Effects of Single Cage Housing on Stress, Cognitive, and Seizure Parameters in the Rat and Mouse Pilocarpine Models of Epilepsy.

Many experimental approaches require housing rodents in individual cages, including in epilepsy research. However, rats and mice are social animals; and individual housing constitutes a stressful situation. The goal of the present study was to determine the effects of individual housing as compared to conditions maintaining social contact on stress markers and epilepsy. Control male mice socially housed during pretest and then transferred to individual cages for six weeks displayed anhedonia, increased anxiety and biological markers of stress as compared to pretest values or mice kept socially housed during six weeks. Pilocarpine (pilo)-treated mice housed together showed increased levels of anhedonia, anxiety and stress markers as well as decreased cognitive performance as compared to the control group. The differences were more significant in pilo-treated mice housed individually. Anxiety correlated linearly with cognitive performance and stress markers independently of the experimental conditions. In the male rat pilo model, seizures were sixteen times more frequent in singly housed animals as compared to animals kept in pairs. Daily interactions with an experimenter in otherwise singly housed animals was sufficient to produce results identical to those found in animals kept in pairs. We propose that social isolation produces a severe phenotype in terms of stress and seizure frequency as compared to animals maintaining social contact (at least in these two models), a factor that needs to be taken into account for data interpretation, in particular for preclinical studies.

The distribution of NPY-like immunoreactivity in the chameleon brain.

The distribution of neuropeptide Y (NPY) immunoreactivity was studied in the brain of the chameleon. Cell bodies and fibers displaying NPY-like immunoreactivity were widely dispersed throughout the brain and at the highest density in the telencephalon and diencephalon. Immunolabeled cell bodies were numerous in the medial and dorsomedial cortex and in the dorsal ventricular ridge, while the striatum and basal telencephalon only contained sparsely scattered NPY-positive somata. Immunopositive neurons were densely distributed in the dorsal thalamus (particularly in the perirotundal belt), the area triangularis, the nucleus geniculatus lateralis pars dorsalis, the periventricular hypothalamus and the medial eminence. In the pretectum, NPY-immunoreactive cell bodies were limited to the nucleus posterodorsalis, while in the mesencephalon immunolabeled somata were found in the stratum album centrale of the optic tectum and in the substantia nigra. Immunopositive fibers and terminals were particularly dense in the dorsomedial cortex, the periventricular hypothalamus, the nuclei accumbens, suprachiasmaticus and griseus tectalis, in the substantia nigra and in the torus semicircularis. These findings show that the NPY system in the chameleon has the same basic organization as in other vertebrate species, and indicate that this peptide could be also implicated in the regulation of several aspects of cerebral functions. In addition, and of particular interest, is the observation of numerous NPY-immunoreactive neurons and fibers in several visual nuclei, suggesting an important involvement of this substance in the visual function.

Cortical control of somato-cardiovascular integration: neuroanatomical studies.

This paper will discuss experiments dedicated to the exploration of pathways linking the sensorimotor cortex (SMC) and the main bulbar nuclei involved in cardiovascular control: the nucleus tractus solitarius (NTS), the dorsal nucleus of the vagus (DMV) and the rostral ventrolateral medulla (RVLM). Results obtained through neurofunctional and neuroanatomical methods are presented in order to bring new answers to relevant points concerning somato-cardiovascular integration: firstly to show the ability of the SMC to influence neurons in bulbar cardiovascular nuclei, and secondly to identify pathways that transmit such influences. The neurofunctional approach, based on the identification of Fos-like immunoreactive neurons, indicated that the SMC has functional connections with cardiovascular bulbar nuclei. The neuroanatomical approach, which employed retrograde and anterograde axonal tracing methods, provided evidence of direct projections from the SMC to NTS/DMV and RVLM. Furthermore, experiments showed clearly that corticospinal neurons sent collaterals to bulbar cardiovascular nuclei, especially to the RVLM. Direct cortical projections to the NTS/DMV and the RVLM provide the anatomical basis for cortical influences on the baroreceptor reflex and sympathetic vasomotor mechanisms for blood pressure control, and support the hypothesis of cortical commands coupling somatic and cardiovascular outputs for action.

