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PubMed1984

Origins of histamine-containing fibers in the cerebral cortex of rats studied by immunohistochemistry with histidine decarboxylase as a marker and transection.

The origins of histamine-containing fibers in the cerebral cortex were examined by means of the retrograde tracer technique of horseradish peroxidase (HRP)-immunohistochemistry with histidine decarboxylase (HDC) as a marker for the histamine neuron system. Total transection of the brain rostral to the posterior hypothalamus resulted in disappearance of HDC-like immunoreactive (HDCI) fibers in the cerebral cortex, but total transection caudal to the posterior hypothalamus did not decrease the number of HDCI fibers in the cortex, suggesting that HDCI fibers in the cerebral cortex originate in the posterior hypothalamus. The projection of HDCI neurons from the posterior hypothalamus to the cerebral cortex seemed to be bilateral because hemi-transection of the brain rostral to the posterior hypothalamus resulted in a bilateral decrease of HDCI fibers in the cerebral cortex with ipsilateral predominance. After injection of HRP into the cerebral cortex, numerous cells containing both HRP granules and HDCI structures were found bilaterally in the tuberal, caudal and postmamillary magnocellular nuclei, with ipsilateral predominance. These findings indicate that HDCI cells in the above nuclei give rise to axons extending bilaterally to the cerebral cortex.

Animals↗

PubMed1995

Ultrastructural localization of delta-opioid receptor and Met5-enkephalin immunoreactivity in rat insular cortex.

The insular cortex has been implicated in the reinforcing properties of opiates as well as in the integration of responses to sensory-motor stimulation. Moreover, the delta-opioid receptor (DOR) and the endogenous opioid ligand, Met5-enkephalin (ENK) are known to be prominently distributed in insular limbic cortex. To examine the anatomical sites for opioid activation of DOR in rat insular cortex, we used immunoperoxidase for detection of an antiserum raised against a peptide sequence unique to the DOR alone, and in combination with immunogold-silver labeling for ENK. Light microscopy showed intense DOR-like immunoreactivity (DOR-LI) in pyramidal cells and interneurons in deep laminae, and in varicose processes in both superficial and deep layers of the insular cortex. Ultrastructural analysis of layers V and VI in insular cortex showed that the most prominent immunoperoxidase labeling for DOR was in dendrites. This labeling was associated with asymmetric excitatory-type junctions postsynaptic to unlabeled terminals. Dendritic DOR-LI was also distributed along selective portions of non-synaptic plasma membranes and subsurface organelles. In dually labeled sections, dendrites containing DOR-LI sometimes received synaptic input from ENK-labeled terminals or more infrequently colocalized with ENK. Other axon terminals were exclusively immunolabeled for DOR or more rarely contained both DOR and ENK immunoreactivity. Within labeled axon terminals, distinct segments of the plasma membrane and membranes of immediately adjacent synaptic vesicles showed the largest accumulation of the peroxidase reaction product for DOR. These results indicate that in rat insular cortex DOR is primarily heteroreceptive, but also serves an autoreceptive function on certain ENK-containing neurons. Our results also provide the first ultrastructural evidence that in rat insular cortex endogenous opioids interact through the DOR (1) to modulate the postsynaptic responses to other excitatory afferents and (2) to presynaptically regulate the release of other neurotransmitters. The modulatory actions on both ENK-containing and non-ENK-containing neurons may contribute significantly to the reinforcing properties of exogenous opiates acting on the DOR in limbic cortex.

Animals↗

PubMed1996

Morphology of identified corticospinal cells in the rat following motor cortex injury: absence of use-dependent change.

