PubMed Health⌕ Search

Biomedical subjects

L L Melo

Publications and source records attributed to L L Melo.

14 recordsLinked to original sources
PubMed2005

Neuroanatomical approaches of the tectum-reticular pathways and immunohistochemical evidence for serotonin-positive perikarya on neuronal substrates of the superior colliculus and periaqueductal gray matter involved in the elaboration of the defensive behavior and fear-induced analgesia.

Deep layers of the superior colliculus, the dorsal periaqueductal gray matter and the inferior colliculus are midbrain structures involved in the generation of defensive behavior and fear-induced anti-nociception. Local injections of the GABA(A) antagonist bicuculline into these structures have been used to produce this defense reaction. Serotonin is thought to be the main neurotransmitter to modulate such defense reaction in mammals. This study is the first attempt to employ immunohistochemical techniques to locate serotonergic cells in the same midbrain sites from where defense reaction is evoked by chemical stimulation with bicuculline. The blockade of GABA(A) receptors in the neural substrates of the dorsal mesencephalon was followed by vigorous defensive reactions and increased nociceptive thresholds. Light microscopy immunocytochemistry with streptavidin method was used for the localization of the putative cells of defensive behavior with antibodies to serotonin in the rat's midbrain. Neurons positive to serotonin were found in the midbrain sites where defensive reactions were evoked by microinjection of bicuculline. Serotonin was localized to somata and projections of the neural networks of the mesencephalic tectum. Immunohistochemical studies showed that the sites in which neuronal perikarya positive to serotonin were identified in intermediate and deep layers of the superior colliculus, and in the dorsal and ventral columns of the periaqueductal gray matter are the same which were activated during the generation of defense behaviors, such as alertness, freezing, and escape reactions, induced by bicuculline. These findings support the contention that serotonin and GABAergic neurons may act in concert in the modulation of defense reaction in the midbrain tectum. Our neuroanatomical findings indicate a direct neural pathway connecting the dorsal midbrain and monoaminergic nuclei of the descending pain inhibitory system, with profuse synaptic terminals mainly in the pontine reticular formation, gigantocellularis nucleus, and nucleus raphe magnus. The midbrain tectum-gigantocellularis complex and midbrain tectum-nucleus raphe magnus neural pathways may provide an alternative output allowing the organization of the fear-induced anti-nociception by mesencephalic networks.

Aggression↗
PubMed1999

Influence of surgically induced gastric and gastroduodenal content reflux on esophageal carcinogenesis--experimental model in Wistar female rats.

Studies in human beings and animals have shown that esophageal exposure to duodenal and gastric contents may be important for the development of Barrett's esophagus and its complications, including adenocarcinoma and epidermoid carcinoma. Diethylnitrosamine (DEN) is a carcinogen that stimulates the development of epidermoid carcinoma in the esophagus of mice. The aim of this study was to evaluate the effect of gastroduodenal and gastric content reflux on induction of esophageal carcinogenesis. Gastroesophageal reflux (GER) and gastroduodenoesophageal reflux (GDER) were produced by cardioplasty and esophagoduodenostomy. The chosen carcinogen was DEN, diluted in drinking water, given 3 days a week for 20 consecutive weeks. One hundred Wistar female rats were divided into six groups, as follows: group 1 (18 rats), cardioplasty without DEN; group 2 (18 rats), cardioplasty with DEN; group 3 (10 rats), only water; group 4 (17 rats), cardioplasty with DEN; group 5 (17 rats), esophagoduodenostomy with DEN; group 6 (20 rats), only DEN. GER in isolation induced papillomatosis or ulceration in 22.2% of rats and, when associated with DEN, induced papillomatosis in 61.1% of rats. GDER in isolation induced marked esophagitis in 61.1% of rats, Barrett's esophagus in 16.7% and esophageal adenocarcinoma in 16.7%; when associated with DEN, 23.5% of rats presented marked esophagitis, papillomatosis or ulceration, whereas 76.5% had esophageal carcinoma, with 70.6% epidermoid carcinoma and 5.9% adenocarcinoma. Rats treated with water alone did not show histologic abnormalities of the esophageal mucosa. Rats treated with DEN alone developed papillomas in 50.0% of the cases and remained histologically unchanged in 50.0%. There was no development of low- or high-grade dysplasia in any group. The conclusions are that (1) GDER is significantly more deleterious to esophageal mucosa than GER; (2) in this study, GER did not present carcinogenic potential in relation to the esophagus; (3) GDER in isolation is an esophageal carcinogen, producing Barrett's esophagus and esophageal adenocarcinoma; (4) esophageal oncogenesis caused by GDER is potentiated by DEN, inducing esophageal epidermoid carcinoma; (5) in this study, DEN in isolation did not generate tumors in the esophagus of rats.

