bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrophysiological and pharmacological characterization of identified nigrostriatal and mesoaccumbens dopamine neurons in the rat
Authors: Clark David , Chiodo Louis A.
Published: January 2005

Extracllular single‐unit recording techniques were used to compare the basal activity and pharmacological responsiveness of identified nigrostriatal and mesoaccumbens dopamine (DA)‐containing neurons. The projection area of each DA cell was determined by antidromic activation techniques. The forebrain stimulation used for the cell identification procedure did not alter the pharmacological responsiveness of DA neurons; the inhibitory effect of apomorphine (and d‐amphetamine) was identical when stimulation was applied either prior to or following drug administration. Analysis of the spike discharge pattern revealed that a higher proportion of mesoaccumbens DA cells exhibited burst‐firing activity. Although the firing pattern of the two populations of burst‐firing DA cells was similar in many regards, mesoaccumbens DA cells exhibited a longer postburst inhibition than did nigrostriatal DA cells. Each of the DA agonists, apomorphine, pergolide, B‐HT 920, and d‐amphetamine, inhibited nigrostriatal and mesoaccumbens DA neuronal activity in a similar fashion. However, there was a marked population difference in the recovery of cell firing in the 10 minutes following apomorphine‐induced inhibition; the recovery of mesoaccumbens spike discharges was considerably slower. Although this population difference was apparent to some extent following administration of pergolide or B‐HT 920 (but not d‐amphetamine), it was considerably less marked. The present findings are discussed with respect to the known regulatory control of midbrain DA neurons.
[3H]vesamicol binding in brain: Autoradiographic distribution, pharmacology, and effects of cholinergic lesions
Authors: Altar C. Anthony , Marien Marc R.
Published: January 2005

An autoradiographic analysis of high‐affinity binding sites for the vesicular acetylcholine transport blocker [3H]vesamicol (2‐(4‐phenylpiperidino) cyclohexanol; AH 5183) was conducted in rat brain. [3H]Vesamicol binding was displaced 52–99% by DPPN ([2,3,4,8]‐decahydro‐3‐(4‐phenyl‐1‐piperidinyl)‐2‐napthalenol) (IC50=14nM) and by ketanserin (500 nM), haloperidol (43 nM), and vesamicol analogs, but not by drugs selective for adenosine, adrenergic, amino acid, calcium channel, monoaminergic, opioid, PCP, sigma, or several other receptor classes. [3H]Vesamicol binding was most concentrated in the interpeduncular nucleus and fifth and seventh cranial nerve nuclei. Moderate binding was found in the lateral caudate‐putamen, medial nucleus accumbens, olfactory tubercle, vertical and horizontal diagonal bands of Broca, and basolateral amygdala. The distribution of [3H]vesamicol binding was similar to distributions of acetylcholine (r = 0.88), acetylcholine esterase (r = 0.97), choline acetyltransferase (ChAT) (r = 0.97), and [3H]hemicholinium‐3 binding sites (r = 0.95−0.99). Lower correlations were obtained between [3H]vesamicol and muscarinic receptor densities (r = 0.50−0.70). Few exceptions to the match between binding and cholinergic neuronal markers were found, e.g., the molecular layer of the cerebellum and the thalamus. Lesions of cholinergic neuronal projections to the neocortex or hippocampus reduced [3H]vesamicol binding in each of these regions, but to a lesser extent than reductions in ChAT. [3H]Vesamicol binding sites appear to be anatomically associated with brain cholinergic neurons, a locus that is consistent with the control by this site of vesicular acetycholine uptake.
Chloral hydrate anesthesia alters the responsiveness of identified midbrain dopamine neurons to dopamine agonist administration
Authors: Kelland Mark D. , Freeman Arthur S. , Chiodo Louis A.
Published: January 2005

Single‐unit electrophysiological recording techniques were used to sample the basal activity of antidromically identified nigrostriatal and mesoaccumbens dopamine (NSDA and MADA, respectively) neurons and to examine the responsiveness of these cells to dopamine agonist‐induced inhibition of cell firing rate in either chloral hydrate‐anesthetized or paralyzed rats. Paralyzed rats exhibited a greater percentage of burst‐firing cells (69%) than did anesthetized animals (37%). Furthermore, paralyzed rats were less sensitive to the mixed D1/D2 DA receptor agonist apomorphine and the selective D2 DA receptor agonist quinpirole. However, significantly higher doses of d‐amphetamine were required in paralyzed animals only with respect to inhibiting MADA neurons. The abilities of apomorphine and quinpirole to inhibit NSDA cell firing were rate‐dependent in both anesthetized and paralyzed rats, whereas d‐amphetamine‐induced inhibition was rate dependent only in anesthetized animals. In contrast, apomorphine‐ and quinpirole‐induced inhibition of MADA neurons were rate‐dependent only in anesthetized rats, whereas d‐amphetamine‐induced inhibition was rate‐dependent only in paralyzed animals. These results suggest that general anesthesia exerts subtle effects on the basal activity and pharmacological responsiveness of midbrain dopamine neurons.
Afferent axons from the antenna influence the number and placement of intrinsic synapses in the antennal lobes of Manduca sexta
Authors: Tolbert Leslie P.
Published: January 2005

