Biomedical subjects

M E Castelló

Publications and source records attributed to M E Castelló.

6 recordsLinked to original sources

PubMed2003

Probability and amplitude of novelty responses as a function of the change in contrast of the reafferent image in G carapo.

Pulse electric fish evaluate successive electrosensory images generated by self-emitted electric discharges, creating a neural representation of the physical world. Intervals between discharges (system resolution) are controlled by a pacemaker nucleus under the influence of reafferent signals. Novel sensory stimuli cause transient accelerations of the pacemaker rate (novelty responses). This study describes quantitatively the effect of changes in contrast of reafferent electrosensory signals on the amplitude and probability of novelty responses. We found that: (i). alterations of a single image in an otherwise homogeneous series cause a novelty response; (ii). the amplitude of the elicited novelty response is a linear function of the logarithm of the change in image contrast; (iii). the parameters of this function, threshold and proportionality constant, allowed us to evaluate the transference function between change in stimulus amplitude and the amplitude of the novelty response; (iv). both parameters are independent of the baseline contrast; (v). the proportionality constant increases with the moving average of the contrast of hundreds of previous images. These findings suggest that the electrosensory system (i). calculates the difference between each reafferent electrosensory image and a neural representation of the past electrosensory input ('template'); (ii). creates the comparison template in which the relative contribution of every image decreases with the incorporation of successive images. We conclude that contrast discrimination in the electrosensory system of G. carapo obeys the general principle of appreciating any instantaneous input by the input's departure from a moving average of past images.

Animals↗

PubMed2001

Electroreception in Gymnotus carapo: differences between self-generated and conspecific-generated signal carriers.

Local electric fields generated by the electric organ discharge of Gymnotus carapo were explored at selected points on the skin of an emitter fish ('local self-generated fields') and on the skin of a conspecific ('local conspecific-generated fields') using a specially designed probe. Local self-generated fields showed a constant pattern along the body of the fish. At the head, these fields were collimated, much stronger than elsewhere on the fish, and had a time waveform that was site-independent. This waveform consisted of a slow head-negative wave followed by a faster head-positive wave. In contrast, time waveforms in the trunk and tail regions were site-specific, with field vectors that changed direction over time. Local conspecific-generated fields were similar to the head-to-tail field, but their spatio-temporal pattern at the skin depended on the relative orientation between the receiving fish and the emitting fish. Because self-generated fields had a slow early component at the head region, they displayed a low-frequency peak in their power spectral density histograms. In contrast, the conspecific-generated fields had time waveforms with a sharper phase reversal, resulting in a peak at higher frequency than in the self-generated field. Lesions in emitting fish demonstrated that waveform components generated by the trunk and tail regions of the electric organ predominate in conspecific-generated fields, whereas waveform components generated by the abdominal region prevail in self-generated fields. Similar results were obtained from Brachyhypopomus pinnicaudatus. These results suggest that, in pulse-emitting gymnotids, electrolocation and electrocommunication signals may be carried by different field components generated by different regions of the electric organ.

Animal Communication↗

PubMed2000

Electroreception in Gymnotus carapo: pre-receptor processing and the distribution of electroreceptor types.

This paper describes the peripheral mechanisms involved in signal processing of self- and conspecific-generated electric fields by the electric fish Gymnotus carapo. The distribution of the different types of tuberous electroreceptor and the occurrence of particular electric field patterns close to the body of the fish were studied. The density of tuberous electroreceptors was found to be maximal on the jaw (foveal region) and very high on the dorsal region of the snout (parafoveal region), decaying caudally. Tuberous type II electroreceptors were much more abundant than type I electroreceptors. Type I electroreceptors occurred exclusively on the head and rostral trunk regions, while type II electroreceptors were found along as much as 90 % of the fish. Electrophysiological data indicated that conspecific- and self-generated electric currents are 'funnelled' by the high conductivity and geometry of the body of the fish. These currents are concentrated at the peri-oral zone, where most electroreceptors are located. Moreover, within this region, field vector directions were collimated, constituting the most efficient stimulus for electroreceptors. It can be concluded that the passive properties of the fish tissue represent a pre-receptor device that enhances exafferent and reafferent electrical signals at the fovea-parafoveal region.