Adenocarcinoma↗
PubMed1999

Role of the hippocampus in contextual memory after classical aversive conditioning in pigeons (C. livia).

We investigated the effects of hippocampal lesions with ibotenic acid (IBO) on the memory of the sound-context-shock association during reexposure to the conditioning context. Twenty-nine adult pigeons were assigned to a non-lesioned control group (CG, N = 7), a sham-lesioned group (SG, N = 7), a hippocampus-lesioned experimental group (EG, N = 7), and to an unpaired nonlesioned group (tone-alone exposure) (NG, N = 8). All pigeons were submitted to a 20-min session in the conditioning chamber with three associations of sound (1000 Hz, 85 dB, 1 s) and shock (10 mA, 1 s). Experimental and sham lesions were performed 24 h later (EG and SG) when EG birds received three bilateral injections (anteroposterior (A), 4.5, 5.25 and 7.0) of IBO (1 microl and 1 microg/microl) and SG received one bilateral injection (A, 5.25) of PBS. The animals were reexposed to the training context 5 days after the lesion. Behavior was videotaped for 20 min and analyzed at 30-s intervals. A significantly higher percent rating of immobility was observed for CG (median, 95.1; range, 79.2 to 100.0) and SG (median, 90.0; range, 69.6 to 95.0) compared to EG (median, 11.62; range, 3.83 to 50.1) and NG (median, 7.33; range, 6.2 to 28.1) (P<0.001) in the training context. These results suggest impairment of contextual fear in birds who received lesions one day after conditioning and a role for the hippocampus in the modulation of emotional aversive memories in pigeons.

Animals↗
PubMed1997

Bilateral ablation of the auditory cortex in the rat alters conditioned emotional suppression to a sound as appraised through a latent inhibition study.

Latent inhibition consists of a retardation of conditioning seen when the to be conditioned stimulus is presented a number of times with no other consequence. This phenomenon likely reflects processes of selective attention whereby irrelevant stimuli come to be ignored. Using physiological models for auditory attention, some investigators have suggested that selective attention acts as a filtering mechanism capable of inhibiting or gating unattended stimuli relative to attended ones in the auditory cortex. In the present work, an on-baseline conditioned suppression response procedure was used to study the effects of stimulus preexposure in rats submitted to bilateral auditory cortex ablation. Our results indicate that both auditory cortex lesioned and control animals exhibit latent inhibition to a sound. However, learning after preexposure to that sound was particularly slow in animals with bilateral auditory cortex lesion, i.e. in these animals, the latent inhibition effect appeared to be enhanced. Conditioning from one day to the next also varied slightly. Thus, the auditory cortex appears to modulate learning when the conditioned stimulus is a sound.

Acoustic Stimulation↗
PubMed1997

Active avoidance learning using brain stimulation applied to the inferior colliculus as negative reinforcement in rats: evidence for latent inhibition.

The inferior colliculus has been implicated in aversive or anxiogenic aspects of defensive behavior. Animals learn to turn off electrical stimulation applied to the inferior colliculus. The purpose of the present study was to determine (1) whether this aversion induced by electrical stimulation can be conditioned to a conditioned stimulus (CS, light) and (2) whether pre-exposure to the CS will diminish the extent of such conditioning, i.e. whether latent inhibition can be established with this paradigm. Rats were placed inside an open field, and thresholds for the escape response to electrical stimulation of the inferior colliculus were determined. The rats were then placed inside a shuttle box and submitted to a two-way avoidance paradigm. Electrical stimulation of the inferior colliculus at the escape threshold was used as negative reinforcement and shuttle box illumination as the CS. The rats quickly learned to avoid or terminate the inferior-colliculus stimulation. Furthermore, the performance of the animals in this paradigm was significantly disrupted when they were pre-exposed to 50 presentations of the CS before the session. These data suggest that the inferior colliculus has neural substrates for supporting associative learning and latent inhibition.

