Rat Striatal Neurons Research Articles

Previous dopaminergic innervation is not necessary for the development of dopamine supersensitivity in rat striatal neurons

The development of supersensitivity to dopamine by striatal neurons is widely considered to be a response to interruption of dopaminergic synaptic function. However, it is not clear whether pre-existing dopaminergic innervation is in fact necessary for supersensitivity to develop. In this study, rat foetal striatal cells were obtained prior to their innervation by dopaminergic fibres, and grafted into the cortex or thalamus of adult rats. In the absence of dopaminergic innervation, the grafts developed and became organized into striatum-like and non-striatum-like patches. Both in animals with intrathalamic and in animals with intracortical grafts, systemic administration of a low dose of apomorphine (0.25 mg/kg) induced intense fos expression in striatum-like patches not innervated by dopaminergic fibres. These results indicate that pre-existing dopaminergic innervation is not required for the development of supersensitivity, and that dopaminergic innervation is necessary to develop an adequate synergistic interaction between D 1 and D 2 receptors.

Zolpidem functionally discriminates subtypes of native GABA A receptors in acutely dissociated rat striatal and cerebellar neurons

The whole-cell patch-clamp technique was used to compare the properties of native GABA A receptors in Purkinje and striatal neurons acutely dissociated from neonatal rat brains (7–11 days old). In symmetrical chloride concentrations and at a negative holding voltage, GABA induced inward currents in a concentration-dependent manner with EC 50 values of 4 and 8 μM in Purkinje and striatal neurons, respectively. Diazepam potentiated the current induced by 1 μM GABA in Purkinje and striatal neurons with EC 50 values of 28 and 42 nM and maximal potentiations of 128 and 182 %, respectively. Zolpidem potentiated this GABA-induced current in Purkinje and striatal neurons with EC 50 values of 33 and 195 nM and maximal potentiations of 189 and 236%, respectively. These results show that zolpidem, in contrast to diazepam, functionally discriminates subtypes of native GABA A receptors. Zolpidem has greater affinity for GABA A receptors containing ω 1 (Purkinje cells) than for those with ω 2 (striatum) sites and has higher intrinsic activity at these receptors than diazepam. These properties of zolpidem may contribute to its hypnoselective profile.

Association of dopaminergic terminals and neurons releasing nitric oxide in the rat striatum: An electron microscopic study using NADPH-diaphorase histochemistry and tyrosine hydroxylase immunohistochemistry

To examine synaptic input and association of terminals containing dopamine and other transmitters to rat striatal nitric oxide synthase-expressing neurons, an electron microscopic study using tyrosine hydroxylase (TH) immunohistochemistry combined with histochemistry for NADPH-diaphorase (NADPHd) was performed. NADPHd-positive neurons had medium-sized cell bodies containing a highly invaginated nucleus and received relatively sparse synaptic input; 3.6% of boutons apposed to the NADPHd-positive neurons were TH-immunoreactive. Of these TH-immunoreactive boutons, two synaptic contacts showing symmetrical synaptic specializations were found on a cell body and a proximal dendrite of a NADPHd-positive neuron. Other nonsynaptic TH-immunoreactive boutons were occasionally associated with unlabeled terminals adjacent to the NADPHd-positive dendrites and also forming asymmetric synaptic contacts with unlabeled spinous or dendritic profiles. These results suggest that activity of the striatal neurons that release nitric oxide may be regulated by direct synaptic input from dopaminergic neurons and also suggest that the TH-immunoreactive terminals associated with the dendrites of nitric oxide synthase-expressing neurons provide the sites where nitric oxide influences dopamine release from neighboring terminals.

