Combinations of active striatal neurons connected selectively with certain behavioral actions of the monkey Macaca mulatta

At present there is widely spread concept of populational coding of information by brain neurons; it is based first of all on results of comparison of neuronal activity with parameters of the used stimulus. Relation between the neuronal activity coding and the observed behavioral actions has been practically not studied. In the present work, neuronal impulse activity has been studied in groups of 6 neurons recorded in parallel. Distribution of frequencies of the presence of cases of excitation of one or several cells has been established to differ statistically significantly form the theoretical distribution of the same values; this indicates that under real conditions, the appearance of individual combinations of active neurons is not random, but is connected to a certain degree with conditions of experiment. The selective combinations of neuronal activity have revealed to be different at stages of program. This indicates that organization of different behavioral actions is associated with activities of certain combinations of neurons.     

Combinations of active striatal neurons connected selectively with certain behavioral actions of the monkey <Emphasis Type="Italic">Macaca mulatta</Emphasis>

At present there is widely spread concept of populational coding of information by brain neurons; it is based first of all on results of comparison of neuronal activity with parameters of the used stimulus. Relation between the neuronal activity coding and the observed behavioral actions has been practically not studied. In the present work, neuronal impulse activity has been studied in groups of 6 neurons recorded in parallel. Distribution of frequencies of the presence of cases of excitation of one or several cells has been established to differ statistically significantly from the theoretical distribution of the same values; this indicates that under real conditions, the appearance of individual combinations of active neurons is not random, but is connected to a certain degree with conditions of experiment. The selective combinations of neuronal activity have been revealed to be different at stages of program. This indicates that organization of different behavioral actions is associated with activities of certain combinations of neurons.     

Populations of behavior-reactive neurons in the monkey neostriatum

Comparative analysis of the unit activity of the monkey putamen during multistage behavior showed that neurons of the putamen are active during all the behavioral actions. It was established that the number of the behavior-related neurons changes considerably less than number of neurons which reorganize their activity at the time. Reorganization of unit activity in the putamen is considered as reflecting the efferent code which controls behavior, and the degree of reorganization--as a measure of change of this code in relation to organization of ongoing behavioral action. It has been discovered that the change in the number of the active neurons at various steps of behavior and reorganization of their activity occurs independently. It may be related to two main afferent systems of striatum: ascending from rhe brain stem, and corticofugal which brings differentiated information to the neuronal net of striatum from various parts of the cortex.     

Coding the differently directed behavioral actions by the putamen neurons of the monkey brain

Spike activity related to the problem of alternative choice of behavioral actions was recorded in the putamen of the monkey brain. The patterns of low and high activities were identified. Each neuron during different behaviour actions could generate any kind of patterns. The differences between neuronal compositions with patterns of high activity, at the left and right direction of the task, were obtained during decision making about the movement direction, and also at the end of the movement. Distinctions between neuronal compositions with patterns of low activity at this time, on the contrary, diminished. The neuronal compositions with patterns of low activity were much more before the conditioned signal, when the animal did not yet know the task, and at the end of the program when the problem was already solved. The data obtained show that the putamen units control different directions of actions by a multilevel address coding, mainly through reorganizing the neuronal compositions with patterns of different level activity.     

Blocks of neuron correlates of behaviour in the monkey brain prefrontal cortex and striatum

The dynamics of tonic neuron activity of the putamen and prefrontal cortex of monkey's brain is researched by studying sequential stages of executive behavior program. It is determined that tonic responses in both structures are classified in separate blocks. The blocks are timed to key moments of behavior connected with intermediate goals framed by a common task. As to the structures of the aforesaid blocks of tonic activity in cortex and striatum, they are different in instructive part of the program and similar in executive one. More differential attitude of cortex is revealed to the sequence of executive behavior activity.     

