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PubMed1984

Forelimb and hindlimb stepping by the anesthetized rat elicited by electrical stimulation of the diencephalon and mesencephalon.

Thirty rats anesthetized with a combination of chloralose, urethane and nembutal or nembutal alone were fixed in a stereotaxic apparatus and suspended over a moving treadmill belt. Electrical stimulation (100 microA, 10-sec trains, 0.5-msec cathodal pulses, 50-Hz pulse frequency) was applied every 200-microns through 109 movable electrodes. The patterns of stepping elicited ranged from well-coordinated stepping of all four limbs to spastic stepping of only one limb. In the hypothalamus, stepping-positive sites were found in and dorsal to the medial forebrain bundle, the paraventricular, dorsomedial and posterior nuclei, and the supramammillary areas. Dorsally, effective regions extended to the medial zona incerta and the fields of Forel. In the thalamus only the parafascicular nucleus and the anterior parts of the rhomboid and reuniens nuclei were positive. Positive sites were particularly dense in the ventral tegmental area. In the dorsal midbrain positive sites were most common at caudal levels dorsal and dorsolateral to the central gray. At sites in the area of the medial raphe, stepping was elicited only at the offset of the train. The distribution of positive sites resembled that found in unanesthetized rats and indicates that pathways at which electrical stimulation elicits stepping are separated into dorsal and ventral systems at the level of the midbrain.

Animals↗
PubMed1988

Dual progesterone action in diencephalon facilitates the induction of sexual receptivity in estrogen-primed golden hamsters.

In order to identify and characterize the progesterone (P) sensitive neural system that regulates feminine sexual behavior, 28-gauge P-filled cannulae were implanted in the medial preoptic area (MPO), ventromedial hypothalamus (VMH), and central gray (CG) of ovariectomized estrogen-primed golden hamsters. Dual implants of P were placed either ipsilaterally or contralaterally in brain sites consisting of MPO-VMH, MPO-CG, or VMH-CG combinations. Tests for sexual receptivity commenced 44 hr after estrogen priming and consisted of a preimplantation test followed 4.5 to 5.5 hr later by a postimplantation test. In the preimplantation test, stimulus males were attacked when placed into the female's home cage which indicated that the subsequent display of sexual receptivity occurring in the postimplantation test was due to the action of P. Dual implants of P placed either ipsilaterally or contralaterally in MPO-VMH regions were significantly more effective in facilitating lordosis behavior than dual P implants placed in MPO-CG or VMH-CG regions. However, the duration of lordotic responsiveness produced by dual P implants in MPO and VMH regions appears to be shorter than the duration of lordosis typically observed in intact females on proestrus. Results suggest that MPO and VMH regions are sensitive to the lordosis facilitating actions of small dual implants of P.

Animals↗
PubMed1990

Latency to initiate locomotion elicited by stimulation of the diencephalon positively correlates in awake and anesthetized rats.

Locomotor stepping can be elicited by brain stimulation at various diencephalic sites under moderate levels of Nembutal. This study determined if locomotor initiation measured under anesthesia provides a valid measure of the intersite factors which determine initiation in the awake condition. We compared the latencies to initiate locomotor stepping elicited by electrical stimulation (50 microA, 0.5-msec pulses, 10 to 160 Hz) by rats tested while awake and unrestrained in a rotary runway or anesthetized and held in a stereotaxic apparatus. In the latter tests, initial anesthesia was provided by Nembutal (25 mg/kg) and 2% halothane and maintenance anesthesia was provided by 7 mg/kg as needed and local injections of lidocaine. For 30 sites in 16 rats, average locomotor initiation latency in the awake condition and the shortest latencies in the anesthetized condition were positively correlated (r = .78). Locomotion at sites with long latencies in the awake condition was frequently blocked in the anesthetized condition, but sites with short latencies were rarely blocked. The results indicate that the shortest locomotor latencies in the anesthetized condition approximate the latencies measured in the awake condition. It is concluded that the anesthetized condition can provide valid initiation measures, but sites with long latencies in the awake condition are prone to depression under anesthesia.

