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Biomedical subjects

J Tan

Publications and source records attributed to J Tan.

At least 289 records · Page 16Linked to original sources
PubMed1987

Supraspinal control of motoneurons innervating the striated muscles of the pelvic floor including urethral and anal sphincters in the cat.

The nucleus of Onuf (ON) in mammals contains motoneurons innervating the pelvic floor muscles including the external urethral and anal sphincters. Recently, direct pathways from the dorsolateral pons to the ON, probably involved in supraspinal micturition control, have been reported (Holstege et al., 1986). Since the pelvic floor muscles are involved not only in micturition but also in various other functions (e.g., coughing, vomiting, defaecation, parturition), an attempt has been made to establish whether, in the cat, there exist other direct brainstem pathways to the ON motoneurons. Our results indicate that specific projections to the ON are derived from 3 different areas: (1) the ipsilateral paraventricular hypothalamic nucleus; (2) the ipsilateral caudal pontine lateral reticular formation; and (3) the contralateral caudal nucleus retroambiguus. More diffuse projections (to all motoneuronal cell groups in the spinal cord including the ON) are derived from (1) neurons in the area of the nucleus subcoeruleus in the dorsolateral pontine reticular formation, (2) the nucleus raphe pallidus, and (3) the ventral part of the medullary medial reticular formation. Possible functional implications of these pathways are discussed.

Anal Canal↗
PubMed1987

Eye diseases in the elderly in Singapore.

Ocular disorders in the elderly have become more important because of increased longevity and the demand for good vision. Many serious ocular conditions are age-related and they include cataract, glaucoma, diabetic retinopathy and other retinal conditions. The most important ocular disorder is cataract which fortunately is curable with excellent results when a posterior chamber implant is inserted. Angle closure glaucoma is common in the elderly Singapore Chinese and can be effectively treated with microscopic peripheral iridectomy or trabeculectomy. Blindness from diabetic retinopathy can be prevented with argon laser photocoagulation. In most cases blindness is preventable with early diagnosis e.g. in glaucoma and diabetic retinopathy. Severe visual loss in the elderly requires careful explanation and compassion by doctors and social workers.

Aged↗
PubMed1986

Afferent projections to the orbicularis oculi motoneuronal cell group. An autoradiographical tracing study in the cat.

The motoneurons innervating the orbicularis oculi muscle from a subgroup within the facial nucleus, called the intermediate facial subnucleus. This makes it possible to study afferents to these motoneurons by means of autoradiographical tracing techniques. Many different injections were made in the brainstem and diencephalon and the afferent projections to the intermediate facial subnucleus were studied. The results indicated that these afferents were derived from the following brainstem areas: the dorsal red nucleus and the mesencephalic tegmentum dorsal to it; the olivary pretectal nucleus and/or the nucleus of the optic tract; the dorsolateral pontine tegmentum (parabrachial nuclei and nucleus of Kölliker-Fuse) and principal trigeminal nucleus; the ventrolateral pontine tegmentum at the level of the motor trigeminal nucleus; the caudal medullary medial tegmentum; the lateral tegmentum at the level of the rostral pole of the hypoglossal nucleus and the ventral part of the trigeminal nucleus and the nucleus raphe pallidus and caudal raphe magnus including the adjoining medullary tegmentum. These latter projections probably belong to a general motoneuronal control system. The mesencephalic projections are mainly contralateral, the caudal pontine and upper medullary lateral tegmental projections are mainly ipsilateral and the caudal medullary projections are bilateral. It is suggested that the different afferent pathways subserve different functions of the orbicularis oculi motoneurons. Interneurons in the dorsolateral pontine and lateral medullary tegmentum may serve as relay for cortical and limbic influences on the orbicularis oculi musculature, while interneurons in the ventrolateral pontine and caudal medullary tegmentum may take part in the neuronal organization of the blink reflex.

Afferent Pathways↗
PubMed1986

Anatomical observations on the afferent projections to the retractor bulbi motoneuronal cell group and other pathways possibly related to the blink reflex in the cat.

In the cat retractor bulbi (RB) muscle reflexively retracts the eye ball into the orbit. This reflex action is called the nictitating membrane response which, together with the reflex contraction of the orbicularis oculi muscle, constitutes the blink reflex. The retractor bulbi (RB) motoneuronal nucleus is a small cell group located in the lateral tegmentum of the caudal pons, just dorsal to the superior olivary complex. The nucleus is identical to the accessory abducens nucleus and sends its fibers through the abducens nerve. Autoradiographical tracing results indicate that the RB nucleus receives some fibers from the principal and rostral spinal trigeminal nuclei and from the dorsal red nucleus and dorsally adjoining tegmentum. The same areas project to the intermediate facial subnucleus, containing motoneurons innervating the orbicularis oculi muscle. It is suggested that the trigeminal projections take part in the anatomical framework for the R1 component of the blink reflex. Two other brainstem areas i.e.: a portion of the caudal pontine ventrolateral tegmental field and the medullary medial tegmentum at the level of the hypoglossal nucleus were also found to project to the RB motoneuronal cell group and to the intermediate facial subnucleus. These projections were much stronger than those derived from the trigeminal nuclei and red nucleus. Moreover, the medullary premotor area projects not only to the blink motoneuronal cell groups but also to the pontine premotor area. It is suggested that both areas are involved in the R2 blink reflex component. The medullary blink premotor area receives afferents especially from oculomotor control structures in the reticular formation of the brainstem while the pontine blink premotor area receives afferents from the olivary pretectal nucleus and/or the nucleus of the optic tract and from the dorsal red nucleus and its dorsally adjoining area. Because the oculomotor control structures in the reticular formation (by way of the superior colliculus) and the red nucleus receive afferents from trigeminal nuclei, they may play an important role in tactually induced reflex blinking, while the pretectum could take part in the neuronal framework of the visually induced blink reflex.