The present study compares the placement and frequency of occurrence of synapses in normally developing antennal lobes of the brain of the moth Manduca sexta and in lobes developing in the absence of afferent axons from the antenna. The antennal lobes develop during the metamorphosis from larva to moth, and require antennal afferent input to develop their characteristic knots of synaptic neuropil, the glomeruli, that are arrayed around a central core of coarse neuropil. Synapses begin to form throughout the neuropil of the antennal lobe before ingrowth of antennal axons into the lobe. During normal development, almost all synapses (those among intrinsic neurons as well as those made by antennal afferent axons) become segregated into glomeruli as the glomeruli are established. Thus, in normal mature lobes, the radial segregation between synaptic (glomerular) and nonsynaptic (central) regions is virtually complete. In lobes that have never been allowed to receive antennal axons, an outer ring of “protoglomerular” neuropil develops in place of the glomeruli. A similar segregation of synaptic and nonsynaptic regions occurs, with two major differences: the frequency of synapses that develops in the outer ring of fine‐textured neuropil is almost 50% higher than in normal glomeruli, and the small number of synapses that occur in the coarse central neuropil now occur on aberrant fine processes in that neuropil. Apparently, in the absence of their normal massive input from the antenna, elements intrinsic to the antennal lobe are induced to form extra synapses with each other, and to send aberrant fine branches to synapse in a region of neuropil normally containing predominantly large‐caliber neurite trunks and few synapses.
Antagonism of ethanol effects by Ro 15‐4513: An electrophysiological analysis
Authors: Marrosu Francesco , Carcangiu Giampaolo , Passino Nicola , Aramo Stefano , Mereu Giampaolo
Published: January 2005

Ethanol (ETH) and general anesthetics have been reported to facilitate the chloride channel opening, possibly, or at least partly, through an interaction with the GABA‐benzodiazepine (BZ) receptor‐gated chloride ionophore “supramolecular complex”. Recently Ro 15‐4513, a novel BZ ligand, has been indecated as a potent and selective antagonist of various ETH‐induced behavioral and biochemical effects. However, since its precise characterization is still a matter of debate, we have tested and compared the effect of Ro 15‐4513, as well as its antagonism against ETH, in two objective electrophysiological parameters, i.e., the electroencephalograph (EEG) pattern in freely moving rats and single unit activity of reticulata neurons.

Ro 15‐4513 produced an EEG state of alertness and antagonized the behavioral impairment and the EEG deterioration by ETH. However, while its protective action was consistent against moderate doses (2 g/kg) of ETH, it was much less evident versus higher doses. (4 and 8 g/kg).

On reticulata cells, Ro 15‐4513 potently stimulated their spontaneous firing and reversed the depression by both ETH and Na‐pentobarbital. Moreover, the ß‐carboline DMCM also had similar effects.

The “pure” BZ antagonist Ro 15‐1788 was completely inefective against ETH, yet fully cancelled the reversing actions of Ro 15‐4513 and DMCM upon ETH or Na‐pentobarbital effects.

It is concluded that Ro 15‐4513 behaves as a BZ inverse agonist, so that its opposition to ETH and Na‐pentobarbital is probably the result of its “negative” coupling with the BZ recognition site that triggers the closing of chloride channels. It suggests that BZ inverse agonists might constitute, in the near future, a new class of analeptic drugs.
Primary afferent excitatory transmission recorded intracellularly in vitro from rat medial vestibular neurons
Authors: Lewis Michael R. , Phelan Kevin D. , Shinnick‐Gallagher Patricia , Gallagher Joel P.
Published: January 2005

Intracellular recordings were made from rat medial vestibular nucleus (MVN) neurons in transverse brain slices containing the root of the vestibular nerve (N. VIII). Electrical stimuli applied to the N. VIII tract evoked an orthodromic excitatory postsynaptic potential (EPSP) that lasted about 50 ms following a 0.5 to 1.5 ms delay between the stimulus artifact and synaptic potential. These orthodromic EPSPs were insensitive to the following antagonists: atropine, hexamethonium, dephenhydramine, and caffeine. Based on these results we conclude that the primary afferent excitatory transmitter is not acetylcholine, histamine, or adenosine, respectively. However, kynurenic acid, a general excitatory amino acid receptor antagonist, blocked the orthodromic EPSP while having no effect on the resting membrane potential, input resistance, or action potential configuration of MVN neurons. Our data suggest that an excitatory amino acid, or amino acid‐like substance, is responsible for primary afferent excitatory transmission in the rat medial vestibular nucleus.
Age‐dependent effects of 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP): Correlation with monoamine oxidase‐B
Authors: Walsh Sharon L. , Wagner George C.
Published: January 2005

The effects of 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) administration on whole brain dopamine content and monoamine oxidase subtype B (MAO‐B) activity were assessed in Swiss‐Webster male mice. Groups of mice at six different ages (1,2,4,8,16, and 52 weeks) were treated with either MPTP(12.5 mg/kg) every 2 hours for four subcutaneous injections or with the saline vehicle in the same injection volume. A third group of subjects was untreated and sacrificed at the same ages. The animals were sacrificed 1 week following treatment. The brains were removed and divided into right and left halves. The right brain halves from all subjects of a given age were assayed for MAO‐B activity. The left brain halves were assayed for dopamine content using high performance liquid chromatography.

