Neurophysiology of converging synaptic inputs from the rat prefrontal cortex,amygdala, midline thalamus,and hippocampal formation onto single neurons of the caudate/putamen and nucleus accumbens

Neurophysiological responses mediated by projections from five telencephalic and diencephalic regions (the infra- and prelimbic portions of the prefrontal cortex, amygdala, midline and intralaminar thalamic nuclei, entorhinal cortex and subiculum/CA1) to the caudate/putamen (CPu) and nucleus accumbens (Acb) of the dorsal and ventral striatum were studied in chloral-hydrate-anesthetized rats. Both extra- and intracellular in vivo recording techniques were used. A retrograde tracer (wheatgerm agglutinin-apo-horseradish peroxidase-5 nm colloidal Gold) was deposited in some animals in the vicinity of recording sites to confirm that stimulating electrodes were located near cells that projected to the striatum. Electrical stimulation of these five regions, respectively, evoked excitatory responses in 60%, 22%, 51%, 25%, and 17% of striatal neurons. Some responses, particularly with thalamic stimulation, showed short-term frequency potentiation in which 5/s stimulation increased the probability of spike firing. About half of responsive cells showed convergent excitation to more than one stimulating site. It was possible with convergent excitatory responses to show synaptic interactions: simultaneous activation of more than one site produced spatial and temporal summation to increase the probability of spike firing. Up to 5-way convergence onto single striatal neurons and up to 3-way interactions could be shown. These results indicate that functional influences from the hippocampal formation can converge with other excitatory input onto single striatal neurons to effect synaptic integration. © 1996 Wiley-Liss, Inc.     

Thalamic paraventricular nucleus neurons collateralize to innervate the prefrontal cortex and nucleus accumbens

The prefrontal cortex and nucleus accumbens are primary recipients of medial thalamic inputs, prominently including projections from the thalamic paraventricular nucleus. It is not known if paraventricular neurons collateralize to innervate both the prefrontal cortex and nucleus accumbens. We used dual retrograde tract tracing methods to examine this question. A small population of paraventricular neurons was found to innervate the prefrontal cortex and medial nucleus accumbens. These data suggest that the thalamic paraventricular nucleus may coordinately influence activity in the prefrontal cortex and ventral striatum.     

Polarization of caudate nucleus and excitability of neurons in motorsensory cortex.

Responses of neurons in the anterior sigmoid gyrus of the cat were found to be characterized by depolarization when the dorsal portion of the caudate nucleus was anodally polarized in reference to the ventral portion. Hyperpolarization responses were recorded when the dorsal portion of the caudate was cathodally polarized. The threshold of the hyperpolarization response was higher than the threshold of the depolarization response. These responses were synaptically evoked and might have been the result of spatial and temporal activation of the cells and fibers in the caudate nucleus and its related structures.     

Muscarinic cholinergic receptor binding and electrophysiological response to acetylcholine in cultured rat caudate putamen nucleus neurons

Binding sites with specificity for N-[3H]methylscopolamine ([3H]NMS) are present in homogenates of primary culture neurons from the rat caudate putamen nucleus (CPN). Specific binding is saturable with respect to [3H]NMS. The Scatchard analysis indicates a dissociation constant of 0.6 nM and a density of 7.0 X 10(3) per cell, or 78 fmol/mg protein. In electrophysiological measurements, excitatory postsynaptic currents (EPSCs) in larger cells were increased by pressure application of acetylcholine under voltage clamp condition. The EPSCs may come from neighboring smaller cells with muscarinic acetylcholine receptors.     

Dissociation of prefrontal cortex and nucleus accumbens dopaminergic systems in conditional learning in rats