Immunocytochemical detection of fos protein combined with anterograde tract-tracing using biotinylated dextran.

The present report deals with an axonal tract-tracing procedure in rat enabling visualization of anterogradely transported biotinylated dextran amine (BDA) combined with immnunocytochemical detection of Fos protein following electrical stimulation of the brain. This method allows us to evaluate whether a given structure, receiving both injection of BDA and electrical stimulation, elicits neuronal activation in another part of the brain via direct or indirect projections. We have used the method at the light microscopic level to determine the connectivity of the sensorimotor cortex in the rat. In various parts of the forebrain and brainstem, BDA-labeled fibers originating from the cortex were observed in close apposition to Fos-like immunoreactive cells (FLI) activated by stimulation. This result suggests a direct (probably monosynaptic) projection. On the contrary, FLI neurons were observed in areas devoid of direct afferents, indicating a cascade of activations. The method described in this protocol is applicable for functional anatomy purposes elsewhere within the central nervous system. It constitutes a preliminary step in identifying the validity of a pathway before examination of the reality of the monosynaptic relationship at the electron microscopic level.

Pyramidal control of heart rate and arterial pressure in cats.

The pyramidal control of the heart rate (HR) and the arterial pressure (AP) was investigated in the cat. Experiments were conducted in order to determine relative contribution of vagal and sympathetic components to this control. In eighteen anesthetized and curarized cats, electrical stimulations were applied to the pyramidal tract (PT), followed by pharmacological blockade of the sympathetic cardiac control or by bivagotomy. HR and mean arterial pressure (MAP) were recorded in response to pyramidal stimulations before and after bulbar transections sparing only the PT, beta 1-blockade by atenolol administration and/or bilateral vagotomy. Results showed that the stimulation of the PT elicits significant cardiac accelerations and MAP increases in all animals. Furthermore, bulbar transections allowed to conclude that pyramidal influences acted at bulbar level and not on spinal cardiovascular neurons. After beta 1-blockade by atenolol, HR increases were reduced by about 70% and those of MAP by about 30%; after bilateral vagotomy, cardioaccelerations were reduced by about 30% but no significant reductions of MAP were observed; finally, beta 1-blockade combined with vagal section suppressed cardioaccelerations and significantly reduced the MAP increases. These results suggest the existence of a direct cortical control, via the pyramidal tract, to cardiovascular centers of the medulla, probably mediated by pyramidal collaterals. This control appears to be organized following a reciprocal autonomic pattern where the suppression of the vagal inhibition is associated with a concomitant sympathetic excitation. The present work also provides data in favour of a central command coupling somatic programs and cardiac adjustments during motor acts.

Modulation of central GABAA receptor complex by somatostatin: a pharmacological study.

The goal of the present study was to determine the possible interactions between somatostatin (SST) and gamma-aminobutyric acid (GABA). We thus investigated the SST interaction with [35S]-tertiary butylbicyclophosphorothionate (TBPS) binding sites of the cortical and hippocampal regions of the rat brain. The method used to identify such effects is in vitro quantitative autoradiography. Thus, the binding of the cage convulsant [35S]-TBPS to a picrotoxin-sensitive site in the rat brain was used to investigate the modulatory action of SST on the GABAA receptor complex. The addition of the peptide to the incubation medium results in a dose-dependent inhibition of [35S]-TBPS in cortical and hippocampal structures. Detailed analysis showed a dose-related effect of SST with relative potencies comparable to those observed for 5 alpha 3 alpha P and 5 beta 3 alpha P. In addition, these neurosteroids were able to enhance the efficacy of SST in inhibiting [35S]-TBPS binding. The efficacy of SST in enhancing the inhibitory action of neurosteroids was also evidenced. Furthermore, SST seems to mimic the effects of these neurosteroids as well as GABA and picrotoxin on [35S]-TBPS binding to the rat brain in every context examined. This suggests that somatostatin allosterically modifies [35S]-TBPS binding through a mechanism similar to that of GABA. On the other hand, a possible action of SST via transduction systems on the GABAA receptor complex could also be suggested. These results illustrate the importance of interactions in SST-mediated GABA transmission in these brain regions.

