Two new fluorescent retrograde neuronal tracers which are transported over long distances

Two new fluorescent retrograde neuronal tracers are reported: Nuclear Yellow (Hoechst S 769121), which mainly labels the neuronal nucleus; and Fast Blue (diamidino compound 253/50), which mainly labels the neuronal cytoplasm. Both tracers appear to be transported effectively over long distances in rat and cat.

Double retrograde neuronal labeling through divergent axon collaterals, using two fluorescent tracers with the same excitation wavelength which label different features of the cell

Recent studies show that several fluorescent substances are transported retrogradely through axons to their parent cell bodies and label in different colors different features of the cell at the same 360 nm excitation wavelength. Thus, Bisbenzimide (Bb) and "Nuclear Yellow" (NY; Hoechst S 769121) produce green and golden-yellow retrograde labeling of the neuronal nucleus. "True Blue" (TB) and "Fast Blue" (FB) produce blue retrograde labeling of the neuronal cytoplasm. In the present study the possibility of retrograde double labeling of neurons by way of divergent axon collaterals using combinations of Bb or NY with TB or FB has been explored in rat and cat. The findings show that in these animals these tracer combinations are transported retrogradely through two axon collaterals to one and the same cell. Neurons which are retrogradely double-labeled with these tracer combinations display a blue fluorescent cytoplasm and a white or golden-yellow fluorescent nucleus at the same 360 nm excitation wavelength. Therefore, these tracer combinations can be successfully used to demonstrate the existence of divergent axon collaterals in the brain.

Thalamic midline cell populations projecting to the nucleus accumbens, amygdala, and hippocampus in the rat

The organization of the thalamic midline efferents to the amygdaloid complex, hippocampal formation, and nucleus accumbens was investigated in the rat by means of multiple retrograde fluorescent tracing. The present findings indicate that these connections derive from separate cell populations of the thalamic midline, with a low degree of divergent collateralization upon more than one of the targets examined. The neural populations projecting to the amygdala, hippocampus, or accumbens are highly intermingled throughout the thalamic midline, but display some topographical prevalence. Midline thalamo-hippocampal cells are concentrated in the nucleus reuniens; thalamo-accumbens neurons prevail in the ventral portion of the paraventricular nucleus, and in the central medial nucleus. Thalamo-amygdaloid cells display a topographical prevalence in the rostral third of the thalamic midline and are concentrated in the dorsal part of the paraventricular nucleus and in the medial part of the nucleus reuniens. Both dorsally in the paraventricular nucleus and ventrally in the nucleus reuniens, thalamo-amygdaloid cells are located closer to the ependymal lining than the neurons projecting to the hippocampus or nucleus accumbens. Further, thalamo-amygdaloid cells, especially in the paraventricular nucleus, extend their dendritic processes in the vicinity of the ependymal lining, where they arborize profusely. These features indicate a close topographical relationship of neurons projecting to the amygdala with ependymal cells. The fairly discrete origin of midline outputs to the amygdala, hippocampus, and accumbens indicates that the flow of information is conveyed through separate channels from the thalamic midline to limbic and limbic-related targets. Together with the literature on the limbic afferents to the thalamus, these findings emphasize the relationships between the thalamus and the limbic system subserved by parallel input-output routes. However, because of the overlap of the projection cell populations, the thalamic midline may represent a locus of interaction among neurons connected with different parts of the limbic system. The functional implications of these findings are discussed in relation to the "nonspecific" thalamic system, as well as to the circuits involved in memory formation.

The organization of the efferent projections of the substantia nigra in the rat. A retrograde fluorescent double labeling study

The organization of three of the efferent projections of substantia nigra has been investigated in rat by means of combined injections of two fluorescent retrograde tracers: red fluorescent Evans Blue and blue fluorescent DAPI-primuline mixture. First the distributions of the retrogradely labeled neurons in substantia nigra after injections of each of the two tracers in the striatum, thalamus and superior colliculus were compared with the distributions of the retrogradely labeled nigral neurons after HRP injections in these same structures. The findings in these sets of experiments were the same. This indicates that the two fluorescent retrograde tracers are as effective as HRP in tracing the efferent fiber connections of the substantia nigra. Subsequently the retrograde labeling of the substantia nigra neurons was studied after combined injections of the two fluorescent retrograde tracers in two of the above structures, in different combinations. In these experiments both single labeled neurons fluorescing either red or blue, as well as double labeled neurons fluorescing both red and blue were found. Double labeled neurons were present only in pars reticulata and occurred only after injections of the two tracers in thalamus and superior colliculus respectively. From this it has been concluded that in rat the various efferent projections from the substantia nigra are mainly derived from different neurons, but that at least part of the neurons which distribute fibers to superior colliculus also distributes collaterals to the thalamus.

