Hitoshi Kita

Parvalbumin-immunoreactive neurons in the rat neostriatum: a light and electron microscopic study

Parvalbumin (PV)-immunoreactive neurons in rat neostriatum were studied under light and electron microscopes. A small number of neurons in the striatum were immunoreactive for PV (a Ca-binding protein). Most of them were also strongly immunoreactive for glutamate decarboxylase but were negative for NADPH-diaphorase activity. Light microscopic analysis revealed that PV-containing neurons have somata with fusiform or polygonal shape and are medium to large in size. The dendrites were smooth and cylindrical at the proximal portion but were varicose at the distal portion. Thin PV-immunoreactive fibers with large boutons were unevenly distributed in the striatum. Electron microscopy revealed that the somata of PV-immunoreactive neurons had a deeply indented nucleus with a nucleolus and often an intranuclear rod. These are the morphological features reported for interneurons of the striatum. Gap junctions formed between two neighboring PV-immunoreactive dendrites. A total of 175 boutons forming synapses with somata and dendrites of PV-immunoreactive neurons were examined. Of these, 115 were small in diameter (less than 1 micron), contained densely packed round vesicles and formed asymmetrical synapses mainly with dendrites. The other 60 boutons formed symmetrical synapses with somata and dendrites of PV-immunoreactive neurons. Both myelinated and unmyelinated axons with boutons were observed. PV-immunoreactive boutons had a diameter of 0.3-2 microns and contained round or elongated vesicles which were about 35 nm in diameter. The boutons formed symmetrical synapses with postsynaptic targets. Of the 100 PV-immunoreactive boutons, 51 were found on somata and proximal dendrites of medium-sized neurons containing a large, round, centrally located nucleus. The others formed synapses with dendrites of various sizes. It was occasionally observed that varicose dendrites free of spines were contacted by a large number of PV-immunoreactive boutons. The study indicates that, in the striatum, immunocytochemistry for PV selectively stains GABAergic interneurons and that the GABAergic interneurons are incorporated in a feed-forward inhibitory circuit of the striatum.

Glutamate decarboxylase immunoreactive neurons in rat neostriatum: their morphological types and populations.

Morphological types and populations of glutamate decarboxylase (GAD)-immunoreactive neurons in rat neostriatum (Str) were studied. Str of colchicine-treated animals contained 3 types of neurons immunoreactive for GAD. The first type, which makes up 80-84% of Str neurons, was medium in size and showed moderate intensity GAD-staining. The somatic morphology of the neurons was identical to the medium-spiny projection neuron. The second type, 3-5% of Str neurons, was small to medium in size and was intensely stained for GAD. The somata of the neurons were round or oval and contained a narrow ring of cytoplasm surrounding the nucleus, which often had nuclear invaginations. There were only a few in each section of the third type, which were large, polygonal, and intensely stained, GAD-immunoreactive neurons, including all 3 types, ranged from 85-87% of the total neuron population. The present study indicated that GABAergic neurons in the Str are not a single morphological type and that most Str projection neurons are GABAergic.

Circadian rhythmic changes of neuronal activity in the suprachiasmatic nucleus of the rat hypothalamic slice

Abstract The present study, utilizing rat brain slice of the suprachiasmatic nuclei (SCN) demonstrated single neuronal activity of SCN cells which changed in correspondence to environmental light-dark (L-D) schedules. The unit discharge rates of cells from animals kept on normal LL-D) cycles reached peaks at about 14.00 h and had a lowest point at around 02.00 h. The unit activity in slices from animals kept on reversed (L-D) cycles was shifted approximately 12 h.

The morphology of globus pallidus projection neurons in the rat: an intracellular staining study

The morphology of 23 intracellularly stained projection neurons of rat globus pallidus (GP) was studied in light microscopic preparations. The somatic size of these projection neurons was highly variable. The somatic area ranged from 78 to 353 microns 2. The 23 neurons were divided into aspiny and spiny types, based on the existence of dendritic spines. Sixteen neurons were aspiny and 7 were of the spiny type. The aspiny neurons tended to have a larger soma than the spiny neurons. Fourteen of the 23 projection neurons possessed a discoidal dendritic field with the flat plane parallel to the border between the GP and the neostriatum. All of the 14 neurons having a discoidal dendritic field were of the aspiny type and were located throughout the GP. The other 9 neurons, which include all of the 7 spiny types, had radiating dendritic fields with a variety of shapes and were located only in the medial region of the GP. The axons of a majority (i.e. 21 of 23) of the projection neurons emitted multiple collaterals with large boutons en-passant and boutons terminaux within the GP. The main axons were traced to varying distances from their somata. Four of them were traced into the substantia nigra. Two of these 4 emitted multiple collaterals at various rostro-caudal levels in the entopeduncular nucleus, and all 4 axons had one or two collaterals in the subthalamic nucleus. This study revealed that the rat GP contains two types of projection neurons having different dendritic morphologies. The axon reconstructions indicate that the activity of both types of neurons can influence multiple basal ganglia targets, including the GP itself.