The results revealed a significant age‐dependent increase in both dopamine content and MAO‐B activity in the untreated controls. It was also found that the toxic effect of MPTP as measured by whole brain dopamine depletion was increased at each successive age tested. There was a significant correlation (r = + 0.96) between the baseline levels of MAO‐B activity and the degree of lesion induced by MPTP treatment. These results indicate that the increased sensitivity to MPTP reported in aged animals may, in part, be attributable to the increase in MAO‐B activity in older animals.
Fade of the response to prolonged glutamate application in the rat hippocampal slice
Authors: Cole Alison E. , ffrench‐Mullen Jarlath M. H. , Fisher Robert S.
Published: January 2005

The effect of prolonged glutamate (GLU) application was examined on 60 CA1 pyramidal neurons in the in vitro rat hippocampal slice preparation. Continuous application of L‐GLU, either by bath perfusion (0.5–2mM) of the slices or iontophoresis (200 mM) into the dendritic region of the neurons, elicited a transient depolarization which faded to a mean of 53% of the initial peak amplitude despite continued exposure to the agonist. Membrane depolarization to aspartate (ASP) and the d‐isomer of GLU also faded with time. In contrast, the depolarizing response to the excitatory amino acid agonists N‐methyl‐D, L‐aspartate (NMA), quisqualate (QUIS), and kainate (KA) did not fade significantly during continuous application. The fade of the GLU depolarization was not affected by the NMDA antagonist D‐2‐amino‐5‐phosphonovalerate (APV) or by blocking synaptic transmission with tetrodotoxin. At the time of maximum fade of the GLU depolarization, there was no change in input resistance or GLU reversal potential. In addition, fade of the response was not a consequence of changes in extracellular potassium concentration, GLU uptake mechanisms, or the electrogenic pump. The most likely explanation for fade is postsynaptic receptor desensitization.
Colocalization of taurine‐ and cysteine sulfinic acid decarboxylase‐like immunoreactivity in the hippocampus of the rat
Authors: Magnusson Kathy Ruth , Clements Jane Reichert , Wu Jang‐Yen , Beitz Alvin James
Published: January 2005

It is proposed that taurine is an inhibitory neurotransmitter/neuromodulator in the CNS. The present study localized taurine‐containing neurons within the rat hippocampus with the use of a monoclonal antibody against conjugated taurine (Tau2) in conjuction with an antiserum against cysteine sulfinic acid decarboxylase (CSADC), a synthesizing enzyme for taurine. Taurine‐like immunoreactivity (Tau‐LI) and CSADC‐LI were colocalized in neurons of the dentate gyrus, CA1(/CA2), CA3, and CA4. Of all the cells examined, pyramidal basket cells within the granule cell layer of the dentate gyrus were most intensely stained with both Tau2 and CSADC. Granule cells were also double‐labeled with Tau‐LI and CSADC‐LI Cell nuclei and dendrites in the CA1 region stained more intensely with Tau2 than somata. CSADC‐LI was colocalized with Tau‐LI within these neurons. Light staining with both Tau2 and the CSADC antiserum was inconsistently present in CA3 and CA4 neurons and was found to be highly dependent on the type of fixation and delay to fixation. Tau‐LI was more consistently present in increased numbers of neurons in CA3 when glutaraldehyde was added to the paraformaldehyde fixative solution. Hippocampi which were immersion‐fixed in paraformaldehyde following a 0‐, 6‐, or 24‐hour postmortem delay exhibited a lack of Tau2 staining in the CA3 region in the majority of animals studied, similar to some paraformaldehyde perfusion‐fixed rats. These studies suggest that taurine was present in the majority of neurons within the major cell layers of the rat hippocampus, but Tau‐LI was more easily lost from neurons in the CA3 region following delay to fixation. The localization of Tau‐LI in excitatory neurons such as granule cells and pyramidal cells is not consistent with its proposed inhibitory transmitter role. However, the prominent Tau2 staining in dendrites of the CA1 region provides anatomical support for the hypothesis that taurine may be released from dendrites in the CA1 region and may function as a neuromodulator of calcium flux in these pyramidal neurons.
Motor effects of two sigma ligands mediated by nigrostriatal dopamine neurons
Authors: Goldstein Susanne R. , Matsumoto Rae R. , Thompson Tina L. , Patrick Robert L. , Bowen Wayne D. , Walker J. Michael
Published: January 2005

(+)‐Pentazocine, a potent sigma ligand that lacks affinity for PCP receptors, produced dose‐dependent contralateral circling behavior following microinjections in the substantia nigra of rats. This effect was attenuated by 6‐hydroxydopamine (6‐OHDA) lesions of ascending dopamine neurons and enhanced by systemic injections of amphetamine. 6‐OHDA lesions also attenuated the circling produced by another selective sigma ligand, 1,3‐di‐o‐tolylguanidine (DTG). These findings suggest that sigma receptors are involved in the neural control of movement and the regulation of the ascending dopamine system. Since all typical antipsychotic drugs tested bind to sigma receptors with Ki values less than 1 μM, these findings further suggest that sigma receptors may mediate some of the motor side effects of antipsychotic drug therapy.
Dopamine agonists at repeated “autoreceptor‐selective” doses: Effects upon the sensitivity of A10 dopamine autoreceptors
Authors: Jeziorski Michael , White Francis J.
Published: January 2005