Anesthesia↗
PubMed1996

The prepubertal ontogeny of luteinizing hormone releasing hormone-like immunoreactivity in the diencephalon and telencephalon of the male Meishan pig brain.

Luteinizing hormone releasing hormone (LHRH) is a decapeptide that regulates reproductive function and behaviors in mammalian species. Because of the importance of proper reproductive function and efficiency in agricultural species, we have investigated the prepubertal ontogeny of LHRH-like immunoreactivity (IR) in the male Meishan pig. The Meishan is a Chinese breed known for reproductive traits including increased litter size and precocious puberty, but slow growth and obesity. Brains of animals from gestational day (g) 30, 50, 70, 90 and 110 and postnatal day (pn) 1, 10, 20 and 50 (duration of pregnancy averaged 114 days) were processed using a standard immunohistochemical technique utilizing a commercially available rabbit anti-LHRH antibody. LHRH-IR in cell bodies and fibers was detected at g30 entering the brain via the terminal nerve and in the septal region of the basal telencephalon. The number of immunoreactive cells increased at g50 and cells were localized primarily to the septum, organum vasculosum of the lamina terminalis, preoptic area and lateral hypothalamus, whereas immunoreactive fibers were present throughout the septum and hypothalamus and had reached the median eminence. The density and distribution of immunoreactive fibers increased by g70 and g90, but did not change dramatically from g90 to pn50. These results indicate that LHRH may be present in the Meishan brain earlier during development and fibers containing LHRH-IR appear to reach the median eminence earlier than previously reported for the domestic pig. These results suggest a breed difference in the ontogeny of reproductive control systems in the pig. Future studies utilizing direct comparisons between domestic and Chinese breeds will be required to investigate the apparent differences in the ontogeny of LHRH-containing systems in the pig.

Animals↗
PubMed1984

Afferents to a midbrain periaqueductal grey region involved in the 'defense reaction' in the cat as revealed by horseradish peroxidase. II. The diencephalon.

Horseradish peroxidase injections were made at the same sites, within the midcollicular portion of the midbrain periaqueductal grey region (PAG), at which electrical stimulation and microinjections of excitatory amino acids elicited defensive behaviour. The diencephalic afferents to these sites were then studied. Seventy eight percent of the labelled diencephalic neurons were found within the tuberal portion of the hypothalamus, specifically in 3 regions: (a) the ventromedial hypothalamic nucleus and adjacent perifornical area; (b) the region of the tuber cinereum, ventral and medial to the ventromedial hypothalamic nucleus; (c) the region of paraventricular and parvocellular hypothalamic nuclei. A control injection of HRP at a site, in the tegmentum immediately adjacent to the PAG, at which electrical stimulation elicited defensive behaviour, but excitatory amino acid injections did not, suggested that the extensive labelling of neurones within the tuberal region of the hypothalamus was specific to the HRP injections being made at PAG sites at which excitatory amino acid injections elicited defensive behaviour.

Aggression↗
PubMed1995

Thiamine deficiency in rats produces cognitive and memory deficits on spatial tasks that correlate with tissue loss in diencephalon, cortex and white matter.

