Biomedical subjects

J H Pazo

Publications and source records attributed to J H Pazo.

At least 19 recordsLinked to original sources

PubMed1992

Spontaneous and evoked activity of the caudate neurons to central and peripheral stimuli after brain lesions.

The involvement of the cerebral cortex, commissural fibers and thalamus on caudate-caudate relations was studied in locally anesthetized, paralysed and artificially ventilated cats. This type of experimental preparation was necessary since a complete suppression of spontaneous and evoked activity is produced by subanesthetic doses of general anesthesia. Two types of caudate action potentials were encountered on the basis of their waveform characteristics: biphasic and triphasic spikes, the former being the largest population (80%). These waveforms were independent of the microelectrode resistance and the distance to recorded neurons. However, their responses were very similar to both central and peripheral stimuli. Caudate stimulation depressed the spontaneous discharges of the majority of the responsive units recorded within the opposite nucleus, while striatal neurons were activated by stimulation of the contralateral cortex. Decortication, thalamic lesion (motor nuclei and massa intermedia) and section of the corpus callosum decrease the firing rates of caudate neurons with biphasic spikes, while the discharges of the neurons with triphasic action potentials remained unchanged. Bilateral ablation of the cerebral cortex decreased the responsiveness of striatal neurons to contralateral nucleus and sciatic nerve and reduced the number of spontaneously active cells per recording tract. Section of the commissural fibers also depressed the caudate responses to the contralateral nucleus, and to the opposite precruciate cortex, although thalamic lesion did not affect the responsiveness of caudate cells to both central and peripheral stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1991

Role of the mesopontine area in the circling behavior induced by apomorphine in rats bearing unilateral lesion of the entopeduncular nucleus.

The role of the mesopontine area and superior colliculus in turning behavior induced by systemic administration of apomorphine was studied in rats bearing a unilateral entopeduncular lesion. Bilateral electrolytic damage of the superior colliculus resulted in an enhancement of the ipsilateral circling response to apomorphine, perhaps as a consequence of an increased locomotor drive in such animals. Bilateral electrolytic lesions of the mesopontine area decreased apomorphine-induced turning in entopeduncular rats, while a bilateral kainic acid lesion of the same region was ineffective. It was concluded that the pedunculopontine nucleus and adjacent reticular formation are not an essential link for the striopallidal complex output mediating circling in this model. Fibers running through this region could be implicated in the expression of the behavior under study. Since a unilateral electrolytic lesion of the mesopontine area contralateral to the damaged entopeduncular nucleus reduced drug-induced turning, we propose that an uncrossed pathway from the intact striopallidal complex mediates circling in our rats.

Animals↗

PubMed1991

Effects of central and peripheral inputs on single pineal cell activity in the rat.

The influences exerted by central and peripheral afferents to the pineal gland have been studied in rats anesthetized with urethane (1.2 g/kg, i.p.). Spontaneous action potentials arising from the pinealocytes were recorded by means of glass micropipettes filled with 3 M NaCl containing a dye. The electrical stimulation of suprachiasmatic nucleus, superior cervical ganglia, sciatic nerve and retina evoked discharge changes in a significant number of pineal cells. However, a relatively higher proportion of pinealocytes failed to respond to these afferents. Three types of responses could be observed. Inhibitions were the predominant response patterns to suprachiasmatic nucleus, superior cervical ganglia and sciatic nerve, while excitations were mainly elicited following photic stimulation, whereas the remaining evoked activity was biphasic responses, which were observed in a small number of cells after stimulation of suprachiasmatic nucleus, superior cervical ganglia and retina. These data confirm some previous neural inputs to the pineal and demonstrate the existence of a modulatory effect of the suprachiasmatic nucleus on pinealocyte discharges as well as somatosensory afferents to the gland by way of the sciatic nerve.

Action Potentials↗

PubMed1990

Responses elicited by species-specific models in the cichlid Crenicichla lepidota (Heckel).

Species recognition by the cichlid fish C. lepidota was studied by measuring species-specific aggressive behavior toward either live conspecifics (control) or toward different two-dimensional models. A plain fish-shaped model elicited aggressive behavior, but the responses were mostly absent when the model was a rectangle. Adding heavy stripes to the fish-shaped form increased the responses, which were further enhanced by adding a spot. Comparable aggressive responses were also induced by adding spots and eye to dummies with thin stripes. We conclude that in our experimental conditions, fish-like shape and contrast seem to be of great significance for recognition of conspecifics in the cichlid C. lepidota (Heckel).