Previous reports have established the ability of dopamine (DA) agonists to stimulate inhibitory DA autoreceptors at doses which minimally stimulate postsynaptic DA receptors, suggesting that hyperactive DA transmission may be controlled clinically by treatment with DA agonists. Little is known, however, about the possible loss of autoreceptor sensitivity that may occur after repeated treatment with low doses of DA agonists. Extracellular single cell recording and microinotophoretic techniques were used to measure the sensitivity of impulse‐regulating DA autoreceptors on A10 DA cells in the ventral tegmental area (VTA) of chloral hydrate‐anesthetized rats pretreated for seven days with repeated subcutaneous (s.c.) doses of the DA agonist apomorphine (APO). The ability of intravenous (i.v.) administration of the potent D2 DA agonist quinpirole (QUIN) to inhibit the firing of A10 cells was not attenuated in rats pretreated with repeated low doses (2 X 50 μg/kg/day, s.c.) of APO for 7 days, although higher doses (2 X 250 or 500 μg/kg/day) did cause subsensitive responses to QUIN. In rats pretreated with repeated low doses of APO, microiontophoretic application of DA on A10 cells revealed somewhat subsensitive responses. However, ibotenic acid lesions of postsynaptic cells in the nucleus accumbens (NAc) prior to initiation of APO treatment (2 X 50 μg/kg/day) did not alter the response of A10 cells to systemic QUIN, contradicting the possibility that the feedback projection from the NAc to the VTA was compensating for autoreceptor downregulation during systemic challenge with QUIN. In contrast, administration of the irreversible DA antagonist EEDQ (2 mg/kg, i.p.) to control and APO‐treated rats (2 X 50 μg/kg/day) 24 hr prior to recording did reveal a difference in A10 cell sensitivity to systemic QUIN and to microiontophoretic DA between the two groups, suggesting that “spare” DA autoreceptors may have concealed the down‐regulation of autoreceptors induced by repeated low doses of APO. Challenge of A10 DA cells with the partial DA autoreceptor agonist (–)‐3‐(3‐hydroxyphenyl)‐N‐n‐propylpiperidine [(–)3‐PPP], for which an autoreceptor reserve should not exist, produced slightly attenuated responses in APO‐treated rats (2 X 50 μg/kg/day). These findings provide evidence for the existence of spare somatodendritic DA autoreceptors on A10 DA cells with respect to potent DA agonists, suggesting that repeated administration of “autoreceptor‐selective” doses of DA agonists may not result in a diminished inhibition of DA neuronal activity.
Human cortical neurons contain both nicotinic and muscarinic acetylcholine receptors: An immunocytochemical double‐labeling study
Authors: Schröder Hannsjörg , Zilles Karl , Luiten Paul G. M. , Strosberg Andre D. , Aghchi Alireza
Published: January 2005

Using immunofluorescence histochemistry, in the human cerebral cortex neurons immunoreactive for both nicotinic and muscarinic acetylcholine receptor proteins could be demonstrated. Vibratome sections of biopsy and autopsy specimens of human temporal and occipital lobes were incubated with monoclonal antibodies specific for muscarinic (M 35) and nicotinic (WF 6) acetylcholine receptor protein. Immunoreactive sites were visualized using a biotin‐streptavidin‐phycoerythrin system (M 35, red fluorescence) and fluorescein‐conjugated immunoglobulins (WF 6, green fluorescence). Immunofluorescence of both antibodies was preponderant in pyramidal neurons located in layers II/III and V and their apical dendrites. Some round and ovoid immunolabeled cells were encountered in layers VI and IV. About 30% of the cholinoceptive cortical neurons, in particular the pyramidal cells, displayed immunoreactivity for both receptor types. The present investigation shows a subpopulation of human cortical neurons to contain both nicotinic and muscarinic receptors. The coexistence of acetylcholine receptors may provide the morphological basis of simultaneous impact of acetylcholine on both receptor types in the same neuron of the human cerebral cortex.
D1 dopamine receptor stimulation enables the postsynaptic, but not autoreceptor, effects of D2 dopamine agonists in nigrostriatal and mesoaccumbens dopamine systems
Authors: Wachtel Stephen R. , Hu Xiu‐Ti , Galloway Matthew P. , White Francis J.
Published: January 2005

Possible functional interactions between D1 and D2 dopamine (DA) receptors were examined using extracellular single‐cell recording with microiontophoretic application of selective D1 and D2 receptor agonists both postsynaptically, in the rat nucleus accumbens (NAc) and caudate‐putamen (CPu), and presynaptically, at impulse‐regulating somatodendritic DA autoreceptors in the ventral tegmental area (A10) and substantia nigra pars compacta (A9) In addition, synthesis‐modulating nerve terminal DA autoreceptors were studied in both the CPu and NAc using the gammabutyrolactone (GBL) neurochemical model of isolated nerve terminal autoreceptor function in vivo.

In both the NAc and CPu, the inhibition of neurons produced by iontophoresis of the D2 receptor agonists quinpirole or RU‐24213 was attenuated by acute DA depletion via the tyrosine hydroxylase inhibitor α‐methyl‐p‐tyrosine (AMPT). However, during iontophoresis of the selective D1 DA receptor agonist SKF 38393, the inhibitory effects of the D2 agonists were again evident, suggesting that the attenuation of D2 agonist‐induced inhibition was due to decreased D1 receptor activation. In contrast, the inhibitory effects produced by the non‐selective D1/D2 agonist apomorphine or by SKF 38393 were unaffected by AMPT pretreatment. Thus, D1 receptor activation appears necessary for D2 receptor‐mediated inhibition of NAc and CPu neurons, whereas D2 receptor activation is not required for the inhibition produced by D1 receptor stimulation.

