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At least 1,495 records · Page 83Linked to original sources
PubMed1989

Ventral tegmental area-mediated inhibition of neurons of the nucleus accumbens receiving input from the parafascicular nucleus of the thalamus is mediated by dopamine D1 receptors.

Microiontophoretic experiments were performed to determine whether inhibition mediated by the ventral tegmental area neurons of the nucleus accumbens, receiving input from the parafascicular nucleus of thalamus, is mediated by dopamine D1 or D2 receptors, using rats anesthetized with chloral hydrate. Spikes, elicited by test stimuli applied to the parafascicular nucleus were inhibited by conditioning stimuli to the ventral tegmental area, given 30 msec before the test stimuli. This inhibition was antagonized by iontophoretic application of SCH 23390, a D1 antagonist, in 18 of 25 neurons of the nucleus accumbens, but in only 3 of 22 neurons of the nucleus accumbens during application of domperidone, a D2 antagonist. The reduction by conditioning stimulation of the ventral tegmental area of the mean number of spikes of the 25 neurons upon stimulation of the parafascicular nucleus, was abolished by SCH 23390. In contrast, domperidone did not affect the mean number of spikes of the 22 neurons upon stimulation of the parafascicular nucleus in the presence of conditioning stimulation of the ventral tegmental area. In addition, spikes elicited by stimulation of the parafascicular nucleus were dose-dependently inhibited by iontophoretic application of both SKF 38393, a D1 agonist and bromocriptine, a D2 agonist. These results suggest that inhibition by dopamine, derived from the ventral tegmental area of neurons of the nucleus accumbens, receiving input from the parafascicular nucleus, is mediated mainly by dopamine D1 receptors, although both D1 and D2 receptors are expressed on the same neuron of the nucleus accumbens, which is also inhibited by exogenously applied D2 agonists.

Animals↗
PubMed1977

Deficits in behavioral responding to regulatory challenges after lesions of ventrobasal thalamus in rats.

Electrolytic lesions of the posteromedial portion of the ventrobasal thalamic complex of rats impaired the feeding response to glucoprivation produced by systemic injection of 2-deoxy-D-glucose and the sodium appetite induced by injections of desoxycorticosterone, and produced abnormally low water intake in the absence of food. Drinking elicited by intracellular dehydration was not consistently affected. Lesions of the ventral anterior nucleus of the thalamus only impaired the feeding response to glucoprivation. The behavioral changes observed after posterior ventrobasal thalamic damage may be related to a disruption of gustatory, visceral, and somatosensory thalamic connections with the corpus striatum and neocortex.

Animals↗
PubMed1995

Destruction of neurons in the VPM thalamus prevents rabbit heart rate conditioning.

The present study examined the role of the ventral posterior medial nucleus of the thalamus (VPM) in classical heart rate (HR) conditioning using an acoustic conditioned stimulus (CS) and a corneal air puff unconditioned stimulus (US). Previous research suggests that VPM neurons are activated during the presentation of a corneal air puff US. Rabbits were given ibotenic acid lesions in the VPM and subjected to one Pavlovian HR conditioning session. The results of the present study demonstrate that destruction of cell bodies in the VPM reduces HR conditioning to the level of a pseudoconditioning control without affecting HR baseline, or orienting responses to the CS. Lesions of the VPM also significantly augment the tachycardiac unconditioned response, suggesting that VPM lesions alter the somatosensory processing of the US.

Animals↗
PubMed1986

Diagnosis of germinal neoplasm in the thalamus and basal ganglia.

Germinal neoplasms originating in the thalamus and basal ganglia were histologically verified by stereotactic biopsies in five cases and by other methods in three cases. Immunoperoxidase staining was performed on the tumors using antibodies against human chorionic gonadotropin and placental alkaline phosphatase. The presence of human chorionic gonadotropin was demonstrated in one germinoma and two mixed tumors, but not in three germinomas. Placental alkaline phosphatase was demonstrated to be present in four germinomas and one mixed tumor. Stereotactic biopsy specimens can be studied immunohistochemically, and the placental isoenzyme of alkaline phosphatase appears to be a new tumor marker for germinoma.

Adolescent↗
PubMed1986

Autonomic changes elicited by chemical stimulation of mediodorsal nucleus of the thalamus.

Chronic indwelling cannulas were implanted in the mediodorsal nucleus (MD) of the thalamus in New Zealand albino rabbits. Heart rate (HR), blood pressure (BP), respiration and electromyographic activity (EMG) were recorded subsequent to the injection of saline, l-glutamate, or carbachol through the previously implanted cannulas. Dose related decreases in HR and increases in BP were obtained after administration of both l-glutamate and carbachol at doses in the micromolar range. Control injections through cannulas chronically implanted in the overlying hippocampus or adjacent ventricles resulted in dramatic HR and BP baseline changes in a parasympathetic direction (viz HR and BP decreases) suggesting that the effects obtained with MD placements were due to chemical stimulation of MD. Responses elicited from MD in the present experiment were similar, but not identical, to those produced by electrical stimulation of MD, suggesting that the latter effects were not due to stimulation of fibers of passage.

