Neither perirhinal/entorhinal nor hippocampal lesions impair short-term auditory recognition memory in dogs.

Visual, tactile, and olfactory recognition memory in animals is mediated in part by the perirhinal/entorhinal (or rhinal) cortices and, possibly, the hippocampus. To examine the role of these structures in auditory memory, we performed rhinal, hippocampal, and combined lesions in groups of dogs trained in auditory delayed matching-to-sample with trial-unique sounds. The sample sound was presented through a central speaker and, after a delay, the sample sound and a different sound were played alternately through speakers placed on either side of the animal; the animal was rewarded for responding to the side emitting the sample sound. None of the lesion groups showed significant impairment in comparison either to their own preoperative performance or to the performance of intact control dogs. This was the case both for relearning the delayed matching rule at a delay of 1.5 s and for task performance at variable delays ranging from 10 to 90 s. From these findings we suggest that the tissue critical for auditory recognition memory is located outside both the perirhinal/entorhinal cortices and the hippocampus.

Regional and laminar variations in acetylcholinesterase activity within the frontal cortex of the dog.

Two different histochemical methods were applied to analyse acetylcholinesterase (AChE) activity within the frontal lobe cortex (FC) of the dog. Both staining methods revealed AChE reactivity in neuronal cell bodies and fibres. AChE-positive neuronal perikarya varied in size, shape, character and intensity of staining. Both pyramidal and non-pyramidal AChE-rich neurons were found. The pyramidal neurons predominated in layers III and V of the dog FC. The non-pyramidal cells were present in deep cortical layers and white matter. Labelled cells were distributed in a consistent pattern across regions of the dog frontal lobe. AChE reactivity in fibres showed, in general, a characteristic bilaminar appearance due to the more intense staining in cortical layers I and V. However, in contrast to the cellular labelling, differences in the laminar distribution of AChE-rich fibre bands distinguished three subregions of the FC: (1) rostral and middle prefrontal and anterior premotor areas, where AChE was distributed in a bilaminar pattern with two bands of similar, medium-intensive staining overlying layers I and V; (2) dorso-caudal primary and secondary motor areas distinguished by much lighter staining of the deep band of AChE activity in layer V; and (3) ventro-caudal subcallosal region in which the bilaminar pattern of extremely dark labelling in layers I and V was augmented by a third band of strong AChE activity in layer VI. These findings show that differences in the pattern of AChE activity parallel some of the cytoarchitectonic zones of the FC previously described in this laboratory (Rajkowska and Kosmal, 1988).

The distribution of cholinergic muscarinic receptors in the dog frontal lobe.

The topographical distribution of cholinergic muscarinic receptor (MChR) sites was studied by means of quantitative receptor autoradiography using [3H]quinuclidinyl benzilate ([3H]QNB) in the frontal (prefrontal, premotor and motor) cortex of the dog. The mean binding value in the frontal cortex was 408 +/- 5.0 fmol/mg tissue and the only area that differed significantly from the mean was the primary motor cortex, where the binding value was significantly lower. In the dorsal part of the prefrontal and premotor cortical subregions studied, a tri-laminar pattern of [3H]QNB labelling was observed, with a superficial dense band of label corresponding to cortical layers I, II and III. The deep high density band overlaid layer V and the upper part of the layer VI. In the ventral part of the prefrontal cortex this pattern gradually disappeared and in the most ventral part no laminar differences were seen. In contrast, in primary motor areas, the deep band of labelling corresponding to layer V was much less pronounced than in the frontal association cortex. Variations in the distribution of MChR sites seem to reflect to some extent the greater cytoarchitectonic differentiation of the dorsal zone and also the similarity between the ventral zone and the limbic cortex described by us previously.

Loss of object discrimination after ablation of the superior colliculus-pretectum in binocularly deprived cats.

The effects of ablation of the superior colliculus-pretectum on a previously elaborated object discrimination task were compared in cats reared in normal conditions, in cats reared in the laboratory, and in cats deprived of patterned vision. The normally reared cats were least deficient postoperatively, whereas deprived cats were most deficient. Seven of 8 deprived cats failed to re-reach criterion. Previous results showed that after removal of the visual cortex deprived cats were less deficient than normally reared controls. It is concluded that in discrimination learning the function of the abnormal visual cortex of deprived cats is partially taken over by the superior colliculus-pretectum.

