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H M Sinnamon

Publications and source records attributed to H M Sinnamon.

At least 37 records · Page 2Linked to original sources
PubMed1990

Midbrain areas required for locomotion initiated by electrical stimulation of the lateral hypothalamus in the anesthetized rat.

Locomotor stepping in the Nembutal-anesthetized rat was elicited by electrical stimulation of either of two sites in the right or left posterolateral hypothalamus. Essential midbrain loci were identified by reversibly blocking the elicited locomotion through local injections of the anesthetic procaine (15%, 0.5 microliter). Two types of critical midbrain sites were found. At ipsilateral block sites (n = 21), procaine blocked only that locomotion elicited by ipsilateral stimulation. These sites could be along the course of a direct descending ipsilateral pathway although a possible bidirectional pathway is not to be excluded. At bilateral block sites (n = 21), procaine blocked locomotion elicited by both ipsilateral and contralateral stimulation. These sites could be involved in functions prerequisite for the initiation of locomotion or in the generation of the stepping pattern. Procaine injections in 35 sites had no effect on locomotion. Ipsilateral and bilateral block sites were intermixed and generally located in regions ventral to the midbrain central gray: chiefly the anterior ventromedial midbrain, the pontis oralis nucleus and the pedunculopontine nucleus. Negative sites were located in both the dorsal and ventral midbrain. Ipsilateral block sites were relatively prevalent in the anterior midbrain, indicating that the locomotor initiation signals are lateralized at this level. Bilateral block sites were more prevalent in the posterior levels, suggesting that the initiation signals are proximal to, or interact with, circuits that have a bilateral influence on locomotion.

Animals↗
PubMed1990

Locomotor stepping initiated by glutamate injections into the hypothalamus of the anesthetized rat.

Glutamate (50 mM, 50 nl) injected into the tuberal and posterior hypothalamus was tested for capacity to elicit locomotor stepping. Rats (n = 23) were anesthetized with Nembutal and suspended by a sling in a stereotaxic apparatus such that locomotor stepping rotated a wheel. In 61 of 275 sites tested, stepping was initiated by glutamate injections within 60 s. Positive sites were widespread and contained in the lateral hypothalamus, the perifornical area, the dorsomedial nucleus, and the zona incerta. The perifornical and lateral hypothalamic sites were most likely to have locomotor responses and the shortest latencies. These findings indicate that selective activation of hypothalamic neurons as opposed to fibers of passage can initiate locomotion.

Animals↗
PubMed1988

Lateral neglect in a head movement task: more impairment with unilateral than bilateral lesions of the superior colliculus in the rat.

Unilateral lesions of the superior colliculus produce contralateral neglect. This study determined if bilateral lesions would impair head orientation in a way expected from the summation of two contralateral neglects. Rats were trained to make various head movements to get water at a 3 x 3 array of holes, each with a recessed water-baited dipper. On each of 20 trials in a session, a water-deprived subject approached and sampled the array by orienting its head and inserting its snout in the holes in a self-determined sequence. The measures recorded for each position and for each trial were: the order in which a baited position was sampled (selection order), the number of times it was not sampled (misses), and the number of times it was sampled when dry (perseverations). Radio-frequency lesions were made and testing was resumed after 3 days. Large unilateral lesions of the superior colliculus produced a neglect of contralateral positions and increased perseverations to ipsilateral positions. Center positions were also neglected but to a lesser extent. Bilateral lesions of the superior colliculus produced only a moderate increase in lateral misses and no increase in lateral perseverations. Bilateral lesions did produce a neglect of upper positions on both sides. The results indicate that a major contributor to contralateral neglect produced by a unilateral lesion is an antagonistic process that promotes orientation to the side ipsilateral to the lesion.

Animals↗
PubMed1988

Unilateral and bilateral lesions of the anteromedial cortex increase perseverative head movements of the rat.

Lesions of the anteromedial cortex were made in rats trained to orient their heads to 9 positions located laterally and centrally in upper, middle and lower regions of space. The water-deprived subjects were tested in sessions of 20 trials in each of which all positions were baited once with a small amount of water. Training continued until no position was consistently missed and the number of returns to positions already selected on that trial (perseverative responses) was low and stable. In Expt. 1, rats with unilateral anteromedial lesions tested with 3 days recovery did not miss any position or significantly change the order in which correct positions were selected but they made more perseverative responses to all positions. Bilateral anteromedial lesions moderately increased misses but markedly increased perseverations. Visual cortex lesions comparable in size produced no changes. In Expt. 2, unilateral anteromedial lesions tested with 7 days' recovery did not increase misses and only slightly increased perseverations. In Expt. 3, unilateral anteromedial lesions tested within 1 day increased perseverations more than lesions tested with 6 days' recovery. Neither group increased misses or changed selection order. The perseverations appeared on a trial after 6 of the 9 correct selections and were directed to both recently and remotely selected positions. Lesions of the anteromedial cortex appear to produce a deficit in the suppressive control of head orienting.