In contrast to postsynaptic D2 receptors, the ability of DA agonists to stimulate D2 DA autoreceptors was not altered by manipulations of D1 receptor occupation. Enhancing D1 receptor stimulation with SKF 38393 or reducing D1 receptor occupation with either the selective D1 receptor antagonist SCH 23390 or AMPT failed to alter the rate‐inhibitory effect of i.v. quinpirole on A9 or A10 DA neurons. Similarly, iontophoresis of SKF 38393 failed to alter the inhibitory effects of iontophoretic quinpirole. SKF 38393 also failed to affect the inhibition of GBL‐induced increases in DOPA accumulation (tyrosine hydroxylase activity) produced by quinpirole in either the NAc or CPu. Furthermore, reversal of GBL‐induced increases in DOPA accumulation by apomorphine or quinpirole was unaffected by pretreatment with SCH 23390. Therefore, D1 receptor occupation appears to be necessary for the expression of the functional effects of postsynaptic D2 receptor stimulation but not presynaptic D2 DA autoreceptor stimulation.
Autoradiographic quantification of serotonin1A receptors in rat brain following antidepressant drug treatment
Authors: Welner S. A. , De Montigny C. , Desroches J. , Desjardins P. , Suranyi‐Cadotte B. E.
Published: January 2005

There is growing evidence that the serotonergic (5‐HT) system is involved in the pathogenesis and treatment of major depression. The 5‐HT receptor subtype involved in the enhancing effect of antidepressant treatments, however, has not been identified. The present study was undertaken to quantify 5‐HT1A sites in the rat brain by autoradiography and membrane binding, using the selective ligand [3H]8‐hydroxy‐N, N‐dipropyl‐2‐aminotetralin (8‐OH‐DPAT), following long‐term antidepressant treatment. Following a 21‐day treatment with amitriptyline (10 mg/kg/day), there was a significant increase of [3H]8‐OH‐DPAT binding measured by autoradiography in the dorsal hippocampus, but there was no change in the nucleus raphe dorsalis; whole brain membrane binding revealed an increase in the number of binding sites, with no change in the affinity for [3H]8‐OH‐DPAT. Conversely, fluoxetine (10 mg/kg/day), a selective blocker of 5‐HT reuptake, and gepirone (10 mg/kg/day), a 5‐HT1A agonist, both administered for 21 days, significantly reduced [3H]8‐OH‐DPAT binding measured by autoradiography in the nucleus raphe dorsalis without altering hippocampal binding sites. The control active treatment with diazepam (2 mg/kg/day) did not alter [3H]8‐OH‐DPAT binding in the hippocampus or in the nucleus raphe dorsalis. All groups were compared to a 21‐day vehicle‐treated control group. These results are fully consistent with previous electrophysiological and behavioral studies and suggest that alterations of 5‐HT1A receptors might underlie the enhancement of 5‐HT neurotransmission by antidepressant treatments.
Stimulation of d2 dopamine receptors decreases intracellular calcium levels in rat anterior pituitary cells but not striatal synaptosomes: A flow cytometric study using indo‐1
Authors: Wolf Marina E. , Kapatos Gregory
Published: January 2005

An important question is whether all D2 dopamine (DA) receptors employ the same signal transduction mechanisms. Anterior pituitary cells and striatal synaptosomes, which possess pharmacologically similar D2 DA receptors, were compared with respect to the effect of D2 DA receptor stimulation on free intracellular Ca2+ levels ([Ca2+]i). Flow cytometry, in combination with either the fluorescent calcium indicator indo‐1 or fluorescent voltage‐sensitive dyes, was used to measure [Ca2+]i and to detect changes in membrane potential. In subpopulations of anterior pituitary cells, increases in [Ca2+]i were produced by elevated K+, veratridine, thyrotropin‐releasing hormone, and BAY K 8644. These increases were blocked by nifedipine, suggesting the involvement of L‐type voltage‐sensitive calcium channels (VSCC's). In 10–15% of the cells, D2 agonists decreased resting [Ca2+]i, reversed stimulus‐induced increases in [Ca2+]i, and caused a hyperpolarization. In striatal synaptosomes, elevated K+ and veratridine also increased [Ca2+]i. However, the K+‐induced increase was eliminated if choline was substituted for Na+ in the medium, suggesting that Ca2+ entry in response to sustained K+ depolarization resulted from reversal of Na+/Ca2+ exchange. Nifedipine and verapamil inhibited K+‐induced increases in [Ca2+]i only at concentrations greater than 10 μM, while ω‐conotoxin had no effect. D2 agonists had no effect on resting or stimulated [Ca2+]i but did hyperpolarize 10–20% of the synaptosomes, indicating that D2 DA receptors are functional in this preparation. The ability of pituitary but not striatal D2 DA receptors to modulate [Ca2+]i may reflect the fact that the two systems differ with respect to pathways for Ca2+ influx.
Morphological correlates of long‐term potentiation imply the modification of existing synapses, not synaptogenesis, in the hippocampal dentate gyrus
Authors: Desmond Nancy L. , Levy William B.
Published: January 2005

This report evaluates two morphological markers of synaptogenesis following the induction of long‐term potentiation (LTP) in the dentate gyrus of the anesthetized rat. These two morphological features, polyribosomes and multiple synaptic contacts, are known to increase in number with synaptogenesis in the mature hippocampus.