Fuorescent retrograde neuronal labeling in rat by means of substances binding specifically to adenine-thymine rich DNA

Six fluorescent substances, binding specifically to adenine-thymine rich DNA, were injected in rat caudate-putamen. This resulted in retrograde axonal transport and fluorescent retrograde labeling of neurons in center-medium parafascicular nucleus, substantia nigra and dorsal raphe. Two of these substances, i.e. "True Blue' and 'Granular Blue', give a very striking blue fluorescent retrograde neuronal labeling. Mid-thoracic spinal injections of these two substances in rat also resulted in a pronounced retrograde fluorescent labeling of neurons of the descending brainstem pathways and of neurons in the sensori-motor cortex.

Retrograde transport of bisbenzimide and propidium iodide through axons to their parent cell bodies

Two fluorescent substances bisbenzimide (Bb), which fluoresces yellow-green and propidium iodide (PI), which fluoresces orange were found to be transported retrogradely through axons to their parent cell bodies in rat and cat. Bb gives a very strong and long lasting fluorescent retrograde neuronal labeling and is very effectively transported over long distances both in rat and cat. Bb and PI also label glial nuclei around retrogradely labeled neurons. Bb in addition labels glial nuclei along axons through which it is transported. Bb and PI can be transported retrogradely through two divergent collaterals to one and the same cell.

Retrograde neuronal labeling by means of Bisbenzimide and Nuclear Yellow (Hoechst S 769121). Measures to prevent diffusion of the tracers out of retrogradely labeled neurons

Bisbenzimide and Hoechst S 769121 (Nuclear Yellow, NY), when transported retrogradely through axons to their parent cell bodies, may migrate out of the axons and the cell bodies, as indicated by fluorescence of adjoining glial nuclei. This migration was found to take place both in vivo and in vitro during storage of the sections in water. When using the tracers in 1% concentrations the in vivo migration may be controlled by restricting the survival time. The in vitro migration may be prevented by rapid histological processing of the material.

Magnetic resonance imaging of changes elicited by status epilepticus in the rat brain: diffusion-weighted and T2-weighted images, regional blood volume maps, and direct correlation with tissue and cell damage

The rat brain was investigated with structural and functional magnetic resonance imaging (MRI) 12 h after the arrest of pilocarpine-induced status epilepticus lasting 4 h. Histopathological data, obtained immediately after MRI analysis, were correlated with the images through careful evaluation of tissue shrinkage. Diffusion-weighted and T2-weighted imaging showed changes throughout the cerebral cortex, hippocampus, amygdala, and medial thalamus. However, only T2-weighted imaging, based on rapid acquisition relaxation-enhanced sequences, revealed in the cortex inhomogeneous hyperintensity that was highest in a band corresponding to layer V. Regional cerebral blood volume (rCBV) maps were generated using T2*-weighted gradient-echo images and an ultrasmall superparamagnetic iron oxide contrast agent. In the cortex, rCBV peaked in superficial and deep bands exhibiting a distribution complementary to the highest T2-weighted intensity. Selective rCBV increase was also documented in the hippocampus and subcortical structures. In tissue sections, alterations indicative of marked edema were found with Nissl staining in areas corresponding to the highest T2-weighted intensity. Degenerating neurons, revealed by FluoroJadeB histochemistry, were instead concentrated in tissue exhibiting hyperperfusion in rCBV maps, such as hippocampal subfields and dentate gyrus, cortical layers II/III and VI, and medial thalamus. The data indicate that:(i) T2-weighted imaging provides a sensitive tool to investigate edematous brain alterations that follow sustained seizures; (ii) rCBV maps reveal regional hyperperfusion; (iii) rCBV peaks in tissue exhibiting marked neurodegeneration, which may not be selectively revealed by structural MRI. The findings provide an interpretation of the brain response to sustained seizures revealed in vivo by different strategies of MRI analysis.