Differential expression of inducible transcription factors in basal ganglia neurons

The dopamine receptor antagonist, haloperidol, produced a time-dependent differential induction of inducible transcription factors (ITFs) in rat striatal neurons: Fos, Fos B, Jun B, Jun D, Krox 20, and Krox 24, but not c-Jun, were induced in the caudate putamen and nucleus accumbens with varying time courses. The induction of Fos by haloperidol was stronger in anterior versus posterior regions of the striatum. In contrast, induction of Fos by the muscarinic agonist pilocarpine was stronger in the posterior regions of the striatum suggesting that muscarinic receptors do not play a role in the induction of ITFs in striatal neurons by haloperidol. Although c-Jun was not induced in caudate neurons by haloperidol it was strongly induced in these neurons following prolonged seizure activity. The differential pattern of Jun protein expression suggests that haloperidol induces a specific transcriptional program in basal ganglia neurons. These effects of haloperidol may be involved in producing its extrapyramidal side effects.

Role of cyclic AMP in dopamine modulation of potassium channels on rat striatal neurons: regulation of a subconductance state.

Role of cyclic AMP in dopamine modulation of potassium channels on rat striatal neurons: regulation of a subconductance state.

Effects of AMPA receptor modulators on the production of arachidonic acid from striatal neurons

The abilities of different compounds acting at α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors to modulate the overflow of [ 3H]arachidonic acid from rat striatal neurons were examined. The combination of AMPA (0.1 mM) and carbachol (1 mM) stimulated [ 3H]arachidonic acid production, this effect could be dose-dependently enhanced by the newly discovered allosteric modulator of AMPA receptors: cyclothiazide. Competitive (6-cyano-7-nitroquinoxaline-2,3-dione [CNQX] and 6-(1-imidazolyl)-7-nitroquinazoline-2,3-dione [YM 900]) and non-competitive antagonists, like 1-(amino-phenyl)-4-methyl-7,8-methylenedioxy-5 H-2,3-benzodiazepine (GYKI 52466), antagonized the responses induced by either AMPA + carbachol or AMPA + carbachol + cyclothiazide. In order to appreciate the respective part of AMPA-versus kainate-preferring receptors experiments were performed with kainic acid (0.1 mM) and the more specific kainate agonist domoic acid (0.1 mM). Kainic acid behaves like AMPA, but the response induced by the combination domoic acid + carbachol could not be potentiated by cyclothiazide. On the contrary, concanavalin A potentiated the responses evoked by kainic acid or domoic acid (in combination with carbachol) but did not enhance the AMPA-evoked response. It could be concluded that both AMPA-and kainate-preferring receptors are present in cultured rat striatal neurons and that these two types of receptors were involved together with muscarinic receptors in the overflow of [ 3H]arachidonic acid.

Stimulation of Immediate Early Gene Expression in Striatal Neurons by Nitric Oxide

Exposure of primary cultures of embryonic rat striatal neurons to agents releasing nitric oxide (NO), including sin-1 molsidomine, S-nitroso-n-acetyl-penicillamine (SNAP), and S-nitrosoglutathione, resulted in an increase in the levels of expression of the immediate early genes c-fos and zif/268 in the cultured neurons. The membrane-permeable cGMP analogue, 8-bromo-cGMP, did not significantly affect c-fos and zif/268 mRNA levels, and the highly selective inhibitor of cGMP-dependent protein kinase, KT5823, was unable to inhibit the elevation in c-fos and zif/268 mRNA levels induced by SNAP. The induction of c-fos by the calcium ionophore A23187 was reduced by treatment with SNAP or 8-bromo-cGMP. Inhibitors of ADP-ribosyltransferases attenuated the stimulation of c-fos expression by SNAP. These results demonstrate for the first time that NO can induce immediate early gene expression in neurons, suggesting that NO may act as a mediator of neuronal plasticity via alterations in the expression of downstream genes. In addition, the results suggest that NO may exert these effects through a pathway that does not involve guanylate cyclase and cGMP-dependent protein kinase.

Induction of c-fos and zif/268 gene expression in rat striatal neurons, following stimulation of D1-like dopamine receptors, involves protein kinase A and protein kinase C.