Exploratory activity, spontaneous alternation, learning and memory abilities were examined in the pyrithiamine-induced thiamine deficiency (PTD) rat model of Wernicke-Korsakoff's syndrome and pair-fed controls (CT). PTD and CT animals showed normal retention of a single trial of a passive avoidance task acquired prior to the acute stages of thiamine deficiency. While there were no significant group differences in spontaneous activity, PTD animals with extensive damage to internal medullary lamina (IML-lesioned) of thalamus and mammillary body nuclei demonstrated a significant decrease in spontaneous alternation and were significantly impaired in learning both the initial spatial non-matching-to-position (NMTP) task and the reverse MTP task. PTD animals without IML damage (IML-spared) were only impaired on the acquisition of NMTP. Examination of response patterns suggest that the learning impairment was related to an inability to adopt or shift to the appropriate response rule. Performance of PTD IML-lesioned animals on NMTP mixed-delay sessions (4, 30, 60, 90 s) was similar to controls and PTD IML-spared, but was significantly lower on MTP delay trials. These IML-lesioned rats also had significant reductions in thickness of frontal and parietal cortex, corpus callosum and severe neuronal loss in anterior and reticular thalamic nucleic. Four PTD IML-lesioned animals that were unable to learn the NMTP task had more extensive cortical, white matter and thalamic damage than the PTD IML-lesioned animals that did learn the task. These results demonstrate that thiamine deficiency in the rat produces behavioral changes ranging from mild cognitive deficits to severe learning and memory impairments. Pathologic damage following a bout of thiamine deficiency also varies from neuronal loss in select thalamic nuclei to tissue loss in large regions of thalamus, mammillary bodies and cortex. Learning and memory deficits are closely related to the degree of cortical and diencephalic damage.

Animals↗
PubMed1979

Ascending projection from the respiratory centre to mesencephalon and diencephalon.

The brainstem reticular formation, subthalamus and thalamus were explored in a search for units modulated by the respiratory centre. Experiments were performed on cats under local anesthesia, in which respiratory center oscillation was independent of movement of the lungs and thorax. A large proportion of units firing tonically showed an increasing frequency, phase related to phrenic nerve activity. Respiration related units (RRUs) rostral to the pneumotaxic centre were concentrated in definite areas of the brainstem reticular formation, subthalamus and thalamus. Respiratory modulation disappeared rostral to a section performed at the ponto-mesencephalic junction.

Animals↗
PubMed1980

Projections to the superior colliculus from the dorsal hypothalamic area and other prosencephalic structures derived from the embryonic subthalamic longitudinal band of the diencephalon.

After injections of an aqueous solution of horseradish peroxidase (HRP) restricted to the superior colliculus of the cat, labeled neurons were found ipsilaterally in the dorsal hypothalamic area, lateral hypothalamus, zone incerta, reticular thalamic nucleus and ventral lateral geniculate. In most cases labeled neurons were observed in the same structures of the contralateral side. Some scattered neurons were observed in other hypothalamic structures and the globus pallidus. Most of these prosencephalic formations are subthalamic derivatives, thus having a common embryologic origin.

Animals↗
PubMed1984

Coerulear projections to the lateral diencephalon in the rat. An anatomical study using wheat-germ agglutinin conjugated to HRP.

The orthograde axonal transport of wheat-germ agglutinin conjugated to horseradish peroxidase has been used to define the projections of the locus coeruleus toward the lateral thalamic nuclei in the rat. These projections had been overlooked in studies using neuroanatomical tract tracing techniques, despite the demonstration of the presence of norepinephrine in the lateral thalamus using histofluorescence and immunocytochemical techniques. Results obtained confirm the presence of a rather dense network of coeruleo-thalamic afferents. Terminal fibers appear thin and contorted, which could explain previous negative results. These anatomical data underline the possible role of the locus coeruleus in the modulation of the various sensory systems at the thalamic level.

Afferent Pathways↗
PubMed1990

Glial cells in the optic chiasm arise from the suboptic necrotic centers of the diencephalon floor: morphological evidence in the chick embryo.

During early development of the optic chiasm in the chick embryo, before the arrival of the first optic axons (Stage 20), a characteristic spongy tissue appears medially between the suboptic necrotic centers (SONCs). By the time the first optic axonal fascicles arrive in the contralateral tract (Stage 23), cell death has ceased to occur in the SONCs, which become dense clusters of primitive glial cells. The clusters are steadily displaced medially during development, invading the spongy tissue and converging on the midline at Stage 27. These cell clusters appear to defect rostrocaudally the course of optic axons arriving at the chiasm.