Organization of connections underlying the processing of auditory information in the dog.

1. The canine temporal cortex includes the ectosylvian, composite posterior and sylvian gyri. 2. The distinctive features of the canine temporal cortex include the ectosylvian sulcus closed in its dorsal side and the substantial development of neocortex located within the posterior composite gyrus. 3. Thalamofugal connections from particular nuclei of the medial geniculate body, posterior thalamus and lateromedial-suprageniculate complex project to specific areas of the canine temporal cortex and are arranged as dominant and non-dominant projections. 4. Local intracortical connections distinguish the ectosylvian and posterior composite areas as unimodal auditory cortex. Long distant connections and polymodal convergence indicate that the composite ectosylvian area of the anterior ectosylvian gyrus and the anterodorsal sylvian areas are higher order association cortex. 5. Analysis of both thalamo-cortical and intracortical connections indicate that auditory processing in the cortex occurs in successive, hierarchically organized stages and in two main, anterior and ventral pathways.

Subcortical connections of the prefrontal cortex in dogs: afferents to the proreal gyrus.

Afferent subcortical connections to the proreal gyrus of the prefrontal cortex (PFC) in the dog were investigated using the horseradish peroxidase retrograde transport method. The afferent projections derive mainly from dorsal-intermediate and caudal regions of the mediodorsal nucleus (MD), from $he ventral as well as from the lateral thalamic nuclei. In the ventral nuclei, the distribution of labeled cells showed a topography correlated with injections localized in the anteroposterior direction. Furthermore, single cells were labeled in midline and intralaminar thalamic nuclei as well as some extrathalamic structures. The data obtained in behavioral and anatomical experiments with dog and monkey are discussed. The distribution of afferent projection from MD and the functional division on particular subfields of PFC seems to be in accordance in both species.

Subcortical connections of the prefrontal cortex in dogs: afferents to the medial cortex.

Afferent subcortical connections to the medial prefrontal cortex (PFC) in the dog were investigated using the horseradish peroxidase retrograde transport method. The dorsal and ventral regions of the medial PFC receive different projections both from the mediodorsal and the ventral thalamic nuclei. The dorsomedial PFC receives projection from a dorsolateral region of the "parvocellular" MD subdivision, while the ventromedial PFC - from the medial, "magnocellular" MD subdivision. The area precruciata medialis (XM) is involved in significant MD projection and should be included in the "prefrontal" not the "premotor" cortex. The ventral thalamic nuclei project mainly to the dorsomedial but not the ventromedial cortex. The distribution of this projection was correlated with antero-posterior cortical localization of injections. The main criterion for distinguishing "prefrontal" and "motor" cortex remains its projections either from MD or from VL nuclei. Only the ventromedial prefrontal cortex receives projection from anterior thalamic nuclei. The caudal region of the ventromedial prefrontal cortex seems to receive richer projection from "non-specific" thalamic nuclei as well as from the amygdaloid complex.

Topographical organization of frontal association cortex afferents originating in ventral thalamic nuclei in dog brain.

The frontal associatron cortex involves the prefrontal (PFC) and premotor (PMC) areas which are reached by projections originating in the ventral medial (VM), ventral anterior (VA) and ventral lateral (VL) thalamic nuclei. Afferents arising in particular thalamic nuclei cover various PFC-PMC regions. On the basis of afferents distribution three territories can be distinguished in this cortex. The first or ventral territory involving ventral and ventrolateral PFC (subgenual, subproreal and orbital, paraorbital areas) is reached only by VM afferents. In the second, dorsal PFC territory (proreal and medial precruciate areas) afferents originated in VM and VA thalamic nuclei terminate. The third cortical territory, involving the extreme caudal belt of the frontal association cortex (dorsal and posterior precruciatal region as well as the anterior composite area of the lateral presylvian wall), is reached by VM, VA and VL projections. The density of these projections increases in the caudal direction. VM and VA afferents are concentrated in the medial precruciate PFC-PMC area, whereas VL afferent in the dorsal PMC and fissural region.