Changes in the level of dopaminergic activity in the rat striatum lead to the induction of a number of immediate-early genes, including c-fos and zif/268. These immediate-early genes are thought in turn to alter the rate of transcription of downstream genes. There is evidence that the dopaminergic activation of the c-fos and zif/268 genes in the striatum in vivo is linked to stimulation of D1-like dopamine receptors. We have used primary cultures of embryonic rat striatal neurons to identify the intracellular pathways involved in this response. Dopamine (10 nM-5 microM) caused a marked increase in the levels of c-fos mRNA and zif/268 mRNA in cultured striatal neurons, an effect that was reproduced by the D1-like dopamine receptor agonist SKF38393 (10 nM-5 microM). These actions were attenuated by the D1-like antagonist SCH23390 (1 microM) but not by the D2-like antagonist eticlopride (1 microM). The D2-like agonist quinpirole did not increase zif/268 mRNA above basal levels at concentrations up to 5 microM, but caused a slight increase in the levels of c-fos mRNA. The stimulation of c-fos mRNA levels caused by 1 microM SKF38393 was reduced by 45% following pretreatment with the selective protein kinase A inhibitor KT5720, and by 87% following pretreatment with the selective protein kinase C inhibitor calphostin C. The stimulation of zif/268 mRNA levels caused by 1 microM SKF38393 was reduced by 90% following pretreatment with KT5720, but was not significantly affected by pretreatment with calphostin C. In addition, the actions of SKF38393 to stimulate the expression of both immediate-early genes were attenuated by coadministration of quinpirole. These results suggest that SKF38393 acts on striatal neurons to stimulate c-fos expression predominantly through protein kinase C, but also partially through protein kinase A. Conversely, SKF38393 induces zif/268 expression through protein kinase A. The ability of quinpirole to antagonize the actions of SKF38393 on cultured neurons is consistent with the presence of both D1-like receptors on the same neuronal population.

Action of intravenously administered talipexole on the rat striatal neurons receiving excitatory input from nigral dopamine neurons.

Electrophysiological studies using rats anesthetized with chloral hydrate were performed to elucidate whether or not intravenously injected talipexole acted as a D2 receptor agonist on the striatal neurons in comparison with the action of bromocriptine. The activities of the striatal neurons were extracellularly recorded using a glass microelectrode attached along a seven-barreled micropipette, each barrel of which was filled with talipexole, bromocriptine, SCH23390 (D1 antagonist), domperidone (D2 antagonist), glutamate or 2 M NaCl. These drugs were iontophoretically applied to the immediate vicinity of the target neuron being recorded. The effects of talipexole and bromocriptine were examined on the neurons, whose spikes (induced by the stimulation of the substantia nigra pars compacta) were inhibited by the iontophoretic application of domperidone. Iontophoretic application of talipexole or bromocriptine increased spontaneous firing of these neurons and this increase in firing was also inhibited by iontophoretically applied domperidone. In the same neurons, intravenously administered talipexole (0.01, 0.02 and 0.04 mg/kg) dose-dependently increased firing, and this increase was inhibited by microiontophoretically applied domperidone, but not by SCH23390. On the other hand, the intravenous injection of bromocriptine (0.1, 0.2 and 0.4 mg/kg) also increased the firing rate. However, the increase was not dose-dependent and fluctuated; the firing transiently decreased during the increase in firing with intravenously administered bromocriptine. However, the bromocriptine-induced increase in firing was also suppressed by domperidone, and decrease in firing was inhibited by SCH23390. These findings suggest that talipexole acts as a D2 agonist on the striatal neurons receiving input from substantia nigra pars compacta and increases firing when intravenously applied.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine-modulated potassium channels on rat striatal neurons: specific activation and cellular expression