Aggression↗

PubMed1989

Automatic temperature controller for maintaining body temperature in experimental animals.

A system for autoregulation of body temperature of large and small animals is described. The device uses the IC AD590 as a temperature transducer. It operates on the basis of continuous regulation of the heating current, and does not emit transients which interfere with electrical recordings. A panel meter shows either the rectal temperature of the animal or the current flow to the blanket.

Body Temperature Regulation↗

PubMed1989

Changes in pancreatic exocrine secretion after repeated haloperidol administration.

The effect of repeated administration of haloperidol on the pancreatic secretion was studied in urethane-anesthetized Swiss mice. Haloperidol (2 mg/kg) injected daily i.p. for 7 days, increase the volume and protein content of the basal pancreatic juice significantly. This secretory activity was partially blocked by i.p. injection of atropine (5 mg/kg), both in control and treated animals. The volume of the secretory response to bethanechol, a cholinergic agonist, was decreased by haloperidol without any change in amylase release. From these findings it is concluded that repeated haloperidol treatment produces an increase of basal pancreatic secretion, which is probably the result of changes in the sensitivity of dopamine receptors of the gland.

Adrenergic Fibers↗

PubMed1989

Increase of muscarinic cholinergic receptors in the rat submandibular glands after parasympathectomy and repeated administration of haloperidol.

1. The mechanisms of the supersensitivity to cholinergic drugs after chronic haloperidol was studied in normal and parasympathectomized submandibular glands of the rats. 2. Both parasympathectomy and haloperidol treatment for 7 days (2 mg/kg/day, i.p.) increased the sialogogue response of the glands to methacholine, a cholinomimetic drug. 3. Both denervation and haloperidol administration induce up-regulation of the muscarinic receptors as expressed per gram of the tissue. 4. Haloperidol causes no further increase in sensitivity than denervation alone. 5. These data demonstrate that secretory supersensitivity to cholinergic drugs in the rat submandibular glands, after chronic haloperidol and parasympathectomy is related to an increase in muscarinic cholinergic receptors.

Animals↗

PubMed1989

Central and peripheral modulation of spontaneous neuronal activity in the caudate nucleus.

The modulatory action of the caudate on the neural activity of the contralateral nucleus was studied in locally anesthetized, paralysed and artificially ventilated cats. This type of preparation was necessary because of a complete suppression of spontaneous spike activity after subanesthetic doses of general anesthesia. Two types of caudate action potential were characterized according to their waveform: biphasic and triphasic spikes, with a predominance of the former. These waveforms appeared to be independent of recording distance; however, their responses were similar to both central and peripheral stimuli. Caudate stimulation modified the spontaneous activity of the majority of the single units recorded within the opposite nucleus. This effect was mainly inhibitory and keeps up certain somatotopic distribution in the rostrocaudal extent of the nucleus. Kainic lesion of the site of stimulation suppressed the responses in the contralateral caudate nucleus, whereas the responses to substantia nigra and precruciate cortex remained unaltered. On the other hand, stimulation of the precruciate cortex opposite to the recording sites always excited the caudate neurons. The responses evoked by stimulation of ipsilateral substantia nigra and of contralateral sciatic nerve followed a similar pattern to those elicited by caudate stimuli. These results suggest a mostly inhibitory effect of the caudate on neuronal activity within the opposite nucleus, which is reinforced by the action of central and peripheral somatosensory inputs.

Action Potentials↗

PubMed1987

Selective increase of alpha 1-adrenoceptors and muscarinic cholinergic receptors in rat cerebral cortex after chronic haloperidol.

The effect of chronic administration of haloperidol on alpha 1-, alpha 2-, and beta-adrenoceptors, cholinergic muscarinic, GABAA and benzodiazepine receptors in the cerebral cortex of the rat was investigated. Doses of 0.3 and 2 mg/kg of haloperidol during 7 days increased markedly the density of alpha 1-adrenoceptors without changes in affinity. The alpha 2- and beta-adrenoceptors were not modified after neuroleptic administration. The number of muscarinic receptors were also increased after haloperidol treatment (2 mg/kg/day). However, the GABAA and benzodiazepine binding sites remained unchanged. In the brainstem an increment in the alpha 1-, but not the beta-adrenoceptors was observed. The well known increase in the dopamine receptors in the striatum was confirmed. These observations demonstrate a multireceptor effect of haloperidol in the cerebral cortex.

Animals↗

PubMed1987

Effect of chronic administration of haloperidol on secretory response mediated by cholinergic receptors in rat submandibular glands.