Efferent connections of the basolateral amygdaloid part to the archi-, paleo-, and neocortex in dogs.

Small electrolytic lesions were placed in the basal and lateral amygdaloid nuclei of the dog and the distribution of degenerating fibers was studied with Nauta and Fink-Heimer modifications of the impregnation methods. Degenerating axons were followed into the hippocampal region and entorhinal cortex as well as insular and temporal cortices. The present results suggest that: (i) The hippocampal region receives projections from the basal parvocellular and basal magnocellular nuclei; (ii) the entorhinal cortex from the lateral and basal parvocellular nuclei; (iii) the insular cortex, cortex of the anterior ectosylvian and sylvian gyri, and to a smaller degree the claustrum, from the lateral and basal magnocellular nuclei; (iv) the temporal cortex of the posterior suprasylvian gyrus from all nuclei of the basolateral part of the amygdala. It is concluded that the basolateral part of the amygdala in the dog has a complex and highly developed connections with the archi-, paleo- and neocortex.

Intrinsic connections and cytoarchitectonic data of the frontal association cortex in the dog.

Organization of intrinsic connections of the frontal association cortex (FAC) in dogs was studied using retrograde HRP-transport method. For cytoarchitectonic observations and measurements of thickness of the cortex and its particular layers, additional sections stained with Nissl method were examined. Organization of intrinsic connections showed that within the dog's FAC two main cortical zones could be distinguished - the dorsal and the ventral one. The dorsal zone involves dorsally situated areas on the lateral and medial aspects of the hemisphere, which belong to the prefrontal and premotor regions. The vientral zone consists only of prefrontal areas situated ventrally on both aspects of the hemisphere. Each of the zones is characterized by strong mutual intrinsic connections and weak connections with the other zone. At the border there is a transitional area in which connections from both dorsal and ventral zones overlap. The cytoarchitectonic observations indicated that the dorsal and ventral zones can be distinguished in the central and caudal, but not in the rostral FAC subregion. The dorsal zone is characterized by considerable thickness of the cortex, cortical layers III and V, and the presence in these layers of scattered, large pyramidal neurons. The ventral zone has thinner cortex and layers III and V, and their pyramidal neurons are more uniform in size. In none of the zones clearly defined granular layer IV was observed.

Cytoarchitecture and acetylcholinesterase activity of the amygdaloid nuclei in the dog.

The cellular structure and distribution of histochemically demonstrated acetylcholinesterase (AChE) activity were studied in the amygdaloid body of 9 dogs. Cytoarchitectonic observations were made in series of paraffin and celloidin sections stained with cresyl violet. For the demonstration of the acetylcholinesterase activity, modifications of Koelle method were used. The general pattern of morphological structure of the dog's amygdaloid body is similar to that in other mammalian species. The corticomedial group of the nuclei was characterized generally by cytoarchitectonic uniformity of small, lightly stained cells and low intensity of the AChE reaction, except for the nucleus of the lateral olfactory tract and the lateral part of the central nucleus. The latter showed further differentiation in both cellular arrangement and distribution of AChE activity and may be divided into three subdivisions. The basolateral group of nuclei was characterized by higher differentiation of the cellular arrangement and distribution of the AChE activity. The highest enzyme activity was observed in the basal magnocellular nucleus. These findings support the homology of particular amygdaloid nuclei in various mammalian species.

Distribution of mediodorsal thalamic nucleus afferents originating in the prefrontal association cortex of the dog.

The nediodorsal thalamic nucleus (MD) afferents originating in the prefrontal cortex (PFC) were studied in 14 dogs, using the method of retrograde horseradish peroxidase transport. Injections limited to small areas of MD indicated that projection between MD and PFC shows precise topography and reciprocity. However, the distribution of labeled neurons suggests a division of MD into two main segments related to the corresponding projection zones in the prefrontal cortex. The medioventral PFC zone is specifically related to the medial MD segment, while the dorsolateral PFC zone is related to its lateral segment. Transitional areas located on the lateral and medial surfaces were identified between the two main cortical zones. They are connected with both lateral and medial segments of MD.

Subcortical afferents to the mediodorsal thalamic nucleus of the dog.