Animals↗
PubMed1987

Locomotion elicited by lateral hypothalamic stimulation in the anesthetized rat does not require the dorsal midbrain.

Locomotor stepping elicited by lateral hypothalamic stimulation in the anesthetized rat is blocked by lesions in the anterior ventromedial midbrain. This study determined in acute experiments whether the dorsal midbrain regions implicated in locomotion were also part of the necessary pathway. Rats were anesthetized with Nembutal and held in a stereotaxic apparatus so that stepping responses rotated a wheel. Stepping was elicited by stimulation of the lateral hypothalamus (up to 100 microA, 0.5 ms cathodal pulses, 50 Hz, 10-s train length). Nine rats received unilateral lesions ipsilateral to the locomotor electrode and 3 rats received bilateral lesions. None of the dorsal midbrain lesions reduced locomotion elicited by ipsilateral lateral hypothalamic stimulation. Therefore the following regions are unnecessary for this type of locomotion: the dorsal and lateral central gray, the tegmentum lateral to the central gray, and in particular the area cuneiformis and the dorsal aspect of the pedunculopontine region. The neural systems required for lateral hypothalamic locomotion are located ventral to the superior cerebellar peduncle.

Animals↗
PubMed1987

Glutamate and picrotoxin injections into the preoptic basal forebrain initiate locomotion in the anesthetized rat.

This study determined the locomotor effects of glutamate and picrotoxin injections and electrical stimulation in the preoptic basal forebrain. Male rats, anesthetized with Nembutal, were held in a stereotaxic apparatus such that stepping rotated a wheel. Cathodal stimulation (0.5-ms pulses, 50-Hz frequency, 10-s train, less than 100 microA) was applied through a 30-gauge stainless-steel, insulated cannula to find locomotor sites. Glutamate (20 mM or 2 M) or picrotoxin (100 or 200 ng) were injected in volumes of 0.2 or 0.1 microliter of saline at a rate of 1 microliter/5 min. Electrical stimulation elicited locomotion (principally hindlimbs) in 32 sites which included the lateral and medial preoptic areas and the bed nucleus of the stria terminalis (BST). Stimulation in 23 sites, most in the BST and septal area, failed to produce locomotion. Stepping was elicited by glutamate and electrical stimulation in 15 sites. Glutamate was ineffective at 21 sites, at 6 of these sites electrical stimulation was effective. Longer bouts of locomotion were produced by 20 nM glutamate. Picrotoxin produced more intense and prolonged locomotion than glutamate. It was effective in 15 sites, at 12 of which electrical stimulation was also effective. At some ventral sites, picrotoxin-elicited stepping was continuous, at others it appeared in bursts of 5-20 s duration. At dorsal sites, the locomotor bursts were punctuated by episodes of pelvic flexion. Picrotoxin was ineffective at 12 sites, 7 of which were effective with electrical stimulation. These results indicate that activity of neurons in the preoptic basal forebrain can initiate locomotion.

Anesthesia↗
PubMed1987

Midbrain stimulation in the anesthetized rat: direct locomotor effects and modulation of locomotion produced by hypothalamic stimulation.

The midbrain contains circuits that modulate locomotion. To delineate some of the involved regions, low-level stimulation (25 microA, 10 s train of 0.5 ms pulses at 50 Hz) was applied to the midbrain during locomotor stepping. Stepping was elicited in the anesthetized (pentobarbital, 40 mg/kg) rat by stimulating the hypothalamus with 0.5 ms pulses at 40 Hz at various currents. The rat was held in a stereotaxic apparatus such that locomotor stepping movements turned a wheel. Facilitation of locomotion was produced by stimulation in the anterior ventromedial midbrain and in the posterodorsal midbrain. When presented alone, such stimulation produced locomotion. Inhibition of locomotion was produced by stimulation of the superior colliculus (ventral layers) and the ventromedial midbrain. Additional inhibitory sites were found in the central gray and the lateral tegmentum. Inhibitory collicular stimulation, when presented alone, was characterized by the absence of any hindlimb response. Inhibitory ventromedial stimulation, when presented alone, frequently produced poststimulation locomotion and when presented with hypothalamic stimulation was characterized by postinhibitory increases in locomotion. These results indicate that: (1) the locomotor effects of stimulation in midbrain and hypothalamic sites can summate: (2) multiple locomotor suppressive systems are present in the midbrain and among them are a collicular system and a ventromedial system.