Convergence of Signals and Reorganization of Neuronal Activity in a Model of Neuronal Network and in Striatum of the Monkey Brain

To elucidate principles of neuronal organization providing preservation of informational content of converging impulse flows in afferent impulsation of neurons, a comparison is performed of results obtained in the previously carried out experiments on a model of neuronal network and in a study of correlates of behavior in the neuronal network of the monkey brain neostriatum (putamen). This comparison has shown that responses of the neuronal network model to different ratio of input impulse flows and changes of the neostriatal neuronal activity, which accompany different behavioral actions, are seen the most clearly in reorganization of composition of the most active neurons. Each combination of input signals and each behavioral action of the animal correspond to a non-repeated mosaic of neuronal activity. The data obtained indicate that the neuronal network, both real and in the simplest model variant, is able to transform the converging input signals into the mosaic equivalent to their entire combination and thereby to transmit the result of generalization of the input signals of the network to the innervated brain structures.     

Neuronal activity of the monkey striatum points at the integration of successive actions into functional blocks

In order to study the role of the striatum in generation of multistage behavior, the spike activity of 148 cells was recorded in the monkey brain putamen. Two kinds of neuron responses were observed. Phasic response involved activity during only one stage of the behavior program, and tonic response involved activity during more than one sequential stage. The tonic responses were recorded in 132 neurons out of 148, 11 neurons responding only as tonic. Other 121 cells show under different conditions both tonic and phasic responses. Beginnings and ends of "tonic" responses as a rule corresponded to the start and completion of the nearest behavioral aim. The obtained data suggest that the neuron activity of striatum is related not only to the control of individual movements but also to the whole structure of behavior.     

Morphine-induced increase in D-1 receptor regulated signal transduction in rat striatal neurons and its facilitation by glucocorticoid receptor activation: Possible role in behavioral sensitization

One month (but not 1–3 days) after intermittent morphine administration, the hyperresponsiveness of rats toward the locomotor effects of morphine and amphetamine was associated with an increase in dopamine (DA) D-1 receptor-stimulated adenylyl cyclase activity and enhanced steady state levels of preprodynorphin gene expression in slices of the caudate/putamen and nucleus accumbens. Such an enduring increase in postsynaptic D-1 receptor efficacy also occurred in cultured γ-aminobutyric acid (GABA) neurons of the striatum obtained from rats prenatally treated with morphine. Interestingly, in vitro glucocorticoid receptor activation in these cultured striatal neurons by corticosterone potentiated this neuroadaptive effect of prior in vivo morphine exposure. Since activation of glucocorticoid receptors by corticosterone did not affect D-1 receptor functioning in cultured neurons of saline-pretreated rats, prior intermittent exposure to morphine (somehow) appears to induce a long-lasting state of corticosterone hyperresponsiveness in striatal neurons. Therefore, DA-sensitive striatal GABA neurons may represent common neuronal substrates acted upon by morphine and corticosterone. We hypothesize that the delayed occurrence of these long-lasting morphine-induced neuroadaptive effects in GABA/dynorphin neurons of the striatum is involved in the enduring nature of behavioral sensitization to drugs of abuse and cross-sensitization to stressors. Special issue dedicated to Dr. Eric J. Simon.     

Soman toxication in hypoxia acclimated rats: Alterations in brain neuronal RNA and survival

Effects of prior hypoxia acclimation (14-day at 380 mm Hg) on soman (pinacolyl methylphosphonofluoridate) induced brain neuronal RNA and acetylcholinesterase (AChE) depletion and lethality were monitored in rats following their return to ambient oxygenation. Quantitative cytochemical techniques were used to measure RNA and AChE changes in individual cerebrocortical (Layer III) and striatal (caudate plus putamen) neurons. In ambient P_{O 2} controls, soman eventuated in a moderate diminution of neuronal RNA in both brain regions and severe, dosedependent suppression of AChE activity. Hypoxia acclimation per se induced RNA alterations as manifested in cortical RNA depletion and increased variability of striatal neuron RNA contents. In hypoxia acclimated rats, the extent of neuronal RNA depletion following soman injection was attenuated in both brain regions, yet there were no discernible differences in saline control AChE levels or in the extent of soman-induced AChE inhibition in ambient control versus hypoxia acclimated treatment groups. Hypoxia acclimated rats, however, were found to be even more susceptible to lethal actions of soman as assessed using 24- and 48-hour survival following a three-point treatment regimen. These data indicate that while compensatory systemic and central metabolic adjustments associated with 14d acclimation to reduced oxygen availability may retard soman-induced neuronal RNA depletion, resistance to lethal or near-lethal soman exposure is not enhanced. It is postulated that hypoxia acclimation is associated with complex adaptive and maladaptive neurophysiological alterations influencing CNS responsiveness to soman toxication, and that detrimental consequences exceed protection afforded by metabolic adaptation.     

