Functional and ultrastructural neuroanatomy of interactive intratectal/tectonigral mesencephalic opioid inhibitory links and nigrotectal GABAergic pathways: Involvement of GABAA and μ1-opioid receptors in the modulation of panic-like reactions elicited by electrical stimulation of the dorsal midbrain

In the present study, the functional neuroanatomy of nigrotectal-tectonigral pathways as well as the effects of central administration of opioid antagonists on aversive stimuli-induced responses elicited by electrical stimulation of the midbrain tectum were determined. Central microinjections of naloxonazine, a selective mu(1)-opiod receptor antagonist, in the mesencephalic tectum (MT) caused a significant increase in the escape thresholds elicited by local electrical stimulation. Furthermore, either naltrexone or naloxonazine microinjected in the substantia nigra, pars reticulata (SNpr), caused a significant increase in the defensive thresholds elicited by electrical stimulation of the continuum comprised by dorsolateral aspects of the periaqueductal gray matter (dlPAG) and deep layers of the superior colliculus (dlSC), as compared with controls. These findings suggest an opioid modulation of GABAergic inhibitory inputs controlling the defensive behavior elicited by MT stimulation, in cranial aspects. In fact, iontophoretic microinjections of the neurotracer biodextran into the SNpr, a mesencephalic structure rich in GABA-containing neurons, show outputs to neural substrate of the dlSC/dlPAG involved with the generation and organization of fear- and panic-like reactions. Neurochemical lesion of the nigrotectal pathways increased the sensitivity of the MT to electrical (at alertness, freezing and escape thresholds) and chemical (blockade of GABA(A) receptors) stimulation, suggesting a tonic modulatory effect of the nigrotectal GABAergic outputs on the neural networks of the MT involved with the organization of the defensive behavior and panic-like reactions. Labeled neurons of the midbrain tectum send inputs with varicosities to ipsi and contralateral dlSC/dlPAG and ipsilateral substantia nigra, pars reticulata and compacta, in which the anterograde and retrograde tracing from a single injection indicates that the substantia nigra has reciprocal connections with the dlSC/dlPAG featuring close axo-somatic and axo-dendritic appositions in both locations. In addition, ultrastructural approaches show inhibitory axo-axonic synapses in MT and inhibitory axo-somatic/axo-axonic synapses in the SNpr. These findings, in addition to the psychopharmacological evidence for the interaction between opioid and GABAergic mechanisms in the cranial aspects of the MT as well as in the mesencephalic tegmentum, offer a neuroanatomical basis of a pre-synaptic opioid inhibition of GABAergic nigrotectal neurons modulating fear in defensive behavior-related structures of the cranial mesencephalon, in a short link, and through a major neural circuit, also in GABA-containing perikarya and axons of nigrotectal neurons.

Neuroanatomical and neuropharmacological study of opioid pathways in the mesencephalic tectum: effect of μ1- and κ-opioid receptor blockade on escape behavior induced by electrical stimulation of the inferior colliculus

Deep layers of the superior colliculus (DLSC), the dorsal and ventral periaqueductal gray matter (PAG), and inferior colliculus (IC) are midbrain structures involved in the generation of defensive behavior. beta-Endorphin and Leu-enkephalin are some neurotransmitters that may modulate such behavior in mammals. Light microscopy immunocytochemistry with streptavidin method was used for the localization of the putative cells of defensive behavior with antibodies for endogenous opioids in rat brainstem. Midbrain structures showed positive neurons to beta-endorphin and Leu-enkephalin in similar distributions in the experimental animals, but we also noted the presence of varicose fibers positive to endogenous opioids in the PAG. Neuroanatomical techniques showed varicose fibers from the central nucleus of the inferior colliculus to ventral aspects of the PAG, at more caudal levels. Naloxonazine and nor-binaltorphimine, competitive antagonists that block mu(1)- and kappa-opioid receptors, were then used in the present work to investigate the involvement of opioid peptide neural system in the control of the fear-induced reactions evoked by electrical stimulation of the neural substrates of the inferior colliculus. The fear-like responses were measured by electrical stimulation of the central nucleus of the inferior colliculus, eliciting the escape behavior, which is characterized by vigorous running and jumping. Central administration of opioid antagonists (2.5 microg/0.2 microl and 5.0 microg/0.2 microl) was performed in non-anesthetized animals (Rattus norvegicus), and the behavioral manifestations of fear were registered after 10 min, 2 h, and 24 h of the pretreatment. Naloxonazine caused an increase of the defensive threshold, as compared to control, suggesting an antiaversive effect of the antagonism on mu(1)-opioid receptor. This finding was corroborated with central administration of nor-binaltorphimine, which also induced a decrease of the fear-like responses evoked by electrical stimulation of the inferior colliculus, since the threshold of the escape behavior was increased 2 and 24 h after the blockade of kappa-opioid receptor. These results indicate that endogenous opioids may be involved in the modulation of fear in the central nucleus of the inferior colliculus. Although the acute treatment (after 10 min) of both naloxonazine and nor-binaltorphimine causes nonspecific effect on opioid receptors, we must consider the involvement of mu(1)- and kappa-opioid receptors in the antiaversive influence of the opioidergic interneurons in the dorsal mesencephalon, at caudal level, after chronic (2-24 h) treatment of these opioid antagonists. The neuroanatomical study of the connections between the central nucleus of the inferior colliculus and the periaqueductal gray matter showed neuronal fibers with varicosities and with terminal bottons, both in the pericentral nucleus of the inferior colliculus and in ventral and dorsal parts of caudal aspects of the periaqueductal gray matter.

