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Biomedical subjects

R Baker

Publications and source records attributed to R Baker.

At least 469 records · Page 26Linked to original sources
PubMed1983

The effect of phenylephrine hydrochloride on the resting point of accommodation.

Previous models for ocular accommodation have suggested a dual sympathetic/parasympathetic innervation to the ciliary muscle. Such models would predict that sympathomimetic drugs should change the resting point or dark focus of accommodation. The effect of an alpha-adrenergic agonist (10% phenylephrine hydrochloride) on accommodation was examined; the results show a decrease in the near point of accommodation, without a change in the resting point of accommodation. These results suggest that the accommodative state of the eye is not the result of a simple balance between sympathetic and parasympathetic innervation as proposed by previous models of accommodation.

Accommodation, Ocular↗
PubMed1982

Comparison of the morphology of physiologically identified abducens motor and internuclear neurons in the cat: a light microscopic study employing the intracellular injection of horseradish peroxidase.

Abducens motoneurons and internuclear neurons were identified electrophysiologically in anesthesized, paralyzed cats and stained by intracellular injection of horseradish peroxidase. Neurons were reconstructed and surface area of selected cells measured by light microscopy. Surface area of motoneurons and internuclear neuron with similar soma size and shape were roughly comparable. Dendrites of motoneurons were highly tapered and highly branched. By contrast, dendrites of internuclear neurons were less tapered and less branched. Axons of motoneurons had no collaterals within the brainstem. Internuclear axons crossed the midline at the level of their parent somata and ascended in the medial longitudinal fasciculus toward the oculomotor nucleus. Approximately 30% of the internuclear axons branched in the contralateral medial longitudinal fasciculus sending a fine collateral caudal toward the prepositus hypoglossi nucleus. The results suggest that, on the average, structural correlates of injected neurons (i.e., soma-dendritic morphology) can account at least in part for the earlier firing and higher intraburst frequencies of internuclear neurons versus motoneurons during on-direction rapid eye movements in alert cats.

Abducens Nerve↗
PubMed1982

Electron microscopic observations of axon collateral synaptic endings of cat oculomotor motoneurons stained by intracellular injection of horseradish peroxidase.

Motoneurons in the cat oculomotor nucleus have been identified electrophysiologically and stained by intracellular injection of horseradish peroxidase. Axon collateral arborizations with preterminal and terminal boutons identified by light microscopy corresponded to synaptic endings observed by electron microscopy. Despite variations in size and shape, synaptic endings showed similar ultra-structural features and established asymmetrical predominantly axodendritic synaptic contacts usually characterized by the presence of subjunctional dense bodies underlying the postsynaptic membrane densification.

Animals↗
PubMed1982

Bromocriptine reduces pituitary tumor size and hypersection. Requiem for pituitary surgery?

Twelve patients with pituitary tumor whose prior treatment included surgery and radiotherapy in four, surgery alone in four, radiotherapy alone in one, and none in three were studied. Nine had hyperprolactinemia, two had elevated serum growth hormones, and one had no pituitary hormone excess. Visual field defects were present in six. All had pituitary-gonadal insufficiency manifested as impotence or amenorrhea. All were tested with bromocriptine, 7.5 to 25 mg daily, and followed up for eight to 27 (mean 15) months. Serum prolactin levels decreased to normal in seven of nine patients. Serum growth hormone values were normalized in both acromegalics. When hormone levels were reduced to normal, pituitary tumor size decreased. Vision was restored to normal in five of six patients, including one patient with pituitary tumor but no pituitary hormone excess. Bromocriptine corrects the physiological defects associated with pituitary tumors that have been incompletely treated with surgery, radiotherapy, or both and may be a useful primary treatment for patients with pituitary tumors.

Adult↗
PubMed1982

Neuronal activity in prepositus nucleus correlated with eye movement in the alert cat.