There is converging evidence that the prefrontal and mesolimbic dopaminergic (DAergic) systems are involved in the performance of a variety of tasks that require the use of contextual, or task-setting, information to select an appropriate response from a number of candidate responses. Performance on tasks of this nature are impaired in schizophrenia and in rats exposed to psychotomimetics; impairments that are often attenuated by administration of dopamine (DA) antagonists. Rats were trained on either a complex instrumental discrimination task, that required the use of task-setting cues, or a simple discrimination task that did not. Following training, microdialysis probes were implanted unilaterally in either the medial prefrontal cortex (mPFC) or nucleus accumbens (NAc) and samples were collected in freely moving animals during a behavioural test session. In Experiment 1, we found no difference in levels of DA in the mPFC of rats while they were performing the two discrimination tasks. Rats that performed the complex task did, however, show significantly higher mPFC DA levels relative to rats in the simple discrimination condition following the end of the behavioural test session. In Experiment 2, rats performing the conditional discrimination showed lower levels of DA in the NAc compared to the simple discrimination group both during the test session and after it. These results provide direct evidence that conditional discrimination tasks engage frontal and mesolimbic DAergic systems and are consistent with the proposal that regulation of fronto-striatal DA is involved in aspects of cognitive control that are known to be impaired in individuals with schizophrenia.     

In vivo release of endogenous dopamine from rat caudate putamen and nucleus accumbens by 40 mM potassium chloride

1. 1. The resting and K⁺-stimulated release rates of endogenous dopamine (DA) have been measured in vivo at four different sites in the rat caudate putamen and nucleus accumbens.

2. 2. A push-pull cannula was inserted into the brain sites chosen, and the tissue was perfused with artificial cerebrospinal fluid (CSF) containing 2.6 or 40 mM KC1. The DA content of the perfusates was determined by a radioenzymatic procedure.

3. 3. DA release was significantly increased above unstimulated levels by 40 nM KC1 in all areas tested. Neither unstimulated nor K⁺-stimulated release rates varied significantly among the regions examined.

4. 4. K⁺-stimulated DA release was not significantly diminished by perfusing the tissue with calcium-free medium, suggesting that release was probably supported by residual amounts of calcium in the tissue.

Ultrastructure of reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase-positive neurons in the cat cerebral cortex, amygdala and caudate nucleus

The ultrastructure of reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase-positive neurons in cat cerebral cortex, amygdala and caudate nucleus was investigated by electron microscopy using a modified method applicable to aldehyde-fixed tissues. These NADPH diaphorase-positive neurons were morphologically similar to neurons immunohistochemically positive for somatostatin. They had large amounts of electron-dense formazan reaction products scattered through the whole cytoplasm but not in the mitochondria or nucleus. Similar electron-dense reaction products were visible in the dendrites of these neurons. The results indicate that NADPH diaphorase histochemistry is a useful method for the ultrastructural examination of particular groups of neurons.     

Activity of neurons in the caudate and putamen during a visuomotor task

Evidence supporting a role of the caudate and putamen nuclei in associative learning is present. We recorded the activity of 21 caudate and 26 putamen cells in one macaque monkey while performing a visuomotor task, which involved a visual stimulus and the execution of a motor response. Ninety-one percent of caudate cells and 65% of putamen cells showed changes in activity while the monkey was performing the task. Approximately half of the caudate cells and one third of the putamen cells showed changes in activity without a motor response. Our results show that caudate and putamen cells are activated regardless of the presence or absence of a motor action. These findings are consistent with the idea that these nuclei may play a role in associative learning.     

Changes in multiunit activity of nigral neurons induced by cholinergic and dopaminergic stimulation of the caudate nucleus

The effects of stimulation of the caudate cholinergic and dopaminergic receptors on multiunit activity in the ipsilateral substantia nigra were studied in cats locally anesthetized, paralyzed and artificially respired. Cholinergic stimulation by intracaudate micro-injections of 10 μg of carbachol diminished multiunit activity by 36% in the ventral substantia nigra (SN) and increased activity by 48% in the dorsal SN. This effect was abolished after electrolytic lesion of the ipsilateral striatonigral pathway. Opposite responses were observed following intracaudate administration of 20 μg of dopamine or 20 μg ofd-amphetamine. Multiunit activity in the ventral SN increased by 36% and 34%, respectively, while the activity in the dorsal SN was reduced by 56% and 53%, respectively. Similar results were obtained in response to systemic administration of d-amphetamine.Extracaudate microinjections of carbachol and dopamine left multiunit activity in the SN unaffected.In conclusion, our results indicate an opposite action of caudate cholinergic and dopaminergic receptors on multiunit activity in the SN of the cat.     

Tyrosine hydroxylase-immunoreactive neurons in the nucleus basalis of the common marmoset (Callithrix jacchus).

