Biomedical subjects

M F Montaron

Publications and source records attributed to M F Montaron.

17 recordsLinked to original sources

PubMed1998

Behavioural recovery after unilateral lesion of the dopaminergic mesotelencephalic pathway: effect of repeated testing.

Functional recovery following a complete unilateral lesion of the nigrostriatal pathway in adult rats was studied. We examined the effect of training on the spontaneous or induced postural bias following the lesion. Two tasks measuring lateralization were used to assess the lesion-induced postural bias: spontaneous asymmetry was evaluated in the Y-maze, whereas induced body bias was measured by hanging the rat by its tail. Recovery was assessed at three different times following the lesion. The effects of lesion in adult rats in the short, medium and long term were evaluated and compared with the effects of dopaminergic transplants. In adult lesioned rats, destruction of dopaminergic innervation of the neostriatum induced initially an ipsilateral bias as measured in the "tail hang test" and the Y-maze. Recovery of function was observed in the tail hang test as ipsilateral bias declined on repeated testing. Apart from this effect, there was a post-lesion interval effect, since the postural bias disappeared more rapidly on repeated testing in the long-term lesioned rats. This spontaneous recovery was impaired by intrastriatal dopaminergic grafts. Furthermore, no spontaneous recovery was observed in the Y-maze test. These observations show that repeated testing can influence the long-term effects of damage to the nigrostriatal dopamine system.

Animals↗

PubMed1997

Decrease in highly polysialylated neuronal cell adhesion molecules and in spatial learning during ageing are not correlated.

Age-dependent spatial memory impairments have been related to a decline in hippocampal plasticity. Highly polysialylated neuronal cell adhesion molecules (PSA-NCAM) show a strong expression during adulthood within regions associated with neuroplastic events. Furthermore, NCAM molecules have been proposed to mediate neuronal plasticity during learning and memory. The aim of the present study was to examine the effect of ageing on the expression of PSA-NCAM within the hippocampus. To investigate whether age-dependent changes in expression of PSA-NCAM were accentuated in aged rats with learning impairment, animals were in a first step assessed for their cognitive abilities using a Morris water maze. Seven-month-old and 24-month-old-rats were tested for their performance in the Morris water maze. The animals were sacrificed and brain sections were processed for PSA-NCAM immunohistochemistry. Ageing was accompanied by an overall decrease in PSA-NCAM-immunoreactivity (-IR) within the forebrain, presenting a important decrease of the number of PSA-NCAM-IR perikarya within the hippocampus. These results were confirmed by Western blot analysis. No difference in PSA-NCAM immunoreactivity was observed in aged rats with or without spatial learning impairment. It is concluded that although changes in PSA-NCAM accompanied the decrease in cognitive abilities, our data did not evidence a causal relationship between these two parameters.

Aging↗

PubMed1996

Effect of lesioning the nucleus accumbens on attentive preparation and performance of a reaching movement in the cat.

The nucleus accumbens is often considered as an interface between limbic and motor brain structures. In the present experiment, we investigated the effect of a bilateral lesion of the nucleus accumbens on a motor task with attentional constraints. Four male cats were trained to reach for a mobile target that was only accessible for a short period of time and after a variable delay of expectation. They were food-rewarded. Their visuomotor performance was analyzed in speed and accuracy. Their ECoG was recorded to evaluate the occurrence of beta-rhythms that have been shown to be related to a behaviour of focalized attention. After stabilization of their visuomotor performance, all subjects underwent a bilateral neurotoxic lesion of the nucleus accumbens. After lesion, cats were able to maintain their focalized attention while waiting for the target for longer periods of time and the probability of beta-activity increased. Their visuomotor performance showed an improvement both in accuracy and in speed. Moreover, unexpected external stimuli were less efficient in diverting the cats' attention from their task, so that the proportion of unsuccessful trials due to inattention decreased after lesion. The data showed that the lesion induced a focalization of attention resulting in an improvement of motor performance. The role of the nucleus accumbens both in attention control and in modulating motor output is discussed together with the possible cerebral pathway involved.

Animals↗

PubMed1996

Prefrontal cortex inputs of the nucleus accumbens-nigro-thalamic circuit.

