Medial Sector Research Articles

The normal and abnormal postnatal development of retinogeniculate projections in golden hamsters: An anterograde horseradish peroxidase tracing study

In adult hamsters, the dorsal lateral geniculate nucleus (LGd), which lacks a noticeable pattern of cellular lamination, receives fibers predominantly from the contralateral eye except for a medial segment which receives fibers from the ipsilateral eye. Using the method of anterograde transport of horseradish peroxidase (HRP), it is shown in this study that the contralateral and ipsilateral retinogeniculate fibers innervate the LGd by day 0 with the development of the contralateral fibers slightly ahead of the ipsilateral ones. The entire contralateral LGd is filled with retinal fibers by day 1. The ipsilateral LGd is almost completely covered with retinal fibers on day 2 but with the fiber density much higher in the dorsal half of the nucleus. Thus, fibers from both eyes overlap with each other completely beginning on day 2 in the LGd. The segregation of these fibers becomes obvious on day 6 as indicated by a decrease in the density of ipsilateral fibers in the ventral portion of the LGd while the ipsilateral projection continues to concentrate in the dorsal half of the nucleus. A low density area in the dorsomedial part of the contralateral LGd is observed on day 7. By day 8, the segregation of the contralateral and ipsilateral projections has achieved an adult-like pattern. Thus, there seems to be two phases for the normal development of the retinogeniculate fibers. In the first phase, axons from both eyes grow in and occupy the entire LGd. In the second phase, those axons occupying inappropriate areas of the LGd are eliminated to form the adult pattern. The effect of unilateral eye removal at birth on the development of the retinogeniculate projection from the remaining eye was also studied with the anterograde HRP method. The ipsilateral fibers in the experimental animals are distributed in the lateral portion of the nucleus in the first two postnatal days. The entire LGd is not filled with ipsilateral fibers until day 4. From day 6 onwards, the ipsilateral fibers are more extensive than those of the normal animals. In addition to a dense projection to the dorsal two-thirds of the LGd, moderate amount of ipsilateral axons can be detected in the remaining ventral portion of the nucleus in day 6 and older experimental animals. The development of the contralateral retinal fibers in the experimental animals is similar to that of the normal from day 1 to day 6, i.e. the entire LGd is densely filled with crossed optic axons. However, on day 7, there is no decrease in the density of the contralateral fibers in the medial sector of the LGd. The lack of restriction of retinal fibers is observed in all subsequent stages of development. These results suggest that axo-axonal interaction is important for the process of segregation of retinogeniculate projections observed in normal developing hamsters.

Demonstration of synaptic input from prefrontal cortex to the habenula in the rat

Using lesion-degeneration techniques at the EM level, it is confirmed that a pathway from prefrontal cortex projects to the lateral habenula, and further that it makes synaptic contacts predominantly with dendrites of neurons in the medial sector of the lateral nucleus. The available neuroanatomical evidence points to a role for habenula as a regulator of the activity of the meso-cortical dopamine pathway by the interaction of this cortico-habenular pathway with a wide variety of limbic inputs in the medial sector of lateral habenula.

Dopamine neurones of the ventral tegmentum project to both medial and lateral habenula

Using the techniques of microdissection and microradiochemical assay for catecholamines, it has been shown that a specific subgroup of ventral tegmental area (VTA) dopamine neurones project to the medial sector of lateral habenula. In addition a new dopamine pathway, arising from midline VTA neurons, has been shown to project to the medial sector of medial habenular. These findings are discussed and some implications for habenular functions are stated.

Prefrontal cortex of the guinea pig (Cavia porcellus) defined as cortical projection area of the thalamic mediodorsal nucleus.

The cortical projection area of the thalamic mediodorsal nucleus (MD) was investigated using the horseradish peroxidase technique. Distinct relationships between subdivisions of MD and of the prefrontal cortex were established: the medial sector of MD projects to sulcal cortex dorsal to the rhinal fissure and to the lateral frontopolar region; the lateral sector of MD reaches mainly cortex within the medial part of the hemisphere from the frontopolar region up to a mid corpus callosal level. The projection area of the lateral sector of MD overlaps with the projection fields of the paratenial and anteromedial nuclei. It is concluded that the guinea pig's prefrontal cortex, defined as the projection area of MD, has strong similarities with the prefrontal cortices of rats and rabbits, that is with the prefrontal cortices of species of two different orders.

Spatial distribution of the copepod parasiteLernanthropus kroyerion the gills of bass,Dicentrarchus labrax(L.)