Administration of haloperidol influences peripheral non-dopaminergic receptors. The sialagogue response of the submandibular glands of the rats to methacholine was enhanced by chronic administration of haloperidol. The binding of [3H]QNB to muscarinic receptors in the submandibular glands was not changed by chronic haloperidol. The supersensitivity of postsynaptic cholinergic receptors to drugs in haloperidol treated rats is not related to changes in the number or affinity of such receptors. This paper confirmed the sialagogue supersensitivity to adrenergic drugs related to an increase in alpha 1-adrenoceptors in the submandibular glands of haloperidol injected rats.

Animals↗

PubMed1987

Spinal cord substrate of the turning behavior induced by unilateral lesion of the entopeduncular nucleus.

The neural pathways in the spinal cord mediating circling behavior in animals with unilateral kainic acid lesion of the entopeduncular nucleus were studied in rats. The circling activity toward the lesioned side was indiced by i.p. administration of apomorphine (3 mg/kg). Section of the lateral funiculus ipsilateral to the lesioned entopeduncular nucleus, reduced significantly the rate of drug induced rotations. The above was a common lesion of ventrolateral and dorsolateral transections of the cervical spinal cord. However, the latter transection was more effective than the former to block the circling. On the other hand, lesion of the contralateral spinal cord fails to modify turning behavior. These findings suggest that crossed fibers descending in the dorsolateral quadrant directly from the basal ganglia or mediating synaptic relay in the lower brainstem may be the anatomical substrate of the circling produced by striatal stimulation.

Animals↗

PubMed1986

The sialagogue response of striatal dopamine receptors to L-dopa is not influenced by castration or chronic estrogen treatment.

The secretory response of salivary glands to L-dopa, elicited by stimulation of dopamine receptors in the striatum and the circling behavior induced by apomorphine in animals bearing a unilateral kainic lesion of the entopeduncular nucleus, was studied in intact and ovariectomized female rats. Castration did not modify the sialagogue response to L-dopa, while the turning behavior was significantly increased. Daily administration of 17-beta-estradiol benzoate during 7 days to ovariectomized rats decreased the circling activity to the level of intact female rats, while the salivary secretion to L-dopa was unaffected. The above findings suggest that the sialagogue response induced by L-dopa may be due to the interaction of this agonist with D1 striatal receptors, whose activity is not influenced by estrogens. However, we cannot rule out any possible alteration in the metabolism and/or presynaptic conversion of L-dopa to dopamine by estrogen treatment. The changes in turning behavior may be attributed to an antidopaminergic effect of estrogens and/or, like L-dopa, to modifications in the metabolism of apomorphine induced by the hormone.

Animals↗

PubMed1985

Chronic haloperidol causes increase in salivary response and alpha 1-adrenoceptors in submandibular gland of the rat.

The effect of chronic haloperidol on the receptor-secretion coupling of the submandibular glands of the rat was studied. After injection of 2 mg/kg haloperidol daily for 7 days, the dose-response curve to L-noradrenaline was displaced to the left, with lowering of the threshold and enhancement of the maximal response. This was accompanied by a 73% increase in alpha 1-adrenoceptors in the glands. The effect was selective, since no changes were observed in alpha 2- and beta-adrenoceptors.

Animals↗

PubMed1984

Salivary secretion induced by L-DOPA in haloperidol-treated rats.

The effect of chronic haloperidol treatment on salivary secretion induced by L-dopa, was studied in male Sprague-Dawley rats. Dose-response relationships for L-dopa, obtained 24 h after haloperidol treatment, showed that salivary secretion was greater in rats that had been injected with haloperidol (2 mg/kg/day, i.p.) for 7 days than in controls. The threshold doses requirements were significantly reduced in that group. Pretreatment with carbidopa suppressed the salivary secretion produced by L-dopa in haloperidol-treated and control rats whose glands had been denervated. The secretory response in innervated glands was higher in haloperidol-treated animals than in controls. Haloperidol treatment also increased salivation induced by L-noradrenaline as determined by dose-response relationships. This was associated with a decrease in the threshold doses requirement. In controls and in rats chronically treated with haloperidol, the salivary responses to L-noradrenaline were temporarily depressed by 80-90% by a prior acute injection of haloperidol (2 mg/kg, i.v.) presumably acting as an alpha blocker. A similar reduction was observed after acute treatment with phentolamine (3 mg/kg, i.v.). The data obtained in this study, i.e. that chronic administration of haloperidol increases the salivary response to L-dopa and L-noradrenaline, suggests that such an affect could be due to the development of supersensitivity of striatal dopamine receptors as well as of peripheral alpha-adrenergic receptors.