Animals↗
PubMed1986

Tactile stimulation inhibits locomotion produced by stimulation of the lateral hypothalamus in the anesthetized rat.

Rats were anesthetized with Nembutal and suspended in a stereotaxic apparatus so that their limbs contacted the outer surface of a 30-cm diameter wheel. Stimulation in the lateral hypothalamus (0.5 msec cathodal pulses at 50 Hz, up to 150 microA) produced locomotor stepping which turned the wheel. During continuous locomotion maintained by electrical stimulation, tactile stimulation was applied manually for 5-sec periods to various body regions in six subjects. Profound inhibition of locomotor stepping was produced in all subjects by mild pressure applied to the nose or the vibrissae pad. Vibrissae pad stimulation either ipsilateral or contralateral to the stimulation site was effective. Stroking of the vibrissae inhibited locomotion in only 2 of 6 subjects and in these cases the effective stimulation was contralateral to the brain stimulation site. With pressure applied to more caudal body regions, including the dorsum, the abdomen and the tail, the inhibition was less pronounced and less consistent than that produced by pressure on the snout region. The findings indicate that the tactile system provides an important modulation of locomotion and that the anesthetized locomoting rat offers a useful preparation for its further study.

Anesthesia, General↗
PubMed1984

Head movements elicited by electrical stimulation of the anteromedial cortex of the rat.

Electrical stimulation, 5-sec trains, 0.5 msec rectangular pulses, 20 Hz pulse frequency, was applied to the anteromedial cortex of awake rats (N = 28) to determine if head orienting behavior could be elicited. Following recovery from surgery in which up to six monopolar electrodes were implanted, the rats were adapted to and tested on a small platform surrounded by water. Elicited behavior patterns reliable at 150 microA or less in Experiment 1 (66 sites) and at 100 microA or less in Experiment 2 (32 sites) were analyzed. The most common response was a single head turn in a direction contralateral to the side of stimulation. Positive sites occurred throughout the anterior cingulate and the medial precentral regions. Coordinated forelimb movements were associated with contralateral head movements at dorsal anterior cingulate sites. Ipsilateral head turns were elicited at sites in the most rostral and ventral parts of the anteromedial cortex, including the prelimbic area. Lateral scanning sites were widespread but tended to concentrate at the mergence of the contralateral and ipsilateral movement fields. Vertical movements were often elicited with ipsilateral movements; dorsal sites supported downward head movements and ventral sites supported upward head movements. Sites supporting forward head movements were concentrated in the anterior cingulate region caudal to the genu of the corpus callosum. Neck extension usually appeared in conjunction with lateral head movements and frequently with forelimb movements.

Animals↗
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↗
PubMed1984

Forelimb and hindlimb stepping by the anesthetized rat elicited by electrical stimulation of the pons and medulla.

This study determined the lower brainstem sites at which electrical stimulation elicits stepping movements of the forelimbs and hindlimbs. Rats (N = 45), anesthetized with nembutal, were fixed in a stereotaxic apparatus so that their limbs contacted a moving treadmill belt. Electrical stimulation (100 microA, 10-sec trains, 0.5-msec cathodal pulses, 50-Hz pulse frequency) was applied every 200 micron through 173 movable electrodes. Well coordinated quadrupedal stepping was elicited by stimulation at dorsal posterior mesencephalic sites including the inferior collicular commissure, the central gray, the nucleus cuneiformis and lateral aspects of the pedunculopontine tegmental nucleus. Caudal and ventral to this general region, sites supporting quadrupedal stepping appeared mainly in or near the spinal trigeminal nucleus. Stepping with only the forelimb and hindlimb contralateral to the stimulation site was associated with the corticospinal tract, the lateral pontis oralis, the lateral pontis caudalis and the ventral reticular nucleus of the medulla. Bilateral forelimb stepping was associated with the trigeminal system and the gigantocellular reticular nucleus. At the level of the rostral medulla, systems involved in bilateral forelimb stepping and contralateral hindlimb stepping appear to be located medially. Systems concerned with bilateral hindlimb stepping appear to be located laterally.

Animals↗
PubMed1984

Locomotor stepping elicited by electrical stimulation of the lateral hypothalamus requires an ipsilateral descending pathway.

