Effects of saccades on the activity of neurons in the cat lateral geniculate nucleus

Effects of saccades on individual neurons in the cat lateral geniculate nucleus (LGN) were examined under two conditions: during spontaneous saccades in the dark and during stimulation by large, uniform flashes delivered at various times during and after rewarded saccades made to small visual targets. In the dark condition, a suppression of activity began 200-300 ms before saccade start, peaked approximately 100 ms before saccade start, and smoothly reversed to a facilitation of activity by saccade end. The facilitation peaked 70-130 ms after saccade end and decayed during the next several hundred milliseconds. The latency of the facilitation was related inversely to saccade velocity, reaching a minimum for saccades with peak velocity >70-80 degrees /s. Effects of saccades on visually evoked activity were remarkably similar: a facilitation began at saccade end and peaked 50-100 ms later. When matched for saccade velocity, the time courses and magnitudes of postsaccadic facilitation for activity in the dark and during visual stimulation were identical. The presaccadic suppression observed in the dark condition was similar for X and Y cells, whereas the postsaccadic facilitation was substantially stronger for X cells, both in the dark and for visually evoked responses. This saccade-related regulation of geniculate transmission appears to be independent of the conditions under which the saccade is evoked or the state of retinal input to the LGN. The change in activity from presaccadic suppression to postsaccadic facilitation amounted to an increase in gain of geniculate transmission of approximately 30%. This may promote rapid central registration of visual inputs by increasing the temporal contrast between activity evoked by an image near the end of a fixation and that evoked by the image immediately after a saccade.     

Response characteristics of neurons in the medial component of the medial geniculate nucleus during Pavlovian differential fear conditioning in rabbits.

The amygdaloid central nucleus (ACE) may contribute significantly to Pavlovian fear-conditioned bradycardic responses during the presentation of conditioned emotional stimuli. Because the medial component of the medial geniculate nucleus (MGm) is a major source of input to the region of the ACE, the extracellular single-unit responses of MGm neurons were examined during Pavlovian differentially conditioned bradycardic responding in rabbits. Conditioning involved pairing one tone (CS+) with paraorbital shock and presenting another tone (CS–) in the absence of shock. Two general classes of MGm neurons were identified based on their conditioned-response characteristics. One group responded with greater increases in activity and at a shorter latency to the CS+ compared with the CS–, whereas the other group responded with greater increases in activity and at a shorter latency to the CS– compared with the CS+. Recordings from MGm neurons in naive rabbits prior to conditioning provided evidence that the acoustic stimuli used subsequently as the CS+ and CS– did not evoke differential responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Response of cat cortical neurons to position and movement of the femur

The contribution of joint afferents to the response of cortical neurons in area 3a to mechanical stimulation of the contralateral hindlimb was evaluated in cats anesthetized with sodium pentobarbital and paralyzed with pancuronium bromide. The hindlimb projection to the pericruciate cortex was established by recording the evoked potentials to electrical stimulation of the sciatic nerve and some of its branches, the bicepssemitendinosus and the quadratus femoris. Out of 169 neurons, 63 responded exclusively to cutaneous stimuli (superficial), whereas the others could be activated by local pressure of hindlimb muscles and/or by joint rotation (deep). Deep neurons were classified as slowly adapting (SA) or rapidly adapting (RA) units. In the neurons responding exclusively to joint rotation, the site of the receptive field could not be identified with certainty. In 13 deep neurons, their firing was affected by rotation of multiple joints of the contralateral hindlimb. In an attempt to identify the source of activation of cortical neurons, partial denervations and muscle disconnections were performed in five animals to isolate and stimulate the hip capsule. In these preparations, in 14 of 15 cortical neurons the source of activation was localized in the periarticular muscles, with no response to mechanical stimulation of the joint capsule. Only one neuron (SA) could be selectively excited by punctate pressure on the hip capsule. Our results suggest that in neurons of area 3a of the cat, the information about the position of the femur relies mainly on muscle afferents.     