The functional organization of the cortico-nucleus accumbens-substantia nigra pars reticulata circuit was investigated in the rat using combined anatomical and electrophysiological approaches. The nucleus accumbens neurons which project to the substantia nigra pars reticulata are located in a circumscribed region of the core immediately adjacent and extending dorsally to the anterior commissure. As shown by retrograde and anterograde transports of wheatgerm agglutinin conjugated to horseradish peroxidase, the region of the nucleus accumbens related to the substantia nigra was found to receive bilateral inputs from restricted areas of the medial and lateral prefrontal cortex, i.e., prelimbic/medial orbital and dorsal agranular insular areas. The electrical stimulation of these medial and lateral prefrontal cortical areas induced excitatory responses in nucleus accumbens neurons projecting to the dorsomedial substantia nigra pars reticulata. Interestingly, an important proportion (61%) of the nucleus accumbens-nigral cells responding to the stimulation of the lateral prefrontal cortex were also excited by the stimulation of the medial prefrontal cortex, demonstrating the existence of a convergent influence of these cortical areas on single nucleus accumbens cells. Furthermore, the present data also show that the stimulation of the medial prefrontal cortex results in a powerful inhibition of the tonic firing of the substantia nigra pars reticulata neurons. In conclusion, this study reveals the existence of a functional link between the prefrontal cortex (prelimbic/medial orbital and agranular insular areas) and the nucleus accumbens neurons which innervate the dorsomedial region of the substantia nigra pars reticulata. Since the dorsomedial region of substantia nigra pars reticulata is known to project to subfields of the mediodorsal and ventromedial thalamic nuclei related to the prefrontal cortex, the present data further demonstrate the existence of a prefrontal-nucleus accumbens-thalamo-cortical circuit involving the substantia nigra pars reticulata.

Animals↗

PubMed1992

Effects of mediodorsalis thalamic nucleus lesions on vigilance and attentive behaviour in cats.

In this study performed on 10 cats we analysed the effects of limited lesions of nucleus medialis dorsalis of the thalamus (MD) on behaviour and on some specific electrocorticographic (ECoG) patterns, known from previous works to accompany various states of waking attentiveness. The animals were tested during 90 min in three distinct behavioural situations; a neutral one (NS) where they simply explored their environment and then usually went to sleep; a second one (FA) where they could watch a mouse (but not catch it), which favoured 'focussed' attentiveness accompanied by the development of rhythmic ECoG activities in the anterior frontoparietal cortex ('beta rhythms' at 40 Hz); a third one (EX) with a hidden mouse whose appearance the cat was waiting for ('expectancy') which rather than favouring the development of beta rhythms elicited the appearance of another rhythmic activity dominating in somatic area SI, 'mu rhythms' at 14 Hz. The duration of each waking behaviour and its ECoG concomitant as well as that of slow wave and of paradoxical sleep were compared in each cat before and after lesion. Our results showed that MD lesions situated in the posterior part of the nucleus tended to increase the time occupied by focussed attentive behaviour and the accompanying beta rhythms. On the other hand, anteriorly located MD lesions elicited a concomitant reduction of both manifestations, behavioural and electrocortical. No such contrasting effects could be systematically noticed for the durations of expectancy, of slow sleep and of paradoxical sleep. These findings were discussed considering previous data showing that at least two systems project upon MD, that play distinct--in a way even antagonistic--roles in focussed attention upon a target. Both originate from the ventral tegmental mesencephalic area; one reaches MD through the ventral striatum (nucleus accumbens), the other one through the amygdala. The MD nucleus thus receiving contrasting information may participate in a final adjustment of the attentive state of the animal to its environment.

Animals↗

PubMed1992

Cryoblockade in limbic brain (amygdala) prevents or delays ventricular fibrillation after coronary artery occlusion in psychologically stressed pigs.

Neomammalian and paleomammalian (limbic) brain structures control different behaviors and the autonomic support specific to each. Both neural systems are involved in cardiovascular disorders. Our previous studies showed that bilateral cryoblockade of a neomammalian structure (the frontal lobes) reduces blood pressure elevations in experimental hypertension and prevents lethal arrhythmogenesis in experimental myocardial infarction. Other studies showed that bilateral lesions in a paleomammalian structure (amygdala) also reduce the blood pressure elevations. Thus, we hypothesized that cryoblockade of the amygdala would prevent lethal arrhythmogenesis. We found that cooling of cryoprobes implanted bilaterally in the amygdala prevented ventricular fibrillation in five of eight pigs during a 20-minute period of reversible myocardial ischemia, whereas cryoblockade in structures surrounding the amygdala (five pigs), unilateral cryoblockade in the amygdala (two pigs), or sham operations (three pigs) did not prevent ventricular fibrillation (p less than 0.003). In two of the five pigs with amygdaloid blockade, the cooling was reversed at 20 minutes while the coronary occlusion continued (24 hours), and still ventricular fibrillation did not occur. In all other cases, ischemia was reversed at 20 minutes so that the heart could recover; this enabled histochemical documentation that the heart was normal at the time(s) ischemia was induced, and it allowed within-subject control experiments. Amygdaloid cryoblockade produced a small but significant increase in heart rate (10 beats per minute) without a change in blood pressure. We conclude that the paleomammalian brain, like its neomammalian counterpart, mediates brain effects on fatal arrhythmogenesis.