We have used cell-attached patch-clamp electrophysiology to characterize the activation and distribution of an 85 pS K+ channel on freshly dissociated rat striatal (caudate-putamen) neurons. In recordings from 643 cells, openings of this channel showed an absolute dependence on the presence of dopamine or the D2-like dopamine receptor agonist quinpirole in the cell-attached patch pipette, but were never seen when the D2 antagonist domperidone was applied along with quinpirole, or in the absence of drug. This channel displayed inward rectification at depolarized membrane potentials, but its activation was otherwise voltage insensitive. It was largely restricted to a subset of dissociated cells with diameters > or = 10 microns, with channel openings seen in about 25% of patches. When present, there were typically multiple channels per patch. Cells of this size were immunocytochemically stained for neuron-specific enolase but not glial fibrillary acidic protein; about 40% were also labeled for gamma-amino butyric acid (GABA) and about 60% for NADPH diaphorase, with GABAergic cells displaying a shape most similar to that of cells expressing the channel. A large number of distinct types of other channels were also present, comprising inwardly rectifying channels of 5-35 pS conductance and voltage-activated channels of 100-250 pS, but the frequencies of occurrence and fractional open times of these channels were independent of the presence or absence of dopaminergic agonists. Thus, the 85 pS K+ channel uniquely requires activation by a D2-like dopamine receptor on rat striatal neurons, and is selectively expressed by a subset of these cells, which are most likely to be GABAergic neurons.

ATP-evoked potassium currents in rat striatal neurons are mediated by a P 2 purinergic receptor

The effect of ATP on cultured striatal neurons was examined by whole cell voltage clamp recordings. ATP produced outwardly rectifying currents that reversed near the expected equilibrium potential for the potassium ion and the currents were blocked by intracellular Cs +. Purinergic receptor agonists such as ADP, AMP adenosine, and 2-methylthio ATP (2-MeSATP) also evoked similar outward currents. The order of their potencies was ATP ⪢ (2-MeSATP) ≥ ADP > adenosine > AMP, corresponding to a P 2 purinergic receptor. ATP-evoked currents were blocked by a specific protein kinase C (PKC) inhibitor, GF109203X. In addition, the intracellular perfusion of a G-protein inactivator, GDPβS abolished ATP-induced currents, whereas pertussis toxin (PTX) had no effect on the currents. These results suggest that ATP activates a potassium channel in striatal neurons, which is regulated by protein kinase C (PKC) activation through a P 2 purinergic receptor linked to PTX-insensitive G protein.

Stimulation of zif/268 gene expression by basic fibroblast growth factor in primary rat striatal cultures

The presence of basic fibroblast growth factor (bFGF) in the basal ganglia, and its known neurotrophic activity, has created interest in its possible role as an agent to attenuate striatal neurodegeneration. However, little information is available on the mechanisms through which bFGF might exert a long-term influence on striatal function. Primary cultures of embryonic rat striatal neurones were used to ascertain whether bFGF can alter the pattern of striatal gene expression. Treatment of cultures with bFGF (500 pM) resulted in a dramatic increase in the levels of zif/268 mRNA within 45 min. This induction was attenuated by the tyrosine kinase inhibitor genistein (100 μM), but not by its inactive structural analogue genistin (100 μM). The induction of zif/268 mRNA was found to occur in non-neuronal cells, with no increase in mRNA levels being observed in neurones. A similar induction was noted for another putative transcription factor, jun B, although no induction of the related factor jun D could be detected. These results show that bFGF can induce immediate-early gene expression in striatal cultures, and therefore that this may provide a mechanism, mediated by non-neuronal cells, which allows bFGF to cause a long-term change in striatal neurochemistry.

