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Biomedical subjects

P Pacheco

Publications and source records attributed to P Pacheco.

At least 73 records · Page 4Linked to original sources
PubMed1983

Effects of leucine5 - and methionine5 - beta h - endorphin on behavior and electroencephalogram in cats.

Intracerebroventricular administration of leu5 - and met5 - beta h - endorphin produces sequential behavioral changes characterized by restlessness, eye fixation, head tremor, and exaggerated orienting reaction to external auditory stimuli, accompanied by EEG alterations. These changes take place during three stages. Met5- produces an increase in amplitude and reactivity of the theta rhythm in the hippocampus. Leu5- produces a masking of the theta rhythm by the appearance of spiking activity. Leu5- produces a loss of reactivity to visual stimuli not observed with met5-. The exaggerated reaction to auditory stimuli accompanied by an increased response of the reticular formation indicates a sensitivity of some mesencephalic structures (concerned with the modulation of sensory input) to both endorphins. Naloxone blockade of the subcortical (limbic) activity prominent in Stage II reveals the persistence of the first seen Stage I characteristics. These reticular-neocortical effects persist also into Stage III where they are seen intermixed with the limbic effects most prominent in Stage II. This suggests the presence of two endorphin-sensitive neural systems, only one of which is Naloxone reversible, and is that which in the cat covaries with the excited, hyperattentive state rather than the sedation and immobility phase seen in the rat. This dual system is compared to that described by Jacquet (13).

Animals↗
PubMed1983

Neuroendocrine control of adrenocortical ornithine decarboxylase activity.

The increase in activity of adrenocortical ornithine decarboxylase (ODC) elicited by the administration of apomorphine (APM) was studied in rats, four days after transection of the spinal cord or 24 h after various types of brain surgery: transection of the mesencephalon or of the diencephalon, or hypothalamic deafferentation (creation of a "hypothalamic island"). Section of the cord elevated endogenous adrenocortical ODC activity and potentiated the induction of the enzyme by APM. Incomplete sections of the brain at the level of the mesencephalon or diencephalon produced no change in either endogenous or induced ODC activity. In contrast to this, interruption of the mesencephalic-diencephalic connections by complete diencephalic transection produced profound decreases of endogenous ODC and of the response to APM. Deafferentation of the hypothalamus raised endogenous ODC concentrations of the adrenal cortex and potentiated the response to APM. The results strongly suggest that APM acts at the level of the diencephalon (hypothalamus) to increase adrenocortical ODC activity. Diencephalic-mesencephalic connections must be intact for this to occur. Peripheral and extrahypothalamic influences play a modulatory role in this effect.

Adrenal Cortex↗
PubMed1982

Adrenomedullary ornithine decarboxylase activity: its use in biochemical mapping of the origins of the splanchnic nerve in the rat.

The activity of ornithine decarboxylase in the adrenal medulla of the rat can be induced transsynaptically by the repeated administration of apomorphine. Unilateral section of one to four ventral spinal cord roots from T4 to T12 partially prevents this effects. Interruption of the intercostal nerves (T7--T13), with preservation of the autonomic innervation of the adrenal medulla, does not produce any alteration in the response of the medullary ODC to APO in the operated side as compared to the intact side. Dorsal root section at T7--T10 leads to a small reduction, while section at T2--T4 has no effect at all. Thus, selective surgical interruption of spinal cord roots indicates that the bulk of splanchnic fibers mediating the transsynaptic induction of adrenomedullary ornithine decarboxylase course in the ventral roots between T7 and T10. Dorsal rhizotomy demonstrates a modulatory role in this induction of afferent information to sympathoadrenal preganglionic neurons involved in innervation of the chromaffin cells.

Adrenal Medulla↗
PubMed1982

Two retinal processes displayed in the cat electroretinogram.

Local stimulation of dark adapted cat's retina with spots of light of various intensities elicits a complex b-wave in which four deflections can be consistently identified. An analysis of these wavelets recorded with the low frequency cut off at 80 Hz is made in an attempt to infer their origin. The experimental conditions under which these wavelets were studied were standardized by stimulation with a spot of light at different intensities, frequencies and positions in the visual field. The changes in amplitude and latency by those different conditions of stimulation and by the intravenous (i.v.) injection of additional doses of nembutal, suggests that these peaks are triggered by two retinal excitatory processes related to the scotopic system. It is also pointed out that components 1-2 are mainly determined by the activation of retinal cells which correspond to the area centralis and that components 3-4 represent the activity of retinal cells from the lateral regions (nasal and temporal). The possible clinical use of our results is discussed.

Action Potentials↗
PubMed1980

Effect of electrical stimulation of mammary nerve upon pituitary and plasma prolactin concentrations in anesthetized lactating rats.

A 50-70% depletion in the anterior pituitary concentration of PRL occurred within 5 min of electrical stimulation of a single abdominal mammary nerve of urethane-anesthetized lactating rats previously nonsuckled for 6-8 h. The stimulus parameters were: 1-msec pulses, 10-20/sec at 5-30 V applied 5 sec on and 10 sec off. The anterior pituitary concentration of PRL remained low for another 15-30 min after depletion, then repleted to prestimulus levels by the 90th min. The same pattern of depletion-repletion occurred when mammary nerve stimulation was applied for 5 min as when it was applied for 180 min. In other experiments, plasma PRL concentration rose swiftly and attained a maximal level, 4- to 5-fold in Wistar rats and 8- to 10-fold in Holtzman rats, above basal concentrations within 10-15 min of mammary nerve stimulation. The maximal level was sustained throughout the time the nerve was stimulated and for 45 min after the stimulation was stopped, i.e. the sustained secretion of PRL into the plasma occurred at the same time that depleted PRL was repleting. Ligation of both adrenals or iv injection of the beta-adrenergic blocker, propranolol, before stimulation of the nerve had no effect upon the plasma PRL profile in response to mammary nerve stimulation. These data indicate that mammary nerve stimulation mimics that of suckling upon depletion, repletion, and the release of PRL into the circulation and add further support to the hypothesis that these phases are independent processes.

Animals↗
PubMed1976

Possible phylogenetical significance of the corpus callosum with special reference to the dolphin brain (Stenella graffmani).

The surface area of the corpus callosum was measured in several animals as compared to the brain weight. A general consideration of the importance of this structure on the phylogenetic scale, with special reference to the corpus callosum of the dolphin, Stenella graffmani, is given. Some theoretical considerations about the significance of this structure upon some specialized features are mentioned.

Anatomy, Comparative↗