Responses of reticulospinal neurons in intact lamprey to vestibular and visual inputs. (73/2436)

A lamprey maintains the dorsal-side-up orientation due to the activity of postural control system driven by vestibular input. Visual input can affect the body orientation: illumination of one eye evokes ipsilateral roll tilt. An important element of the postural network is the reticulospinal (RS) neurons transmitting commands from the brain stem to the spinal cord. Here we describe responses to vestibular and visual stimuli in RS neurons of the intact lamprey. We recorded activity from the axons of larger RS neurons with six extracellular electrodes chronically implanted on the surface of the spinal cord. From these multielectrode recordings of mass activity, discharges in individual axons were extracted by means of a spike-sorting program, and the axon position in the spinal cord and its conduction velocity were determined. Vestibular stimulation was performed by rotating the animal around its longitudinal axis in steps of 45 degrees through 360 degrees. Nonpatterned visual stimulation was performed by unilateral eye illumination. All RS neurons were classified into two groups depending on their pattern of response to vestibular and visual stimuli; the groups also differed in the axon position in the spinal cord and its conduction velocity. Each group consisted of two symmetrical, left and right, subgroups. In group 1 neurons, rotation of the animal evoked both dynamic and static responses; these responses were much larger when rotation was directed toward the contralateral labyrinth, and the dynamic responses to stepwise rotation occurred at any initial orientation of the animal, but they were more pronounced within the angular zone of 0-135 degrees. The zone of static responses approximately coincided with the zone of pronounced dynamic responses. The group 1 neurons received excitatory input from the ipsilateral eye and inhibitory input from the contralateral eye. When vestibular stimulation was combined with illumination of the ipsilateral eye, both dynamic and static vestibular responses were augmented. Contralateral eye illumination caused a decrease of both types of responses. Group 2 neurons responded dynamically to rotation in both directions throughout 360 degrees. They received excitatory inputs from both eyes. Axons of the group 2 neurons had higher conduction velocity and were located more medially in the spinal cord as compared with the group 1 neurons. We suggest that the reticulospinal neurons of group 1 constitute an essential part of the postural network in the lamprey. They transmit orientation-dependent command signals to the spinal cord causing postural corrections. The role of these neurons is discussed in relation to the model of the roll control system formulated in our previous studies.  (+info)

Physical and physiological components of the graviresponses of wild-type and mutant Paramecium Tetraurelia. (74/2436)

Wild-type and the morphological mutant kin 241 of Paramecium tetraurelia showed improved orientation away from the centre of gravity (negative gravitaxis) when accelerations were increased from 1 to 7 g. Gravitaxis was more pronounced in the mutant. A correlation between the efficiency of orientation and the applied g value suggests a physical basis for gravitaxis. Transiently enhanced rates of reversal of the swimming direction coincided with transiently enhanced gravitaxis because reversals occurred more often in downward swimmers than in upward swimmers. The results provide evidence of a physiological modulation of gravitaxis by means of the randomizing effect of depolarization-dependent swimming reversals. Gravity bimodally altered propulsion rates of wild-type P. tetraurelia so that sedimentation was partly antagonized in upward and downward swimmers (negative gravikinesis). In the mutant, only increases in propulsion were observed, although the orientation-dependent sensitivity of the gravikinetic response was the same as in the wild-type population. Observed swimming speed and sedimentation rates in the wild-type and mutant cells were linearly related to acceleration, allowing the determination of gravikinesis as a linear (and so far non-saturating) function of gravity.  (+info)

Effects of prenatal aflatoxin B1 exposure on behaviors of rat offspring. (75/2436)

The effects of prenatal aflatoxin B1 (AFB) exposure on eight behavioral parameters in Jcl:Wistar rat offspring were assessed. Pregnant rats were injected subcutaneously with 0.3 mg/kg/day of AFB dissolved in dimethylsulfoxide on days 11-14 (Group A) or 15-18 (Group B) of gestation. Controls received the vehicle similarly on days 11-18 of gestation. Before weaning, the offspring were examined using the cliff avoidance response (5 days of age), the negative geotaxis reflex (7 days), and swimming development (6, 8, and 10 days). After weaning, animals were examined using the rotarod test (5 weeks of age), the open field test (6 weeks), a conditioned avoidance learning test (14 weeks), an underwater T-maze test (15 weeks), and a reproduction test (16 weeks). The preweaning offspring in the AFB-A group showed significantly lower success rates than controls in cliff avoidance responses. In swimming development, the offspring in the AFB-A group had significantly lower scores than controls for swimming direction. In the rotarod test, the AFB-A group remained on the rod for a significantly shorter time than the controls at 15 rpm on both the first and second trial days. The avoidance performance of the rats in AFB-A and AFB -B groups was significantly poorer than that of controls. These results indicate that prenatal exposure to AFB produced a delay of early response development, impaired locomotor coordination, and impaired learning ability in the offspring of rats exposed to AFB during middle pregnancy, and the early gestational exposure appears to produce more effects than latter exposure.  (+info)

Spatial training and high-frequency stimulation engage a common pathway to enhance glutamate release in the hippocampus. (76/2436)