Differential expression of mGluR5 metabotropic glutamate receptor mRNA by rat striatal neurons

Metabotropic glutamate receptors (mGluRs) mediate the effects of glutamate neurotransmission on intracellular second messenger systems. Among the seven distinct mGluR receptor isoforms currently identified, the mGluR5 isoform is expressed particularly prominently in the striatum, where it may contribute to neuronal plasticity, motor behaviors, and excitotoxic injury. mGluR5 mRNA expression in striatal enkephalinergic, somatostatinergic, and cholinergic neurons was examined using double label in situ hybridization techniques. mGluR5 expression is abundant in a large number of medium-sized striatal cells but is absent in a significant minority of neurons. Double label in situ hybridization with 35S-dATP- and digoxygenin-dUTP-tailed oligonucleotide probes demonstrated that mGluR5 message is highly expressed by enkephalinergic striatal neurons but is not detectable in cholinergic or somatostatin interneurons. In addition, some nonenkephalin, presumably substance P, neurons were also strongly labeled for mGluR5. The differential expression of mGluR5 in striatal projection neurons vs. interneurons may contribute to the selective vulnerability of these neurons to disease processes.

Acute and chronic amphetamine treatments differently regulate neuropeptide messenger RNA levels and Fos immunoreactivity in rat striatal neurons.

Repeated administration of amphetamine results in the well known phenomenon of reverse tolerance or sensitization. However, little is known about cellular and molecular mechanisms underlying acute versus chronic response to amphetamine. In this paper, we investigated the effects of acute (1.5 or 5 mg/kg) and chronic (5 mg/kg/day for 14 days) amphetamine treatment on locomotor activity, stereotypy, Fos immunoreactivity and messenger RNA levels of molecules implicated in dopamine transmission in the rat striatum and substantia nigra. In agreement with other studies, acute amphetamine induced a dose dependent increase in locomotor activity and stereotypy. Also, a comparison between the behavior observed after the first injection and the last injection of amphetamine in chronically treated rats showed sensitization as demonstrated by a higher rating of stereotypy. We have found that acute and chronic amphetamine treatments differently modulate the activity of several output neurons. A double labeling procedure with Fos immunohistochemistry coupled with in situ hybridization demonstrated that acute amphetamine treatment induces Fos immunoreactivity predominantly in striatal neurons expressing substance P messenger RNA (77.07 +/- 1.42%). Only 32.6 +/- 2.07% of Fos immunoreactive neurons expressed preproenkephalin A messenger RNA. In chronic amphetamine treated rats, 56.21 +/- 1.32% of the Fos immunoreactive neurons expressed substance P messenger RNA while 52.12 +/- 1.84% expressed preproenkephalin A messenger RNA. Statistical analysis revealed that this difference is mainly due to a decrease in the density of substance P immunoreactive neurons in chronically treated rats in comparison to acute. Amphetamine treatments induced Fos immunoreactivity in the substantia nigra in non-dopamine neurons. As measured by quantitative in situ hybridization, acute amphetamine induced an increase in substance P, preproenkephalin A and dynorphin messenger RNA levels (+23 +/- 0.05%, +45 +/- 0.07% and +24 +/- 0.05%, respectively). No difference in these increases was observed in relation with the dose injected (1.5 or 5 mg/kg). Chronic amphetamine treatment enhanced only substance P and dynorphin messenger RNA levels (+23 +/- 0.04% and +42 +/- 0.04%, respectively). Neither acute nor chronic amphetamine treatment had any effects on D1 or D2 dopamine receptor messenger RNA levels. Our main conclusions are: (1) in acutely treated rats Fos is essentially expressed by substance P neurons; (2) in chronically treated rats, Fos immunoreactivity is expressed by the two efferent striatal populations (i.e. preproenkephalin A and substance P neurons) and the number of Fos immunoreactive neurons is reduced as compared with acute; (3) neuropeptide messenger RNA levels, but not dopamine receptor messenger RNAs, are affected in the response to acute or chronic treatment with amphetamine.