The subcortical afferents of the mediodorsal thalamic nucleus (MD) were studied using the method of retrograde horseradish peroxidase transport. Analysis of the distribution of labeled cells following injections into particular MD segments established specific and unspecific projections originating in various subcortical structures. The medial MD segment is related to such structures of the limbic system as: the anterior olfactory nucleus, olfactory tubercle, nucleus of diagonal band, arnygdala and septum, whereas the lateral MD segment receives afferentation from such structures involved in motor activity regulation as: the substantia nigra, entopeduncular nucleus, and cerebellar nuclei.Moreover, this segment is connected with the structure of the primary visual system, the lateral geniculate body. Nonspecific projections terminating in the entire MD nucleus originate in numerous structures at different CNS levels. The hypothalamus and reticular thalamic nucleus seem to have the strongest relationship with MD.

Differential projection from the motor and limbic cortical regions to the mediodorsal thalamic nucleus in the dog.

The cortical afferents to the mediodorsal thalamic nucleus in the dog were studied by using horseradish peroxidase. Small injections allowed to establish two specific projection zones connected separately with the lateral and medial segments of the nucleus. The lateral segment received the major projection from the dorsal half of the hemisphere. It included premotor and part of the motor cortices in the anterior sigmoid gyrus and precruciate areas as well as the presylvian cortex. The medial segment of the nucleus was innervated by the limbic areas of the ventral half of the hemisphere. These areas included the medioventrally located genual, subcallosal and piriform cortices, as well as the cortex of the ventral bank of the anterior rhinal sulcus and the caudal part of the orbital gyrus. The cortical fields situated between these two main cortical zones, both on the lateral and medial surfaces (rhinal and sylvian sulci and anterior cingular gyrus, respectively) sent projections to both medial and lateral segments of the nucleus. These results indicate that in the mediodorsal thalamic nucleus may take place the integration of information from two functionally defined systems, the motor and limbic ones.

Subcortical connections of the prefrontal cortex in dogs: afferents to the orbital gyrus.

Afferent subcortical connections to the lateral prefrontal cortex (orbital gyrus) in the dog brain were investigated using the horseradish peroxidase retrograde transport method. It was shown that: (i) the main projection to this area derives from the ventral and intermediate regions of the mediodorsal nucleus of the thalamus, (ii) fairly rich projection arises from the midline, intralaminar as well as from ventromedial and lateroposterior thalamic nuclei, (iii) scanty extrathalamic projection to the lateral prefrontal area originates from several other structures like claustrum, hypothalamus, amygdala, ventral tegmental area, raphe nuclei and locus coeruleus. Distribution of labeled cells after particular injections showed that in the orbital gyrus two subdivisions may be distinguished: dorsal and ventral. It is suggested that the dorsal orbital subdivision in dog corresponds to the lateral prefrontal cortex in monkey.

Contralateral connections of the dog's frontal association cortex.

We studied the topography of contralateral connections of both prefrontal and premotor regions of the dog's frontal association cortex (FAC) by charting distributions of retrogradely labeled cells following unilateral HRP injections to various areas of this cortex. Generally, in the contralateral hemisphere the labeled cells were most numerous in the FAC areas localized homotopically to the injection sites, less numerous in FAC areas heterotopic to injections, and the least numerous in cortical areas situated outside the frontal lobe. The nonfrontal areas which project to the dorsal and ventral FAC differ from one another. Dorso-caudal parts of the cingular and insular areas, as well as the auditory, somatosensory and visual association cortices project to the dorsal FAC, while the ventro-rostral parts of the cingular and insular areas, together with the prepiriform and periamygdaloid areas of the olfactory cortex as well as the subcallosal area send their axons to the ventral FAC. Thus, the dorsal and ventral FAC areas are supplied by contralateral afferents originating from different cortical areas. Similar organization of ipsilateral FAC connections was described previously.

Organization of cortical afferents to the frontal association cortex in dogs.