Oscillatory entrainment of striatal neurons in freely moving rats

Oscillations and synchrony in basal ganglia circuits may play a key role in the organization of voluntary actions and habits. We recorded single units and local field potentials from multiple striatal and cortical locations simultaneously, over a range of behavioral states. We observed opposite gradients of oscillatory entrainment, with dorsal/lateral striatal neurons entrained to high-voltage spindle oscillations ("spike wave discharges") and ventral/medial striatal neurons entrained to the hippocampal theta rhythm. While the majority of units were likely medium-spiny projection neurons, a second neuronal population showed characteristic features of fast-spiking GABAergic interneurons, including tonic activity, brief waveforms, and high-frequency bursts. These fired at an earlier spindle phase than the main neuronal population, and their density within striatum corresponded closely to the intensity of spindle oscillations. The orchestration of oscillatory activity by networks of striatal interneurons may be an important mechanism in the pathophysiology of neurological disorders such as Parkinson's disease.     

Emergence of Motor Circuit Activity

In the developing nervous system, ordered neuronal activity patterns can occur even in the absence of sensory input and to investigate how these arise, we have used the model system of the embryonic chicken spinal motor circuit, focusing on motor neurons of the lateral motor column (LMC). At the earliest stages of their molecular differentiation, we can detect differences between medial and lateral LMC neurons in terms of expression of neurotransmitter receptor subunits, including CHRNA5, CHRNA7, GRIN2A, GRIK1, HTR1A and HTR1B, as well as the KCC2 transporter. Using patch-clamp recordings we also demonstrate that medial and lateral LMC motor neurons have subtly different activity patterns that reflect the differential expression of neurotransmitter receptor subunits. Using a combination of patch-clamp recordings in single neurons and calcium-imaging of motor neuron populations, we demonstrate that inhibition of nicotinic, muscarinic or GABA-ergic activity, has profound effects of motor circuit activity during the initial stages of neuromuscular junction formation. Finally, by analysing the activity of large populations of motor neurons at different developmental stages, we show that the asynchronous, disordered neuronal activity that occurs at early stages of circuit formation develops into organised, synchronous activity evident at the stage of LMC neuron muscle innervation. In light of the considerable diversity of neurotransmitter receptor expression, activity patterns in the LMC are surprisingly similar between neuronal types, however the emergence of patterned activity, in conjunction with the differential expression of transmitter systems likely leads to the development of near-mature patterns of locomotor activity by perinatal ages.     

Developmental and Activity-Dependent miRNA Expression Profiling in Primary Hippocampal Neuron Cultures