After unilateral injury to the forelimb area of the motor cortex, rats are reported to show relatively increased use of the ipsilateral forelimb during exploratory behavior and a concomitant transient increase in dendritic growth in neurons in the undamaged motor cortex. To identify the specific population of cells in motor cortex that undergo such use-dependent change, we examined the morphology of corticospinal pyramidal cells in the intact hemisphere 18 days following unilateral motor cortex damage. Corticospinal neurons in the motor cortex were retrogradely labeled with injections of the fluorescent tracer, DiO, into the cervical enlargement of the spinal cord. Seven days later, the rats received a lesion in the forelimb area of the contralateral motor cortex and 18 days following the lesion, limb use was assessed in two behavioral tests after which the rats were sacrificed. Under fluorescent light, corticospinal cells were visualized and injected with a horseradish peroxidase-fluorescein conjugate that was then reacted with diaminobenzidine. The labeled cells were reconstructed and the number and centrifugal order of the branches were analyzed. The increased use of the paw contralateral to the intact motor cortex was not associated with an increase in dendritic arborization in corticospinal motor neurons in the intact motor cortex. The results are discussed in light of methodological and theoretical considerations relevant to the study of neural plasticity in the motor system.

Animals↗

PubMed1991

Dopamine modulates the inhibition induced by GABA in rat cerebral cortex: an iontophoretic study.

Effects of iontophoresed gamma-aminobutyric acid (GABA) and two GABA agonists, 4,5,6,7-tetrahydroisooxazolo-[5,4-c]pyridine-3-ol (THIP) and baclofen were quantitatively compared in the anterior cingulate, frontal, and parietal cortex of urethane-anesthetized intact rats after catecholamine (CA) depletion with alpha-methyl-p-tyrosine (alpha-MPT) or selective dopamine (DA) denervation with 6-hydroxydopamine (6-OHDA). As assessed with to the IT50 index, the postsynaptic sensitivity to GABA was significantly higher in anterior cingulate than in frontal and parietal cortex. The responsiveness to GABA was also greater in frontal than in parietal cortex. Sensitivity to GABA was significantly reduced in both anterior cingulate and frontal cortex after CA depletion, and similarly, after DA denervation with 6-OHDA. The difference in the sensitivity to GABA between the three cortical regions in intact rats as well as after CA depletion did not seem to be correlated with either GABAA or GABAB receptors since the responsiveness to both GABA agonists in every region examined was comparable in intact rats, and remained unchanged after alpha-MPT treatment. This finding raises the possibility that some GABA receptors in the cerebral cortex may be pharmacologically distinct from the two main subtypes of GABA receptors, GABAA and GABAB. When GABA was administered by iontophoresis in the anterior cingulate cortex during continuous applications of subthreshold currents of DA, the inhibition induced by GABA was either increased or decreased. As DA innervation density is nearly two-fold greater in anterior cingulate than in frontal cortex, and 30-fold greater in anterior cingulate than in parietal cortex, these results suggest that responsiveness to GABA may be correlated with the regional density of DA innervation and that elevated levels of DA may enhance the sensitivity to GABA.

Animals↗

PubMed1984

Quantitative analysis of the striate cortex in the mutant microphthalmic rat.

A quantitative analysis of the striate cortex of the mutant microphthalmic rat was conducted to determine whether or not transneuronal changes of the visual cortex were induced following the loss of eyes. The area of the striate cortex in the microphthalmic rat was approximately 60% of that in the normal rat. As for the thickness of each layer of the striate cortex, many layers of microphthalmia tended to be thin in comparison with the normal animal, except for layers I and III: the thickness of layers II, IV, V, and VI was about 74, 62, 82, and 82% of normal values, respectively. There was fractically no difference between the number of neurons of each layer of the microphthalmic and the normal striate cortex per unit (10(4) microns2), except for layer IV, in which the density had increased to 117% of the normal value. In many layers, the neurons of the microphthalmic striate cortex were smaller than normal and they had narrow neuroplasmic space. Our study demonstrated that the striate cortex of the microphthalmic rat underwent quantitative and morphometric transneuronal changes. Especially striking changes of the striate cortex were found in the inner granular layer with a reduction in thickness and a diminution of cell size.

Animals↗

PubMed1984

The visual field representation in striate cortex of the macaque monkey: asymmetries, anisotropies, and individual variability.