Animals↗
PubMed1992

Tectal projection to an unusual nucleus in the diencephalon of a teleost fish, Pantodon buchholzi.

Nucleus rostrolateralis, a newly identified nucleus, has been found to date in only three species of ray-finned fishes, two of which are osteoglossomorphs. It is relatively large and well developed in only one of the osteoglossomorphs, Pantodon buchholzi, in which it receives a relatively sparse, primarily contralateral, input from the retina. The present report describes a relatively intense, bilateral projection from the optic tectum to nucleus rostrolateralis.

Animals↗
PubMed1984

Trigeminal afferents to the diencephalon in the rat.

Trigemino-diencephalic connections were studied in the rat using wheat-germ agglutinin conjugated to horseradish peroxidase as an anterogradely transported axonal tracer. Injection of the tracer into the subnucleus principalis produced two foci of dense labelling: one ventromedial: and one dorsal within the medial part of the ventrobasal complex. Other diencephalic structures containing granules of reaction product were the medial part of the medial geniculate body, the ventral area of the zona incerta and the nucleus lateralis posterior, pars lateralis. Injection of the tracer into the subnucleus interpolaris labelled the same structures, but less densely. After an injection into the subnucleus caudalis, labelling was observed in the same thalamic areas, although projections to the zona incerta or the lateralis posterior were not consistent. Additional labelling was observed in the subfascicular area of the mesodiencephalic junction, the nucleus submedius and the intralaminar nuclei centralis medialis and lateralis. In those cases of injection into the subnuclei principalis and interpolaris, all observed thalamic sites of projection were contralateral to the injection site. Following injection into the subnucleus caudalis, projections toward lateral thalamic structures were contralateral, but the nucleus submedius and the intralaminar nuclei exhibited bilateral labelling. Using high magnification (1250 X) with bright-field illumination, an analysis of the morphology of some terminal arborizations was attempted. Despite some technical limitations, the analysis indicated that in the ventrobasal complex, some terminal ramifications of axons originating from the three trigeminal subnuclei under study arborize so as to encompass a rounded area, the diameter of which could be as large as 100 microns, thereby resembling the classically described "bushy arbors". Such arborizations could not be distinguished in the axons projecting to the medial part of the medial geniculate body. In this latter nucleus, the terminals appeared to arise from a stem fiber as short side branches at approximately right angles to the parent stem axon. In the other areas where afferent terminal labelling was observed, the density of the network of the labelled fibers often complicated the analysis of morphological features. However, arborizations such as those observed in the ventrobasal complex or the medial geniculate nucleus could not be distinguished.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Interaction of the transplanted olfactory placode with the optic stalk and the diencephalon in Xenopus laevis embryos.

The effect of olfactory placode transplantation on the differentiation of the optic vesicle and stalk has been studied in Xenopus laevis embryos. Host embryos (stages 23-24) received the transplant of two olfactory placodes from same-stage donors in place of a partially or totally removed optic vesicle. All tadpoles were sacrificed at stages 47-50. The host tadpoles were subdivided in three groups according to the amount of optic vesicle removed. In the first group all of the optic vesicle was removed. At sacrifice a lobar mass of nervous tissue, continuous with and protruding from the diencephalic wall, was penetrated by the olfactory nerves from the transplanted placodes and a well-defined glomerular layer was present at the entrance zone of the olfactory nerves. The lobar protrusion contained a normal ventricular cavity, connected by a foramen to the third ventricle. The ventricle was lined by a mitotically active ependymal layer. In the second group the host embryos were deprived of two-thirds of the optic vesicle. In these animals we observed the development of a round mass of nervous tissue connected by a peduncle to the diencephalic wall. A ventricle lined by ependyma was present in the formation; however, the cavity was not continuous with the third ventricle. Olfactory nerves from the transplanted placodes penetrated the rostral portion of the nervous mass and formed a distinct glomerular layer. In the third group of embryos only one-third of the optic vesicle was removed. These animals developed irregularly shaped structures where ocular tissue and nervous tissue coexisted. The termination of the supranumerary olfactory nerves and the glomerular layer were restricted to the non-ocular nervous tissue. The interpretation of the histogenetic phenomena determining the protrusions is difficult and further studies are needed. It seems highly probable, however, that the fate of such determined structures as the optic peduncle and vesicle can be influenced by the olfactory input, supporting the hypothesis that the ectopically directed olfactory fibres interfere with the differentiation of the optic structures.