The history of radial glia

Radial glial cells are now recognized as a transient population that serves as scaffolding for neuronal migration. The recognition of the existence and role of radial glia has not been smooth, and here we provide a brief historical overview on the pioneering studies on this subject. The histologists and embryologists Albert Kölliker and Wilhelm His performed seminal investigations on cortical morphogenesis in the last decades of the 19th century. However, the introduction of the silver impregnation Golgi technique, and its diffusion in the late 1880s, played a crucial role in the detection of radial glial processes. The radial arrangement of fibers emerging from the neuroepithelium lining the central canal was initially detected in the embryonic spinal cord by Camillo Golgi himself. The first Golgi impregnation of the cerebral cortex of mammalian fetuses was performed by Giuseppe Magini, who detected radial fibers extending from the ventricular neuroepithelium, and observed cells intercalated along these processes. Radial fibers, regarded as epithelial or ependymal processes, were then observed in the developing spinal cord and cerebral cortex by several investigators. Santiago Ramón y Cajal was the first to suggest that radial fibers were modified astrocytic processes functioning as a support during cortical histogenesis. Cajal acknowledged Magini's findings, but he criticized Magini's observations on the existence of neurons along radial fibers. With the advent of electron microscopy, the existence of radially arranged glial processes along which young neurons migrate was finally ascertained in the early 1970s by Pasko Rakic, thus opening a new era in the cellular and molecular biology of radial glia.

The thalamo-caudate versus thalamo-cortical projections as studied in the cat with fluorescent retrograde double labeling

The distribution of thalamic cells projecting to the head of the caudate and their interrelations with thalamo-cortical cells were studied in the cat with different combinations of fluorescent tracers. Injections in the head of the caudate were combined with the injections in the pericruciate, proreal, suprasylvian, anterior cingulate, occipital and ectosylvian cortices. The following results were obtained: (i) Injections in the head of the caudate resulted in retrograde labeling of thalamic cells medially and laterally to the anteromedial (AM) nucleus, and in the medioventral part of the ventral anterior (VA) nucleus. Further, labeled cells were distributed throughout the anterior intralaminar central medial (CeM), paracentral (Pc) and central lateral (CL) nuclei, and the posterior intralaminar center median-parafascicular complex (CM-Pf). Labeled cells were mainly grouped in the mediodorsal parts of the anterior intralaminar nuclei; they were also found in the more dorsal part of the mediodorsal (MD) nucleus, ventral to the thalamic paraventricular (Pv) nucleus and to the habenular complex. (ii) Thalamo-cortical and thalamo-caudate cells overlapped in the medial part of the VA; in the anterior intralaminar nuclei they were either intermingled or were distributed in separate clusters or longitudinal bands. The two cell populations also overlapped in the posterior intralaminar complex. The greatest overlap occurred with the thalamic cell population projecting to the pericruciate cortex. (iii) Thalamic cells bifurcating to the head of the caudate and to the pericruciate cortex were found lateral to the AM, within the VA, and throughout the anterior intralaminar nuclei, especially in the CeM and in the posterior part of the CL; a few branched cells were also found in the CM. Thalamic cells bifurcating to caudate and anterior suprasylvian cortex were also found in the VA. Very few cells (scattered in the anterior thalamus lateral to the AM, as well as in the CeM, Pc and CL) were found to bifurcate to the head of the caudate and the other cortical fields here examined.

c-fos mRNA is spontaneously induced in the rat brain during the activity period of the circadian cycle

