Lesions Of Medial Prefrontal Cortex Research Articles

Neuroanatomical correlates of sparing of function after neonatal medial prefrontal cortex lesions in rats

In rats, the possibility of neuroanatomical changes in response to partial medial prefrontal cortex lesions at postnatal day 6, concominant with behavioural sparing, was investigated. The projections from the mediodorsal nucleus of the thalamus (MD) and the mesocortical dopaminergic (DA) projection were examined. No indications were found for a changed pattern of projection from MD in response to either a neonatal or an adult medial prefrontal cortex (mPFC) lesion. However, the DA innervation was changed after neonatal mPFC lesions. In the remainder of the mPFC, the DA fibre network proved to be denser, fibres were thicker, had more varicosities, and often the background staining was higher. None of these phenomena were seen in operated adult rats or in controls. It is postulated that the changes in DA innervation might contribute to the sparing of function observed in the spatial delayed alternation task.

Comparison of the effects of neonatal and adult medial prefrontal cortex lesions on food hoarding and spatial delayed alternation

Performance in food hoarding, a species-typical task, and spatial delayed alternation, a learning task, was investigated in male rats with bilateral medial prefrontal cortex (mPFC) lesions sustained in adulthood or at the age of 6 days. Animals with adult mPFC lesions hoarded significantly fewer food pellets than their controls. The mPFC lesion effect on hoarding behaviour of the neonatally operated rats was unclear because of the unexpectedly low hoarding score of their controls. In the spatial delayed alternation task, the animals with mPFC lesions in adulthood exhibited a permanent deficit, while the animals with neonatal mPFC lesions showed no significant deficits. It is concluded that a bilateral lesion in adulthood, mainly affecting the frontal area 2 and the dorsal anterior cingulate area of the mPFC, results in a permanent deficit in food hoarding and spatial delayed alternation performance, whereas a similarly restricted mPFC lesion at the age of 6 days shows a complete sparing of the spatial delayed alternation task performance.

Ibotenic acid lesions of the medial prefrontal cortex potentiate FG-7142-induced attenuation of exploratory activity in the rat

Six weeks after induction of bilateral sham or ibotenic acid lesions of the medial prefrontal cortex (MPFC), groups of rats were injected with the anxiogenic β-carboline FG-7142 (15 mg/kg IP) or vehicle (VEH) before exposure to a novel open field. The attenuation of exploratory activity by FG-7142 was markedly enchanced in the MPFC-lesioned rats. The results suggest that the behavioral effects of MPFC lesions may be amplified under stressful conditions. Secondly, the inhibition of exploratory activity by FG-7142 does not depend on its action within the MPFC.

Memory for frequency in rats: Role of the hippocampus and medial prefrontal cortex

On a radial arm maze rats were tested for frequency memory of specific spatial locations, a task that presumably involves the coding of temporal information. On any trial during the study phase rats were allowed to visit three different spatial locations only once and one spatial location twice. During the test phase the rats were given a choice between a spatial location that had been visited once and spatial location that had been visited twice. The rats were reinforced for selecting the twice-visited spatial location. The number of spatial locations between a repetition (lag) was varied from one to three. After extensive training rats displayed memory for frequency only for a lag of three spatial locations, i.e., they displayed a repetition lag effect. Animals then received control, medial prefrontal cortex, or hippocampal lesions. Upon subsequent retests control rats continued to display frequency memory, but animals with medial prefrontal cortex or hippocampal lesions displayed a marked impairment. These data support the idea that both the hippocampus and medial prefrontal cortex code temporal order information.

Double dissociation of egocentric and allocentric space following medial prefrontal and parietal cortex lesions in the rat.

Animals with medial prefrontal cortex or parietal cortex lesions and sham-operated and non-operated controls were tested for the acquisition of an adjacent arm task that accentuated the importance of egocentric spatial localization and a cheese board task that accentuated the importance of allocentric spatial localization. Results indicated that relative to controls, animals with medial-prefrontal cortex lesions are impaired on the adjacent arm task but displayed facilitation on the cheese board task. In contrast, relative to controls, rats with parietal cortex lesions are impaired on the cheese board task but show no impairment on the adjacent arm task. The data suggest a double dissociation of function between medial prefrontal cortex and parietal cortex in terms of coding of egocentric versus allocentric spatial information.

The stress response of dopaminergic systems after lesions of medial prefrontal cortex

The stress response of dopaminergic systems after lesions of medial prefrontal cortex

Dissociation of item and order memory following parietal cortex lesions in the rat.

Rats with parietal cortex lesions were tested for both item and order memory for a list of spatial events in a probe recognition procedure. Rats with parietal cortex lesions were impaired for all events within the item memory task but had good memory for the early events within the order memory task. These data suggest a dissociation of function between item and order memory for parietal cortex damaged animals. In conjunction with previous findings with rats with medial prefrontal cortex lesions, these data suggest that item and order memory can be coded and represented independently.

Retrospective and prospective coding of information: role of the medial prefrontal cortex.

Animals with sham-operations or medial prefrontal cortex lesions were trained in a task which required memory for short or long lists of items (spatial locations). On any one trial a rat is presented with 2, 4, 6, 8 or 10 items (spatial locations) on a 12-arm radial maze followed 15 min later by a win-shift test comprising a choice between a place previously visited and a novel place. Sham-operated animals showed an increase in errors as a function of set size (2 to 8 items) followed by a decrease in errors with a set size of 10 items suggesting the use of both retrospective and prospective memory codes. In contrast, animals with medial prefrontal cortex lesions made most of their errors for the longest list length reflecting an inability to shift from a retrospective to prospective memory code. The results are interpreted as support for a medial prefrontal cortex role in mediating a prospective code perhaps via knowledge systems based on temporal information.

