergic neurons were labeled with the diaminobenzidine precipitate, whereas those of the enkephalinergic neurons were labeled with silver-intensified colloidal gold. Ultrastructural examination revealed that both the enkephalinergic and the cholinergic boutons generally formed symmetric synapses with unlabeled dendrites and, occasionally, with unlabeled dendritic spines. Enkephalin-immunoreactive terminals which were much larger than cholinergic boutons, seldom apposed or formed synapses with cholinergic structures in the nucleus. In the core, cholinergic terminals were frequently found apposed to enkephalin-immunoreactive dendrites and perikarya and were often seen in synaptic contact with enkephalinergic dendrites, whereas in the shell, cholinergic boutons seldom apposed or contacted enkephalinergic targets. These findings show that enkephalinergic and cholinergic neurons differ in their synaptic arrangements within the nucleus accumbens and provide further evidence for differentially organized intrinsic connections of shell and core territories.

Alterations in striatal acetylcholine overflow by cocaine, morphine, and MK-801: relationship to locomotor output

The activity of cholinergic interneurons in the striatum appears to be modulated by a variety of different systems including dopamine, opiate, and glutamate. The purpose of this study was to characterize the effects of drugs known to act on these three systems (i.e., cocaine, morphine, and MK-801) on striatal ACh overflow with microdialysis procedures, and to determine if alterations in ACh function induced by these agents are related to changes in locomotor activity. Cocaine was found to increase striatal ACh following intraperitoneal injections of 20 and 40 mg/kg, but not 10 mg/kg. The increases in locomotor activity induced by cocaine appeared to be dose dependent, while the effects on striatal ACh were not. Injections of 0.1 mg/kg MK-801 (a non-competitive NMDA receptor antagonist) produced dramatic increases in locomotor activity while decreasing striatal ACh overflow. A lower dose (0.03 mg/kg) of MK-801 failed to alter locomotor activity or striatal ACh. Morphine produced an apparent dose-dependent elevation in striatal ACh while only the lowest dose (5 mg/kg) increased locomotor activity. There appears to be no relationship between alterations in striatal ACh and locomotor output following systemic administration of these psychoactive agents.

Light and electron microscopic characterization of cholinergic and dopaminergic structures in the striatal complex and the dorsal ventricular ridge of the lizard Gekko gecko

The purpose of the present study was to visualize the morphological substrate underlying acetylcholine-dopamine interactions in the striatal complex of the lizard Gekko gecko and to compare the results with data obtained by others in mammals. The results are also discussed in the light of data obtained previously by us on neurochemical aspects of acetylcholine-dopamine interactions in Gekko and in rats. The study is part of a large research program in which the cholinergic and dopaminergic elements of the striatum of rats and reptiles are studied at morphological and neurochemical levels. We employed light microscopic immunocytochemistry, using single-label staining with antibodies against choline acetyltransferase (ChAT) and dopamine (DA) and double-staining with antibodies against ChAT and tyrosine hydroxylase (TH). A detailed analysis of ultrastructural characteristics of ChAT- and DA-immunolabeled striatal tissue was undertaken. The morphology and synaptic relations of the ChAT-immunopositive neurons in the basal forebrain of the lizard Gekko gecko are very similar to those of the cholinergic cells in the striatum of mammals. Probably, the cholinergic cells are in both mammals and reptiles interneurons that receive inputs of intrinsic or extrinsic origin and project upon output neurons. The location of ChAT-immunopositive somata outside the patches of high TH- or DA-immunoreactivity is at odds with the situation in the striatum of mammals and suggests the possibility of axoaxonal or axodendritic contacts at the level of these patches. We found no essential differences between the synaptic relations of the dopaminergic fibers in the striatal complex of Gekko and the conditions described for rats. In conclusion, we found little evidence for the presence of synaptic interaction between the cholinergic and dopaminergic systems in the striatum of this reptile. The possibility of nonsynaptic interaction, however, remains open.

Autoradiographic quantification of muscarinic cholinergic synaptic markers in bat, shrew, and rat brain

We employed radioligand binding autoradiography to determine the distributions of pre- and post-synaptic cholinergic radioligand binding sites in the brains of two species of bat, one species of shrew, and the rat. High affinity choline uptake sites were measured with [3H]hemicholinium, and presynaptic cholinergic vesicles were identified with [3H]vesamicol. Muscarinic cholinergic receptors were determined with [3H]scopolamine. The distribution patterns of the three cholinergic markers were similar in all species examined, and identified known major cholinergic pathways on the basis of enrichments in both pre- and postsynaptic markers. In addition, there was excellent agreement, both within and across species, in the regional distributions of the two presynaptic cholinergic markers. Our results indicate that pharmacological identifiers of cholinergic pathways and synapses, including the cholinergic vesicle transport site, and the organizations of central nervous system cholinergic pathways are phylogenetically conserved among eutherian mammals.