The basal expression of the proto-oncogene c-fos was studied by Northern blot analysis in different regions of the rat brain during 24 h. A striking spontaneous oscillation of c-fos mRNA expression was detected in animals kept in basal conditions with a 12 h light/12 h dark cycle. In these animals c-fos mRNA was just detectable during the rest hours (morning through afternoon), and was high during the activity hours (night). The periodicity of this oscillation persisted and became free-running when the animals were exposed for 6 consecutive days to constant light or darkness. It was thus demonstrated that the fluctuation of c-fos expression is circadian and is not created by the light-dark cycle, but the latter exerts a synchronizing effect. The oscillation of c-fos mRNA was modified by manipulations of the rest-activity cycle. In particular, the fluctuation observed in basal conditions was inverted, keeping the animals awake during the rest hours (diurnal) and allowing them to sleep in the activity period (nocturnal). These data indicated a close relationship between the oscillation of c-fos expression and the rest-activity cycle. Finally, electroencephalographic (EEG) monitoring was performed under behavioural control for 3 h before the animals were killed. These experiments confirmed that, irrespective of the time of day, the EEG pattern typical of a state of sleep (including both slow waves and paradoxical sleep) was associated with low or undetectable c-fos levels, whereas the protracted EEG desynchronization corresponding to wakefulness was associated with high c-fos expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Divergent axon collaterals from rat cerebellar nuclei to diencephalon, mesencephalon, medulla oblongata and cervical cord. A fluorescent double retrograde labeling study

The existence of divergent axon collaterals of neurons in the deep cerebellar nuclei has been investigated in rat by means of the fluorescent retrograde double labeling technique. The results have led to the following conclusions. A. Many of the neurons in the lateral, the interpositus as well as the caudal half of the medial nucleus project to the diencephalon. Some of these neurons distribute divergent axon collaterals to the superior colliculus, but few neurons project only to the latter structure. B. Some of the deep cerebellar neurons located laterally, i.e. in the dorsomedial part of the lateral nucleus, as well as some others located medially, i.e. in the medial part of the interpositus nucleus and the adjoining part of the medial nucleus, distribute divergent axon collaterals to the diencephalon and the spinal cord. C. Deep cerebellar neurons located laterally: in the cell group of the dorsolateral hump (Dlh) and in the adjoining lateral part of the interpositus nucleus, as well as some other located medially, i.e. in the dorsolateral part of the median nucleus (Mdlp), distribute divergent axon collaterals to the diencephalon and to the medulla oblongata, probably primarily its medial reticular formation. However, only few of the neurons, which distribute descending collaterals to the spinal cord or the medulla oblongata, distribute ascending collaterals to the superior colliculus. D. After injections in the medulla oblongata a population of small sized single labeled neurons was encountered especially in the lateral and interpositus nuclei. On the basis of other findings in rat they were assumed to represent cerebello-olivary neurons.

The organization of the claustroneocortical projections in the cat studied by means of the HRP retrograde axonal transport

The projections from the claustrum to the cerebral cortex were examined in the cat by means of horseradish peroxidase (HRP) injections in various different areas of the lateral and medial surfaces of the neocortex. In all cases retrogradely labeled cells were observed in the ipsilateral claustrum insulare (ClI). In most of the cases some labeled cells were also observed in the contralateral ClI. The number of labeled cells was higher following large HRP injections in some cortical areas, such as the motor and visual cortex, than following large HRP injections in other areas, such as the second somatic sensory cortex. The patterns of distribution of labeled cells in the ClI following the different HRP injections evidenced a prevalent anteroposterior and dorsoventral topographical arrangement. However, some degree of overlapping was evident in the distribution of cells retrogradely labeled from injections in different cortical fields. The results of the present study indicate that: a) in all likelihood the claustral projections are distributed upon the entire neocortex; b) they are not uniformly distributed upon the neocortex from the quantitative point of view; c) the arrangement of the claustrocortical projections is predominantly but not strictly topographical. The widespread distribution of the claustral inputs suggests that they must be integrated in different models of cortical activity.

A method for specific transmitter identification of retrogradely labeled neurons: immunofluorescence combined with fluorescence tracing

In the present article a method is described which allows the delineation of the projections of a single neuron as well as the identification of one or more of its chemical components. The technique is a combination of retrograde tracing and fluorescent dyes based on the work of Kuypers and collaborators and indirect immunofluorescence histochemistry as originally described by Coons and collaborators. The crucial parameters including the selection of the dyes, the injection technique and tissue processing as well as the appropriate immunohistochemical fluorescent markers and filter combinations are discussed. The method of choice involves the use of the retrogradely transported dyes Fast Blue, True Blue or Propidium Iodide, and in addition, for double labeling experiments, Diamidino Yellow or Primuline. They are combined with FITC (Propidium Iodide) or TRITC (Fast Blue, True Blue, Diamidino Yellow, Primuline) as immunofluorescence markers.