The analysis focused on the middle third of the dentate molecular layer. As shown previously, this is the region of primary synaptic activation in our electrophysiological protocol and the region of localized morphological changes with LTP. Here the incidence of a polyribosome at the base of a dendritic spine declined 57% with LTP. In addition, the number of multiple synaptic contacts decreased 18% there with LTP. Both decreases were more pronounced immediately following conditioning stimulation than at later intervals. Beacause both morphological features decrease with LTP but increase with synaptogenesis, the data do not support the hypothesis that new synapses form with LTP. Instead, the data add further support to the view that the strengthening of existing excitatory synapses underlines LTP.
Levels of biogenic amines, their metabolites, and tyrosine hydroxylase activity in the human epileptic temporal cortex
Authors: Pintor Manuela , Mefford Ivan N. , Hutter Ingrid , Pocotte Susan L. , Wyler Allen R. , Nadi N. Suzan
Published: January 2005

The levels of serotonin (5‐HT), 5 hydroxyindoleacetic acid (5‐HIAA), dopamine (DA), homovanillic acid (HVA), norepinephrine (NE), and tyrosine hydroxylase (TH) activity were measured in the focus (spiking) and nonfocus (nonspking) regions of the temporal neocortex of 20 patients with intractable complex partial seizures. The levels of 5‐HT, DA, 5‐HIAA, and HVA were higher in the focus when compared to the nonfocus. Values for NE and TH activity were not different when focus and nonfocus were compared. The ratios of metabolite to precursor for 5‐HT and DA were not significantly different between the focus and the nonfocus, suggesting that the changes observed were the result of a modification in the synthesis and release of these amines. Such changes in the epileptic focus could be caused by altered transsynaptic regulatory processes, which occur as a result of neuronal loss, gliosis, or neuronal sprouting.
Effects of glycine on neurons in the rat substantia nigra zona compacta: In vitro electrophysiological study
Authors: Mercuri Nicola Biagio , Calabresi Paolo , Bernardi Giorgio
Published: January 2005

The effects of bath‐applied glycine to substantia nigra zona compacta neurons of rat were investigated byintracellular recording techniques in vitro. Superfusion of glycine (1 mM) in the medium hyperpolarized 53% of the neurons recorded with KCI electrodes, whereas 32% of the cells were depolarized. The remaining 15% of neurons was hyperpolarized and then depolarized by the amino acid. In spite of these membrane changes, the action potential firing was depressed. Both hyperpolarization and depolarization were correlated to an outward and an inward current, respectively, when recording in single‐electrode voltage‐clamp mode.

In response to bath application of glycine, the neurons showed a concentration‐dependent conductance increase. Micromolar concentrations of glycine (100–300 m̈M) in the superfusion medium produced a membrane hyperpolarization (outward current) in most of the tested cells, whereas millimolar concentration of amino acid could cause depolarization (inward current) in the same neurons.

When the recording electrodes contained K acetate, only hyperpolarizations (outward current) were produced. The potential and current changes and the increase in membrane conductance produced by glycine showed little desensitization when neurons were recorded with K acetate electrodes. The mean reversal potential for the membrane hypolarization was –80 mV with intracellular electrodes containing KCI and –84 mV with electrodes containing K acetate. The mean null potential for the depolarizing effect was –46 mV.

The reversal potential for the glycinergic responses was shifted to less negative values upon lowering the extracellular concentration of chloride or increasing the extracellular concentration of potassium. Strychnine (1–10 m̈M) reversibly antagonized both the conductance increase and the membrane changes produced by glycine. Bath application of bicuculline (100 m̈M) and picrotxin (200 m̈M) did not affect glycine responses, while depressing the actions of GABA and muscimol.

It is concluded the glycine exerts and inhibition on substantia nigra zona compacta neurons by acting on strychnine‐sensitive receptors. The membrane effects produced by glycine result from the activation of a cloride current. In addition, the simultaneous involvement of porassium ions may contribute to the overall effects of glycine.
Mapping muscarinic receptors in human and baboon brain using [N‐11C‐methyl]‐benztropine
Authors: Dewey Stephen L. , Macgregor Robert R. , Brodie Jonathan D. , Bendriem Bernard , King Payton T. , Volkow Nora D. , Schlyer David J. , Fowler Joanna S. , Wolf Alfred P. , Gatley S. John , Hitzemann Robbert
Published: January 2005

The muscarinic cholinergic system has been mapped in vivo inhuman and baboon brain using [N‐11C‐methyl]‐benztropine and high resolution positron emission tomography (PET). [N‐11C‐methyl]‐benztropine uptake was observed in frontal, parietal, occipital, and temporal cortices as well as in subcortical structures including the corpus striatum and thalamus. Uptake continued to increase in baboon and human brain in all areas over an 80 minute experimental period with the exception of the exception of the cerebellum wehere the accumulation of radioactivity began to decrease by 25 minutes potinjection. The ratio of incorporation of [N‐11C‐methyl]‐benztropine between corpus striatum/cerebellum was 1.53 and 1.46 in humans and baboons, respectively, at 60 minutes. Blocking studies in baboons using the muscarinic cholinergic antagonists scopolamine and benztropine and the muscarinic cholinergic agonist pilocarpine combined with blocking studies in humans using benztropine indicate that the binding of this compound is specific for the muscarinic cholinergic system. Pretreatment with the potent dopamine reuptake blocker nomifensine produced no effect on the incorporation of radioactivity in any baboon brain region examined. Analysis of labelled plasma metabolites indicates that in humans, the rate of metabolism of [N‐11C‐methyl]‐benztropine is slow (83.0% unchanged at 30 minutes postinjection) differeing quite dramatically from the rate of metabolism observed in baboons (43.4%% unchanged at 30 minutes postinjection). These data combined with postmortem studies in humans and primates demonstrate that [N‐11C‐methyl]‐benztropine is a suitablemuscarinic cholinergic ligand for use in humans and baboons with PET.
Anatomical localization of calmodulin mRNA in the rat brain with cloned cDNA and synthetic oligonucleotide probes
Authors: Roberts‐Lewis Jill M. , Cimino Mauro , Krause Rudolph G. , Tyrrell Daniel F. , Davis Leonard G. , Weiss Benjamin , Lewis Michael E.
Published: January 2005

