Biomedical subjects

P Pacheco

Publications and source records attributed to P Pacheco.

At least 19 recordsLinked to original sources

PubMed1992

Visceral and postural reflexes evoked by genital stimulation in urethane-anesthetized female rats.

The present study describes several muscular reflexes produced by genital stimulation, the nerves that subserve them, and the visceral and postural effects induced by these reflexes. Electrical stimulation of the iliococcygeus (ic) and pubococcygeus (pc) (striated) muscles produced movement of the vaginal orifice and wall, membranous urethra, tail and pelvis. Electrical stimulation of the psoas major (pm) or iliacus (i) (striated) muscles produced movements of the lumbar vertebrae and extension of the ipsilateral hindlimb. Sensory mechanostimulation elicited responses of these muscles as follows: stimulation of the perineal skin, clitoral sheath or distal vagina produced reflex contraction of the ic and pc muscles. Stimulation of the cervix produced reflex contraction of the pm and i muscles and also blocked the above reflex contraction of the ic and pc muscles. Both the cervical stimulation-induced blockage of the ic and pc reflex response, and the cervical stimulation-induced activation of pm and i muscles was prevented by bilateral transection of the viscerocutaneous branch of the pelvic nerve. Based on the above observations, it is proposed that stimulation of the vaginal surface of the cervix resulting from penile intromission and/or seminal plug deposition during mating behavior in the rat may reflexively active pm and i, thereby contributing to the hindleg postural rigidity and lordotic dorsiflexion that are characteristic of the normal mating posture in female rats.

Abdominal Muscles↗

PubMed1991

Xanthine oxidase inhibitory activity of Chilean Myrtaceae.

Twenty-one Myrtaceae collections belonging to 10 species, 5 of which are used in Chilean folk medicine, were assayed for inhibitory activity towards the enzyme xanthine oxidase. Most leaf and stem extracts were devoid of activity or showed a weak inhibitory effect. Chilean ethnobotanical data on the species are linked to the astringent properties of Myrtaceae and their use for treating wounds and diarrhea. The results show the advantage of using proper plant selection criteria when searching for new drugs to treat human gout.

Chile↗

PubMed1989

Somato-motor components of the pelvic and pudendal nerves of the female rat.

The efferent innervation of the pelvic and pudendal nerves was characterized in this study by identifying the muscles activated by electrical stimulation of the nerves distal to the point at which they bifurcate from the L6-S1 trunk. Pelvic nerve electrical stimulation produced EMG-monitored contraction of the ipsilateral ilio- and pubococcygeus muscles, which was abolished by cutting one ('muscular') branch of the bifurcated nerve. (This 'muscular' branch receives proprioceptive input activated by tail displacement, whereas the other, 'viscero-cutaneous' branch receives sensory innervation from the midline perineal region.) Pudendal nerve electrical stimulation produced contraction of the coccygeus, external anal sphincter, and ischiocavernosus muscles. Movements of the orifice and wall of the vagina were directly visualized during electrical stimulation of the two nerves. Intravaginal pressure measured by balloon was increased by pelvic nerve stimulation and decreased by pudendal nerve stimulation. Reflexive contraction of the ilio- en pubococcygeus muscles was produced by mechanostimulation of the perineum, clitoral sheath and distal vagina. This response was abolished by gentle cervical mechanostimulation. One implication of this finding is that passage of the fetuses through the cervix during parturition may relax the ilio- and pubococcygeus muscles, thereby facilitating delivery.

Animals↗

PubMed1989

Behavioral and electrophysiological effects of crustacean neurohormone on freely moving cats.

The behavior of freely moving cats was assessed in an observation chamber during prolonged periods of time. Four patterns of behavior were consistently scored during the mid-day period: a) exploration, b) attention, c) grooming and d) drowsiness. Intracerebroventricular injections of crustacean neurodepressing hormone (NDH) greatly extended the time spent in drowsiness. The threshold dose of NDH for this effect was 300 units. The effect was established a few minutes after the injections and lasted for several hours. During this time the animals sat quietly and showed complete or semicomplete closure of the eyelids. Conspicuous changes in brain electrical activity were also observed under NDH. At low doses, the predominant electrophysiological pattern matches the activity recorded under spontaneous lapses of drowsiness, i.e., spindle bursts in trains of 8-16 Hz in cortical areas and mesencephalic reticular formation. At higher doses, the brain electrical activity changes into a nonconvulsive spiking activity in limbic areas. The time course of the effects differs in the various structures recorded. These results suggest a multiple substrate of NDH activity.