Changes in responses of medial pontomedullary reticular neurons during repetitive cutaneous, vestibular, cortical, and tectal stimulation

1. In cats anesthetized with chloralose, responses of medial pontomedullary reticular neurons to stimulation of the body surface, vestibular nerves, superior colliculi, pericruciate cortices, cerebral peduncles, and spinal cord were studied at different stimulus rates. Raising the rate from 1/10 s to between 1/4 s and 2/s caused a significant decrement or increment in the response of most neurons tested. Response decrement typically began near the beginning of the higher frequency stimulus sequence and increased throughout the sequence. Response increment usually began somewhat later, rose to a peak, and then declined. Recovery from response decrement or increment usually occurred within 30-60 s at a 1/10 s stimulus rate.2. Measurements of response latency and of changes occurring in the initial and longer latency portions of responses indicated that all components of a response typically decreased or increased in parallel. Background spontaneous activity did not change during response decrements, but sometimes increased during response increment.3. Where changes could be detected, response decrement usually developed more rapidly when a sequence of repetitive stimulation was repeated.4. Response decrement was most pronounced at the highest stimulation rates and lowest stimulus intensities. Response increment was usually maximal at a stimulus rate of 1/s: at lower rates less increment occurred; at higher rates responses began to exhibit decrement.5. Response changes varied with the type of stimulus applied. Response decrements predominated when the body surface, vestibular nerves, or ipsilateral superior colliculus were stimulated. Approximately equal amounts of response increment and decrement were produced by repetitive stimulation of the cerebral peduncles and contralateral superior colliculus. Stimulation of the surface of the pericruciate cortex or of the spinal cord usually produced a long-lasting response increment.6. Generalization of response decrement and increment was observed in cases where trains of stimuli at a rate of 2/s applied to one point produced changes in the response to stimulation of another point which was tested once per 10 s and where single-shock stimulation of the first point was without effect on the test response. Generalization of response decrement occurred most often when two nearby points were stimulated. Generalization of response increment appeared to spread widely between distant cutaneous points and stimuli of different kinds.7. The response decrement and increment observed in medial pontomedullary reticular neurons displayed most of the parametric features of behavioral habituation and sensitization (8, 33) and therefore appear to represent neural analogs of these latter phenomena. The properties of response decrement suggest that it may occur to a large extent within afferent pathways leading to medial reticular neurons...     

Monaural spectral contrast mechanism for neural sensitivity to sound direction in the medial geniculate body of the cat

Monaural spectral contrast mechanism for neural sensitivity to sound direction in the medial geniculate body of the cat. J. Neurophysiol. 78: 2754-2771, 1997. Central auditory neurons vary in sound direction sensitivity. Insensitive cells discharge well to all sound source directions, whereas sensitive cells discharge well to certain directions and poorly to others. High-frequency neurons in the latter group are differentially sensitive to binaural and monaural directional cues present in broadband noise (BBN). Binaural directional (BD) cells require binaural stimulation for directional sensitivity; monaural directional (MD) cells are sensitive to the direction of monaural stimuli. A model of MD sensitivity was tested using single-unit responses. The model assumes that MD cells derive directional sensitivity from pinna-derived spectral cues (head related transfer function, HRTF). This assumption was supported by the similarity of effects that pinna orientation produces on locations of HRTF patterns and on locations of MD cell azimuth function peaks and nulls. According to the model, MD neurons derive directional sensitivity by use of excitatory/inhibitory antagonism to compare sound pressure in excitatory and inhibitory frequency domains, and a variety of observations are consistent with this idea. 1) Frequency response areas of MD cells consist of excitatory and inhibitory domains. MD cells exhibited a higher proportion of multiple excitatory domains and narrower excitatory frequency domains than BD cells, features that may reflect specialization for spectral-dependent directional sensitivity. 2) MD sensitivity requires sound pressure in excitatory and inhibitory frequency domains. Directional sensitivity was evaluated using stimuli with frequency components confined exclusively to excitatory domains (E-only stimuli) or distributed in both excitatory and inhibitory domains (E/I stimuli). Each of 13 MD cells that were tested exhibited higher directional sensitivity to E/I than to E-only stimuli; most MD cells exhibited relatively low directional sensitivity when frequency components were confined exclusively to excitatory domains. 3) MD sensitivity derives from excitatory/inhibitory antagonism (spectral inhibition). Comparison of responses to best frequency and E/I stimuli provided strong support for spectral inhibition. Although spectral facilitation conceivably could contribute to directional sensitivity with direction-dependent increases in response, the results did not show this to be a significant factor. 4) Direction-dependent decreases in responsiveness to BBN reflect increased sound pressure in inhibitory relative to excitatory frequency domains. This idea was tested using the strength of two-tone inhibition, which is a function of stimulus levels in inhibitory relative to excitatory frequency domains. The finding that two-tone inhibition was stronger at directions where BBN responses were minimal than at directions where they were maximal supports the model.     