We have measured depolarization-induced release of endogenous glutamate in synaptosomes prepared from the dentate gyrus after the induction of LTP by high-frequency stimulation in anesthetized rats, and after training in the water maze. Both spatial training and LTP in untrained rats were accompanied by an increase in glutamate release from dentate synaptosomes. The enhancement of synaptosomal glutamate release induced by high-frequency stimulation was abolished in well-trained rats, and was reduced in partially trained rats and in rats trained in a nonspatial task. However, the magnitude of LTP was similar in well-trained and untrained groups. These results indicate that spatial training activates a glutamate release pathway that converges with that activated in LTP, and demonstrate an unexpected dissociation between increased glutamate release and LTP.  (+info)

Dishabituation of the Tritonia escape swim. (77/2436)

When repeatedly elicited, the oscillatory escape swim of the marine mollusc Tritonia diomedea undergoes habituation of the number of cycles per swim. Although similar in most respects to habituation observed in vertebrates and other invertebrates, one key feature, dishabituation, has been surprisingly difficult to demonstrate. Here we evaluate the hypothesis that this is due to interference from short-term sensitization, which is manifested as a reduction in swim onset latency, that occurs simultaneously during habituation training. Robust dishabituation was obtained using a multisession habituation protocol designed to allow this sensitization to dissipate before the dishabituatory stimulus was applied. These results extend the similarity of habituation in Tritonia to that described in other species, strengthening the usefulness of this preparation as a model system for studies of the cellular basis of habituation.  (+info)

The ageing of the low-frequency water disturbances caused by swimming goldfish and its possible relevance to prey detection. (78/2436)

Wakes caused by swimming goldfish (Carassius auratus) were measured with a particle image velocimetry system and analyzed using a cross-correlation technique. Particle velocities in a horizontal plane (size of measuring plane 24 cmx32 cm or 20 cmx27 cm) were determined, and the vorticity in the plane was derived from these data. The wake behind a swimming goldfish can show a clear vortex structure for at least 30 s. Particle velocities significantly higher than background noise could still be detected 3 min after a fish (body length 10 cm) had passed through the measuring plane. Within this time span, the lateral spread of fish-generated wakes could exceed 30 cm for a 10 cm fish and 20 cm for a 6 cm fish. Measurements in a man-made open-air pond showed that water velocities in a quasi-natural still water environment can be as small as 1 mm s(-)(1). Background velocities did not exceed 3 mm s(-)(1) as long as no moving animal was present in the measuring plane. The possible advantage for piscivorous predators of being able to detect and analyze fish-generated wakes is discussed.  (+info)

Effects of the novel NMDA receptor antagonist gacyclidine on recovery from medial frontal cortex contusion injury in rats. (79/2436)

Gacyclidine, a novel, noncompetitive NMDA receptor antagonist, was injected (i.v.) into rats at three different doses to determine if the drug could promote behavioral recovery and reduce the behavioral and anatomical impairments that occur after bilateral contusions of the medial frontal cortex (MFC). In the Morris water maze, contused rats treated with gacyclidine at a dosage of 0.1 mg/kg performed better than their vehicle-treated conspecifics. Rats given gacyclidine at either 0.3 or 0.03 mg/kg performed better than brain-injured controls, but not as well as those treated with 0.1 mg/kg. Counts of surviving neurons in the nucleus basalis magnocellularis (NBM) and the medial dorsal nucleus (MDN) of the thalamus were used to determine whether gacyclidine treatment attenuated secondary cell death. In both the NBM and the MDN, the counts revealed fewer surviving neurons in untreated contused rats than in gacyclidine-treated rats. Increases in the size and number of microglia and astrocytes were observed in the striatum of gacyclidine-treated contused brains. Although most consequences of MFC contusions were attenuated, we still observed increases in ventricle dilation and thinning of the cortex. In fact, the ventricles of rats treated with 0.1 mg/kg of gacyclidine were larger than those of their vehicle treated counterparts, although we observed no behavioral impairment.  (+info)

Escape swim network interneurons have diverse roles in behavioral switching and putative arousal in Pleurobranchaea. (80/2436)

Escape swimming in the predatory sea slug Pleurobranchaea is a dominant behavior that overrides feeding, a behavioral switch caused by swim-induced inhibition of feeding command neurons. We have now found distinct roles for the different swim interneurons in acute suppression of feeding during the swim and in a longer-term stimulation of excitability in the feeding network. The identified pattern-generating swim neurons A1, A3, A10, and their follower interneuron A-ci1, suppress feeding motor output partly by excitation of the I1 feeding interneurons, which monosynaptically inhibit both the feeding command neurons, PC(P), PSE, and other major interneurons, the I2s. This mechanism exerts broad inhibition of the feeding network suitable to an escape response; broader than feeding suppression in learned and satiation-induced food avoidance and acting through a different presynaptic pathway. Four intrinsic neuromodulatory neurons of the swim network, the serotonergic As1-4, add little to direct suppression of feeding. Rather, they monosynaptically excite the serotonergic metacerebral giant (MCG) neurons of the feeding network, themselves intrinsic neuromodulators of feeding, as well as a cluster of adjacent serotonergic feeding neurons, with both fast and slow EPSPs. They also provide mild neuromodulatory excitation of the PC(P)/PSE feeding command neurons, and I1 and I2 feeding interneurons, which is masked by inhibition during the swim. As1-4 also excite the serotonergic pedal ganglion G neurons for creeping locomotion. These observations further delineate the nature of the putative serotonergic arousal system of gastropods and suggest a central coordinating role to As1-4.  (+info)