Afferent Pathways↗
PubMed1986

Anatomical evidence that the pontine lateral tegmental field projects to lamina I of the caudal spinal trigeminal nucleus and spinal cord and to the Edinger-Westphal nucleus in the cat.

Autoradiographical tracing results in the cat indicate that the lateral pontine tegmental field projects mainly contralaterally to the marginal layer of the spinal trigeminal nucleus, to laminae I and II and the lateral part of laminae V and VI of the spinal cord and the Edinger-Westphal nucleus. It is pointed out that the projections from the lateral pontine tegmentum are very similar to the ones derived from the Edinger-Westphal nucleus and that these two areas are reciprocally connected. It is postulated that both areas may play a role in supraspinal pain control.

Afferent Pathways↗
PubMed1984

Mesencephalic projections to the facial nucleus in the cat. An autoradiographical tracing study.

In 33 cats the projections of different parts of the mesencephalon to the facial nucleus were studied with the aid of the autoradiographical tracing method. The results indicate the existence of many different mesencephalo-facial pathways. The dorsomedial facial subnucleus, containing motoneurons innervating ear muscles, receives afferents from 4 different mesencephalic areas: a, the most rostral mesencephalic reticular formation; b, the nucleus of Darkschewitsch and/or the ventral part of the rostral PAG; c, the interstitial nucleus of Cajal and/or the mesencephalic tegmentum dorsomedial to the red nucleus. These areas project bilaterally by way of an ipsilateral medial tegmental pathway. The medial part of the deep tectum. This area projects bilaterally by way of the tecto-spinal tract. The lateral mesencephalic tegmentum close to the parabigeminal nucleus. This area projects mainly contralaterally by way of a separate contralateral lateral tegmental fiber bundle. The mesencephalic tegmentum just dorsolateral to the red nucleus and perhaps from the dorsolateral red nucleus itself. This area projects contralaterally by way of the rubrospinal tract. The intermediate facial subnucleus containing motoneurons innervating the muscle around the eye, receives afferents from two different mesencephalic areas: The dorsal part of the rostral as well as caudal red nucleus (but not from its caudal pole) and from the dorsally adjoining mesencephalic tegmentum including the area of the nucleus of Darkschewitsch and the interstitial nucleus of Cajal. These areas project contralaterally by way of the contralateral rubrospinal tract. The nucleus of the optic tract and/or the olivary pretectal nucleus. This area projects contralaterally by way of a contralateral medial tegmental pathway. The lateral and ventrolateral facial subnuclei containing motoneurons innervating the muscles around the mouth receive afferents from two different mesencephalic areas: The lateral part of the deep tectal layers. This area projects contralaterally by way of the tecto-spinal tract. The nucleus raphe dorsalis and perhaps the nucleus centralis superior. This area projects by way of the lateral tegmentum of caudal pons and medulla.

Animals↗
PubMed1984

The organization of the gastric efferent projections in the brainstem of monkey: an HRP study.

Topographic localization of neurons in the dorsal motor nucleus (DMN) of the vagus innervating the stomach and the extent of central decussation of its fibers were investigated in the monkeys after chronic unilateral cervical vagotomy. This study presents findings in regard to the non-topographic representation of the stomach in both DMN and lack of a well-defined decussation of its fibers in the brainstem of monkeys. Reported findings in the rat and cat vis-a-vis our own results in the monkey indicate species difference in the organization of efferent vagal gastric fibers. The evidence of a very small number of HRP-labeled cells in DMN on the vagotomized side after intervals of 2-36 weeks is being reported here, for what we believe to be the first time, and its significance has been discussed.

Animals↗
PubMed1981

Does infection play a role in breast capsular contracture?

The formation of capsular contracture around silicone implants continues to be the most common complication of augmentation mammaplasty. To date, the etiologic factors in the formation of capsular contractures have remained inconclusive. In the present study, the role of subclinical infection with S. epidermidis as a cause of capsular contracture was evaluated in 16 rabbits using miniature silicone implants. All the implants on the side contaminated with varying concentrations of S. epidermidis developed breast capsular contractures. Using Baker's classification, they were graded III or IV, while the controls were all considered to be either grade I or II. Grossly, the capsules on the contaminated side were firm, fibrous, and 2 to 3 times thicker than the controls, and this was confirmed histologically using micrometry. Implants contaminated with 10(7) bacteria uniformly extruded. The present study seems to indicate that subclinical infection with Staphylococcus epidermidis may be one of the causes of capsular contracture around breast implants.

Animals↗