1. In nine alert chronically prepared cats the activity of 177 neurons was recorded in the prepositus nucleus during either spontaneous eye movement or that induced by natural vestibular and optokinetic stimulation. 2. In 116 cells, eye position and/or eye velocity was precisely and unequivocally encoded whatever the origin of the eye movement. These cells were separated into different populations according to the eye movement variable encoded and the directionality of the neuronal response. The firing rates of the remaining 61 cells were loosely related to eye movements because a variety of discharge patterns were observed during identical eye movements. In the latter case, some other unmeasured variable (e.g., neck or visual) was suggested to be encoded in the firing frequency. 3. Discharge rate changed before the eyes began to move and reached a new steady level during fixation following a saccade into a particular direction of the orbit. The ondirection was horizontal for 59% of the neurons, vertical for 17%, and oblique for 24%. 4. Regardless of their preferred direction, the discharge rate in 19% of the neurons was closely proportional to eye position. The range in sensitivity was from 1.1 to 7.5 spikes X s-1/deg. Weak velocity responses were occasionally observed during the slow phase of vestibular and optokinetic nystagmus including during saccades. This class of neurons exhibited a very regular interspike interval for a given position of fixation. Since mainly eye position was encoded, these cells were called position neurons. 5. Other prepositus neurons showed both position and velocity sensitivity during saccades and fixation. Their firing rate encoded eye position over the same range as above and also coded velocity during the slow phase of vestibular and optokinetic nystagmus. Depending on the weighting between the position and velocity proportionality constants, these neurons were classified into position-velocity (48%) or velocity-position (33%) groups. 6. The distribution of the above responses led to the conclusion that the prepositus nucleus plays a role in vertical and horizontal spatial integration. The predominance of horizontal activity suggested that the nucleus may be a significant site underlying genesis of horizontal eye position.

Animals↗
PubMed1982

Effects of benactyzine hydrochloride on dynamic vision functions.

We have investigated the effects of an anticholinergic drug, benactyzine HCl on vision and vision function. Our experiments assess the time course and severity of benactyzine effects on visual acuity for static and moving targets, amplitude and dynamics of accommodation, pupil response to light and the spatial contrast sensitivity function. A single dose of the drug (4.14 mg/70 kg body weight, which is within the therapeutic range) and placebo were administered intramuscularly to 12 subjects. Large and significant decrements in visual function were demonstrated after the administration of benactyzine, particularly for those functions performed at near focus. The drug effect was rapid in onset, beginning 7-10 min after injection, peaked at approximately 30-40 min, and declined to baseline values over the next 2 h. The drug increased pulse rate and blood pressure, and induced an intoxicated state involving loss of concentration, attention, and short-term memory.

Accommodation, Ocular↗
PubMed1981

Stimulated gastric prostaglandin output, and the effect of inhibition of prostaglandin synthetase, in the conscious cat.

1. In the conscious gastric fistula cat there was no correlation between the outputs of gastric acid and PGE secreted in response to incremental doses of pentagastrin and histamine acid phosphate. 2. PGE secreted in response to pentagastrin and histamine was not dose dependent. 3. Flurbiprofen significantly inhibited the gastric output of PGE but did not influence acid or pepsin secretion. Inhibition of PGE secretion was accompanied by evidence of gastric mucosal haemorrhage. 4. It is concluded that gastric juice PGE is unlikely to be involved in the physiological control of acid secretion.

Animals↗
PubMed1981

Uterine oestrogen and progesterone receptors in the ovariectomized rat.

The effect was studied of repeated injections of oestradiol-17 beta (5, 10, 25, 50 micrograms) given for various lengths of time (3, 5, 9 days) on total cell content of oestrogen receptors and cytosol progesterone receptors in the uteri of ovariectomized rats. An additional group of rats was injected daily with 50 micrograms oestradiol benzoate (OB) for 9 days in order to achieve a more sustained concentration of oestradiol in the blood. Injections were begun 24h after ovariectomy and the rats were killed 24h after the last injection. Daily administration of 5 micrograms oestradiol prevented the initial transient rise in oestrogen receptors which was observed in the uteri of untreated rats after ovariectomy. Repeated injections of 10 micrograms oestrogen produced an initial lowering in oestrogen receptors after 3 days of treatment which was followed by a prompt rise at 5 and 9 days when treatment was continued. A significant reduction in oestrogen receptors occurred at all times studied when rats were injected daily with 25 and 50 micrograms oestradiol. A more profound reduction in oestrogen receptors was observed in the group of rats treated for 9 days with 50 micrograms OB. Synthesis of progesterone receptors was stimulated by all doses of oestrogen studied. Concentrations of progesterone receptors were significantly higher after 3 and 5 days of treatment with 25 and 50 micrograms oestrogen. After 9 days of treatment, however, concentrations of progesterone receptors were virtually identical in all treated groups, including the group treated with OB. We have concluded that large doses of oestrogen significantly decrease oestrogen receptor content in the rat uterus, especially when OB is used. The degree of reduction, however, is only moderate under these experimental conditions and is insufficient to inhibit synthesis of progesterone receptors.

Animals↗