Animals↗
PubMed1987

The development of neurons in the cat perigeniculate nucleus and reticular nucleus of the thalamus.

The postnatal development of soma size and cytochrome oxidase activity was examined in the perigeniculate nucleus (PGN) and reticular nucleus of the thalamus (RNT). Neurons in the PGN and RNT exhibited a rapid increase in soma size between 2 and 4 weeks of age. During this period of cell growth there is an increase in the intensity of cytochrome oxidase staining within the cell body. Cells in both the PGN and RNT decrease in size after 4 weeks of age, and become very fusiform in shape. During this postnatal period, there is also a shift in cytochrome oxidase staining from the cell body to the dendrites.

Age Factors↗
PubMed1985

Effects of lesions of prefrontal cortex and dorsomedial thalamus on delayed go/no-go alternation in rats.

The effect of prefrontal cortex (PFC) and/or dorsomedial thalamus (DMT) lesions on a delayed go/no-go alternation task was studied in the rat. The lesion gave rise to the impairment of smooth alternation of one response to another, resulting in the generation of some successive repetitions of either response. However, either type of response was generated in virtually equal frequencies during pre- and post-surgery sessions. These results suggest that the DMT and PFC are involved in the memory and response control process for generating the alternation response, and they do not mediate either one type of response. Furthermore, DMT or DMT/PFC lesions induced a larger behavioral impairment than PFC lesions indicating that the DMT plays a major role in generating the alternation behavior based on the memory for the previous response.

Animals↗
PubMed1986

Multiple unit activity of prefrontal cortex and dorsomedial thalamus during delayed go/no-go alternation in the rat.

While the rat was performing a go/no-go alternation task with a 10-s delay period, neuronal activity was recorded from electrodes chronically implanted in the prefrontal cortex (PFC) and the dorsomedial thalamus (DMT). In both PFC and DMT, neuronal activity during the delay period prior to a 'go' response was different from that prior to a 'no-go' response. The results suggest that during the delay period the PFC and DMT maintain a memory for the generation of the response. Furthermore, it was found that DMT neuronal activity in the delay period was different between correct and error trials. Therefore, the DMT may be primarily important in performing the alternation behavior.

Animals↗
PubMed1985

Synaptic organization of the cerebello-thalamo-cerebral pathway in the cat. II. Input-output organization of single thalamocortical neurons in the ventrolateral thalamus.

Input-output neural organization of single thalamocortical (T-C) neurons in the ventrolateral nucleus (VL) of the thalamus was investigated using an intracellular recording technique in the anesthetized cat. Stimulation of the dentate (DN) and the interpositus (IN) nuclei produced monosynaptic unitary EPSPs of large amplitude in T-C neurons projecting to the motor cortex or area 6 over the entire mediolateral region of VL. The thalamic projections from DN and IN are very wide and there is a considerable overlap between the dentate and the interpositus projection areas in VL. And in this overlapping area, a considerable number of T-C neurons (50%) receive inputs from both DN and IN. More than 40% of T-C neurons were antidromically activated from widely separated electrodes in the motor cortex, indicating that the cortical arbolization of single T-C neurons is very wide and the number of these neurons with widely divergent projections is considerably large.

Animals↗
PubMed1996

Characterization of the metabotropic glutamate receptors (mGluRs) which modulate GABA-mediated inhibition in the ventrobasal thalamus.

The ventrobasal thalamus (VB) relays and processes somatosensory information ascending to the cerebral cortex. Several types of mGluR are known to be present in VB, and we have previously shown that Group II and Group III mGluR agonists can reduce inhibitory synaptic transmission by acting at presynaptic receptors on GABAergic terminals in this structure. We have tested the action of several antagonists against the disinhibitory action of the Group II agonist CCG-I [(2S,3S,4S)-alpha-(carboxycyclopropyl)-glycine] and the Group III agonist L-AP4 [L-2-amino-4-phosphonobutyrate] in the VB of anaesthetized rats using extracellular single-neurone recording techniques and iontophoretic applications of mGluR antagonists and agonists. The antagonists MAP4 [alpha-methyl-L-AP4] and MPPG [(+/-)-alpha-methyl-4-phosphonophenylglycine] reduced the disinhibitory actions of L-AP4 whilst having little effect on the disinhibitory action of CCG-I. In contrast, MCCG [alpha-methyl-CCG-I] and MCPG [(+)-alpha-methyl-4-carboxyphenylglycine] antagonized CCG-I, whilst having less effect against L-AP4 responses. These results support the hypothesis that GABAergic inhibitory transmission in VB can be modulated by at least two types of mGluR, belonging to Group II and Group III. Furthermore, the novel antagonists appear to be useful tools for the future study of the physiological role of these receptors in thalamic sensory processing.

Action Potentials↗
PubMed1980

Connections of the mediodorsal nucleus of the thalamus in the tree shrew. II. Efferent connections.