Animals↗

PubMed1989

Inverse relationship between intensity of vaginal self-stimulation-produced analgesia and level of chronic intake of a dietary source of capsaicin.

Women who chronically ingest a diet rich in capsaicin, the pungent ingredient in hot chili peppers, showed a significantly lower magnitude of analgesia in response to vaginal self-stimulation than women with relatively low or medium levels of ingestion. Vaginal self-stimulation-produced analgesia was quantified by measuring (on the hand) pain detection thresholds, pain tolerance thresholds and tactile thresholds. Whereas vaginal self-stimulation produced a 32.6-43.8% increase in pain detection and pain tolerance thresholds in the low chili diet group, it produced only a 2.3-7.3% increase in these measures in the high chili diet group. The medium chili diet group showed an intermediate effect on the pain thresholds. Tactile thresholds were not increased by the vaginal self-stimulation. Baseline (no stimulation) pain thresholds did not differ significantly among the three groups. These findings are consistent with earlier studies in laboratory rats, in which capsaicin administered neonatally abolished vaginal stimulation-produced analgesia, but did not affect baseline pain thresholds to mechanostimulation.

Adult↗

PubMed1989

Mutagenicity of rutin and the glycosidic activity of cultured cell-free microbial preparations of human faeces and saliva.

Genotoxic testing of flavonol glycosides, which account for most of the human intake of flavonoids, is dependent on the use of enzymatic extracts that exhibit beta-glycosidic activity. This study was aimed at characterizing further the beta-glycosidic activity of cultured cell-free microbial extracts from human faeces (faecalase) and saliva (salivase). Using o-nitrophenyl-beta-D-galactoside as substrate, the optimum pH and apparent Km and energy of activation were shown to be 7.6, 3.5 x 10(-4) M and 8.65 kcal/mol, respectively, for faecalase, and 7.4, 8.7 x 10(-5) M and 3.8 kcal/mol, respectively, for salivase. Rutin (quercetin-3-O-rutinoside) was shown to be a competitive inhibitor for faecalase, whereas no inhibitory activity could be found for salivase. Enzymatic hydrolysis of rutin gave the mutagenic product quercetin that was detected in the Ames assay and using high-performance liquid chromatography.

Cell-Free System↗

PubMed1988

Analgesia produced by vaginal self-stimulation in women is independent of heart rate acceleration.

In the present study, the analgesia produced by vaginal stimulation (VS) in women was found to be dissociated from heart rate. The VS-produced analgesia was not accompanied by an acceleration of heart rate. Heart rate acceleration produced by exercise did not result in analgesia. The independence of VS-produced analgesia from this index of autonomic activity is consistent with recent findings in rats.

Analgesia↗

PubMed1987

Ventral root potentials of the cat's sacrococcygeal segments evoked by stimulation of intact and transected dorsal roots.

The latency and amplitude of reflex-evoked potentials in the sacrococcygeal ventral roots of acute spinalized cats were investigated. The characteristics of the potentials were examined in response to electrical stimulation of intact and acutely transected dorsal roots. We found that: the last sacral and caudal (coccygeal) segments of the cat's spinal cord are endowed with electrophysiologic characteristics that distinguish them from other spinal segments (e.g., L7-S1); afferent stimulation of the corresponding intact dorsal roots evokes in the ventral root of segment S2 a small monosynaptic response, whereas no monosynaptic response is seen in segment Ca6; acute transection of the dorsal roots provokes an increment of the monosynaptic response in all segments studied except for Ca6; rhizotomy provokes in Ca5 the appearance of polysynaptic responses to electrical stimulation of the corresponding dorsal root; and transection of the cutaneous afferent fibers of the coccygeal motoneurons resulted in an increment of monosynaptic and polysynaptic responses, indicating the removal of inhibitory effects.

Animals↗

PubMed1987

Reflex responses evoked from cats' coccygeal ventral roots by electrical stimulation of the tail nerves.

In the terminal cone of the cat spinal cord, the coccygeal segments give rise to the ventrolateral and dorsomedial nerves of the tail. Extracellular recording was made from the ventral root of the coccygeal segments after stimulation of each or both ventrolateral and dorsomedial nerves. Stimulation of either nerve caused a polysynaptic response of 5- or 10-ms latency. A monosynaptic response was not seen unless posttetanic potentiation was carried out, or both nerves were stimulated simultaneously. It is suggested that the ventrolateral and dorsomedial nerves are linked by a common pathway, allowing spatial summation to take place, thus facilitating the elicitation of a monosynaptic response. The neural organization underlying the muscle movements of the cat's tail is discussed.