The topographic organization of striate cortex in the macaque was studied using physiological recording techniques. Results were displayed on two-dimensional maps of the cortex, which facilitated the quantitative analysis of various features of the visual representation. The representation was found to be asymmetric with more cortex devoted to lower than to upper fields. Over much of striate cortex the representation is anisotropic, in that the magnification factor depends upon the direction along which it is measured. There is considerable individual variability in these features as well as in the overall size of striate cortex. Outside the fovea, the cortical representation shows only modest deviations from a logarithmic conformal mapping, in which the magnification factor is proportional to the inverse of eccentricity in the visual field. Comparison of receptive field size with cortical magnification was used to estimate the "point image size" in the cortex (i.e. the extent of cortex concerned with processing inputs from any given point in the visual field). Our evidence supports a previous report that point-image size varies significantly with eccentricity. This is of interest in relation to anatomical evidence that the dimensions of columnar systems in striate cortex are largely independent of eccentricity.

Animals↗

PubMed1986

Visceral cortex lesions block conditioned taste aversions induced by morphine.

Rats with bilateral ibotenic acid or sham lesions of the visceral (agranular insular) cortex were tested for a conditioned taste aversion (CTA) to saccharin after five pairings of morphine sulphate injections (15 mg/kg IP) with consumption of a novel solution (0.1% saccharin). Lesioned animals demonstrated no evidence of the morphine-induced CTA that was seen in the sham operated animals. A third group of rats received ibotenic acid lesions but had saccharin consumption paired with saline vehicle injections. This group had the normal preference (seen in naive rats) for saccharin on testing, showing that the visceral cortex lesion had no effect on the ability of the rats to discriminate saccharin from water. In order to test if visceral cortex lesions abolish specifically the CTA induced by morphine, we ran a similar set of CTA experiments using two new novel flavours and either 15 or 75 mg/kg IP lithium chloride (LiCl) as the unconditioned stimuli. Dose dependent CTA's to the LiCl were established in all groups indicating that the visceral cortex plays no role in mediating the aversive effect of LiCl. Using the condition place preference paradigm we investigated the role of the visceral cortex in the expression of morphine's rewarding aspects. Identical place preferences were found in groups of rats with or without visceral cortex lesions suggesting that this cortical region plays no role in either the perception of morphine's rewarding effects or the association of morphine's rewarding properties with sensory stimuli. Visceral cortex lesions also had no effect on the establishment of a conditioned place aversion to a high dose of LiCl (75 mg/kg IP). Thus, visceral cortex appears critical for the establishment of a morphine-induced CTA, but is not crucial for mediating gross taste discrimination, the aversive aspects of LiCl nor the rewarding properties of morphine.

Animals↗

PubMed1984

Effects of bicuculline-induced epileptiform activity on development of receptive field properties in striate cortex and lateral geniculate nucleus of the rabbit.

Studies have shown that normal development of receptive field properties in striate cortex and lateral geniculate nucleus (LGN) of the rabbit is severely altered in the presence of penicillin-induced disruption of cortical neuronal activity. We wished to replicate these studies using a different convulsant drug in order to rule out possible effects due to the penicillin drug itself. Aqueous bicuculline was injected twice daily into a cannula implanted over the monocular region of one striate cortex. Drug administration was initiated on postnatal day 8-9 and was discontinued either on postnatal day 19-24 or on postnatal day 24-30 for studies of the LGN and striate cortex, respectively. Coincidental with the bicuculline injections, control solutions were similarly applied to the monocular region of the contralateral striate cortex. Single-unit recordings made from LGN ipsilateral to bicuculline-treated cortex revealed normal percentages of receptive field types. However, in single-unit recordings made from bicuculline-treated striate cortex, an abnormal percentage distribution of receptive field types was found. In such cortex there was an unusually high proportion of no-response type cells and a substantially reduced proportion of oriented type cells. These developmental abnormalities are virtually the same as those found in the striate cortex of similarly reared animals treated with penicillin. Our present results lend support to our previous conclusion that in the rabbit, disruption of orderly neuronal activity in the geniculostriate system has a detrimental effect on the development of receptive fields in this system.