Intracellular study of rat globus pallidus neurons : membrane properties and responses to neostriatal, subthalamic and nigral stimulation

Physiological properties of globus pallidus (GP) neurons were studied intracellularly in anesthetized rats. More than 70% of the neurons exhibited continuous repetitive firing of 2-40 Hz, while others exhibited periodic burst firing or no firing. The repetitively firing neurons exhibited the following properties: spike accommodation; spike frequency adaptation; continuous firing with a frequency of about 100 Hz generated by intracellular current injections; fast anomalous rectification; ramp-shaped depolarization upon injection of depolarizing current; and post-active hyperpolarization. The burst firing neurons evoked a large depolarization with multiple spikes in response to depolarizing current, and a similar response was observed after the termination of hyperpolarizing current. The few neurons which did not fire spontaneous spikes exhibited strong spike accommodation when they were stimulated by current injections. The continuously firing neurons were antidromically activated by stimulation of the neostriatum (Str) (23 of 68), the subthalamic nucleus (STh) (55 of 75), and the substantia nigra (SN) (25 of 46). The antidromic latencies of the 3 stimulus sites were very similar (about 1 ms). None of the burst firing neurons were antidromically activated. Three non-firing neurons evoked antidromic responses only after Str stimulation. Only repetitively firing neurons evoked postsynaptic responses following stimulation of the Str and the STh. Stimulation of the Str evoked initial small EPSPs with latencies of 2-4 ms and strong, short duration IPSPs with latencies of 2-12 ms. Stimulation of the STh evoked short latency EPSPs overlapped with IPSPs. Frequently, these responses induced by Str and STh stimulation were followed by other EPSPs lasting 50-100 ms. These results indicated: (1) that the GP contains at least 3 electrophysiologically different types of neurons; (2) that GP projections to the Str, the STh, and the SN are of short latency pathways; (3) that Str stimulation evokes short latency EPSPs followed by IPSPs and late EPSPs in GP neurons; and (4) that STh stimulation evokes short latency EPSPs overlapped with short latency IPSPs and late EPSPs in GP neurons.

Intracellular study of rat substantia nigra pars reticulata neurons in an in vitro slice preparation: electrical membrane properties and response characteristics to subthalamic stimulation

The electrical membrane properties of substantia nigra pars reticulata (SNR) neurons and their postsynaptic responses to stimulation of the subthalamic nucleus (STH) were studied in an in vitro slice preparation. SNR neurons were divided into two types based on their electrical membrane properties. Type-I neurons possessed (1) spontaneous repetitive firings, (2) short-duration action potentials, (3) less prominent spike accommodations, and (4) a strong delayed rectification during membrane depolarization. Type-II neurons had (1) no spontaneous firings, (2) long-duration action potentials, (3) a prominent spike accommodation, (4) a relatively large post-active hyperpolarization, and (5) a less prominent delayed rectification. These membrane properties were very similar to those observed in substantia nigra pars compacta (SNC) neurons in slice preparations. Features common to both types of neurons include that (1) the input resistance was similar, (2) they showed an anomalous rectification during strong hyperpolarizations, and (3) they were capable of generating Ca potentials. Intracellular responses of both types of SNR neurons to STH stimulation consisted of initial short-duration monosynaptic excitatory postsynaptic potentials (EPSPs) and a short-duration inhibitory postsynaptic potential (IPSP) followed by a long-duration depolarization. The IPSP was markedly suppressed by application of bicuculline methiodide and the polarity was reversed by intracellular injection of Cl-. In the preparations obtained from internal capsule-transected rats, STH-induced EPSPs had much longer durations than those observed in the normal preparations, while the amplitude of IPSPs and succeeding small-amplitude long-duration depolarizations was small. The results indicated that SNR contains two electrophysiologically different types of neurons, and that both types of neurons receive monosynaptic EPSPs from STH and IPSPs from areas rostral to STH.

GABAergic circuits of the striatum.