Animals↗

PubMed1986

Retinal degeneration induced by taurine deficiency in light-deprived cats.

The effect of light deprivation on the retinal degeneration induced by taurine deficiency in cats was examined in this study. After 25 weeks of taurine-free diet, taurine levels in plasma, retina, heart, cerebellar and cerebral cortex decrease to 16-25% of normal. The ERG a-wave and b-amplitudes also decreased as a consequence of the taurine-free diet. After 15 weeks of taurine-free diet the b-wave amplitude decreased to 36-41% of normal, and after 25 weeks both the a-wave and the b-wave were undetectable. The structure of the outer segments of photoreceptors, examined by electron microscopy appeared disturbed in the taurine-deficient cats, showing disorientation of the disk membranes, vesiculation and swelling. The time course of taurine deficiency and the retinal degeneration pattern were observed in all cats fed the taurine-free diet, irrespective of the conditions of lighting. These results indicate that the morphological and functional disturbances induced by taurine deficiency in cats are independent of the physiological stimulation of the retina by light.

Animals↗

PubMed1985

Spinal control of pelvic floor muscles.

A prevalent notion in the literature is that the pelvic floor muscles behave as a unitary mass. We examined this proposition experimentally. In spinal cats, we recorded EMG activity from the following pelvic floor muscles: the sphincter ani externus (SAE), the abductor caudae internus (coccygeus), and the levator ani (pubiocaudalis) muscles. The epaxial sacrocaudalis dorsalis lateralis muscle was also exposed and prepared for recording. Electrical stimulation of S2 ventral roots elicited twitch responses of the sphincter ani externus and of the sacrocaudalis dorsalis lateralis muscles. Stimulation of S3 and Cx1 ventral roots elicited responses in the other two muscles studied, the levator ani and abductor caudae internus. Thus a clear segregation of the segmental motor neuron pools innervating the different pelvic floor muscles was demonstrated. The various muscles of the pelvic floor region could be reflexly activated either individually or as a mass unit depending on the intensity of stimulation. Tactile or electrical stimulation of pudendal regions on either side of the body elicited responses of the sphincter ani externus. In contrast, activation of the levator ani and abductor caudae internus muscles could be lateralized: tactile or electrical stimulation of the dorsolateral surfaces at the base of the tail region elicited ipsilateral responses from these muscles. Section of one pudendal nerve did not alter the level of tonic activity (2 to 4/s) of the sphincter ani externus. However, bilateral section of the pudendal nerve entirely abolished both tonic activity and phasic responsiveness of the SAE without affecting the activity of the levator ani and abductor caudae internus muscles. Pudendal nerve stimulation elicited only polysynaptic reflex responses from S2 ventral roots. The results presented show that the neural apparatus of the striated musculature of the pelvic floor is capable of activating individually the different muscles that make up the system, and that the sphincter ani externus from one side, and muscles that conform the diaphragm pelvis from the other, are subserved by different neuronal circuits.

Animals↗

PubMed1983

Neurotransmitter interaction in regulation of adrenocortical ornithine decarboxylase.

Administration of the dopamine receptor agonists apomorphine (APM) and piribedil increases adrenocortical ornithine decarboxylase (ODC) activity. In this paper alterations in the sympathoadrenal system, and in the central dopaminergic and serotonergic systems have been produced to study the possible mechanism of action of APM on adrenocortical ODC. Unilateral splanchnicotomy, unilateral rhizotomy, and bilateral demedullation each attenuated the response of adrenocortical ODC to APM. Intracerebroventricular 6-hydroxydopamine and 5,6-dihydroxytryptamine, intraperitoneal p-chlorophenylalanine and electrolytic lesion of the medial raphe nucleus reduced the APM-induced increase. None of these treatments produced any changes in the endogenous ODC activity of the adrenal cortex. It is postulated that dopaminergic brain structures participate directly in the stimulatory effect on the hypophyseo-adrenal system to increase adrenocortical ODC activity. An intact central serotonergic system seems to be necessary for APM to exert its effect on adrenocortical ODC activity, particularly the medial raphe nucleus.

Adrenal Cortex↗

PubMed1983