In the course of characterizing the distribution of putative catecholaminergic neurons in the brain of the common marmoset, we encountered a population of such cells in the basal forebrain. Tyrosine hydroxylase-immunoreactive neurons are abundant within the nucleus basalis magnocellularis throughout its entire rostrocaudal extent, but not in other cholinergic basal forebrain nuclei. Most tyrosine hydroxylase-immunoreactive cells are large and multipolar. Double staining with antibodies to choline acetyltransferase or nerve growth factor receptor confirmed that these tyrosine hydroxylase-immunoreactive neurons are cholinergic, and compose at least 40% of the nucleus basalis cholinergic cells. The presence of a catecholamine-synthesizing enzyme in the neurons that provide the major cholinergic input to the neocortex may have important consequences for cortical function, and may be relevant to the vulnerability of the nucleus basalis in certain neurodegenerative disorders.     

Projections of the entorhinal area to the striatum, nucleus accumbens, and cerebral cortex in the guinea pig

A study of the efferent projections of the entorhinal area in the guinea pig, by using anterograde (autoradiographic tracing of tritiated amino acids) and retrograde (fluorochrome tracing) methods, revealed the following projections: (1) to nonhippocampal cortices: retrosplenial cortex (area 29), cingulate cortex (areas 23, 24), prelimbic cortex (area 32), infralimbic cortex (area 25), perirhinal cortex (areas 35, 36), prepyriform cortex (area 51B), and insular cortex (areas 13-16). All received direct projection; (2) to subcortical targets: distinct terminations were observed in the lateral thalamic nucleus, the striatum, and the accumbens nucleus. In retrograde experiments, the cells giving rise to the projections to the hippocampus were found to lie in layers II and III, those projecting to the nonhippocampal cortical regions to originate in layer IV, and those projecting to the striatum and the accumbens to lie in layers V and VI. Many of the efferent projections to the cerebral cortical regions are associated with reciprocal projections from these regions to the superficial layers (I-III) of the entorhinal cortex. The entorhinal efferent projections generally terminate ipsilaterally. A weak termination is, however, present at the contralateral side. The efferent projections of the entorhinal area represent a route for important caudally directed, nonfornical hippocampal output.     

Variation in the expression of the mRNA for protein kinase C isoforms in the rat suprachiasmatic nuclei,caudate putamen and cerebral cortex

Using in situ hybridization, we have examined mRNA expression for five isoforms of protein kinase C (PKC α, β1, β2, γ and ε) in the rat suprachiasmatic nuclei (SCN) and other central sites during the 24 h cycle. The signal for each of these isoforms shows a marked local density within the SCN. In the absence of photic cues, there are changes in the expression of the mRNAs for the four isoforms that are Ca²⁺-dependent (α, β1, β2 and γ), but not for one of the Ca²⁺-independent PKCs (ε). PKC α mRNA exhibits a monophasic rhythm of expression in the SCN with a peak at early subjective night, circadian time (CT) 14. In contrast, the mRNAs for PKC β1, β2 and γ show a biphasic rhythm in the SCN with peaks at early subjective day, CT 0, and early subjective night, CT 14. The four Ca²⁺-dependent isoforms may therefore subserve phase-related functions within the SCN at the onset of subjective night and, in the case of β1, β2 and γ, also at the onset of subjective day. Variation in the mRNAs for PKC β1 and γ (but not for α, β2 or ε) is also found in the caudate putamen and in the cingulate and parietal cortex; the biphasic pattern of expression for these mRNAs is precisely in phase with that observed in the SCN. The β1 and γ isoforms may therefore contribute to temporally regulated functions at sites outside the SCN. The present observations raise the possibility that receptor-mediated regulation of circadian functions is modulated or even gated by circadian changes in intracellular components that participate in distinct signal cascades.     