Animals↗

PubMed1998

Structural and functional aspects of the fast electrosensory pathway in the electrosensory lateral line lobe of the pulse fish Gymnotus carapo.

The fast electrosensory pathway (FEP) of gymnotiform fish is mediated by tuberous electroreceptor organs innervated by ganglion cells that synapse with spherical cells of the electrosensory lateral line lobe (ELL). Spherical cells project to the magnocellular mesencephalic nucleus. The electrosensory environment was represented somatotopically within ELL. The mandibular (MN) and the supraorbital (SON) nerves projected to rostral ELL (occupying 19-28% and 4-10%, respectively), and the posterior branch of the anterior lateral line nerve (pALLN) projected to caudal ELL (occupying 56-64%). Labeling with horseradish peroxidase or biotinylated dextran-amine demonstrated three kinds of synaptic endings coupling primary afferents to spherical cells: multiple synaptic knobs, medium-sized calyxes, and very large calyxes. Multiple synaptic knobs arose from MN and SON primary afferents and were found in a narrow rostral area covering the centrolateral (CLS) and lateral (LS) segments of ELL. Medium and large calyxes, proceeding from the same nerves, predominated in the remaining parts of the three segments of ELL containing spherical cells. Calyx-type endings were also found in the LS-occupying regions in which the pALLNs projected. Calyx-type endings formed gap junctions but also contained vesicles and showed submembrane specializations typical of chemical synapses. The postsynaptic spherical cells were linked by dendrosomatic gap junctions and were also contacted by unlabeled en passant synaptic boutons, whose fine structure suggested chemical transmission. Electrophysiological studies indicated that spherical cell responsiveness diminished after electrosensory stimulation. This apparently inhibitory phenomenon may be subserved by the unlabeled synaptic boutons, which possibly originate from interneurons that have yet to be identified.

Animals↗

PubMed1992

Catalepsy induced by striatal acetylcholinesterase inhibition with fasciculin in rats.

The acetylcholinesterase inhibitor peptide fasciculin (FAS) was bilaterally injected into the striatum of rats. Twenty-four hours after injection, animals showed a cataleptic syndrome that was potentiated by haloperidol (HAL). The catalepsy was significantly decreased by IP atropine. Biochemically, only an increase of the homovanillic acid in the striatum was found 24 h and 7 days after FAS treatment. Seven days after the intrastriatal FAS injection, there was no HAL potentiation of catalepsy, which was even lower than that of rats treated with IP HAL after intrastriatal injection of saline. Results are interpreted as showing the central role of the cholinergic system in the induction of catalepsy in the rat.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1989

Neurochemical and behavioral correlates of unilateral striatal acetylcholinesterase inhibition by fasciculin in rats.

Fasciculin 2 (FAS) an anticholinesterase peptide isolated from the venom of the Green mamba (Dendroaspis angusticeps) was injected into the right striatum of albino rats (1.5 micrograms total amount). The inhibition of acetylcholinesterase (AChE) activity was 86 and 60% 24 h and 7 days after FAS injection, respectively. The treatment with apomorphine (APO) (2 mg/kg s.c.) 24 h after FAS provoked a moderate circling towards the lesioned side that was reverted by atropine (30 mg/kg i.p.). The same dose of APO 7 days after FAS, provoked an inconstant contralateral circling. Neither dopamine nor serotonin nor their metabolites were significantly affected 24 h or 7 days after FAS injection. Radioligand binding assays of dopamine, muscarinic and benzodiazepine receptors only showed a decrease of the density of the muscarinic ones 7 days after FAS. These results are interpreted as showing that the changes provoked by FAS would be compensated but the system would remain in an unsteady state only demonstrable after pharmacological challenge. The chronic down-regulation of muscarinic receptors would compensate the increased cholinergic activity and would therefore block its behavioral expression.

Acetylcholinesterase↗