Quinolinic acid-induced increases in calbindin D28k immunoreactivity in rat striatal neurons in vivo and in vitro mimic the pattern seen in Huntington's disease

In Huntington's disease striatal neurons undergo marked changes in dendritic morphology and coincidently exhibit an increase in immunoreactive calbindin D28k (calbindin), a cytosolic calcium-binding protein which is highly abundant in these neurons. Previous studies in the rat striatum have shown that excitotoxic injury, which is linked to a rise in intracellular Ca2+, mimics many of the neurochemical and neuropathological characteristics of Huntington's disease. We speculated, therefore, that the apparent increase in calbindin labeling in Huntington's disease spiny neurons may signal the response to an excitotoxic process. To investigate this possibility, we compared the cellular features of calbindin immunoreactivity in grade 1-4 Huntington's disease cases with those seen in rat striatal neurons in vivo and in vitro following treatment with N-methyl-D-aspartate (NMDA) receptor agonist, quinolinic acid. In human post mortem control cases calbindin immunoreactivity was seen primarily in the somata and proximal dendrites of striatal neurons. In the Huntington's disease cases, calbindin labeling was markedly increased throughout the second and third order dendrites and in spines, and this change was more prevalent in advanced cases (grades 3-4). In the rat brain, two weeks after intrastriatal injection of quinolinic acid (6-20 ng), surviving medium-spiny neurons in the transition zone around the lesion core exhibited a marked increase in calbindin immunoreactivity similar to that seen in Huntington's disease spiny neurons. In more peripheral areas away from the lesion and on the contralateral unlesioned side, calbindin immunostaining was confirmed to somata and proximal dendrites. In situ hybridization histochemistry with an 35S-labeled oligonucleotide probe showed no change or a decrease in calbindin mRNA levels in neurons within the transition zone, suggesting that the observed increase in calbindin staining was not the result of increased transcription. In 12 day old postnatal striatal cultures, 2-6 h exposures to quinolinic acid (0.5 mM) significantly increased the length of neurites exhibiting calbindin immunoreactivity when compared to untreated controls. This effect was blocked by the selective NMDA receptor blocker (+/-)-2-amino-5-phosphonopentanoic acid (AP-5), indicating that an NMDA receptor-mediated mechanism contributed to the change in staining pattern. Results in rats suggest that the subcellular redistribution of calbindin immunoreactivity observed in Huntington's disease spiny neurons may be related to an NMDA receptor-induced excitotoxic process. An increased availability of calbindin protein at dendrites and spines may reflect a greater demand for Ca2+ buffering precipitated by an abnormal rise in in intracellular Ca2+.

Aging-related changes in rat striatal D2 receptor mRNA-containing neurons: a quantitative nonradioactive in situ hybridization study

In situ hybridization of a digoxigenin-labeled oligonucleotide probe combined with computer-assisted image assessment was used to directly visualize D2 receptor mRNA-containing neurons in rat striata, and quantify age-related changes in the sizes and relative mRNA content of these neurons. It was found that: (1) numbers of D2 mRNA-containing neurons appear to decrease in striata of aged rats, (2) relative amounts of D2 receptor mRNA decrease in striatal neurons of aged rats, and (3) neurons of all sizes appear to be lost, with the greatest absolute decrease in those smaller than 90 microns 2. These data confirm the well documented age-associated loss of D2 dopamine receptors, and further suggest that both neuronal death and reduced transcription contribute to this decrement.

Dopamine D1 receptor modulates the voltage‐gated sodium current in rat striatal neurones through a protein kinase A.

1. Whole-cell recordings were made from striatal neurones obtained from neonatal rats and maintained in primary cultures. The effects of dopamine D1 receptor activation were studied on the voltage-gated sodium current. 2. Bath application of a specific D1 agonist, SKF38393 (1 microM), reduced the neuronal excitability recorded in current-clamp by increasing the threshold for generation of action potentials. 3. In voltage-clamp recordings, SKF38393 (1 microM) reversibly reduced the peak amplitude of the sodium current by 37.8 +/- 4.95%. This effect was reversed by the D1 antagonist SCH23390 and was blocked by the intracellular loading of GDP-beta-S (2 mM) suggesting GTP-binding protein involvement. 4. The D1 agonist reduced the peak amplitude of the sodium current without significantly affecting (i) the voltage dependence of the current-voltage relationship, (ii) the voltage dependence of the steady-state activation and inactivation, (iii) the kinetics of the time-dependent inactivation, and (iv) the kinetics of recovery from inactivation. 5. The peak amplitude of the sodium current was progressively reduced by intracellular loading of cyclic AMP-dependent protein kinase (100 U ml-1). 6. Diffusion of a specific peptide inhibitor of the cyclic AMP-dependent protein kinase (PKI; 10 microM) into the cytosol of neurones blocked the effect of the D1 agonist on the sodium current amplitude. 7. These results demonstrate that dopamine acting at the D1 receptor reduces the amplitude of the sodium current without modifying its voltage- and time-dependent properties. This effect involves activation of the cyclic AMP-dependent protein kinase and results in a depression of the striatal neuronal excitability by increasing the threshold for generation of action potentials.