[35S]Methionine was injected into the mediodorsal nucleus of the thalamus of 5 adult tree shrews (Tupaia belangeri) and into the medioventral thalamic nucleus in another tree shrew. Three animals survived for 44 h and three others for two weeks (including the animal with the injection in the medioventral nucleus). Contact autoradiograms were made on an X-ray film. The mediodorsal thalamic nucleus was found to project ipsilaterally to all surfaces of the frontal pole of the cerebral cortex. No other projections of this nucleus have been established. Also in this species, the medioventral nucleus projects to the first layer of the entire neocortex ipsilaterally and to the mesencephalic tegmentum.

Animals↗
PubMed1985

Bifurcating axons of retinal ganglion cells terminate in the hypothalamic suprachiasmatic nucleus and the intergeniculate leaflet of the thalamus.

At least some retinal axons afferent to the hypothalamic suprachiasmatic nucleus (SCN; a circadian oscillator) bifurcate in the optic chiasm (O.E. Millhouse, Brain Res., 137 (1977) 351-355). The termination site(s) of the axonal branch that continues in the optic tract is unknown. Injection of the fluorescent tracer, True Blue, into the SCN and the fluorescent dye, Nuclear Yellow, into the lateral geniculate complex resulted in the labeling of individual retinal ganglion cells with both tracers. However, only Nuclear Yellow injections which included the intergeniculate leaflet (IGL) resulted in double-labeled ganglion cells in the retinae. These results indicate that individual retinal ganglion cells innervate both the hypothalamic SCN and the IGL of the thalamus by means of divergent axonal collaterals. Moreover, neurons of the IGL are afferent to the SCN, thereby forming a complex circuit within which photic information from the same retinal ganglion cell may influence the SCN both directly and after thalamic processing.

Animals↗
PubMed1985

Electrophysiological properties of lemniscal afferents in rat after kainic acid lesions in the ventrobasal thalamus.

Kainic acid (KA) has been largely used as a neurotoxin, and its axon-sparing effect being repeatedly emphasized, on the basis of anatomical and biochemical data. The present study examines this 'axon-sparing' effect from an electrophysiological point of view and demonstrates that lemniscal fibers retain the capacity to convey somesthetic information 5-60 days after an injection of KA in the ventrobasal complex of the thalamus depriving these afferent fibers of their target cells.

Afferent Pathways↗
PubMed1985

Projections of the reticular complex of the thalamus onto physiologically characterized regions of the medial geniculate body.

Afferents from the reticular complex of the thalamus (RE) to the subdivisions of the medial geniculate body (MGB) in the cat were studied by retrograde axonal transport of horseradish peroxidase injected in sites where single unit responses to tones had been characterized. All MGB subdivisions studied received afferents from the same region of RE corresponding to its ventral posterior third, characterized by large neurons. No obvious differences were seen in the localization of labelled neurons within RE according to which MGB subdivision was injected, except that pars lateralis afferents seemed to originate from somewhat more limited portions of RE.

Animals↗
PubMed1985

Metabolic and structural correlates of the vibrissae representation in the thalamus of the adult rat.

Cytochrome oxidase (CO) histochemistry was used to examine patterns of metabolic activity in the ventral posteromedial nucleus of the adult rat thalamus. In sections cut in an oblique horizontal plane, CO staining reveals distinct patches of heightened activity arranged in a fashion remniscent of the pattern of vibrissae on the contralateral face and which corresponds to the known somatotopic organization of the nucleus. The CO-reactive zones coincide with oval cylinders of thalamic neurons that appear to be anatomically linked with corresponding barrels in the contralateral somatosensory cortex.

Afferent Pathways↗
PubMed1987

Cholinergic nucleus basalis neurons may influence the cortex via the thalamus.

The cholinergic neurons of the nucleus basalis of Meynert have been shown to provide the major cholinergic innervation of the cerebral cortex through which cholinergic transmission may modulate cortical activity. This study describes a projection from the cholinergic and non-cholinergic neurons of the nucleus basalis to the reticular nucleus of the thalamus, and a projection from the brainstem cholinergic neurons to the reticular nucleus as well as to other thalamic nuclei. The projection from the nucleus basalis to the reticular nucleus, which itself is synaptically interconnected with other thalamic nuclei, may provide an additional pathway for the modulation of cortical activity by the cholinergic basal forebrain and brainstem groups.

Animals↗
PubMed1988

Immunocytochemical study of serotoninergic and noradrenergic innervation of the ventrobasal complex of the rat thalamus.

Whereas the anatomy and function of monoaminergic afferents to the spinal cord areas involved in somesthesia and pain have been widely studied, little is known about the monoaminergic innervation of the primary somatosensory thalamic relay nucleus. The present study demonstrates immunocytochemically at both the light and the electron microscopic levels the presence of noradrenergic and serotoninergic fibers in the ventrobasal complex of the rat thalamus (VB). Despite the presence of numerous immunoreactive varicosities, synaptic differentiation was not observed at the level of apposition of membranes between monoaminergic afferents and VB neuronal profiles. The hypothesis of a non-synaptic modulation of VB neuronal activity by monoaminergic afferents is discussed.

Adrenergic Fibers↗