Young estuarine bass of the 1976 and 1977 year classes were examined for gill parasites between February 1978 and June 1979. 344 specimens of the copepodLernanthropus kroyeriwere recovered from 177 of 289 fish. The distribution of the copepods on the gills showed clear preferences for site of attachment. With 48 such sites delineated per fish, 143 of 183 female copepods favoured a single site – the internal face of the medial sector of the posterior hemibranch of the second gill arch. 57 of 161 male copepods chose attachment to the external face of the medial sector of the anterior hemibranch of the second gill arch. Only seven copepods in all were found attached at any of the twelve possible sites on the first gill arch, and none at all at the six possible sites on the posterior hemibranch of the fourth gill arch. Explanations for the observed distribution are discussed in terms of the strength of the branchial ventilation currents over the different gills coupled with observations on the special respiratory adaptations of these parasites.

Catecholamine innervation of the basal forebrain. IV. Topography of the dopamine projection to the basal forebrain and neostriatum.

In this study the location of dopamine (DA) neuron perikarya in the rostral mesencephalon of the rat was determined using the glyoxylic acid fluorescence histochemical technique. Subsequently the topography of the projection of these mesencephalic neurons on the basal forebrain and striatum was analyzed using the anterograde transport-autoradiographic tracing method and the retrograde transport-horseradish peroxidase (HRP) technique. The results of these anatomical studies were correlated with the biochemical and histochemical studies presented in previous reports (Moore, '78; Fallon and Moore, '78; Fallon et al., '78) to provide the following conclusions. The topography of the DA neuron projection of the basal forebrain and neostriatum is organized in three planes, dorsal-ventral, medial-lateral and anterior-posterior. DA cells are found almost exclusively in the substantia nigra (SN) and ventral tegmental area (VTA). Ventral cells of the SN and VTA project to the dorsal structures of the basal forebrain such as the septum, nucleus accumbens and neostriatum. The latter includes some DA cells located ventrally in the pars reticulata of the SN. Dorsal cells project to ventral structures. The medial-lateral topography is organized such that the medial sectors of the SN-VTA area project to the medial parts of nuclei in the basal forebrain and neostriatum whereas lateral sectors of the SN-VTA area project to the lateral parts of nuclei in the basal forebrain and neostriatum. An anterior-posterior topography also is evident such that anterior parts of the SN-VTA project anteriorly whereas the posterior SN-VTA projects more posteriorly in these areas. These observations are consistent with the view that the DA neurons of the SN-VTA complex form a single nuclear group with a highly topographically organized projection innervating not only deep nuclei of the telencephalon but allocortical structures as well.

Subdivisions of the auditory cortex of the cat: the retrograde transport of horseradish peroxidase to the medial geniculate body and posterior thalamic nuclei.

AbstractEach subdivision of auditory cortex was injected with horseradish peroxidase (HRP). The amount of HRP injected was varied with the result that in some cases the diffusion of HRP was restricted while in other cases, HRP diffused over an entire cortical subdivision and encroached on adjacent subdivisions. In the case of restricted diffusion only a relatively small number of thalamic cells were “labelled”; in the case of extensive diffusion many times that number of cells were labelled. Whether relatively few or many cells, the distribution of labelled cells fell into distinctive patterns. Each pattern consisted of a focus or concentration of labelled cells in one thalamic subdivision and a sparser population of labelled cells in other thalamic subdivisions. The most striking example of a pattern is produced by injecting AI. This injection resulted in a band in the ventral division of the medial geniculate body densely populated with labelled cells; but even after the smallest injection, labelled cells were also found outside the ventral division, in the magnocellular and dorsal divisions of the medial geniculate body, and in the posterior group. (The ventral extremity of the ventral division was always free of cells and this sector is likely a separate nucleus which projects to Ep.) Other patterns are produced by injecting HRP in other cortical subdivisions: temporal injections produced a concentration in the caudal division of the medial geniculate body; insular injections resulted in a concentration in the medial sector of the posterior group; AII injections led to a concentration in the magnocellular and deep dorsal divisions of the medial geniculate body; injections in ventral Ep led to a concentration of labelled cells in the dorsal division of the medial geniculate body; finally, dorsal Ep seems to be very different from the other divisions inasmuch as injections in it resulted in labelled cells in non‐auditory thalamus–the pulvinar and lateral nuclei, as well as the auditory thalamus.These results lead to the following conclusions. The laminated and principal part of the ventral division of the medial geniculate body projects only to AI. Every other thalamic subdivision projects to two or more cortical subdivisions: the caudal division projects primarily to the temporal area with sparser projections to AII and Ep; the dorsal division projects primarily to Ep with sparser projections to AI, AII, and the temporal area; the medial sector of the posterior group projects primarily to the insular area and to the posterior ectosylvian gyrus; the magnocellular division of the medial geniculate body projects to every subdivision of auditory cortex, including AI and AII.