Calmodulin is a small, acidic calcium‐binding protein that regulates a number of calcium‐dependent enzyme activities and is thought to be involved in neurotransmission to begin to explore further the regulation of this important protein in the brain, we have cloned a rat calmodulin cDNA and designed an oligonucleotide probe based on this sequence. Both the cDNA and oligonucleotide probes revealed a markedly heterogeneous distribution of hybridization signal for calmodulin mRNA in the rat brain. The greatest apparent abundance of mRNA for calmodulin was seen in the hippocampus and cerebral cortex, whereas many brain regions showed relatively low hybridization signal, including the striatum and portions of the hypothalamus and brainstem.
Somatospiny neurons in the rat lateral septal area are synaptic targets of hippocamposeptal fibers: A combined EM/Golgi and degejeration study
Authors: Jakab Robert L. , Leranth Csaba
Published: January 2005

The mediolateral part of the lateral septal area (LSA) is a common target of hipocamposeptal afferents, neuropeptide containing, catecholaminergic, cholinergic, and GABAergic pericellular baskets of different origins. This specific innervation pattern as well as electrophysiological data concerning this area suggest a convergent input from different sources to particular LSA neuron populations. Light and electron microscopy combined with Golgi impregnation and acute anterograde degeneration techniques following ltransection of the fimbria‐fornix were employed to determine whether LSA neurons with hippocampal input have any characteristic and distinctive morphological signs. About 20% of all Golgi impregnated LSA neurons were found to have somatic spine. All of these somatospiny neurons are synaptic targets of hippocamposeptal fibers. The degenerated hippocamposeptal boutons establish asymmetric synaptic contacts on their soma, somatic and dendritic spines, and on dendritic shafts. Somatospiny neurons located in the most medial and dorsal parts of the LSA seem to project toward the medial septum while all of the others appear to send descending fibers to ventral areas. Somatospiny neuron axons occasionally give out recurrent collaterals. Quantitative analysis on the spatial distribution of the somatospiny neurons revealed that practically all of them are encountered in the mediolateral division of the LSA. This area includes the lateral part of the intermediolateral spptal nucleus and adjacent lateral portions of the dorsolateral and the ventrolateral sptal nuclei.
In vivo characterization of locally applied dopamine uptake inhibitors by striatal microdialysis
Authors: Nomikos George G. , Damsma Geert , Wenkstern Danielle , Fibiger Hans C.
Published: January 2005

In vivo brain microdialysis was used to characterize the effects of some dopamine uptake inhibitors on the extracellular concentrations of dopamine (DA) and its metabolitesdihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the striata of awake, freely moving rats. d‐Amphetamine, GBR 12909, cocaine, nomifensine, methylphenidate, bupropion, and benztropine were administered directly to the striatum via the perfusion fluid in increasing concentrations (1–1,000 μM). All drugs increased extracellular DA in a dose‐dependent manner; however, only d‐amphetamine produced dose‐dependent decreases in DOPAC and HVAconcentrations. The shapes of the dose‐reponse functions differed considerably between the drugs. At 100 and 1000 μM d‐amphetamine had biphasic effects (an increase followed by a decrease) on dialysate DA concentration. GBR 12909, methylphenidate, and benztropine also had biphasic effects when applied at the 1,000 μM concentration. In contrast, cocaine, nomifensine, and bupropion produced relatively monophasic increases in extracellular DA. Tetrodotoxin (TTX), which prevents action potentials by blocking voltage‐dependent Na+ channels, did not prevent d‐amphetamine induced increases in extracellular DA, but blocked completely the effects of cocaine, nomifensine, bupropion, and methylphenidate. While low doses (10 μM) of GBR 12909 and benztropine were highly sensitive to TTX, the toxin was only partially effective against higher doses of the compounds. The rank order of potency of the drugs as determined by the increases in extracellular DA produced by 10 or 100 μM (following correction for dialysis efficiency of the test compounds in vitro) was GBR 12909< benztropine< amphetamine= nomifensine= methylphenidate< cocaine< bupropion. The in vivo characterization of changes in extracellular DA following direct, local application of DA uptake inhibitors can be used to provide useful information aboout the mechanisms of action and potency of these compounds.
Cholinergic modulation of responses to single tones produces tone‐specific receptive field alterations in cat auditory cortex
Authors: Metherate Raju , Weinberger Norman M.
Published: January 2005

Acetylcholine (ACh), acting via muscarinic receptors, is known to modulate neuronal responsiveness in primary sensory neocrotex. The administration of ACh to cortical neurons facilitates or suppresses responses to sensory stimuli, and these effects can endure well beyond the period of ACh application. In the present study, we sought to determine whether ACh produces a general change in sensory information processing, or it can specifically alter the processing of sensory stimuli with which it was “paired.” To answer this question, we restricted acoustic stimulation in the presensce of ACh to a single frequency, and determined single neuron frequency receptive fields in primary auditory cortex before and after this pairing. During its adminidstration, ACh produced mostly facilitatory effects on spontaneous activity and on responses to the single frequency tone. Examination of frequency receptive fields after ACh administration revealed receptive field modifications in 56% of the cells. In half of these cases, the receptive field alterations were highly specific to the frequency of the tone previously paired with ACh. Thus ACh can produce stimulus‐specific modulation of auditory information processing. An additional and unexpected finding was that the type of modulation during ACh administration did not predict the type of receptive field modulation observed after ACh administration; this may be related to the physiological “cortext” of the same stimulus in two different conditions. The implications of these findings for learning‐induced plasticity in the auditory cortex is discussed.
Autism: Review of neurochemical investigation
Authors: Cook Edwin H.
Published: January 2005