Psychopharmacological evidences for the involvement of muscarinic and nicotinic cholinergic receptors on sweet substance-induced analgesia in Rattus norvegicus

In order to investigate the effects of sweet substance intake on pain modulation, male albino Wistar rats weighing 180-200 g received either tap water or sucrose solutions (250 g/l) for 14 days as their only source of liquid. Each rat consumed an average of 15.6 g sucrose/day. Their tail withdrawal latencies in the tail-flick test (probably a spinal reflex) were measured immediately before and after this treatment. An analgesia index was calculated from the withdrawal latencies before and after treatment. The index (mean +/- SEM, N = 8) for the groups receiving sucrose solution plus saline (NaCl; 0.9%) for 14 days was 0.70 +/- 0.01. Atropine (1 and 2 mg/kg)-treated rats (N = 8) after intake of sucrose exhibited an analgesia index of 0.39 +/- 0.09 and 0.39 +/- 0.08, respectively, while mecamylamine (1 and 2 mg/kg)-treated rats (N = 10) after intake of sucrose had an index of -0.02 +/- 0.07 and 0.03 +/- 0.07, respectively. These results indicate that the effect of sucrose intake on nociceptive thresholds is controlled by neurotransmission of acetylcholine and depends on the nicotinic cholinergic receptors for its major analgesic effect, although muscarinic receptors were also involved in this antinociceptive process.

Development of an ELISA to assess the potency of horse therapeutic polyvalent antibothropic antivenom

The objective of this study was the search for a suitable venom antigen to be used in an in vitro alternative immunoassay, to the standard antivenom neutralization assay using mice. Bothrops jararaca venom was fractionated in DEAE-Sephacel columns and the fractions were tested for a correlation between antibody capture enzyme linked immunosorbent assay (ELISA) absorbance values and the 'in vivo' antivenom potency. Individual antivenoms from 14 horses and 15 separate FUNED polyspecific Bothrops ampouled antivenoms (final product) were used. Fractions showing the higher correlations were further chromatographed in a Sephadex G-75 column and again tested for the correlation. Two fractions with haemorrhagic activity displayed a correlation of r = 0.77 and r = 0.8 against the individual horse antivenom sera and of r = 0.79 and r = 0.8 for the ampouled antivenom. For all results p < 0.001. Two other fractions with phospholipase A2 activity showed a correlation of r = 0.66 (p < 0.01) and r = 0.56 (p < 0.03) against the individual horse antivenom sera. Electrophoresis results show a similar composition for both antigens with haemorrhagic activity. Results indicate that the fractions purified would be suitable for the desired objective of this study.

[Hospital infections at an oncology hospital]

During 23 months, the authors analyzed 8122 records of cancer patients admitted to the National Institute of Cancer of Rio de Janeiro, Brazil. The rate of hospital infection was of 18.4 infection episodes per 100 admissions. Hospital infections were detected in 556 patients (57.7%) of the surgical department. The overall rate of purulence seen in 4194 surgeries was 10.1%, and among 2153 clean surgeries, the authors found 95 (4.4%) suppurated surgeries. The surgical wound (28.2%), the respiratory tract (19.2%), and the urinary tract (18.7%) were the major sites involved during infections episodes. Of the 319 ICU patients evaluated, 154 acquired infection after the first 72 hours, with a mortality rate of 48.7%. The hospital microbial flora was made-up mostly of gram-negative aerobic bacteria, with a high incidence of micro-organisms that resist to major antibiotics of hospital use. The percentage of positive results in blood culture tests requested was of 23.7%, with a predominance of gram-negative bacteria (50.9%) and a high percentage of gentamicin-resistant micro-organisms. Antibiotics of greater use in surgical interventions were amikacin, first generation cephalosporins, and chloramphenicol, whereas amikacin, carbenicillin, and first and third generation cephalosporins prevailed in nonsurgical treatments. The authors' experience and findings re-emphasize the need and the importance of a broad multidisciplinary understanding and suggest the need of strict action for an effective control and prevention in hospitals of developing countries.