Central connections of receptors on rotated and exchanged cerci of crickets.

The cerci of crickets, paired abdominal appendages bearing sound-sensitive filiform hairs, can be removed and grafted back so that their morphological axes acquire various relationships to those of the body. We have studied both the morphogenetic consequences of such surgery and the central connections made by the regenerating axons of the cercal sensory neurons. If a cercus is rotated and grafted back into its own socket, it back-rotates towards its original orientation in succeeding molts. If left and right cerci are exchanged, with or without rotation, back-rotation does not occur and super-numerary cerci are formed in predictable locations. There are two sub-populations of filiform hairs: those that vibrate transversely to the cercal shaft (T-hairs) in dorsal and ventral sectors, and longitudinally vibrating hairs (L-hairs) in lateral and medial sectors. Two giant interneurons are excited by T-hairs of their own side but not by L-hairs. If cerci are grafted so that they assume various orientations relative to the body, a consistent physiological result is obtained: T-hairs always appear to be the source of excitatory input to the giant interneurons, no matter where they are caused to be located by prior surgery. The phenomena of back-rotation, formation of supernumerary cerci, and formation of connections selectively by T-hairs, can be interpreted on the hypothesis of morphogenetic gradients.

Frontal cortical lesions and prestimulus inhibition of the rat’s acoustic startle reaction

This paper reports two experiments dealing with the effects of lesions of the frontal cortex on the amplitude of the rat’s acoustic startle reaction, both under control (unstimulated) conditions and under conditions where the response is inhibited by delivery of a visual or auditory stimulus just prior to response elicitation. While in no case was brain damage observed to lead to any derangement of the prestimulus inhibition of the response, some animals showed exaggerated levels of reactivity on control trials postoperatively. Correlations between location of brain damage and postoperative responsivity indicated that damage to the medial sector of the frontal cortex was critical in obtaining augmented levels of startle.

The organization of the seventh lumbar spinal ganglion of the cat.

AbstractThe organization of the seventh lumbar dorsal root ganglion (DRG) of the cat has been investigated both anatomically and electrophysiologically. In the first two series of experiments an attempt was made to relate the topographic location of identified groups of cells in the ganglion with the rostro‐caudal position of their central processes in the filaments of the dorsal root. 3H‐proline was injected into various sectors of the ganglion and the distribution of the axonically transported proteins, in individual dorsal rootlets, was determined by means of liquid scintillation spectroscopy and the location of the injections was determined by autoradiography of the sectioned ganglia. The projection pattern was also determined by antidromically activating DRG cells in various parts of the ganglion by sequentially stimulating each of six dorsal root filaments. The results of both groups of experiments indicate that cells located in the medial (caudal) parts of the ganglion project into the most caudal rootlets of the dorsal root; cells in the most lateral (rostral) parts of the ganglion project into the most rostral rootlets, while cells in the intermediate parts of the ganglion project into the middle rootlets. In a third series of experiments, a shifting pattern of overlapping receptive fields was demonstrated for a series of recordings that traversed the ganglion from medial to lateral. This pattern was shown to be nearly equivalent to the organization of receptive fields previously demonstrated by Kuhn ('53) for a rostral to caudal sequence of dorsal rootlets, i.e., foot and leg preaxial fields predominated in the lateral sectors, while postaxial fields were found in the medial sectors of the ganglion.

Visual evoked potentials in the forebrain of the pigeon.

The telencephalon of anaesthetized pigeons was systematically explored for flash evoked potentials. A short latency projection to the hyper striatum was confirmed. A second short latency projection which appears to have a major focus in the medial sector of the neostriatum caudale and a more diffuse representation in the remainder of this structure was also found. Longer latency responses were found in a band of tissue surrounding the ectostriatum although the latency of these potentials was too short to be compatible with their origin in a projection from the thalamic nucleus rotundus. The core of the ectostriatum was not responsive under the conditions of the present study. A previously reported projection to the avian archistriatum was not confirmed and evidence is presented that supposed evoked potentials in this region of the brain were confused with volume conducted electroretinograms. All forebrain evoked potentials were attenuated by repetition rates above 1 hz. The origin of these projections is discussed in conjunction with evoked potentials recorded at lower levels of the pigeon's visual system under the same conditions and in the light of available anatomical and electrophysiological evidence. It is concluded that the information about visual projections to the avian forebrain is as yet too incomplete to be useful as evidence for presumptive avian-mammalian forebrain homologies.