The neurochemistry of autism, the most well‐validated childhood neuropsychiatric disorder, has been studied extensively over the past three decades. Autism is of interest neurochemically because it represents a relatively homogeneous disorder with a triad of social, communicative, and intellectual developmental disturbance. Because a sufficient animal model has been lacking and relatively few diagnosed people with autism have died, most investigation has been of peripheral fluids and tissues. The most consistent finding has been that over 25% of autistic children and adolescents are hyperserotonemic. However, after 29 years of investigation, the mechanism of hyperserotonemia has not been determined. Hyperserotonemia has been found to be familial. Elevated plasma norepinephrine has also been a replicated finding. Cerebrospinal fluid (CSF) opiate activity has been found to be elevated in two studies. Plasma cyclic adenosine monophosphate (cAMP) has been found to be elevated in autistic children. A high rate of nonsuppression after dexamethasone and blunted or delayed growth hormone response to L‐dopa have been found Abnormal cell‐mediated immunity has been replicated consistently in autism. Although several pharmacological trials have been conducted and shown promise in initial open trials, only “typical” antipsychotic drugs have shown replicable chronic ameliorating effects in double‐blind trials. However, chronic neurotoxicity (tardive dyskinesia) has also been revealed. Findings of morphological changes in the cerebellum have been replicated. Findings in need of replication include diminished platelet function, increased baseline CSF homovanillic acid, decreased nerve cell adhesion molecule serum fragment, blunted prolactin response to fenfluramine, amelioration of symptoms by naltrexone and bromocriptine, reduced electroretinographic (ERG) b‐wave amplitude, and morphological changes in the hippocampus, amygdala, and septal nuclei. In addition to refining and replicating past findings, future directions that may be fruitful include investigation of neurochemical aspects of platelet function, of interactions between monoaminergic systems, of phosphatidylinositides, and of pharmacological response to “atypical” antipsychotic agents and relatively selective serotonin receptor subtype agonists or antagonists.
Neurotensin receptor binding levels in basal ganglia are not altered in Huntington's chorea or schizophrenia
Authors: Palacios José M. , Chinaglia Giorgia , Rigo Monique , Ulrich Jürg , Probst Alphonse
Published: January 2005

Autoradiographic techinques were used to examine the distribution and levels of neurotensin receptor binding sites in the basal gangila and related regions of the human brain. Monoido ([125I]‐Tyr3)neurotensin was used as a ligand. High amounts of neurotensin receptor binding sites were found in the substantia nigra pars compacta. Lower but significant quantities of neurotensin receptor binding sites characterized the caudate, putamen, and nucleus accumbens, while very low quantities were seen in both medial and lateral segments of the globus pallidus.

In Huntington's chorea, the levels of neurotensin receptor binding sites were found to be comparable to those of control cases. Only slight but not statistically significant decreases in amounts of receptor binding sites were detected in the dorsal part of the head and in the body of caudate nucleus. No alterations in the levels of neurotensin receptor bindingsites were observed in the substantia nigra pars compacta and reticulata. These results suggest that a large proportion of neurotensin receptoe binding sites in the basal ganglia are located on intrinsic neurons and on extrinsic afferent fibers that do not degenerate in Huntington's disease.
Association of neurotensin receptors with VIP‐containing neurons and serotonin‐containing axons in the suprachiasmatic nucleus of the rat
Authors: François‐Bellan Anne‐Marie , Bosler Olivier , Tonon Marie‐Christine , Lin‐Tong Wei , Beaudet Alain
Published: January 2005

The aim of the present study was to identify cellular elements bearing high‐affinity neurotensin (NT) binding sites in the suprachiasmatic nucleus (SCN) of the rat hypothalamus. Because the distribution of these binding sites had previously been reported to conform to that of both vasoactive intestinal peptide (VIP)‐containing nerve cell bodies and serotonin (5‐HT)‐containing axons, the following experimental approaches were used: (1) the overlap between autoradiographically labeled NT binding sites and immunocytochemically labeled VIP neurons was examined in adjacent 5‐μmthick sections taken across the entire rostrocaudal extent of the SCN; and (2) the density of NT binding sites was examined by quantitative autoradiography following cytotoxic lesioning of 5‐HT afferents. Double‐labeling studies demonstrated precise overlap between 125I‐NT binding and VIP immunostaining throughout the SCN. Moreover, at high magnification intensely VIP‐immunoreactive neurons were found in direct register with 125I‐NT‐labeled cells visualized in adjacent sections. Densitometric autoradiographic studies demonstrated a significant reduction in specific 125I‐NT binding within the SCN following intracerebroventricular injection of the neurotoxin, 5,7‐dihydroxytryptamine. Taken together, these results indicate that within the SCN, NT receptors are present both presynaptically on serotonin axons and postsynaptically on the perikarya and dendrites of VIP‐containing neurons.