Amygdala↗

PubMed1990

Action of tianeptine on focalization of attention in cat.

Tianeptine, an antidepressant substance devoid of sedative action, was investigated for its effects on focalization of attention in cats, using combined behavioural and electrocorticographic (ECoG) observations. The ECoG index was the presence of 40 Hz frontoparietal rhythmic cortical activities, developing while the animal displayed a behaviour suggesting focused attention. Cats were observed in two conditions: a "neutral" one, with no specific target, and another one, "of focused attention" where a live mouse placed in a transparent box was present in the recording room, each test lasting for 90 min. After treatment the animals displayed increased attention even in the neutral situation, where the cat, instead of sleeping like during control sessions, payed sustained attention to its environment. Conversely, at corresponding doses, amitriptyline, another antidepressant drug chosen as a reference, induced uninterrupted slow sleep even in the situation of focused attention.

Amitriptyline↗

PubMed1988

Relationships between nucleus medialis dorsalis, pericruciate cortex, ventral tegmental area and nucleus accumbens in cat: an electrophysiological study.

In anaesthetized cats, single units were recorded from the ventrolateral part of n. medialis dorsalis (MD) of the thalamus. Cells were tested for their ortho- or antidromic short latency responses to single electrical shocks applied to the pericruciate cortex (PCx) and to either the mesencephalic ventral tegmental area (VTA) or the nucleus accumbens (ACC). Some reciprocal direct connections were thus shown to exist between MD and PCx, i.e. a cortical area posterior to the main classical MD "prefrontal" projection zone. Reciprocal direct connections were also identified physiologically between MD and VTA and between MD and ACC. Coupled stimulations showed that some MD cells could serve as a relay for a pathway from VTA to cortex, others for a reciprocal pathway from PCx to VTA, and still others, for a pathway from PCx to ACC. These findings are compared to previous--mostly anatomical--data obtained in other species, mainly rat. Their functional meaning is also discussed, in the light of previous results on the roles of MD, VTA and ACC in the control of immobility during focused attentive behaviour in cat.

Animals↗

PubMed1987

Anatomical localization of cortical beta rhythms in cat.

Beta electrocorticographic rhythms (40 Hz) develop during motionless focused attention in two distinct cortical foci in cats. A cytoarchitectonic study was performed to determine the precise location of these foci. Electrode tips recording beta rhythms were found: (i) in motor areas 4 gamma and 6a beta, in a band extending from the postcruciate cortex to the walls of the presylvian sulcus, crossing the frontal pole (anterior beta focus); (ii) in the posterior parietal associative area 5a, along the divisions of the ansate sulcus, extending to the mesial aspect of the hemispheres (posterior beta focus). The two foci are separated by areas 3, 2 and 1, where beta rhythms were never recorded. The fact that both these areas, containing giant pyramidal cells, develop a specific type of activity during immobility may have a functional meaning: area 5 may be involved in the cat as it is in the monkey in the control of motor behaviour.

Animals↗

PubMed1986

Compulsive attentive behavior after lesion of the ventral striatum in the cat: a behavioral and electrophysiological study.

Bilateral lesions of the nucleus accumbens in cat elicited the following changes: preservation in tests requiring focused attention, with difficulty to shift to other targets; paucity of movements, animals displaying moderate hypokinesia and loss of reaction to changes in the environment. These symptoms were accompanied by a significant increase in the amount of beta rhythms, an activity that has been shown to be concomitant with the development of focused attentive behavior. The observed behavioral and electrocortical modifications are opposite those that have been previously obtained in the same species after lesions of the ventral tegmental area.

Animals↗

PubMed1986

[Cytoarchitectonic localization of foci of electrocortical activity accompanying focused attention in cats].

Beta electrocorticographic rhythms (30-45 Hz) develop during focused immobile attention within two distinct foci in cats. A multiple electrode exploration was performed, followed by post-mortem histological analysis, to determine the precise localization of these foci. Electrode tips recording beta rhythms in the waking attentive cat were located: in motor areas (Brodmann's areas 4 and 6), in a band extending from the postcruciate cortex to the walls of the presylvian sulcus, crossing the frontal pole (anterior beta focus); in the posterior parietal associative area 5a, along the divisions of the ansate sulcus (posterior beta focus). The two foci are separated by somatic areas 3, 2 and 1, where beta rhythms were never recorded. The location of the posterior focus may suggest that area 5 is, in the cat as it is in the monkey, involved in motor control.