Animals↗

PubMed1986

A transient pyramidal tract projection from the visual cortex in the hamster and its removal by selective collateral elimination.

During the early postnatal development of the neocortex in rats there is an axonal projection from the occipital cortex (which includes the visual cortex) to the spinal cord which is subsequently completely removed through a process of selective collateral elimination. In order to determine whether a similar phenomenon occurs during the development of the hamster cortex, we have injected the retrogradely transported fluorescent dye Fast Blue (FB) into the pyramidal decussation of hamsters at various ages. In adult hamsters such an injection results in a band of labeled neurons confined to layer V and to about the rostral two-thirds of the neocortex; no labeled cells are seen in the occipital cortex. However, a similar FB injection made during the first postnatal week results after a 4-day survival in a continuous band of FB-labeled layer V neurons spread throughout the tangential extent of the neocortex, including the occipital cortex. A similar continuous band of FB labeled layer V neurons is seen throughout the tangential extent of the neocortex including the occipital region in hamsters injected during the first postnatal week but allowed to survive until the fourth week (i.e., after the restriction of the widespread neonatal pattern has occurred). Injections of the anterograde tracer wheat germ agglutinin conjugated to horseradish peroxidase made into the occipital cortex, or for comparison, into more rostral cortical regions in hamsters ranging in age from neonates to adults, reveal that the extension of pyramidal tract axons is staggered along the anterioposterior axis of the cortex such that axons originating from the posterior regions lag behind those arising from more rostral areas. The transient occipital projection appears to reach a maximum around the end of the first postnatal week: a large number of labeled occipital axons is seen in the medullary pyramidal tract, and some of these can be followed through the pyramidal decussation and into the dorsal funiculus of the spinal cord. Injections into the occipital cortex on P16 label only a few fibers in the medullary pyramidal tract, and none is labeled in hamsters injected as adults.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

The distribution of M1 and M2 muscarinic acetylcholine receptor subtypes in the developing cat visual cortex.

The binding site characteristics and ontogenesis of [3H]pirenzepine ([3H]PZ) (M1 receptor) and [3H]oxotremorine-M ([3H]OXO-M) (M2 receptor) binding sites were investigated in the cat visual cortex. Scatchard analysis of [3H]PZ binding in adult cat visual cortex revealed a single site with a Kd of 17.3 nm and a Bmax of 352.45 fmol/mg protein. [3H]OXO-M also bound to a single site with a Kd of 7.1 nM and a Bmax of 256.39 fmol/mg protein. Receptor autoradiography revealed that [3H]PZ binding sites were present only in telencephalic structures while [3H]OXO-M sites were distributed heterogeneously throughout the brain. [3H]PZ binding sites in adult visual cortex were present in the superficial and deep cortical layers with the densest labeling in layer I and a distinct band in layer V. [3H]OXO-M sites also avoided the middle cortical layers, but were most prominent in layers V and VI with less pronounced binding in layers I and II. Deafferentation of extrinsic inputs to the visual cortex did not reduce [3H]PZ nor [3H]OZO-M binding, but neuron-specific excitotoxic lesions of visual cortex abolished both populations of binding sites. This indicates that both populations of binding sites are located on cells intrinsic to the cortex. In early postnatal life, both [3H]PZ and [3H]OXO-M binding sites were localized to intermediate cortical layers. Following this, the laminar distribution of both populations redistributed; each with its own idiosyncratic profile. By postnatal day 49, [3H]PZ binding sites redistributed into the superficial and deep layers, the pattern of adult animals, while [3H]OXO-M sites maintained a pattern similar to younger animals, with substantial binding persisting in layer IV. As late as postnatal day 70, well after [3H]PZ binding sites had achieved their mature laminar pattern, [3H]OXO-M binding sites in visual cortex had not achieved their characteristic adult pattern. In addition, the normal laminar redistribution of both [3H]PZ and [3H]OXO-M binding sites during postnatal development of the cat visual cortex was prevented by eliminating cortical afferents in early postnatal life. This indicates that muscarinic receptor rearrangement in development is dependent upon cortical input or output.