Animals↗

PubMed1983

Cholinergic mechanisms within the caudate nucleus mediate changes in blood pressure.

Microinjections of 10 micrograms of carbachol into the caudate nucleus induced changes in the blood pressure of cats anesthetized locally, paralyzed and artificially respired. These responses were dependent on the site of injection. Carbachol, microinjected at rostral levels of the caudate nucleus, elicited pressor responses while a decrease in blood pressure was observed following injections at caudal levels. Both of these effects were blocked by prior microinjection of atropine. Microinjections of carbachol outside the caudate did not affect the resting blood pressure. However, injections of carbachol into the lateral ventricle always produced pressor responses independent of the site of injection along the antero-posterior extension of the ventricle. On the other hand, microinjections of dopamine (20 micrograms) into the caudate nucleus failed to modify blood pressure. From this study, it is concluded that within the caudate nucleus there are two different muscarinic mechanisms, which when activated, mediate changes in blood pressure, possibly through the sympathetic nervous system.

Acetylcholine↗

PubMed1982

Changes in multiunit activity of nigral neurons induced by cholinergic and dopaminergic stimulation of the caudate nucleus.

The effects of stimulation of the caudate cholinergic and dopaminergic receptors on multiunit activity in the ipsilateral substantia nigra were studied in cats locally anesthetized, paralyzed and artificially respired. Cholinergic stimulation by intracaudate microinjections of 10 micrograms of carbachol diminished multiunit activity by 36% in the ventral substantia nigra (SN) and increased activity by 48% in the dorsal SN. This effect was abolished after electrolytic lesion of the ipsilateral striatonigral pathway. Opposite responses were observed following intracaudate administration of 20 micrograms of dopamine or 20 micrograms of D-amphetamine. Multiunit activity in the ventral SN increased by 36% and 34%, respectively, while the activity in the dorsal SN was reduced by 56% and 53%, respectively. Similar results were obtained in response to systemic administration of D-amphetamine. Extracaudate microinjections of carbachol and dopamine left multiunit activity in the SN unaffected. In conclusion, our results indicate an opposite action of caudate cholinergic and dopaminergic receptors on multiunit activity in the SN of the cat.

Animals↗

PubMed1982

Study of the neural basis of circling behavior induced by L-dopa in lesioned entopeduncular cats.

Experiments were carried out in cats bearing unilateral electrolytic lesion of the entopeduncular nucleus. The animals were tested for circling 1-2 weeks after surgery. Postoperatively the cats displayed transient spontaneous ipsiversive turning. The administration i.p. of L-DOPA (80 mg/kg) plus CarbiDOPA (30 mg/kg), suspended in 10% Tween 80, induced rotational behavior toward the lesioned side. This effect began about 26 min after drug administration and reached its maximum 40-110 min after the injection. Electrolytic lesions placed in the superior colliculus, strionigral pathway or pedunculopontine nucleus, contralateral to the lesioned entopeduncular nucleus did not modify the circling behavior induced by L-DOPA. Similar results were observed following unilateral lesion of the sensorimotor cortex or the VL thalamic nucleus. These results suggest that the circus movements induced by L-DOPA, in animals with unilateral lesion of the entopeduncular nucleus, is not mediated by the classic outflow of the striopallidal system.

Animals↗

PubMed1982

The role of the caudate-putamen nucleus in salivary secretion induced by L-DOPA.

Experiments were performed in rats of the Wistar strain anesthetized with alpha-chloralose (100 mg/kg). Electrolytic lesion of either components of the striopallidal complex (corpus striatum, globus pallidus or entopeduncular nucleus) reduced the sensory response to L-DOPA in the contralateral submaxillary glands. Damage to other neural structures, directly or indirectly related to the striopallidal system, left the salivary response unaffected. These structures were: substantia nigra, cerebral cortex, ventromedial and center median-parafascicular thalamic nuclei, nucleus accumbens and posterior hypothalamic areas, including the medial forebrain bundle and lateral habenular nucleus. However, lesions placed in H1-H2 fields of Forel and reticular formation, lateral to the periaqueductal gray, reduced the salivary response in the contralateral glands. This effect was similar to that observed in animals with lesions of the striopallidal complex. From this study, it is concluded that the striatum is the target area for the central effect of L-DOPA on salivary secretion, by activation of pathways descending through the fields of Forel and mesencephalic reticular formation to the contralateral lower brain stem.

Animals↗