Antioxidative and proapoptotic effects of riluzole on cultured cortical neurons

Riluzole is used clinically in patients with amyotrophic lateral sclerosis. As oxidative stress, in addition to excitotoxicity, may be a major mechanism of motoneuron degeneration in patients with amyotrophic lateral sclerosis, we examined whether riluzole protects against nonexcitotoxic oxidative injury. Probably reflecting its weak antiexcitotoxic effects, riluzole (1-30 microM) attenuated submaximal neuronal death induced by 24-h exposure to 30 microM kainate or NMDA, but not that by 100 microM NMDA, in cortical cultures. Riluzole also attenuated nonexcitotoxic oxidative injury induced by exposure to FeCl3 in the presence of MK-801 and CNQX. Consistent with its antioxidative effects, riluzole reduced Fe3+-induced lipid peroxidation, and inhibited cytosolic phospholipase A2. By contrast, riluzole did not attenuate neuronal apoptosis induced by staurosporine. Rather unexpectedly, 24-48-h exposure to 100-300 microM riluzole induced neuronal death accompanied by nuclear and DNA fragmentations, which was attenuated by caspase inhibitor carbobenzyloxy-Val-Ala-Asp-fluoromethyl ketone but not by protein synthesis inhibitor cycloheximide. The present study demonstrates that riluzole has direct antioxidative actions, perhaps in part by inhibiting phospholipase A2. However, in the same neurons, riluzole paradoxically induces neuronal apoptosis in a caspase-sensitive manner. Considering current clinical use of riluzole, further studies are warranted to investigate its potential cytolethal effects.     

Facilitation of acoustic responses of cartwheel neurons of the cat dorsal cochlear nucleus

Responses to clicks were increased in cartwheel cells of the dorsal cochlear nucleus of cats after pairing presentations of the clicks with local iontophoretic delivery of glutamate. The cells were identified by bursting discharges, and were recorded intracellularly in vivo. The findings indicate that inhibitory interneurons such as cartwheel cells can participate in complex adaptive acoustic signal processing. Each cell displayed doublet discharges of > 800 Hz. In 70% of the cells, some of the doublet discharges reached rates > 1000 Hz.     

Synchronization of visual responses between the cortex, lateral geniculate nucleus, and retina in the anesthetized cat

Synchronization of spatially distributed responses in the cortex is often associated with periodic activity. Recently, synchronous oscillatory patterning was described for visual responses in retinal ganglion cells that is reliably transmitted by the lateral geniculate nucleus (LGN), raising the question of whether oscillatory inputs contribute to synchronous oscillatory responses in the cortex. We have made simultaneous multi-unit recordings from visual areas 17 and 18 as well as the LGN and the retina to examine the interactions between subcortical and cortical synchronization mechanisms. Strong correlations of oscillatory responses were observed between retina, LGN, and cortex, indicating that cortical neurons can become synchronized by oscillatory activity relayed through the LGN. This feedforward synchronization occurred with oscillation frequencies in the range of 60-120 Hz and was most pronounced for responses to stationary flashed stimuli and more frequent for cells in area 18 than in area 17. In response to moving stimuli, by contrast, subcortical and cortical oscillations dissociated, proving the existence of independent subcortical and cortical mechanisms. Subcortical oscillations maintained their high frequencies but became transient. Cortical oscillations were now dominated by a cortical synchronizing mechanism operating in the 30-60 Hz frequency range. When the cortical mechanism dominated, LGN responses could become phase-locked to the cortical oscillations via corticothalamic feedback. In summary, synchronization of cortical responses can result from two independent but interacting mechanisms. First, a transient feedforward synchronization to high-frequency retinal oscillations, and second, an intracortical mechanism, which operates in a lower frequency range and induces more sustained synchronization.     