Animals↗
PubMed1994

Neural substrate of defensive behavior in the midbrain tectum.

It has been shown that the gradual increase in the intensity of electrical stimulation of the dorsal periaqueductal gray (DPAG), deep layers of the superior colliculus (DLSC) and inferior colliculus of rats induces, in a progressive manner, characteristic aversive responses such as arousal, freezing, and escape behavior. The DPAG-DLSC together with the periventricular gray substance of the diencephalon, amygdala and the inferior colliculus, constitute the neural substrate of aversion in the brain. In general, the behavioral responses induced by midbrain tectum stimulation are accompanied by increases in the mean arterial blood pressure, heart rate, and respiration. Both the behavioral and autonomic consequences of electrical stimulation of the mesencephalic tectum have been shown to be attenuated by minor tranquilizers, probably through enhancement of GABAergic neurotransmission. Besides GABAergic mechanisms several lines of evidence have clearly implicated opioid, serotonergic, and excitatory amino acids-mediated mechanisms in the control of the neural substrates commanding defensive behavior in the brain aversive system.

Aggression↗
PubMed1993

Mechanisms of defense in the inferior colliculus.

The inferior colliculus (IC) is a well known relay station for auditory pathways in the brainstem. In the present review we are suggesting that aversive states are also generated and elaborated in the inferior colliculus and that this structure may be part of a brain system commanding defensive behavior. The evidences presented in this review have been obtained from experiments carried out with the combined use of intracerebral microinjections and of electrical stimulation of the inferior colliculus. This electrical stimulation caused a behavioral activation together with autonomic reactions usually observed as part of the defense reaction. NMDA--an excitatory amino acid--, or bicuculline--a GABAA antagonist--injected into the IC mimicked the effects of its electrical stimulation. The IC electrical stimulation showed clear aversive properties as rats submitted to a switch-off paradigm quickly learned to interrupt it. Systemic administration as well as IC microinjections of the anxiolytic compound midazolam caused dose-dependent increases in the latency and reductions in the frequency of switch-off responses to the inferior colliculus electrical stimulation. Similar results were obtained following microinjections into this brainstem structure of the GABAA agonist muscimol. These results suggest that neural substrates responsible for defensive behavior in the inferior colliculus may be depressed by benzodiazepines as part of the anxiolytic action of these compounds. This anti-aversive action may be produced by the enhancement of GABAA mechanisms. Serotonergic mechanisms seem also to be involved in the modulation of these aversive states as IC microinjections of zimelidine, a 5-HT uptake blocker, caused a significant inhibition of the switch-off responses in the shuttle-box.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Antiaversive action of benzodiazepines on escape behavior induced by electrical stimulation of the inferior colliculus.

In the present work, evidence is presented for the involvement of inferior colliculus in the generation and elaboration of aversive responses which suggests that this structure may be part of a brain system that commands aversive states. Electrical stimulation of the inferior colliculus of rats placed inside an open field allowed the determination of thresholds for the escape response. Afterward these rats were placed inside a shuttle box and submitted to a switch-off paradigm. Electrical stimulation of the inferior colliculus was applied at a current intensity 5% below the escape threshold. This electrical stimulation showed clear aversive properties: the rats quickly learned to interrupt it. Systemic administration (3 and 5.6 mg/kg) as well as inferior colliculus microinjections (10 and 20 nmol) of the anxiolytic compound midazolam caused dose-dependent increases in the latency and reductions in the frequency of switch-off responses to the inferior colliculus electrical stimulation. Similar results were obtained following microinjections into this brainstem structure of the GABA-A agonist muscimol (0.1 and 0.5 nmol). These results suggest that neural substrates commanding defensive behavior in the inferior colliculus may be depressed by benzodiazepines as part of the anxiolytic action of these compounds. This antiaversive action may be produced by the enhancement of GABA-A mechanisms.

Animals↗
PubMedDate not supplied

Role of 5-HT1A and 5-HT2 receptors in the aversion induced by electrical stimulation of inferior colliculus.