Animals↗

PubMed1990

Elaborate organization of visual cortex in the hamster.

We have studied the organization of visual cortex in the hamster by analyzing and correlating the distributions of callosal and striate-extrastriate connections. Our results show that, in lateral extrastriate cortex, callosal connections form an elaborate pattern which delineates at least 3 regions poor in callosal connections. These regions receive projections from striate cortex which are distributed into multiple separate fields. Two additional striate-projection fields were observed in medial extrastriate cortex, and another field was often observed near the posterolateral border of primary somatosensory cortex. All striate recipient fields are reciprocally connected with striate cortex. The patterns of callosal and striate-extrastriate connections in the hamster are similar, although not identical, to the corresponding patterns in rats and mice. Our results provide evidence that the organization of visual cortex in the hamster is highly elaborate, and suggest that extrastriate cortex is subdivided into multiple visual areas.

Animals↗

PubMed1993

Neurotransmitter organization and connections of turtle cortex: implications for the evolution of mammalian isocortex.

Telencephalic cortex in turtles is a simple three layered-structure. The dorsal most part of this structure is thought to resemble the reptilian forerunner of at least parts of mammalian isocortex. This dorsal part of turtle cortex contains several functionally distinct regions that show similarity in their connections and function to specific areas in mammalian isocortex. The types of neurons found in turtle dorsal cortex (as defined by their morphology and neurotransmitter content) also show great similarity to those observed in mammals, with the major exception that turtle cortex appears to lack the types of neurons found in granular and supragranular layers of mammalian isocortex. Similar results have also been observed in other living reptiles. Thus, one major step in the evolution of reptilian cortex into mammalian cortex must have been the addition of the types of neurons found in the granular and supragranular layers of mammalian isocortex. These observations for turtles also suggest that turtle cortex in particular and reptilian telencephalic cortex in general must differ functionally from mammalian isocortex with respect to those features associated with the laminar and columnar organization of isocortex. These issues are discussed in more detail below and in Reiner (1991).

Animals↗

PubMed1987

The mode of projections of single locus coeruleus neurons to the cerebral cortex in rats.

Axonal distributions of single locus coeruleus neurons within the cerebral cortex were examined with antidromic stimulation technique combined with cortical lesions (frontal lobotomy and lobectomy). In urethan-anesthetized rats, stimulating electrodes were implanted in 10 points extending over nearly the entire cerebral cortex, and antidromic responses of single locus coeruleus neurons to stimulation of these stimulus sites were analysed. Fifty percent of locus coeruleus neurons examined were activated antidromically from at least one cortical point in the cerebral cortex. The pattern and extent of axonal distributions of single locus coeruleus neurons in the cortex appeared to vary from cell to cell. From the results obtained in rats with the cortical lesions, it is concluded that in addition to locus coeruleus neurons with intracortical axons running from rostral to caudal, there are the neurons projecting to the occipital cortex without innervating the frontal cortex and those projecting simultaneously to the frontal and occipital cortex with two axonal branches. There was no topographic order between the recording sites within the locus coeruleus and the projection sites in the cortex.

Afferent Pathways↗

PubMed1987

Regional and laminar density of the dopamine innervation in adult rat cerebral cortex.