Binaural response patterns in subdivisions of the medial geniculate body

Auditory evoked potentials (AEPs) to binaural click stimulation were examined in the ventral (MGv) and caudomedial (MGcm) subdivisions of the medial geniculate body (MG) in guinea pigs. Binaural stimulation caused a decrease in amplitude for the response component recorded from the MGv, but an increase in amplitude for the AEP component recorded from the MGcm. Findings suggest that the evoked responses recorded from MGv and MGcm are functionally distinct. The inhibitory binaural response (BR) pattern seen in MGv was similar to that of the middle latency response (MLR) component recorded over the temporal cortex, while the additive BR pattern typical of the MGcm was similar to that of the surface midline MLR component. Furthermore, these data imply that the binaural response patterns seen in the primary and non-primary auditory cortex may be processed and encoded at the thalamic level. It is concluded that the distinct BR patterns noted for the two MG subdivisions reflect the predominant type of binaurally responsive neurons within the respective pathways.     

Fos expression in rat pontine tegmental neurons following activation of the medial preoptic area

Because murine myeloma plasma cells and normal human lymph node plasma cells express BCL-X, we evaluated BCL-X expression in malignant human plasma cells. BCL-X expression was detected in several human myeloma cell lines, as well as in CD38-sorted bone marrow cells obtained from some patients. Only the antiapoptotic long form of BCL-X (BCL-X-L), was detected. Because BCL-X-L expression can protect tumor cells from apoptotic death induced by chemotherapeutic agents, we tested the clinical relevance of expression in 55 archival bone marrow biopsies. The biopsies were stained by immunohistochemistry, and BCL-X expression was correlated with the subsequent response to treatment. BCL-X expression in malignant plasma cells strongly correlated with decreased response rates in patient groups treated with either melphalan and prednisone or vincristine, Adriamycin, and dexamethasone. Response rates were 83-87% in non-BCL-X-expressing cases and 20-31% in BCL-X-expressing cases. In addition, BCL-X expression was more frequent in specimens taken from patients at relapse (77%), when compared to those at initial diagnosis (29%). Further support for the association of drug resistance with BCL-X-L expression came from studies of the 8226 dox-40 cell line. This line, which expresses p-glycoprotein and serves as a model of multidrug resistance in multiple myeloma cells, demonstrated an up-regulated expression of BCL-X-L, which was relatively specific, in that BCL-2 or BAX expression was not altered. In addition, dox-40 cells demonstrated a generalized resistance to apoptosis that was induced by several different agents. These results indicate that malignant plasma cells can express BCL-X-L and that such expression may be a marker of chemoresistant disease.     

Facilitative responses to species-specific calls in cortical FM-FM neurons of the mustached bat

FM-FM neurons in the auditory cortex of the mustached bat are highly specialized for echolocation, responding facilitatively to the combination of frequency modulated (FM) components of biosonar pulse and its echo. Here we propose they are also specialized for processing bat communication calls. FM-FM neurons respond facilitatively to natural call syllable pairs, and exhibit inter-syllable interval tuning to the natural range of intervals. Our results support a role for 'combination-sensitive' neurons in communication, and suggest that cortical neurons can possess multiple distinct specialized modes of response.     

Conditioning of cortical neurons in cats with antidromic activation as the unconditioned stimulus

Single-cell activity was recorded from the postcruciate cortex of acutely prepared cats during a differential classical conditioning procedure. The conditioned stimuli (CS) were hind paw stimuli, and the unconditioned stimulus (US) was pyramidal tract stimulation that produced an antidromic response in the recorded cortical neuron. A control group was also examined in which the pyramidal stimulus was set below the threshold to produce an antidromic response. Clear differential conditioning was found for the experimental group, with antidromic activation of the neuron as the US. There was no evidence of differential conditioning in the control group without antidromic activation. Any activation of orthodromic pathways should have been the same in the control and experimental groups. The absence of conditioning in the control group demonstrated that orthodromic pathways were not contributing to the differential conditioning observed in the experimental group. This indicates that it was activation of the neuron produced by antidromic firing which was important for conditioning. All the evidence suggests that the site of learning was in the cortex. It is concluded that the the role of the US in conditioning may be simply to activate the neuron at an appropriate interval following the CS.     