Dendritic morphology of neurons in medial prefrontal cortex,hippocampus, and nucleus accumbens in adult SH rats

We have studied, in spontaneously hypertensive (SH) rats at different ages (2, 4, and 8 months old), the dendritic morphological changes of the pyramidal neurons of the medial prefrontal cortex (mPFC) and hippocampus and medium spiny neurons of the nucleus accumbens (NAcc) induced by the chronic effect of high‐blood pressure. As control animals, we used Wistar‐Kioto (WK) rats. Blood pressure was measured every 2 months to confirm the increase in arterial blood pressure. Spontaneous locomotor activity was assessed, and then brains were removed to study the dendritic morphology by the Golgi‐Cox stain method followed by Sholl analysis. SH animals at 4 and 8 months of age showed decreased spine density in pyramidal neurons from the mPFC and in medium spiny cells from the NAcc. At 8 months of age as well the pyramidal neurons from the hippocampus exhibited a reduction in the number of dendritic spines. An increase in locomotion in a novel environment at all ages in the SH rats was observed. Our results indicate that high‐blood pressure alters the neuronal dendrite morphology of the mPFC, hippocampus, and NAcc. The increased locomotion behavior supports the idea that dopaminergic transmission is altered in the SH rats. This could enhance our understanding of the consequences of chronic high‐blood pressure on brain structure, which may implicate cognitive impairment in hypertensive patients. Synapse, 2010. © 2010 Wiley‐Liss, Inc.     

Development of responses of globus pallidus and entopeduncular nucleus neurons to stimulation of the caudate nucleus and precruciate cortex

Extracellular recordings were made from neurons in the globus pallidus and entopeduncular nucleus (GP-ENTO) of anesthetized kittens of 2 to 177 days of age and from four adult cats. Stimulation of the striatum and the precruciate cortex produced responses in GP-ENTO neurons of the youngest kittens tested (2 days of age). In kittens of 1 to 10 days, about 70% of the GP-ENTO neurons responded to either caudate or cortical stimulation with a purely excitatory response (i.e., an evoked action potential). With increasing age the frequency of occurrence of this type of response decreased and the occurrence of inhibitory responses or of sequences of excitation followed by inhibition increased. In addition to these changes in the form of the evoked responses, other response parameters exhibited age-dependent alterations. Latency to response decreased with age and the ability of GP-ENTO neurons to follow repetitive stimuli increased as the kittens became older. These findings suggest that although GP-ENTO neurons are functional as early as 2 days postnatally in the kitten, subsequent maturation of the responsiveness of these neurons continues for several postnatal months.     

The dopaminergic hyper-responsiveness of the shell of the nucleus accumbens is hormone-dependent

The dopaminergic projection to the shell of the nucleus accumbens is the most reactive to stress, reward and drugs of abuse and this subregion of the nucleus accumbens is also considered a target of therapeutic effects of atypical antipsychotic drugs (APD). In this report we show, by means of in vivo microdialysis and Fos immunohistochemistry, that the hyper-responsiveness which characterizes the dopaminergic transmission to the shell is dependent on glucocorticoid hormones. In Sprague-Dawley rats, after suppression of endogenous glucocorticoids by adrenalectomy, extracellular dopamine levels selectively decreased in the shell, whilst they remained unchanged in the core. This effect was observed in basal conditions, after a mild stress (vehicle injection), as well as after subcutaneous administration of morphine (2 mg/kg, s.c. ) or intraperitoneal injection of cocaine (15 mg/kg, i.p.). The decrease in dopamine observed in the shell had a postsynaptic impact, as shown by less induction of Fos-like proteins selectively in the shell in response to cocaine. However, the induction of Fos-like proteins by the full D1 agonist SKF82958 (1.5 mg/kg, i.p.) remained unchanged after adrenalectomy, suggesting that the changes in Fos expression after cocaine injection were likely to depend on changes in extracellular dopamine levels rather than on changes in postsynaptic sensitivity to dopamine. The effects of adrenalectomy were glucocorticoid-specific given that they were prevented by corticosterone treatment. This anatomical specificity in the control of neuronal activity by a hormonal input highlights the role of steroid hormones in shaping the functional activity of the brain.     

Chronic phencyclidine treatment increases dendritic spine density in prefrontal cortex and nucleus accumbens neurons

We examined whether repeated exposure to the noncompetitive NMDA receptor antagonist phencyclidine (PCP) produces enduring changes in dendritic structure in a manner similar to the stimulants cocaine and amphetamine. Adult rats were treated with i.p. injections of PCP (5 mg/kg) or saline, twice a day, for 5 consecutive days, for a total of 4 weeks. One month after the last injection, their brains were removed and processed for Golgi-Cox staining. Prior exposure to PCP increased dendritic spine density in the mPFC and NAcc core, but not in the parietal cortex. These findings, which are similar to those observed after chronic treatment with cocaine and amphetamine, raise the possibility that, despite differences in their mechanisms of action, PCP and stimulant drugs may induce some of their enduring effects via common processes.     