Upregulation of spinal glutamate receptors in chronic pain

Recent studies indicate that glutamate binding to N-methyl-D-aspartate receptors in the spinal cord is involved in triggering the development of chronic pain However, the processes which directly underlie the increased pain remain unclear. Here we report that, following peripheral nerve injury (ligation of the sciatic nerve) in the rat, there is an increase in immunoreactive labelling of non-N-methyl-D-asparatate, AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionate), glutamate receptors in the superficial laminae of the lumbar spinal cord ipsilateral to the ligation. The increase in AMPA receptor expression peaks 14 days after nerve ligation and decreases 35 days post-ligation, corresponding to the time-course of heightened sensitivity to mechanical and thermal noxious stimuli (hyperalgesia) induced by the ligation. Given evidence that AMPA receptors in the superficial laminae mediate fast nociceptive transmission in the spinal cord, our findings suggest that an upregulation of spinal AMPA receptors contributes to hyperalgesia following peripheral nerve injury.

The cortical projections of the thalamic intralaminar nuclei, as studied in cat and rat with the multiple fluorescent retrograde tracing technique

Two retrograde fluorescent tracers were injected in two different areas of the cerebral cortex in rats and in cats. In all the experiments many single labeled cells and only some double labeled ones were seen in the thalamic intralaminar nuclei. The present results suggest that the diffusely distributed intralaminar-cortical projections mainly consist of axons of separate cells, and only to a minor extent of axon collaterals of the same cells.

Absence of callosal collaterals derived from rat corticospinal neurons. A study using fluorescent retrograde tracing and electrophysiological techniques

In rat the presence of axon collaterals from corticospinal neurons to the contralateral hemisphere has been investigated by means of anatomical and electrophysiological techniques. Anatomical Experiments. Several combinations of fluorescent retrograde tracers were used. In eight rats injections of Evans Blue, "True Blue", "Fast Blue" or DAPI-Primuline were made in areas 10, 6, and 4 and in the most medial part of the S1 granular cortex of one hemisphere, 1.5 mm below cortical surface. These injections were combined with injections of "Fast Blue", DAPI-Primuline, "Granular Blue", "Nuclear Yellow", or Bisbenzimide in the ipsilateral corticospinal tract in the C2 segment. Survival times of the animals varied according to the tracers used. In the non-injected hemisphere the retrogradely labeled corticospinal neurons were present in layer V of especially areas 10, 6, 4 and the medial portion of the S1 granular cortex. However, the retrogradely labeled callosal neurons in these areas were present in all layers except layer I. The labeled callosal and corticospinal neurons in layer V were intermingled and frequently situated very close to one another. However, with none of the tracer combinations were double labeled neurons observed. Electrophysioloogical Experiments. In six rats, layer V neurons of hindlimb-sensorimotor cortex were tested for antidromic responses to stimulation of contralateral corticospinal tract (CST) and corpus callosum (CC). Eighty-five CST neurons were identified, none of which responded antidromically to CC shocks. Eighty-two layer V neurons were identified which responded antidromically to CC shocks, but none of them responded antidromically to CST shocks. CC shocks elicited strong synaptic responses in CST neurons and vice versa. Depth measures indicated extensive intermingling of CST and CC neurons. From both sets of findings it was concluded that, in rat, CST neurons do not give rise to callosal collaterals.

The organization of the ipsi- and contralateral claustrocortical system in rat with notes on the bilateral claustrocortical projections in cat