Synthetic versus natural cat odorant effects on rodent behavior and medial amygdala plasticity.

Fear and anxiety behaviors are underpinned by neuronal changes within the amygdala. Here, the effects of exposure to natural and synthetic cat odor on behavior and amygdala plasticity were determined. Exposure to natural odor elicited typical and persistent anxiety-related behaviors, such as avoidance, freezing, and flat-back approach; however, synthetic odorant evoked no significant alteration in behavior. Furthermore, ex vivo induction of long-term potentiation within the medial nucleus of the amygdala, a principal area involved in olfactory perception, was significantly reduced after exposure to natural, but not synthetic, odor. Data presented here suggests that the synthetic odorant utilized may lack the constituents that are required to indicate predator presence in rodents and also the capacity to modulate neuronal plasticity within the medial nucleus of the amygdala. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Microencapsulated nerve growth factor: effects on the forebrain neurons following devascularizing cortical lesions

In this study, we report the effects of nerve growth factor (NGF) delivered into the CNS via a novel delivery system for prolonged, controlled release. The effectiveness of NGF incorporated in the biodegradable microspheres was investigated in the rat model for central cholinergic degeneration. Mature male rats were unilaterally lesioned by disruption of the pia arachnoid vessels and vehicle (alginate microspheres without NGF) and microencapsulated NGF was placed at the site of the lesion. Choline acetyltransferase (ChAT) activity was measured in the nucleus basalis magnocellularis (NBM) and cortex in the (a) non-lesioned control animals; (b) lesioned animals treated with 'empty' microspheres and (c) lesioned animals treated with microspheres containing NGF, 30 days following surgery. Similarly lesioned animals received NGF via permanently installed cannulae in order to compare the novel route of administration with the more conventional one. Immunocytochemical results showed an absence of the cholinergic cell body shrinkage in the NBM otherwise observed in lesioned animals. Furthermore, an increase in intensity of ChAT immunostaining in NGF-treated, lesioned animals was evident. The present results stress the experimental therapeutic possibilities of novel delivery systems for administration of trophic factors in the CNS.     

M100907 and clozapine, but not haloperidol or raclopride, prevent phencyclidine-induced blockade of NMDA responses in pyramidal neurons of the rat medial prefrontal cortical slice

Antiserum to leucokinin I, a neuropeptide originally isolated from the cockroach Leucophaea maderae, was used for immunocytochemical labeling of neurons in the brain and ventral ganglia of the moth Spodoptera litura during postembryonic development. In the ventral ganglia, leucokinin-like immunoreactivity begins to occur in the abdominal ganglion A3 to A7 of first instar larva. One to two weakly labeled pairs of bilateral LK-LI cell bodies are located in the subesophageal ganglion of fourth to sixth instar larvae and in the abdominal ganglia A1 to A7 of second to sixth instar larvae. The abdominal ganglion A1 of fourth to sixth instar larvae and A8 of sixth instar larva each contain one weakly labeled pair of median LK-LI cell bodies. Two strongly labeled pairs of bilateral LK-LI neurons are found in A3 to A7 of third to sixth instar larvae. Abdominal ganglia A1 to A8 of prepupa, pupa and adult contain one to three weakly labeled pairs of bilateral LK-LI neurons. Two strongly labeled pairs of bilateral LK-LI neurons in each of the abdominal ganglia of larva, prepupa, pupa and adult send axons to the neuropil, and then each axon bifurcates into two axonal branches. Theses axonal branches from two bundles. From each of the two pairs of neurons an axon exits through the posterior ventral nerve (N2) which runs to the transverse nerve of the next posterior segment. In larval brains, 2-16 pairs of bilateral LK-LI cell bodies can be found together with LK-LI processes in the central neuropil. The larval brains show large changes in the number of LK-LI neurons throughout postembryonic development. The number of LK-LI cell bodies are reduced in number from sixth instar larval brain. Therefore, prepupal, pupal and adult brains contain a smaller number of LK-LI cell bodies. Two pairs of LK-LI median neurosecretory cells located immediately beside the pars intercerebralis in larval brains increase to three pairs in the 7-day-old pupal brain. In the adult, however, LK-LI median neurosecretory cells decrease to one pair.     