Animals↗
PubMed1991

Collateralization of periaqueductal gray neurons to forebrain or diencephalon and to the medullary nucleus raphe magnus in the rat.

Antinociceptive effects elicited from the midbrain may involve both ascending and descending projections from the periaqueductal gray and dorsal raphe nucleus. To investigate the relationship between these different efferent pathways in the rat, we performed a double-labeling study using two retrograde tracers, colloidal gold-coupled wheatgerm agglutinin-apo horseradish peroxidase and a fluorescent dye. One tracer was microinjected in the medullary nucleus raphe magnus; the second was injected into one of several regions rostral to the periaqueductal gray that have been implicated in nociceptive and antinociceptive processes. The results can be grouped into two categories. First, injections into the ventrobasal thalamus, lateral hypothalamus, amygdala, and cerebral cortex labeled neurons in the dorsal raphe nucleus but not in the periaqueductal gray. Up to 90% of these projection neurons were serotonin immunoreactive, and up to 17% were also retrogradely labeled from the nucleus raphe magnus. Second, only injections into the ventrobasal hypothalamus (which included the beta-endorphin-containing arcuate neurons) or into the medial thalamus labeled neurons in the periaqueductal gray itself. Injections into the medial thalamus, but not into the ventrobasal hypothalamus, also labeled neurons in the dorsal raphe nucleus. Up to 20% of the neurons retrogradely labeled from these regions were also retrogradely labeled from nucleus raphe magnus. The presence of large populations of rostrally projecting periaqueductal gray neurons that collateralize to the nucleus raphe magnus implies that activity in ascending projections necessarily accompanies any activation of the periaqueductal gray-nucleus raphe magnus pathway. Possibly, projections from the medial thalamus and medial hypothalamus mediate antinociceptive effects that complement descending inhibition. Finally, possible antidromic activation of these pathways must be considered when interpreting the results of electrical brain stimulation studies.

Animals↗
PubMed1983

Interhemispheric nigrostriatal projections in the rat: bifurcating nigral projections and loci of crossing in the diencephalon.

The organization of interhemispheric nigrostriatal projections in the rat was studied with (1) a double labeling technique combined with a histofluorescence method for monoamines and with (2) horseradish-peroxidase (HRP) as a tracer. Each animal received an injection of Fast Blue (FB) into the caudate nucleus (NC) of one hemisphere and an injection of Nuclear Yellow (NY) into the NC of the other hemisphere. Brains were processed according to the sucrose-potassium phosphate-glyoxylic acid (SPG) method in order to identify monoaminergic neurons. About 5% of the neurons which were labeled by either of the tracers in the substantia nigra (SN) ipsilateral to the injection site were also labeled in the contralateral SN. Most of these interhemispherically projecting SN-neurons were monoaminergic. A small number of neurons in either SN was labeled with both fluorescent tracers. This suggests that bifurcating, monoaminergic neurons in the SN project to both NC. In the second experiment, rats received a unilateral injection of HRP into NC. After a survival time of several hours the animals were perfused and the brains were processed using benzidine-dihydrochloride. Fibers crossing the hemisphere were found within the massa intermedia of the thalamus and within the inferior thalamic peduncle. The results are discussed with respect to a possible functional role of interhemispheric nigrostriatal connections.

Animals↗