The organization of the claustrocortical system was investigated in rat by means of cortical injections of either lectin-conjugated horseradish peroxidase or retrograde fluorescent tracers. The latter were also employed in cat. Evans Blue, Fast Blue, True Blue, Nuclear Yellow and Diamidino Yellow were used in different combinations and were injected, uni- or bilaterally, in different cortical fields. Cells retrogradely labeled from each cortical injection were observed in the ipsi- and contralateral claustrum. Anterogradely labeled terminals were also seen in the claustra of both sides in the horseradish peroxidase experiments. The topographic and quantitative study of the distribution of labeled neurons showed a topographic organization of the rat's claustrocortical system, although a certain degree of overlap of the cell populations projecting to frontal and occipital fields was also evident. Four types of branched claustrocortical neurons were observed in the double labeling experiments: neurons branching ipsilaterally (A) or contralaterally (B) to anterior and posterior cortical fields; neurons branching bilaterally to homotopic (C) or heterotopic (D) cortical fields. Each population of branched neurons was equivalent to a different percent value of the total labeled cell populations; the percent value decreased from type A to type D. Type C branched neurons were also identified in the claustrofrontal system of the cat. The intricate organization of the claustral-ascending projections suggests that the nucleus is involved in different cortical activities and that its efferents may also provide the substrate of a powerful subcortical mechanism of interhemispheric communication.

Postnatal development of calbindin and parvalbumin immunoreactivity in the thalamus of the rat

The maturation of the calcium binding proteins calbindin-D28k (CB) and parvalbumin (PV) during the first 3 postnatal weeks was studied in the rat thalamus using immunohistochemistry. These two proteins display a non-homogeneous distribution in the adult thalamus. In the rat, CB is mainly localized in the neurons and neuropil of the thalamic midline, intralaminar, and ventromedial nuclei, as well as in the posterior complex. At birth, CB-immunoreactive cell bodies were evident in thalamic midline structures, and especially in the nucleus reuniens. The number of thalamic CB-positive cell bodies, as well as the intensity of the neuropil immunostaining, increased progressively in the first postnatal weeks. This quantitative increase was first apparent in the midline structures and then in the other thalamic territories which are CB-positive in adulthood, and followed a mediolateral gradient. The mature pattern was achieved by the end of the third postnatal week. In the adult rat thalamus the neurons of the reticular nucleus display PV-immunostaining and PV-positive fibers densely innervate most of the dorsal thalamic domains. PV-immunoreactivity was clearly evident at birth in the cell bodies of the reticular nucleus. The density of PV-containing fibers increased progressively after birth in the dorsal thalamus, with a lateromedial gradient. At the end of the third postnatal week the ventroposterior (VP) complex appeared heavily innervated by PV-positive fibers, whose density in more medial structures was still lower than in the adult thalamus. A transient hyperinnervation of PV-immunoreactive fibers, displaying a dishomogenous organization in distinct segments, was observed in VP, and especially in the ventroposteromedial nucleus, during the second postnatal week. Altogether these findings indicate that the maturation of CB and PV requires postnatally a relatively prolonged period of time. The possible involvement of these proteins in different functional aspects of thalamic neuronal maturation is discussed.

C-reactive protein as a marker for cardiac ischemic events in the year after a first, uncomplicated myocardial infarction

The prognostic role of C-reactive protein levels in patients with a first acute myocardial infarction, an uncomplicated in-hospital course, and the absence of residual ischemia on a predischarge ergometer test and with an echocardiographic ejection fraction > or = 50% has not been described. C-reactive protein was determined during hospitalization in 64 patients (55 men, mean age 64.6 +/- 10.4 years). The patients were followed up for 13 +/- 4 months and the following cardiac events were recorded: cardiac death, new-onset angina pectoris, and recurrent myocardial infarction. Patients who developed cardiac events during the follow-up period had significantly higher C-reactive protein values than patients without events (3.61 +/- 2.83 vs 1.48 +/- 2.07 mg/dl, p <0.001). The probability of cumulative end points was: 6%, 12%, 31%, and 56% (p = 0.006; RR 3.55; confidence interval 1.56 to 8.04), respectively, in patients stratified by quartiles of C-reactive protein (< 0.45, 0.45 to 0.93, 0.93 to 2.55 and > 2.55 mg/dl). In the Cox regression model, only increased C-reactive protein levels were independently related to the incidence of subsequent cardiac events (chi-square 9.8, p = 0.001). Thus, increased C-reactive protein levels are associated with a worse outcome among patients with a first acute myocardial infarction, an uncomplicated in-hospital course without residual ischemia on the ergometer test, and with normal left ventricular function.