Involvement of the medial geniculate body in prepulse inhibition of acoustic startle

Prepulse inhibition of acoustic startle is the normal reduction in startle response to an intense auditory stimulus when this stimulus is immediately preceded by a weaker prestimulus. Previous studies have shown that several neuroanatomical structures and pathways in the brain are involved in the modulation of prepulse inhibition. In the present study, the functional importance of the medial geniculate body (MG) in the modulation of prepulse inhibition was investigated. To this end, in vivo brain microdialysis probes were used to infuse drugs locally into the MG of awake, freely moving rats simultaneously with startle response and prepulse inhibition measurements in the same animals. Intrageniculate infusion of the sodium channel blocker, tetrodotoxin, significantly reduced prepulse inhibition without affecting baseline startle amplitude. A similar effect was obtained after intrageniculate infusion of the GABA(B) receptor agonist, baclofen. In addition, intrageniculate infusion of muscimol, an agonist at the GABA(A) receptor complex, reduced prepulse inhibition, although this effect was obtained at a higher concentration of the drug compared to that of baclofen. These studies suggest that the MG is involved in the modulation of prepulse inhibition and that auditory signals relayed via the MG may be subjected to inhibitory control at this level, involving GABA neurotransmission.     

Heterosynaptic long-term facilitation of sensory-evoked responses in the auditory cortex by stimulation of the magnocellular medial geniculate body in guinea pigs.

The magnocellular nucleus of the medial geniculate body (MGm) develops physiological plasticity during classical conditioning and may be involved in learning-induced receptive field plasticity in the auditory cortex. To determine the ability of the MGm to produce long-term modification of evoked activity in the auditory cortex, the experimenters paired electrical stimulation of the MGm with preceding clicks in adult guinea pigs under barbiturate anesthesia. The amplitudes of average click-evoked potentials were significantly facilitated in all Ss. Facilitation endured for 2 hrs, the maximum duration of recording. Sham-stimulated control guinea pigs did not develop facilitation. Thus, a nonlemniscal thalamic sensory nucleus can produce enduring facilitation of sensory-evoked activity in primary sensory cortex, suggesting that long-term physiological plasticity in the sensory cortex during learning may involve nonlemniscal thalamic mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatiotemporal activity patterns of rat cortical neurons predict responses in a conditioned task

Precise and repeated spike-train timings within and across neurons define spatiotemporal patterns of activity. Although the existence of these patterns in the brain is well established in several species, there has been no direct evidence of their influence on behavioral output. To address this question, up to 15 neurons were recorded simultaneously in the auditory cortex of freely moving rats while animals waited for acoustic cues in a Go/NoGo task. A total of 235 significant patterns were detected during this interval from an analysis of 13 hr of recording involving over 1 million spikes. Of particular interest were 129 (55%) patterns that were significantly associated with the type of response the animal made later, independent of whether the response was that prompted by the cue because the response occurred later and the cue was chosen randomly. Of these behavior-predicting patterns, half (59/129) were associated with an enhanced tendency to go in response to the stimulus, and for 11 patterns of this subset, trials including the pattern were followed by significantly faster reaction time than those lacking the pattern. The remaining behavior-predicting patterns were associated with an enhanced NoGo tendency. Overall mean discharge rates did not vary across trials. Hence, these data demonstrate that particular spatiotemporal patterns predict future behavioral responses. Such presignal activity could form templates for extracting specific sensory information, motor programs prespecifying preference for a particular act, and/or some intermediate, associative brain process.