Caffeine-induced expression of c-fos mRNA and NGFI-A mRNA in caudate putamen and in nucleus accumbens are differentially affected by the N-methyl-d-aspartate receptor antagonist MK-801

Caffeine (100 mg/kg, i.p.) induces a rapid increase in the expression of mRNA for the immediate early genes (IEGs) c-fos and NGFI-A in rat striatum. We have examined how this response is affected by pretreatment with either the noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist MK-801 (1 and 3 mg/kg, i.p.), the competitive NMDA receptor antagonist D-CPP (6 mg/kg, i.p.), or the non-selective excitatory amino acid receptor antagonist kynurenic acid (300 mg/kg, i.p.). The two NMDA receptor antagonists significantly reduced the caffeine-induced expression of both c-fos mRNA and NGFI-A mRNA in the medial part of the caudate putamen. The effect was less pronounced in the lateral part of the caudate putamen. MK-801 caused an enancement of c-fos and NGFI-A mRNA expression in nucleus accumbens. Pretreatment with kynurenic acid caused no marked alterations in the caffeine-induced expression of c-fos mRNA and NGFI-A mRNA in any brain region. These findings suggest that glutamatergic transmission via NMDA receptors contributes to the induction of c-fos mRNA and NGFI-A mRNA by caffeine in striatum. In addition we show that MK-801 can either increase or decrease the caffeine effect of IEGs depending on the region studied.     

Co-expression of calretinin and gamma-aminobutyric acid in neurons of the entorhinal cortex of the common marmoset monkey

The gamma-aminobutyric acid (GABA)-containing interneuron population in the entorhinal cortex has been shown to consist of several subpopulations. In addition to GABA, these neurons contain another neurochemical substance, such as a neuropeptide or a calcium binding protein. In the present study, we examined the co-localization of calretinin and GABA in the entorhinal cortex of the common marmoset Callithrix jacchus, a New World monkey. Although the function of calretinin remains unclear, there are indications that it might have a protective role against cell death in a number of neuropathological diseases. Furthermore, it might have a regulatory role in the neurotransmission of GABAergic neurons. In contrast to the rat brain, sparse data exist regarding the degree of co-expression of these two markers in the monkey brain. Using immunofluorescence and confocal laser scanning microscopy, we found that an average of 56% of the calretinin-positive neurons in the monkey entorhinal cortex contained GABA, whereas about 27% of the GABA-positive neurons co-expressed calretinin. Interestingly, these numbers were higher in the superficial layers of the entorhinal cortex in comparison with the deep layers. However, no differences were found in co-localization percentages between the different entorhinal subfields. In general, the degree of co-localization was higher in comparison to findings in the rat entorhinal cortex. The higher amount of co-localization observed in the present study might reflect species differences between the primate and the non-primate brain.     

Responses of cat cerebellar cortex neurons to stimulation of the caudate nucleus, globus pallidus and substantia nigra

Impulsive responses (IR) of the Purkinje cells (PC) and other units of the cerebellar cortex in the paramedian lobules, lobulus simplex and tuber vermis were evoked by stimulation of nucleus caudatus (NC) in cats under chloraloze-nembutal narcosis. The phasic IR as simple discharges (due to mossy fibre activation) were exhibited mainly with a latency of 5-12 and 14-20 ms; a latency of the compound responses ) due to climbing fibre PC activation) was equal to 5-6, 9-22 ms and more. There were differences in rhythmic reproduction of the responses depending on their latency. The recruitment responses were found during a 4-6/s NC stimulation. There was an inhibitory pause as an obligatory component of the tonic neuronal responses. Reactions of the same types (phasic and tonic) as in the case of the NC stimulation, but differing in unit's quantitative distribution according to the latency appeared in the globus pallidus (GP) stimulation. The minimal latency was 4 ms. Recruitment was observed as well. The substantia nigra (SN) stimulation evoked PC responses, activated by the climbing fibres with a stable latency (8.5 +/- 0.3 ms). SN, GP, n. inferior olive as well as thalamic nuclei are considered to play a definite role in realizing caudate-cerebellar connections, both oligosynaptic and polysynaptic.