Further evidence for excitatory amino acid transmission in the lateral habenular projection to the rostral raphe nuclei: lesion-induced decrease of high affinity glutamate uptake.

In previous autoradiographic studies we reported selective retrograde D-[3H]aspartate labelling of lateral habenular afferents to the nuclei raphe dorsalis (NRD) and centralis superior (RCS). This study reports biochemical support, lesion-induced decrease of high affinity glutamate uptake, for excitatory amino acid transmission in the habenulo-raphe connection. Rats received bilateral electrolytic lesions in the lateral habenular nuclei and survived 9-10 days. Brainstems were sectioned on a Vibratome, and NRD and RCS tissue microdissected. Glutamate uptake in sham-operated rats was in the NRD 23.6 +/- 2.3 nmol/g prot. (mean +/- S.E.M.) ([3H]glutamate 10(-7) M, 3 min, 25 degrees C) and in the RCS 14.6 +/- 1.0 nmol/g. Habenular lesions reduced glutamate uptake in the NRD by 20.7 +/- 2.0% (P less than 0.001) and in the RCS by 10.7 +/- 4.3% (P less than 0.05).

Interhemispheric nigrothalamic projections and behavioral recovery following turning behavior induced by unilateral peripheral sensory and motor restriction.

We investigated the relationship between unilateral peripheral lesions plus partial sensory deprivation and interhemispheric nigrothalamic projections. Sensory-motor asymmetries were induced in rats by unilateral ligature of sensory and motor nerves of the forelimbs and hind limbs and partial sensory deprivation (cutting the vibrissae unilaterally and suturing one eyelid). This operation resulted in spontaneous turning which was partially compensated for within the first 5 postoperative days. Sixteen days after the surgery, animals were implanted with horseradish peroxidase in the ventrobasal thalamus of one hemisphere. Brains were processed by the tetramethylbenzidine procedure. Microscopical analysis revealed interhemispheric nigrothalamic projections from the substantia nigra situated ipsilateral but not contralateral to the denervated limbs. The results are interpreted in terms of a reorganization (sprouting) of interhemispheric nigrothalamic projections in response to unilateral peripheral lesions. The lesion-induced behavioral asymmetry and its partial compensation may be one of the determinants of the observed neuronal plasticity.

Hypothalamic self-stimulation in rats with one hemisphere isolated anterior to the midbrain and the other hemisphere devoid of the telencephalon.

The telencephalon was removed unilaterally in rats. In addition, the forebrain of the other hemisphere was isolated from its brain stem by a precollicular transverse cut. This preparation was then tested for self-stimulation via electrodes implanted in the region of the lateral hypothalamus and medial forebrain bundle (LH-MFB) of either hemisphere. Self-stimulation was found to be intact in both hemispheres. Possible pathways connecting the LH-MFB region of one hemisphere to the contralateral diencephalon were also investigated in the bilaterally detelencephalized rat. The technique of retrograde transport of horseradish peroxidase was used for this purpose. Some fibers from the LH-MFB of one hemisphere were found to decussate to the other hemisphere by way of the thalamic commissure. The supraoptic decussation as well as diffusely organized interdiencephalic connections provide additional routes for interhemispheric LH-MFB projections.

Afferents from limbic system-related regions to the frontal cortex in the bush baby (Galago senegalensis).

Afferents from limbic system-related structures (aside from the cingulate and retrosplenial cortex) to medial and lateral regions of the bush baby's frontal cortex were investigated by means of the somatopetal transport of horseradish peroxidase. The frontopolar region received afferents from the subicular cortex, the lateral nucleus of the amygdala, from hypothalamic nuclei, the ventral tegmental area and other brain stem nuclei. Injections of horseradish peroxidase into other frontal regions usually resulted in labeled cells in brain stem nuclei and in the hypothalamus, but not in telencephalic regions; only the large injection into the posterior part of the frontal cortex was followed by labeled amygdaloid neurons. From these results it is concluded that a small number of limbic system-related telecephalic areas projects to the frontal cortex and that a somewhat larger number of diencephalic and brain stem nuclei reaches this part of the cortex.

Plasticity of cortico-thalamic projections and functional recovery in the unilateral detelencephalized infant rat.

Previous results have shown that the unilateral removal of the telencephalon in adult rats leads to the appearance of crossed connections from the remaining telencephalon to the thalamus one week after the ablation. This study extends this finding to infant rats. The telencephalon structures were unilaterally removed in 7-day-old animals. As in adult rats the ablation induced behavioral asymmetries, including active turning behavior which ceased within the first days after the lesion. Either immediately after the ablation or one week thereafter the animals were injected with horseradish peroxidase (HRP) into the posterior part of the thalamus ipsilateral to the lesion. HRP-labeled cells appeared in the remaining contralateral cortex in animals that were injected one week after the lesion. Rapid functional recovery from the lesion-induced behavioral asymmetries, as indicated, for example, by the cessation of spontaneous turning behavior, may be related to the observed appearance of crossed projections between structures that are normally connected only ipsilaterally.