Animals↗

PubMed1984

[Unit activity in the ventral tegmental area and the state of focused attention in the normal awake cat].

Our previous studies had indicated that electrocortical "beta" rhythms (37 Hz) that develop in the fronto-parietal area in waking, immobile and highly attentive cats, are under the control of a dopaminergic system originating from the ventral tegmental area (VTA). A single unit study has now shown that 9% of VTA cells displayed a sustained increased of their firing rate during each beta episode. These data indicate that VTA cells exert a "gate control" on the rhythmic thalamo-cortical beta system.

Animals↗

PubMed1983

[Localized frontoparietal beta rhythms and focused attention in animals].

In normal cats and monkeys, fronto-parietal beta rhythms (averages: 36 and 18 c/sec, respectively) were considered as a sign of focused attention, since they appeared during several different situations having in common that the subject's attention was drawn by a signal or an object of the environment. These regular rhythmic activities, often with a high amplitude, are localized within two small cortical foci. At least one set of beta rhythms corresponds to the end station of a thalamocortical system originating in the posterior group (POm), and are controlled by a dopaminergic system the somas of which are situated in the ventral mesencephalic tegmentum (area A10). Eight percent of the VMT cells, studied with micropipettes in normal awake cats, suddenly increased their spontaneous activity 1 sec before the beginning of the rhythmic volleys. Considering the analogy between these rhythms and the human frontal beta rhythms, it is suggested that these data may contribute to the study of attention in man, whether in a healthy state or suffering from mental disease.

Animals↗

PubMed1982

Ventral mesencephalic tegmentum (VMT) controls electrocortical beta rhythms and associated attentive behaviour in the cat.

When a cat is immobile, very alert and displaying behaviour suggesting focused attention toward a target in its environment, beta rhythms (ca. 40 Hz) develop in the fronto-parietal cortical areas. After bilateral electrolytic lesions of the ventral mesencephalic tegmentum (VMT), these beta rhythms are suppressed (while other cortical activities, with other behavioural correlates, persist), and at the same time, attentive immobility is no longer observed: the same experimental situation as in the control now elicits locomotor hyperactivity. Arguments are produced, favouring the hypothesis that both behavioural immobility and the accompanying thalamocortical beta rhythms are controlled through one of the dopaminergic system that originate from the VMT and are distinct from the nigrostriatal one.

Animals↗

PubMed1981

Fast fronto-parietal rhythms during combined focused attentive behaviour and immobility in cat: cortical and thalamic localizations.

In the cat, fronto-parietal mu rhythms belonging to the 'high frequency range' (35-45 c/sec) develop as the animal becomes immobile in an attitude of focused attention. Two cortical foci were identified, one anterior in the precruciate area, the other posterior in the periansate cortex (posterior parietal area). A thalamic focus, in an area belonging to the medial portion of the posterior thalamic group, appears to be a pacemaker for the posterior cortical focus alone.

Animals↗

PubMed1980

[Parietal electrocortical rhythms in the cat: their relation to a behavior of focused attention and possible mesencephalic control through a dopaminergic pathway].

In the Cat, the development of an electrocortical rhythm at 40 Hz (fast "mu" rhythm) is observed in the parietal cortex whenever the subject immobilizes itself in an attitude of focused attention (e.g. when watching a mouse). This rhythm, as well as the accompanying behaviour, seems to be under the control of a dopaminergic mechanism originating from the ventral tegmental mesencephalic area (cellular dopaminergic group A 10).

Animals↗

PubMedDate not supplied

[Relationship between attention and mu rhythms in the cat and the monkey (author's transl)].

Recording from the cat and monkey parietal cortex reveals the existence of three categories of spontaneous rhythmic activities, with different frequencies, that have the same reactivity and localization as the mu rhythm in man. Each of these rhythms corresponds to a different level of attention and can be preferentially determined through placing the subject in a given situation. The fastest rhythms are observed when the subject displays an attentive behaviour toward a significant target, while those of intermediate frequency are seen during a period of expectancy (like watching a mouse-hole). The slowest rhythms occur when the subject does not show interest to its surrounding. A hypothesis is proposed that mu rhythms are involved in the neurophysiological mechanisms of attention.

Animals↗