The NeurotroDhins BDNF, NT‐3 and NT‐4/5 Promote Survival and Morphological and Biochemical Differentiation of Striatal Neurons In Vitro

The neurotrophins, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin 4/5 (NT-4/5) and nerve growth factor (NGF), were compared for their effects on the survival and differentiation of embryonic rat striatal neurons grown in low-density cultures. Treatment with BDNF for 8 days resulted in a 40% increase in overall neuronal survival, a 3- to 5-fold increase in the number of calbindin-immunoreactive neurons, and an 80% increase in GABA-positive neurons. Treatment with NT-3 or NT-4/5 produced a 2- to 3-fold increase in the number of calbindin-positive neurons and an increase in GABA-positive cell number similar to that induced by BDNF, BDNF treatment produced a striking morphological differentiation of striatal GABAergic neurons, which was characterized by a doubling of the number of neurite branch points, the total area of aborization and the perikaryal area compared to control cultures. All three of these factors increased high-affinity GABA uptake 2-fold. NGF had no effect on any of the parameters examined. Our results show that BDNF, NT-3 and NT-4/5 promote the survival and/or differentiation of calbindin-immunopositive and GABAergic striatal neurons.

Muscarinic receptors modulate N-, P-, and L-type Ca2+ currents in rat striatal neurons through parallel pathways

Muscarinic modulation of calcium currents was studied in acutely isolated striatal neurons from the adult rat using the whole-cell configuration of the patch-clamp technique. Muscarinic agonists reduced calcium currents through two distinct signaling pathways. One pathway depended upon PTX-sensitive G-proteins and targeted N- and P-type currents. The other pathway depended upon PTX-insensitive G-proteins and was rendered inactive by high intracellular concentrations of BAPTA and targeted L-type currents. The modulation of N- and P-type currents was relieved by strong depolarizing prepulses, whereas the modulation of L-type currents was not. These findings support the proposition that parallel signaling pathways exist between muscarinic receptors and calcium channels.

Phenotypic characterisation of rat striatal neurones in primary culture

The aim of this study was to determine to what extent the neuronal phenotypes present in primary cultures of rat striatal neurones correspond to those present in vivo. A large percentage of cultured striatal neurones contained relatively high levels of proenkephalin mRNA. In addition, a high level of expression was found for the prosomatostatin mRNA. Protachykinin mRNA and proneuropeptide Y mRNA were also expressed, but at a comparatively low level. No prodynorphin mRNA could be detected. Considerable numbers of neurones were also found to express NADPH-diaphorase activity, while a smaller number of neurones were positive for acetylcholinesterase. The NADPH-diaphorase and the acetylcholinesterase could be detected both in cell bodies, and in neuronal processes contacting groups of neighbouring neurones. Since nitric oxide does not require synaptic specialisations to exert its intercellular actions, this provides strong evidence that NADPH-positive neurones communicate with other cells in primary culture. These observations demonstrate that when striatal neurones are grown in primary culture, a range of neurochemical phenotypes are present which correspond closely to those present in the mature striatum in vivo. Together with the evidence for cell-cell interactions, this suggests that primary striatal cultures will provide a suitable model to study the molecular mechanisms controlling striatal function.