Regional differences in the dopaminergic regulation of cyclic AMP formation within the rat nucleus accumbens: comparison with the striatal complex of the lizard Gekko gecko

Effects of dopamine D2 receptor activation on the forskolin or D1 receptor stimulated formation of cyclic adenosine monophosphate (cyclic AMP) were investigated in tissue slices of two subregions of the rat nucleus accumbens and in the striatal complex of a lizard. Cyclic AMP production in the tissue was estimated by measuring the conversion of [3H]adenine in a superfusion system. Activation of a D2 receptor appeared to inhibit the D1 receptor agonists or forskolin stimulated formation of cAMP in the rostrolateral but not in the caudomedial part of the rat nucleus accumbens. In the striatal complex of the lizard the formation of cAMP was dramatically stimulated by forskolin, but only marginally by dopamine. Neither the forskolin, nor the dopamine stimulated cyclic AMP formation could be inhibited by activation of D2 receptors. These findings are compatible with previously obtained functional data indicating that especially the caudomedial part of the rat nucleus accumbens has much in common with the striatal complex of the lizard.

Morphological differences between projection neurons of the core and shell in the nucleus accumbens of the rat

The somatodendritic morphology of projection neurons in the shell and core of the rat nucleus accumbens was studied. These cells were retrogradely labelled with Fast Blue from the ventral mesencephalon (substantia nigra/ventral tegmental area) and subsequently injected intracellularly with Lucifer Yellow and processed immunocytochemically. Digitized reconstructions revealed that the cell bodies of neurons located throughout the nucleus are small-to-medium in size. Neurons in the shell have significantly fewer dendritic arbours with fewer branch segments, fewer terminal segments, and lower spine densities than those in the core. Values for the same parameters are significantly greater for cells in lateral than in medial parts of the shell but the same for neurons located within and without enkephalin enriched parts of the core, with an exception of spine density being significantly greater in the enkephalin-rich compartment. Calculations based on these data reveal that neurons in the core have as much as 50% more surface area than those in the shell, which suggests that core neurons have a greater potential for collecting synaptic information than have shell cells. Furthermore, the differential distribution and action of various neurochemicals such as dopamine in the shell and core, supports the idea that different morphologies reflect the presence of distinct neuronal circuits in these two territories.

Scopolamine attenuates haloperidol-induced c-fos expression in the striatum

Haloperidol increases the expression of Fos, the protein product of the proto-oncogene c-fos, in some parts of the central nervous system. Haloperidol also produces catalepsy in rodents and extrapyramidal side effects in humans, both of which are reduced by muscarinic receptor antagonists. In order to gain insight into the neurochemical and neuroanatomical substrates of haloperidol-induced catalepsy we examined the effects of the muscarinic receptor antagonist scopolamine on haloperidol-induced Fos expression in the striatum, nucleus accumbens and lateral septal nucleus. At a dose that reduced the cataleptic effect of haloperidol, scopolamine decreased the neuroleptic-induced Fos expression in the striatum and lateral septal nucleus but not the nucleus accumbens. These results indicate that haloperidol may increase c-fos expression in medium spiny striatal neurons indirectly by enhancing striatal acetylcholine release. They are also consistent with the hypothesis that neuroleptic-induced increases in striatal c-fos expression are predictive of extrapyramidal side effects produced by these compounds.

Regional differences in the regulation of acetylcholine release upon D2 dopamine and N-methyl-D-aspartate receptor activation in rat nucleus accumbens and neostriatum

The effect of D2 dopamine receptor activation on either the electrically, or N-methyl-D-aspartate induced release of radiolabeled acetylcholine (ACh) was investigated in different areas of the nucleus accumbens and the neostriatum of rats, by using a superfusion technique. Sequential slices of 100 microns were chopped along either a rostrocaudal, mediolateral or dorsoventral axis. In every slice the effect of a supramaximal concentration of the selective D2 receptor agonist quinpirole on the release of ACh was measured. In the entire neostriatum the release of ACh was reduced by approximately 70% in the presence of quinpirole. By contrast, in the nucleus accumbens, a gradual decrease in the inhibitory effect of quinpirole on the release of ACh was observed along both the rostral-to-caudal and the lateral-to-medial axes. Whereas in the rostrolateral part a 50% inhibition could be observed, in the caudomedial part no significant inhibition could be detected. Also the N-methyl-D-aspartate induced release of ACh was smaller in the caudomedial part as compared to the rostrolateral part of the nucleus accumbens. It is concluded that the nucleus accumbens is a very heterogeneous structure with respect to the regulation of the release of ACh by D2 dopamine and N-methyl-D-aspartate receptor activation.