MicroRNAs (miRNAs) are evolutionarily conserved non-coding RNAs of ∼22 nucleotides that regulate gene expression at the level of translation and play vital roles in hippocampal neuron development, function and plasticity. Here, we performed a systematic and in-depth analysis of miRNA expression profiles in cultured hippocampal neurons during development and after induction of neuronal activity. MiRNA profiling of primary hippocampal cultures was carried out using locked nucleic-acid-based miRNA arrays. The expression of 264 different miRNAs was tested in young neurons, at various developmental stages (stage 2–4) and in mature fully differentiated neurons (stage 5) following the induction of neuronal activity using chemical stimulation protocols. We identified 210 miRNAs in mature hippocampal neurons; the expression of most neuronal miRNAs is low at early stages of development and steadily increases during neuronal differentiation. We found a specific subset of 14 miRNAs with reduced expression at stage 3 and showed that sustained expression of these miRNAs stimulates axonal outgrowth. Expression profiling following induction of neuronal activity demonstrates that 51 miRNAs, including miR-134, miR-146, miR-181, miR-185, miR-191 and miR-200a show altered patterns of expression after NMDA receptor-dependent plasticity, and 31 miRNAs, including miR-107, miR-134, miR-470 and miR-546 were upregulated by homeostatic plasticity protocols. Our results indicate that specific miRNA expression profiles correlate with changes in neuronal development and neuronal activity. Identification and characterization of miRNA targets may further elucidate translational control mechanisms involved in hippocampal development, differentiation and activity-depended processes.     

Cell death and neuronal replacement during formation of the avian ciliary ganglion

Programmed cell death is a prominent feature of embryonic development and is essential in matching the number of neurons to the target tissues that are innervated. Although a decrease in neuronal number which coincides with peripheral synaptogenesis has been well documented in the avian ciliary ganglion, it has not been clear whether cell death also occurs earlier. We observed TUNEL-positive neurons as early as stage 24, with a large peak at stage 29. This cell death at stage 29 was followed by a statistically significant (P < 0.0001) decrease in total neuron number at stage 31. The total number of neurons was recovered by stage 33/34. This suggested that dying neurons were replaced by new neurons. This replacement process did not involve proliferation because bromodeoxyuridine applied at stages 29 and 31 was unable to label neurons harvested at stage 33/34. The peak of cell death at stage 29 was increased 2.3-fold by removal of the optic vesicle and was reduced by 50% when chCNTF was overexpressed. Taken together, these results suggest that the regulation of neuron number in the ciliary ganglion is a dynamic process involving both cell death and neural replacement from postmitotic precursors prior to differentiation and innervation of target tissues.     

Monosynaptic rabies virus reveals premotor network organization and synaptic specificity of cholinergic partition cells

Movement is the behavioral output of neuronal activity in the spinal cord. Motor neurons are grouped into motor neuron pools, the functional units innervating individual muscles. Here we establish an anatomical rabies virus-based connectivity assay in early postnatal mice. We employ it to study the connectivity scheme of premotor neurons, the neuronal cohorts monosynaptically connected to motor neurons, unveiling three aspects of organization. First, motor neuron pools are connected to segmentally widely distributed yet stereotypic interneuron populations, differing for pools innervating functionally distinct muscles. Second, depending on subpopulation identity, interneurons take on local or segmentally distributed positions. Third, cholinergic partition cells involved in the regulation of motor neuron excitability segregate into ipsilaterally and bilaterally projecting populations, the latter exhibiting preferential connections to functionally equivalent motor neuron pools bilaterally. Our study visualizes the widespread yet precise nature of the connectivity matrix for premotor interneurons and reveals exquisite synaptic specificity for bilaterally projecting cholinergic partition cells.     

Coincident but distinct messages of midbrain dopamine and striatal tonically active neurons

Midbrain dopamine and striatal tonically active neurons (TANs, presumed acetylcholine interneurons) signal behavioral significance of environmental events. Since striatal dopamine and acetylcholine affect plasticity of cortico-striatal transmission and are both crucial to learning, they may serve as teachers in the basal ganglia circuits. We recorded from both neuronal populations in monkeys performing a probabilistic instrumental conditioning task. Both neuronal types respond robustly to reward-related events. Although different events yielded responses with different latencies, the responses of the two populations coincided, indicating integration at the target level. Yet, while the dopamine neurons' response reflects mismatch between expectation and outcome in the positive domain, the TANs are invariant to reward predictability. Finally, TAN pairs are synchronized, compared to a minority of dopamine neuron pairs. We conclude that the striatal cholinergic and dopaminergic systems carry distinct messages by different means, which can be integrated differently to shape the basal ganglia responses to reward-related events.     