Double dissociation of egocentric and allocentric space following medial prefrontal and parietal cortex lesions in the rat.

Double dissociation of egocentric and allocentric space following medial prefrontal and parietal cortex lesions in the rat.

Acquisition of conditional associations and operant delayed spatial response alternation: Effects of lesions in the medial prefrontal cortex.

In this article 8 male Wistar rats received bilateral lesions of the medial prefrontal cortex, whereas another 8 rats were control operated. Three weeks after surgery, they were exposed to an autoshaping procedure in which the insertion of a lever into the experimental chamber (conditioned stimulus) always preceded the delivery of a response-independent food pellet (unconditioned stimulus). Subjects with lesions acquired this conditional association faster than control-operated subjects as evidenced by the fact that they were more likely than control-operated subjects to contact the conditioned stimulus at higher rates. Locomotor activity, observed in a standard open-field preceding autoshaping sessions, decreased for both groups of subjects with repeated exposure to the open-field, whereas differences between groups were not observed. The same subjects were also exposed to an operant delayed spatial response alternation procedure in which they were required to alternate responding between two levers that were inserted into the experimental chamber after delay intervals of either 5, 10, or 20 s had elapsed. Alternation response accuracy of both subjects with lesions and control subjects decreased as a function of the duration of the delay interval, but control-operated subjects responded more accurately than did lesion subjects at each interval duration. Response accuracy increased with prolonged training for both groups of subjects, but faster for control-operated than for subjects with lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Dissociation of item and order spatial memory in rats following medial prefrontal cortex lesions

In order to test whether there is a correspondence in function of prefrontal cortex in rats and humans, rats with medial prefrontal cortex lesions were tested for item and order memory for a list of items (spatial locations in a maze). Results indicate that for order memory rats with medial prefrontal cortex lesions cannot remember the order of presentation of four or eight specific spatial locations. This inability to remember order information can be seen even when animals with lesions have to remember only two spatial locations, can self-order the sequence of four or eight spatial locations, or have been presented with the same study phase on every trial. In contrast, for item memory animals with medial prefrontal cortex lesions retain the first item of the list in the variable study phase situation and remember all the items of the list in a constant study phase situation. However, there are also deficits for the last items within a list in the variable study phase situation for both win-stay and win-shift procedures. This deficit might be a function of an impairment in the utilization of appropriate temporal strategies, which normally would facilitate recognition memory in the win-stay and win-shift tasks. In general, the data suggest a partial, but not complete, dissociation of item-order memory. Furthermore, the data suggest that the medial prefrontal cortex is involved in temporal structuring of information.

Evidence for neocortical involvement in reference memory

Rats were trained on an eight-arm radial maze task using a procedure that provides for an assessment of both working and reference memory. Following training, rats received parietal cortex, medial prefrontal cortex, visual cortex, or nucleus basalis magnocellularis lesions. Rats with visual cortex lesions showed no change in performance on either working or reference memory. Rats with parietal cortex lesions displayed a temporary deficit in reference, but no deficit on working memory. Animals with medial prefrontal cortex lesions showed a temporary deficit on both working and reference memory. Rats with extensive lateral frontal and parietal cortex depletion of acetylcholinesterase following nucleus basalis magnocellularis lesions had a marked disruption only of reference but not of working memory. It is concluded that neocortex and possibly the cholinergic projections to neocortex play an important role in mediating reference memory.

6-Hydroxydopamine and excitotoxin lesions of medial prefrontal cortex fail to affect schedule-induced drinking in the rat

Schedule-induced drinking was examined in rats following 6-hydroxydopamine and N-methyl- d-aspartate lesions of the medial prefrontal cortex. 6-Hydroxydopamine reduced the concentrations of dopamine and noradrenaline in the medial prefrontal cortex to 17 and 37% of control values respectively, while changes were not observed in the nucleus accumbens. Lesions with N-methyl- d-aspartate were confined to the medial prefrontal cortex. Schedule-induced water consumption, determined over 11 consecutive 1 h/day testing sessions, was not significantly altered by either lesion. These results suggest that the mesocortical dopaminergic projection to the medial prefrontal cortex, and reciprocal projections from medial prefrontal cortex to the nucleus accumbens and the ventral tegmental area, are not essential for the acquisition of schedule-induced drinking.

Effects of unilateral microinjections of sulpiride into the medial prefrontal cortex on circling behavior of rats

1. Bilateral 6-OHDA lesions of rats' medial prefrontal cortex increased locomotor activity after 7–10 days suggesting that cortical DA may normally inhibit motor behaviour. However, hyperactivity may have resulted from enhanced subcortical DA function. 2. Acute manipulation of frontal cortical DA neurotransmission in the present experiment avoided lesion-induced subcortical changes. 3. Sulpiride (0, 6, 12, 24 ug in 1 ul) was Injected unilaterallv into the medial prefrontal cortex of rats pretreated with (+)-amphetamine (1.5 mg/kg i.p.). 4. Circling behavior was scored during four 5-min intervals of a 60-min test session which began with injections and placement in a flat, circular arena. 5. SUL resulted in ipslversive circling whereas its vehicle did not. These results were consistent with those seen with other DA drugs and suggest an excitatory influence of frontal cortical DA on locomotor activity.