Epilepsy and hormonal regulation: the patterns of GnRH and galanin immunoreactivity in the hypothalamus of epileptic female rats

Endocrine and reproductive alterations are frequently reported to occur in women with temporal lobe epilepsy as well as in female rats in different experimental models of limbic seizures. We have recently observed that rats with structural damage of limbic structures induced by sustained convulsions triggered by systemic administration of pilocarpine develop spontaneous seizures after a mean latency of 15 days. In order to investigate the possible substrate of endocrine alterations in epilepsy, changes of the gonadotropin-releasing hormone (GnRH) and the neuropeptide galanin (GAL) were studied in the hypothalamus of epileptic female rats after pilocarpine treatment. Female rats injected with pilocarpine (320-350 mg/kg, i.p.) and control cases injected with saline were killed 10-20 h, 10-15 or 60-90 days following treatment. In some of these animals colchicine was injected in the lateral cerebral ventricle 24 h before death. GnRH immunopositivity was observed in the hypothalamus in neuronal cell bodies, fibers and punctate elements of both epileptic and control cases. A striking reduction of the density of GnRH-immunoreactive fibers and puncta was observed in the hypothalamus of the epileptic female rats killed 10-15 or 60-90 days following pilocarpine administration. No significant differences were observed in the number and size of GAL-immunoreactive perikarya of epileptic and control cases. The present findings suggest that a substantial rearrangement of GnRH-containing efferents, and in particular a loss of their terminal branches, occurs in the epileptic rat brain. Comparable regressive changes could account for alterations in endocrine and reproductive functions observed in temporal lobe epilepsy.

Claustroneocortical projections studied in the cat by means of multiple retrograde fluorescent tracing

The topographical interrelations of claustroneocortical cells and their degree of divergent collateralization were investigated in cat by means of retrograde fluorescent double labeling. The tracers Fast Blue (FB) and Nuclear Yellow (NY) were injected in several combinations in two different cortical fields. FB-labeled and NY-labeled cells were found in all cases in the insular portion of the ipsilateral claustrum (CII). The distributions of labeled cells confirmed the organization reported in previous studies. In some cases the two labeled cell populations were segregated in different parts of the CII; in other cases there was more or less overlap in the two distributions. The degree of overlap was not simply related to the topographic proximity of the injected cortical territories. In all cases the vast majority of cells were single labeled. In one case both FB and NY were injected in the same cortical area in order to control that claustral axons can retrogradely transport two tracers back to the same parent cell bodies. In this control case CII cells were double labeled. All together these data indicate that widely divergent claustroneocortical projection take origin mainly from separate cells.

Crosstalk between the two sides of the thalamus through the reticular nucleus: a retrograde and anterograde tracing study in the rat

In order to investigate the possible routes linking the thalamus in the two sides of the brain, the connections of the reticular nucleus (RT), the major component of the ventral thalamus, with contralateral dorsal thalamic nuclei were systematically investigated in the adult rat. This study was performed with several tract-tracing techniques: single and double retrograde labeling with fluorescent tracers, and anterograde tracing with biocytin. Retrograde tracing was also combined with immunocytochemistry to provide additional criteria for the identification of labeled RT neurons. The data obtained with the retrograde transport of one fluorescent tracer showed that RT neurons project to contralateral dorsal thalamic domains. In particular, retrograde labeling findings indicated that the anterior intralaminar nuclei, as well as the ventromedial (VM) nucleus, are preferential targets of the contralateral RT projections. Commissural neurons were concentrated in two portions of RT: its rostral part, including the rostral pole, which projects to the contralateral central lateral (CL) and paracentral (Pc) nuclei, and the ventromedial sector of the middle third of RT, which projects to the contralateral VM and posterior part of CL and Pc. The double retrograde labeling study of the bilateral RT-intralaminar connection indicated that at least part of the commissural RT cells bifurcate bilaterally to symmetrical portions of the anterior intralaminar nuclei. The targets of the RT commissural system inferred from the retrograde labeling data were largely confirmed by anterograde tracing. Moreover, it was shown that RT fibers cross the midline in the intrathalamic commissure. The present data demonstrate that bilateral RT connections with the dorsal thalamus provide a channel for interthalamic crosstalk. Through these bilateral connections with thalamic VM and intralaminar neurons, RT could influence the activity of wide territories of the cerebral cortex and basal ganglia of both hemispheres.