The dynamics of neuron activity level in the striatum of the monkey brain in relation to the realization of multistage behavior

Level of the unit activity was studied in the monkey putamen during multistage behavior. Two groups of neuron activity patterns were distinguished. The first one involved patterns of low level neuron activity less exceeding the background level than the second one; the other group involved patterns of high level neuron activity exceeding the background level in the second time. These kinds of patterns were behavior-related. Patterns with low level neuron activity were recorded preferentially in relation to the trigger stimuli and reward. Patterns of high level neuron activity were recorded in relation to the decision-making, movements of arms in the left and right directions. Besides, their number rose in relation to the auditory cue reported to right realization of the task. It was established that the number of patterns of high level neuron activity rose in key moments of behavior, while the number of the patterns of low level neuron activity decreased.     

Melatonin Ameliorates Injury and Specific Responses of Ischemic Striatal Neurons in Rats

Studies have confirmed that middle cerebral artery occlusion (MCAO) causes striatal injury in which oxidative stress is involved in the pathological mechanism. Increasing evidence suggests that melatonin may have a neuroprotective effect on cerebral ischemic damage. This study aimed to examine the morphological changes of different striatal neuron types and the effect of melatonin on striatal injury by MCAO. The results showed that MCAO induced striatum-related dysfunctions of locomotion, coordination, and cognition, which were remarkably relieved with melatonin treatment. MCAO induced severe striatal neuronal apoptosis and loss, which was significantly decreased with melatonin treatment. Within the outer zone of the infarct, the number of Darpp-32+ projection neurons and the densities of dopamine-receptor-1 (D1)+ and dopamine-receptor-2 (D2)+ fibers were reduced; however, both parvalbumin (Parv)+ and choline acetyltransferase (ChAT)+ interneurons were not significantly decreased in number, and neuropeptide Y (NPY)+ and calretinin (Cr)+ interneurons were even increased. With melatonin treatment, the loss of projection neurons and characteristic responses of interneurons were notably attenuated. The present study demonstrates that the projection neurons are rather vulnerable to ischemic damage, whereas the interneurons display resistance and even hyperplasia against injury. In addition, melatonin alleviates striatal dysfunction, neuronal loss, and morphological transformation of interneurons resulting from cerebral ischemia.     

Striatal interneurons in dissociated cell culture

In addition to the well-characterized direct and indirect projection neurons there are four major interneuron types in the striatum. Three contain GABA and either parvalbumin, calretinin or NOS/NPY/somatostatin. The fourth is cholinergic. It might be assumed that dissociated cell cultures of striatum (typically from embryonic day E18.5 in rat and E14.5 for mouse) contain each of these neuronal types. However, in dissociated rat striatal (caudate/putamen, CPu) cultures arguably the most important interneuron, the giant aspiny cholinergic neuron, is not present. When dissociated striatal neurons from E14.5 Sprague–Dawley rats were mixed with those from E18.5 rats, combined cultures from these two gestational periods yielded surviving cholinergic interneurons and representative populations of the other interneuron types at 5 weeks in vitro. Neurons from E12.5 CD-1 mice were combined with CPu neurons from E14.5 mice and the characteristics of striatal interneurons after 5 weeks in vitro were determined. All four major classes of interneurons were identified in these cultures as well as rare tyrosine hydroxylase positive interneurons. However, E14.5 mouse CPu cultures contained relatively few cholinergic interneurons rather than the nearly total absence seen in the rat. A later dissection day (E16.5) was required to obtain mouse CPu cultures totally lacking the cholinergic interneuron. We show that these cultures generated from two gestational age cells have much more nearly normal proportions of interneurons than the more common organotypic cultures of striatum. Interneurons are generated from both ages of embryos except for the cholinergic interneurons that originate from the medial ganglionic eminence of younger embryos. Study of these cultures should more accurately reflect neuronal processing as it occurs in the striatum in vivo. Furthermore, these results reveal a procedure for parallel culture of striatum and cholinergic depleted striatum that can be used to examine the function of the cholinergic interneuron in striatal networks.