The topographic distribution and density of the dopamine innervation in adult rat cerebral cortex were investigated by means of a recently improved radioautographic procedure for the light microscopic visualization and counting of monoamine axonal varicosities. Dopamine terminals were specifically labeled by high-affinity uptake in whole cerebral hemisphere slices incubated for 15 min at 35 degrees C with 10(-6) M tritiated dopamine in the presence of 10(-4) M pargyline and 5 X 10(-6) M desipramine. The slices were subsequently fixed, embedded in Epon and processed for light microscope radioautography as large 4-micron-thick (whole hemisphere) or smaller, semi-thin sections (selected areas). In radioautographs of serial semi-thin sections exposed for various periods of time, the number of labeled axonal varicosities reached a plateau after 12-14 days of exposure. Counts on such sections of increasing thickness allowed to calculate a correcting factor to transform numbers obtained from 4-micron-thick sections into their equivalent for a tissue thickness of 0.5 micron from which all varicosities were detected. The number of labeled varicosities could then be expressed per mm3 of tissue after measuring their mean caliper diameter in electron microscope radioautographs. As visualized at 3 transverse levels representing most of the major cytoarchitectonic divisions of cerebral cortex, two novel aspects were recognized in the topographic distribution of dopamine terminal: (1) the presence of a dopamine innervation in layer VIb of the frontal, parietal, temporal and occipital neocortex, and (2) a significant contingent of dopamine varicosities within the deep and not only upper layers of supragenual cingulate cortex. A fair number of dopamine varicosities were also detected in the upper layers of the dorsomedial frontal area, in the retrosplenial and adjacent occipital cortex as well as in the ventral subiculum and field CAl of the hippocampus. As measured in 10 sectors representing different cortical regions, the highest density of dopamine innervation was found in the supragenual cingulate cortex (1.7 X 10(6] and particularly in its layers II and III (3.1 X 10(6)). A slightly lower density was measured in the anteromedian "prefrontal" cortex (1.0 X 10(6)). The rostrorhinal and the perirhinal cortex showed moderate dopamine innervation (3.0 and 5.5 X 10(5)) with varicosities in every layer. The piriform and the posterior entorhinal cortex were also moderately and ubiquitously innervated (2.5 and 3.0 X 10(5)).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1989

Evidence for a dopaminergic innervation of cat primary visual cortex.

Experiments have been conducted to determine whether dopamine fulfills the criteria to be considered as a neurotransmitter in cat primary visual cortex. N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine, a neurotoxin with high selectivity for noradrenergic terminals, was administered into kitten cerebral ventricles. Two weeks later, the concentration of norepinephrine in visual cortex was reduced to 15% of control while dopamine and serotonin were not depleted. Receptor binding assays with [3H]SCH 23390 showed that membranes prepared from cat primary visual cortex contain a binding site that has the properties of a D1 receptor. This site was localized by autoradiography to two bands, one in layer VI and the second in upper layers of visual cortex. A dopamine-stimulated adenylate cyclase activity was demonstrated that was inhibited by SCH 23390 but not by alprenolol. Norepinephrine was shown to stimulate adenylate cyclase activity through both a beta-noradrenergic receptor and a D1 receptor. Binding assays with [3H]spiperone indicated that D2 dopamine receptors are absent from cat visual cortex or present in very low amounts. Taken together these results strongly suggest the existence of a dopamine innervation of cat primary visual cortex. The neurotoxin experiments show that some of the dopamine in cat visual cortex is not in noradrenergic terminals while the receptor assays demonstrate the presence of D1 receptors functionally linked to the synthesis of cyclic 3',5'-adenosine monophosphate. The demonstration of a dopaminergic innervation in cat primary visual cortex is also relevant to the interpretation of data on the involvement of catecholamines in developmental plastic phenomena.

Adenylyl Cyclases↗

PubMed1996

Cortico-cortical and cortico-amygdaloid projections of the rat occipital cortex: a Phaseolus vulgaris leucoagglutinin study.