The source of cortical frontal association cortex (FAC) afferents and their terminal distribution in the dog's brain was determined by the HRP tracing method. It was shown that the sources of ipsilateral FAC afferents are limbic and paralimbic areas of allo- and mesocortex and parasensory areas of the neocortex. Most of these areas with the exception of the piriform olfactory cortex could be characterized as cortical association fields. The terminal distribution of FAC afferents gave evidence to distinguish dorsal and ventral FAC zones. The dorsal FAC zone which includes the premotor and dorsal prefrontal regions is supplied by afferents originating in the temporal, parietal, occipital, perirhinal and parahippocampal cortical areas. In contrast, the ventral FAC zone, involving the ventral part of the prefrontal cortex, receives characteristic projections from the subcallosal area and from the anterior parts of the piriform cortex. However, both FAC zones receive intensive projections from the cingular and insular cortices. The organization of FAC afferents in the dog was discussed in comparison with other species.

Diversity of connections of the temporal neocortex with amygdaloid nuclei in the dog (Canis familiaris).

Reciprocal connections of amygdaloid nuclei with the temporal neocortex in the dog were investigated. Injections of fluorescent tracers and BDA into particular temporal areas were made in eleven dogs. The topographical arrangement of connections and variations in their density differentiate the temporal neocortex in the dog into a few regions. Among them, the cortex involving the anterior part of the ectosylvian gyrus did not send any amygdalopetal projection. The middle ectosylvian, dorsal zone of the posterior ectosylvian and the anterior part of the Sylvian gyrus were weakly connected with the amygdala. The cortical region involving the ventral zone of the posterior ectosylvian and composite posterior areas, as well as posterior Sylvian gyrus, was characterized by profuse connections with the amygdaloid complex. Cortico-amygdaloid connections originate in the wide cortical area of the auditory cortex of the middle and dorsal part of the posterior ectosylvian gyrus as well as in the auditory association cortex located in the ventral ectosylvian, composite posterior and posterior Sylvian gyri. The connections showed a dorso-ventral gradient of increasing density, in the direction of association fields. The most substantial projection taking rise from the ectosylvian posterior and posterior composite gyri terminated preferentially in the pericapsular sector of the lateral amygdaloid nucleus and, to a lesser degree, in its medial sector. Terminals of connections originating in the Sylvian gyrus occupied preferentially the intermediate part of the lateral nucleus, slightly more medially than that from the ectosylvian and posterior composite areas. Additionally, axonal terminals derived from the composite posterior and Sylvian posterior areas were observed in the basal parvocellular and magnocellular nuclei. Neocortical projections were reciprocated by amygdalofugal connections with two exceptions: the basal magnocellular nucleus was distinguished by a substantial amygdalofugal projection to the temporal neocortex focused on the dorsal Sylvian gyrus, and the central nucleus of the amygdala, in contrast, received an exclusively corticofugal projection.

The presylvian cortex as a transitional prefronto-motor zone in dog.

Connnections of the cortical region situated in the medial and lateral walls of the presylvian fissure in the dog were investigated using the method of retrograde HRP transport. The patterns of subcortico-cortical and cortico-cortical projections sho,w that the cortical field of the medial presylvian wall (paraorbital area) is related to prefrontal cortex, while the cortical field of the lateral presylvian wall (anterior composite area) is connected with motor cortex. Additionally, short reciprocal connections exist between paraorbital and composite anterior areas. The distribution of these connections and the cytoarchitectonic features of the presylvian cortex suggest that it should be considered as a transitional prefronto-motor zone.

Some aspects of brain morphology of the chronic cat and kitten preparations with brain stem transected at the pretrigeminal level.

In two adult cats and in three kittens aged from 8 to 11 days the brain stem was transected at the pretrigeminal level. The preparations were maintained from 7 to 79 days and processed histologically together with nonoperated controls. In kitten preparations brain was underdeveloped as shown by less numerous secondary sulci on the surface of the cortex. However, both cat and kitten preparations showed similar retrograde and anterograde neuronal degeneration. They also showed a similar transneuronal degeneration apparent in an increased density of neurons and their shrinkage in several structures investigated in the isolated cerebrum and the lower brain stem. Thus in kitten preparations a direct effect of transection predominated that of brain development. In the adult preparations at the level of transection a great accumulation of macrophages was found and the scar was built with connective tissue. In contrast, in kittens the transection scar was well delineated and built by astrocyte processes.