In addition to being a relay station for auditory pathways in the brainstem, the inferior colliculus may also be part of a brain system commanding defensive behavior. In the present work, we present evidence for the serotonergic modulation of the neural substrate of aversion in this structure. Rats implanted with an electrode-cannula in the inferior colliculus were placed inside a shuttle-box and submitted to a switch-off paradigm. Microinjections of zimelidine, a 5-HT uptake blocker, caused dose-dependent increases in latency and reductions in the frequency of switch-off responses to the inferior colliculus electrical stimulation. The 8-OH-DPAT, a classical 5-HT1A agonist, and alpha-methyl-5-hydroxytryptamine, a highly selective 5-HT2 agonist, injected directly into th e inferior colliculus also produced clear antiaversive effects in a dose-dependent manner. The antiaversive effect produced by alpha-methyl-5-hydroxytryptamine was attenuated by the systemic administration of ketanserin, a preferential 5-HT2 receptor antagonist. These results suggest that serotonergic mechanisms modulate the neural substrates commanding defensive behavior in the inferior colliculus, probably through a cooperative mechanism with the activation of 5-HT1A and 5-HT2 receptors.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMedDate not supplied

Estrous cycle influences the response of female rats in the elevated plus-maze test.

The aim of this study was to examine the state of anxiety and the 17beta-estradiol and progesterone levels in rats tested in the elevated plus-maze during the four phases of the estrous cycle. Male rats, female rats during each of the four phases of the estrous cycle, ovariectomized rats, and diestrus female rats treated with estradiol were tested in the elevated plus-maze between 8:00 and 10:00 a.m. Blood was collected from all rats for the determination of 17beta-estradiol and progesterone levels. Female rats in the proestrus group spent more time in the open arms than diestrus rats (P<.05). There were no significant differences in the percentage of entries into the open arms or in the number of entries into the closed arms among the phases of the estrous cycle or between males and normal or ovariectomized females. Serum estradiol levels were higher (P<.05) during proestrus compared to estrus, metestrus, and diestrus in control and plus-maze tested female rats, but there were no significant differences in progesterone levels. Treating diestrus female rats with estradiol to produce estradiol plasma concentrations similar to those seen during proestrus abolished the difference in the percentage of time spent in the open arms by proestrus and diestrus rats. Since the time spent in the open arms of the plus-maze is inversely related to anxiety, we conclude that the anxiety levels of female rats were lower in proestrus than during diestrus, and that the levels of estradiol modulate this response.

Animals↗
PubMedDate not supplied

[Assistance to parents of preterm newborns at neonatal units].

The purpose of this study is to reflect about the assistance to be given to parents of preterm and low weight babies, born in neonatal units, based on existing literature and the authors' practical experiences. Although mothers right to be close to their babies is assured by law, most of the nurseries still keep strict visit schedules to parents. However, there are some units where mothers' permanency is allowed. The question, in these cases, is if parents effective involvement in the care of the baby should or should not be allowed. For the nursing care unit, the authors suggest some intervention strategies to adapt parents to the new situation, and to strengthen the relationship between them and the baby. The recommendations are as follows: parents free access to the nurseries; motivation of early physical contact between parents and baby; implementation of multi-professional support groups to help parents during the different stages of clinical evolution; incentive for breastfeeding, and direct care of the babies; structuring of formal and informal groups of support for parents during and after hospitalization.

Humans↗
PubMedDate not supplied

["...And the light is fading..." The experience of a child with terminal cancer].

The child with a chance of dying faces death in a very peculiar way, because the hope that he or she managed to keep up to this moment changes with the impact of reality reactivating the first feelings of despair and pain for the separation of the loved ones. The main goal of this study is the attendance of a child in a terminal face, using as a path the phenomenological reference. Twelve attendances have been done with children in terminal faces, where they were able to express significant situations of their living process, and reveal with great intensity many fears, like the ones of dying, of being lonely, of leaving the ones they love, among others. Before this we see the necessity of worrying with matters interrelated to the feelings and emotions of these children who walk towards death, taking into consideration the possible means of help.

Attitude to Health↗
PubMedDate not supplied

[Women in the second and third pregnancy trimester: their psychological changes].

The purpose of the paper is to report the authors' experience with a group of pregnant women when coordinating a project in which the objective was to clarify doubts about pregnancy, care of the newborn and contraception. It focuses on the feelings and perceptions of these women regarding the theme of sexuality and psychological aspects of pregnancy. The psychological changes mentioned by the participants in the second and third trimester made evident the importance of the nursing worker's educational when dealing with groups.

Female↗