The efferent projections of the occipital cortex of the rat were investigated using the Phaseolus vulgaris leucoagglutinin anterograde tract tracing technique. Particular attention was focused on projections to the amygdala and amygdalopetal cortical areas. The primary visual cortex had projections to the medial and lateral portions of occipital area 2 and other cortical regions, but no projections to the amygdala or amygdalopetal cortical areas. The only occipital area that had direct projections to the amygdala was the most ventral portion of lateral occipital area 2, located just dorsal to temporal area 2. This occipitotemporal junction region, which received projections from secondary visual cortical areas but not from the primary visual cortex, had projections to the lateral nucleus, magnocellular basal nucleus, and lateral capsular subdivision of the central nucleus of the amygdala. Occipital area 2 had projections to seven amygdalopetal cortical regions: temporal area 2, temporal area 3, frontal area 2, ventrolateral orbitofrontal area, occipitotemporal junction region, lateral entorhinal area, and the perirhinal cortex. Projections to the perirhinal cortex targeted regions located adjacent to the parietal cortex and caudal temporal cortex, but not regions adjacent to the rostral temporal cortex. Other cortical regions receiving projections from medial and lateral portions of occipital area 2 included the presubiculum, retrosplenial areas, and caudal portions of the parietal cortical areas 1 and 2. The results of the present investigation, in conjunction with previous anatomical and neurobehavioral studies, support the concept that rodent cortical visual pathways, like those of primates, consist of a dorsal system involved with visuospatial functions and a ventral system involved with object recognition. As in primates, the ventral pathway projects to the temporal-perirhinal region in a cascading manner; only highly processed information from tertiary visual cortical areas reaches the amygdala. Unlike primates, however, cortical areas in the rat brain that receive highly processed visual information appear to be regions of multisensory convergence.

Amygdala↗

PubMed1984

Basal forebrain efferents reach the whole cerebral cortex of the cat.

Efferent projections from the basal forebrain to the cat's cerebral cortex were traced with the retrograde horseradish peroxidase technique. Different areas of the cerebral cortex of 51 cats were injected with small amounts of horseradish peroxidase. The entire basal forebrain was screened for labeled neurons. Following all injections, retrogradely labeled neurons could be detected in either the medial septum, or the vertical and horizontal limb of the diagonal band of Broca, or the substantia innominata, or in several of these structures. All three basal forebrain structures project heavily to allocortical regions, but only weakly to neocortical regions. An exception is the medial prefrontal cortex which is densily innervated by the substantia innominata (i.e., comparably dense as allocortical regions are innervated by the substantia innominata). Large injections into he basal temporal cortex (including the perirhinal cortex) and into the insular cortex also led to a considerable number of labeled cells in the substantia innominata. The results indicate a widespread innervation of the cat's cerebral cortex by the basal forebrain. This diffuse projection to the cortex has recently been found also in monkeys and rats. Anatomical and functional implications of these projections in the cat are discussed and related to findings in other species.

Animals↗

PubMed1987

Quantitative analysis of synaptogenesis in the cerebral cortex of the cat suprasylvian gyrus.

A quantitative study was made of the synapses in the association cortex of the suprasylvian gyrus and in the adjacent subcortical region, in kittens from birth (P0) to 103 days (P103), and in two adults. The quantitative data were corrected using the neuropil and the growth coefficients. At P0, the synaptic density of the cortex is only 7% of the adult density. The synapses are disposed preferentially in layers I, III and V. The rush of the synaptic density apparently starts at P9, or at P12 after correction using the growth coefficient. At this time, the cortico-cortical connections begin to form. During the rush, the synaptic peaks of the newborn animal disappear; the synaptic density reaches its maximum at P28-P35, exceeding the adult density by 53 to 82%. After P35, there appears a real, although very slow, elimination of synapses. This elimination touches the superficial layers (I to III) first, and then the deep layers. The young neuron, seeking a qualitative and quantitative equilibrium of its afferents and its efferents, seems to be responsible for this elimination. The superficial cortex always contains more synapses (60%) than the subjacent cortex, regardless of the animal's age. The rush is greatest here, as is the elimination. The question of senescence arises: since the majority of the synapses are very probably of cortico-cortical origin in this cortex, this process would seem to be due to a loss of association connections. Indeed, one of the two adults analyzed revealed a loss of synapses in the superficial layers of its cortex, as well as in layer VI. The synapses are present in the subcortical region, without discontinuity with the cortex in all animals. In the youngest, synapses were observed down to 2 mm below the cerebral cortex: the neurons establish a few rare contacts before reaching their definitive site. In the adult, the white matter is totally devoid of synapses. Since the elimination of synapses appears to be a process which continues throughout life, the term "maturity" cannot be attributed solely on the basis of the histologic components, but must result from an evaluation of behavior.

Animals↗