Organization of cortical afferents to the prefrontal cortex in the bush baby (Galago senegalensis).

Cortical afferents to the prefrontal cortex were studied in 10 bush babies (Galago senegalensis) by means of somatopetal transport of horseradish peroxidase. The lateral injections invariably labeled neurons in the temporal cortex and in most cases also in the insular and parietal regions. In some of these brains the cingulate and retrosplenial areas contained labeled perikarya. Injections into the medial cortex, on the other hand, consistently labeled cell bodies in the cingulate cortex, but not in the insular, temporal and parietal regions. When both lateral and medial sites of the bush baby's prefrontal cortex are considered together, apparently fewer cortical areas (as defined by Brodmann's cytoarchitectonic maps) project to the prefrontal cortex in the bush baby than in the rhesus monkey. This statement holds for both ipsi- and contralateral projections.

Neural and behavioral plasticity: crossed nigro-thalamic projections following unilateral substantia nigra lesions.

Unilateral lesions of the substantia nigra of rats by injection of 6-hydroxydopamine or kainic acid induced ipsi- and contraversive turning behavior. Spontaneous turning was no longer exhibited one week after the lesions. This behavioral recovery was correlated in time with the development of crossed projections from the intact contralateral substantia nigra to the ventromedial thalamus of the lesioned hemisphere which, in the intact animal, receives projections only from the ipsilateral substantia nigra.

Kainic acid lesions in the cat's thalamus: morphological and behavioral changes.

Anatomical and behavioral effects of large and of circumscribed kainic acid lesions in the thalamus of the cat are described. Evidence is provided that even "athalamic" preparations seem possible and that cats with destruction of more than two thirds of their thalamus show only transitory disturbance of basic functions (eating, drinking, walking). It is concluded that fiber systems, traversing the thalamus, may be of particular importance for maintaining basic functions.

Prefrontal cortex of the cat: evidence for an additional area.

Direct projections from the mediodorsal nucleus of the thalamus to ventral parts of the insular region of the cat's cortex were demonstrated by using the horseradish peroxidase technique.

The prefrontal cortex of the cat: anatomical subdivisions based on retrograde labeling of cells in the mediodorsal thalamic nucleus.

Different areas of the frontal cortex of the cat were injected with small amounts of horseradish peroxidase. The region of labeled cells in the mediodorsal nucleus of the thalamus (MD) were related to the injected areas. Distinct relations between subdivisions of MD and of the prefrontal cortex were established: a rather large central sector of MD projects to the gyrus proreus and the anterior parts of the gyri sigmoideus, rectus, and frontalis. A narrow lateral band of anterior MD neurons projects predominantly to an area on both sides of the sulcus praesylvius, whereas a postero-lateral band sends fibers to a region on the ventral anterior sylvian gyrus. The area between the presylvian sulcus and the sylvian gyrus is apparently free of MD afferents, but not of other thalamic afferents. A fourth sector of MD, situated dorsomedially, projects to the middle parts of the gyri rectus and frontalis. And a fifth sector, located ventrally to the dorsomedial MD sector, projects to the ventral part of the gyrus rectus. The established subfields of MD and of the prefrontal cortex are discussed with respect to previous anatomical research in the cat.

Single unit activity in cat prefrontal and posterior association cortex during performance of spatial reversal tasks .

Relationships between the performance of complex learning tasks and the firing patterns of single unites in prefrontal and posterior association areas of the neocortex were studied in 9 cats. Recording data from 2 additional cats served as controls for sensory and motor aspects of the tasks employed. During recordings, animals sat in a box, their heads fixed to a stereotaxic instrument, and performed a non-sensory spatial reversal or delayed-alternation task by pressing 1 of 2 lateralized retractable levers. Units obtained were classified into 5 basic types according to their correlation with aspects of the tasks. The first 3 types were related directly to sensory, motor and motivational aspects of the tasks. The fourth type was named associative, as it contained units which changed firing rates in advance or as a consequence of environmental events, rather than in direct relation. Discharge changes of units of the fifth type were rated as non-specific or non-specifiable. Between recording areas and tasks a striking similarity of unit firing patterns was obtained. Differences were observed only between the reactivity of polymodal cells in prefrontal and in posterior fields, and in the proportions of units revealing mnemonic and motor response aspects. It was concluded that a considerable functional overlap between prefrontal and posterior association areas of the cat with respect to processing of complex learning tasks exists on the single neuron level.