The effects of unilateral midbrain lesions on stepping produced by ipsilateral medial forebrain bundle (mfb) stimulation was determined in acute experiments. Rats were anesthetized with nembutal, mounted in a stereotaxic apparatus and suspended over a wheel which rotated when the rat stepped. Stimulation consisted of 10-sec trains of 50 Hz cathodal pulses (0.5 msec) at currents up to 200 microA delivered through monopolar electrodes. The stimulation sites were in the mfb at the level of the subthalamic nucleus. One side of the midbrain was randomly selected to receive a radio-frequency lesion. Certain midbrain lesions (N = 11) abolished or severely reduced stepping elicited from ipsilateral mfb stimulation but produced no effect on contralaterally elicited stepping. Areas of common damage in these lesions included the medial half of the medial lemniscus and the ventral tegmental area (VTA). Lesions that were without effect (N = 18) generally spared the dorsal VTA but damaged extensively either the ventrolateral VTA, medial lemniscus, substantia nigra, red nucleus, or central gray. A supplemental experiment further implicated a critical descending system since neither unilateral nor bilateral mfb lesions blocked stepping elicited by VTA stimulation. Together these results suggest that a descending path through the ipsilateral dorsal VTA mediates stepping elicited by mfb stimulation in the anesthetized rat.

Animals↗
PubMed1983

Activity of basal forebrain neurons in the rat during motivated behaviors.

The activity of single neurons in the basal forebrain was recorded in the freely-moving rat with moveable fine-wire electrodes. Neural activity was observed while the water-deprived male rat was exposed to three different types of motivating stimuli that elicit locomotion in a running wheel: an estrous female rat; a drinking tube containing water; and grasping and lifting by the experimenter. The neural activity was also observed when the subject was presented with standardized sensory tests and during single pulse stimulation of other brain structures. A majority of the 76 neurons recorded in the forebrain changed their firing rate during orienting and/or locomotion in general (23 neurons) or during behavior related to only one of the specific motivational contexts: the conspecific female (4 neurons); water (7 neurons); or grasp by the experimenter (8 neurons). Whereas the neurons related to orienting and/or locomotion in general were scattered through various brain structures, those neurons related to specific motivational contexts were concentrated in specific areas: the sexually dimorphic nucleus of the medial preoptic area (conspecific female); lateral septum (water); and lateral preoptic area (water and grasp). The present results, although based on relatively few neurons, are consonant with results of research using other techniques. This indicates that analyses at the level of the single neuron promise to be useful for understanding the role of the basal forebrain in motivational systems.

Animals↗
PubMed1983

Forward locomotion elicited by electrical stimulation in the diencephalon and mesencephalon of the awake rat.

Stimulation electrodes were implanted in 63 rats at a total of 208 sites in the diencephalon and midbrain. The sites were tested for elicited forward locomotion, i.e., alternate stepping of the forelimbs and/or hindlimbs, while the rats stood on a treadmill belt in a 27 X 9 X 24-cm chamber. Current levels of 50-300 microA and pulse frequencies of 50, 100 and 154 Hz were presented as single 5-sec trains and as 20 repetitive trains of 1-sec duration with a 3-sec intertrain interval. Locomotion was elicited with low current (50 or 100 microA) single trains at 28% of the sites. Of the regions sufficiently well sampled to warrent comparisons, two showed high densities of locomotion-positive sites with single low current trains. They were the medial hypothalamus (the dorsomedial and the posterior nuclei) and the ventral tegmental area. The medial forebrain bundle and the zona incerta were generally positive but many sites in these regions required repetitive trains. Among the regions with few locomotion-positive sites were the subthalamic nucleus, the fields of Forel and the habenular complex. In the dorsal midbrain, in and around the central gray, low current single trains elicited leaping. The results are discussed in terms of the existence of a delimited subthalamic locomotor region and a ventral midbrain locomotor system independent of a dorsal midbrain system.

Animals↗
PubMed1982

Unilateral lesions of the anteromedial cortex in the rat impair approach to contralateral visual cues.

This experiment determined the effects of large unilateral lesions of the anteromedial cortex (AMC) on visually guided performance of rats in a cross maze. Deficits were found in the approach to only visual cues that were located in the arm contralateral to the lesion. The deficit appeared in three testing conditions: when the cue was continuously visible throughout the trial; when it was visible only at the choice point; and when it was seen only at the start of the trial but not at the choice point. The failure to approach a contralateral cue was not due to a simple ipsilateral turning bias; rats with lesions could approach cues in the anterior arm as efficiently as controls. The deficit was most apparent on the initial sessions and recovery occurred for all conditions. The findings indicate that the AMC participates in the visual guidance of approach behavior.

Animals↗