Publisher Summary The neostriatum contains a large number of neurons and terminals that contain y-aminobutyric acid (GABA), an inhibitory transmitter. GABAergic inhibition has been thought to play a major role in regulating the neuronal activities of the striatum. This chapter discusses the studies on the GABAergic circuits and their functions in the striatum. First, it describes the anatomical organizations and then discusses the functional implications of GABAergic elements. The neostriatum contains many GABAergic neurons and GABAergic synaptic terminals, which are considered to be major elements in regulating the neuronal activities of the striatum. Anatomical and physiological studies indicate that GABAergic interneurons play a major role in the regulation of the firing activity of the spiny projection neurons through their feedforward connection. It is also suggested by anatomical studies that cholinergic and dopaminergic inputs affect the activity of GABAergic interneurons.

Response characteristics of subthalamic neurons to the stimulation of the sensorimotor cortex in the rat

Responses of the subthalamic nucleus (STH) neurons to the stimulation of the sensorimotor cortex (Cx) were recorded in intact rats and in those which received lesions in the pallidum, the neostriatum, the brainstem, or the corpus callosum. Most of the STH units (78%) exhibited two excitatory peaks which were interrupted by a brief period of inhibition. Some of units which were located in the peripheral part of the STH tended to lack the brief inhibitory component and exhibited a long period of excitation. These excitations were followed by a long-lasting inhibitory period. Intracellular recording indicated that these responses were EPSPs interrupted by a short IPSP and a long period of disfacilitation of Cx inputs. A quinolinic acid lesion of the neostriatum and a knife cut of the brainstem failed to alter these responses, while an ibotenic acid lesion of the globus pallidus abolished the short inhibition seen in the midst on the excitation. Stimulation of contralateral Cx also evoked excitatory responses in the STH. The responses were completely eliminated by a parasagittal knife cut of the rostral part of the corpus callosum.

An HRP study of the afferent connections to rat medial hypothalamic region.

Afferent connections to the medial hypothalamic region in the rat were studied using horseradish peroxidase (HRP). HRP was injected iontophoretically by a parapharyngeal approach. After HRP injections into the ventromedial hypothalamic nucleus, labeled cells were found mainly in the medial and basolateral amygdaloid nuclei, subiculum, peripeduncular nucleus and the parabrachial area. Labeled cells following HRP injections into the dorsomedial hypothalamic nucleus were found mainly in the lateral septal nucleus, nucleus accumbens, bed nucleus of the stria terminalis, pontine central gray and the parabrachial area. HRP-labeled cells following the medial preoptic area injections were found mainly in the infralimbic cortex, lateral and medial septal nuclei, nucleus accumbens, diagonal band, bed nucleus of the stria terminalis, medial amygdaloid nucleus, subiculum, peripeduncular nucleus and the parabrachial area. The intrahypothalamic connections were also discussed.

Electrical membrane properties of rat substantia nigra compacta neurons in an in vitro slice preparation

The electrical membrane properties of rat substantia nigra pars compacta (SNC) neurons were studied in an in vitro slice preparation. Some of the recorded neurons were intracellularly labeled with HRP and were found to have morphological characteristics resembling the presumed SNC dopaminergic neurons, as reported by others. The input resistance of SNC neurons at resting membrane potential ranged between 70 and 250 M omega. The membrane resistance showed strong anomalous rectification when the membrane was hyperpolarized by current injection. The anomalous rectification was decreased by the addition of tetraethylammonium bromide (TEA) to the bathing Ringer solution. Injection of depolarizing current or termination of hyperpolarizing current induced slow depolarizing potentials. Their amplitude was dependent on the membrane potential and the current intensity. In neurons treated with tetrodotoxin (TTX) and TEA, slow action potentials were triggered from the slow depolarizing potentials. Both the slow depolarizing potential and slow action potential were TTX resistant and abolished by superfusion of Ca2+-free medium. Long duration hyperpolarizations were observed following the injection of depolarizing current pulses. The hyperpolarization was abolished by the superfusion of Ca2+-free medium or decreased by addition of TEA to the Ringer solution indicating an involvement of a Ca2+-dependent K+-conductance in generation of the hyperpolarization. The long duration hyperpolarization was also observed following action potentials. The spike after hyperpolarization consisted of an initial short duration fast component and a long lasting component. The amplitude of both components seems to be reduced but not abolished by TEA (up to 10 mM). When hyperpolarizing current pulses were applied to neurons that were held either continuously depolarized or were superfused with Ca2+-free medium, the pattern of the membrane potential after the offset of current pulses consisted of an initial fast and a later slow ramp-shaped phase. The latter was associated with a membrane conductance increase and interpreted to be due to an early K+ current. This early K+ current was relatively resistant to TEA. Injections of strong depolarizing currents triggered action potentials with multiple inflections on their rising phase. The amplitudes of action potentials changed abruptly during current application. These data indicate that SNC neurons have multiple generation sites for action potential.