Distribution of cortical fibers and fos immunoreactive neurons in ventrolateral medulla and in nucleus tractus solitarius following the motor cortex stimulation in the rat.

The present study demonstrates that the motor cortex (MC) stimulation induces expression of Fos-like immunoreactivity (FLI) in the rostro-caudal parts of ventrolateral medulla (VLM) and nucleus tractus solitarius (NTS). The coupling of biotinylated dextran (BD) injections with the MC stimulation also permits to identify cortical labeled fibers in the vicinity of FLI neurons in the VLM. Results suggest that the MC is involved in a direct and an indirect modulation of bulbar cardiovascular nuclei.

Cholecystokinin-like systems in the chameleon brain.

Immunohistochemical techniques were used to determine the distribution of cholecystokinin-8 (CCK8) immunoreactivity in the brain of the chameleon. In the telencephalon, CCK8-immunopositive somata were sparse and observed principally in the olfactory tubercle at the ventromedial edge of the rostral telencephalon and in the medial septum. Immunopositive fibers were observed mainly in the medial septal region and the ventral telencephalon. In the diencephalon, numerous CCK8-reactive fibers were densely concentrated in the periventricular region, the dorsolateral hypothalamus and the external zone of the median eminence. In the thalamus, labelled fibers were restricted to the peri-rotundal nuclei and the lateral part of the habenula. Immunoreactive cell bodies were observed in the medial part of the dorsal lateral geniculate nucleus, in the periventricular, ventral and lateral regions of the hypothalamus. In the mesencephalon, the densest accumulations of immunopositive fibers were observed in the area pretectalis, the periventricular gray matter, the medial tegmentum and the isthmus. Labelled neurons were observed in the deep, and occasionally intermediate, tectal layers and in the laminar nucleus of the torus semicircularis. In the rhombencephalon, labelled fibers were observed at the highest density in the central gray matter and the locus coeruleus; labelled somata were observed only in the nucleus of the tractus solitarius.

Corticospinal collaterals to medullary cardiovascular nuclei in the rat: an anterograde and a retrograde double-labeling study.

There is little evidence allowing the hypothesis of the existence of direct pathways from the sensorimotor cortex (SMC) to main cardiovascular medullary nuclei: the dorsal motor nucleus of the vagus (DMV), the nucleus of the solitary tract (NTS) and the rostral ventrolateral medulla (RVLM). The purpose of this study was to identify in the rat direct SMC-NTS/DMV and-RVLM projections descending through the pyramidal tract (PT) and corticospinal neurones projecting to spinal somatic centers and sending collaterals to the NTS/DMV and the RVLM. The first group of animals (N = 15) received injections of anterograde tracers into the SMC: wheat germ agglutinin conjugated to horseradish peroxydase (WGA-HRP) or rhodamine-conjugated dextran (DR). In the second group (n = 35), retrograde tracers were injected: fluorogold (FG) into the NTS/DMV or into the RVLM and DR into the lateral thoracic cord (Th2-Th4). Anterograde transport of WGA-HRP and DR allowed corticofugal fibers to be followed inside the PT ipsilaterally to the site of cortical injection and showed bilateral labeled projections to the NTS/DMV and RVLM. After retrograde transport, bilateral FG or DR labeled cells were distributed in the SMC, mainly in the medial (AGm) and lateral (AGl) agranular cortex. After spinal and bulbar injections, double-labeled cells were distributed in same cortical areas. After injections in RVLM, 49% of labeled cells showed a double-labeling in the frontal cortex (rostral AGm and premotor cortex) while only 24% were observed in the posterior SMC (caudal AGl). On the contrary, when injections were done in NTS/DMV, double-labeled neurons were respectively of 11% in the frontal cortex and 4% in the posterior SMC. In the present work it was shown that the SMC sent direct projections to bulbar cardiovascular nuclei by means of fibers descending through the PT and corticospinal collaterals. The hypothesis which may be drawn from this study is that cortical motor areas probably program cardiovascular adjustments, preparatory or concomitant to the control of striate muscles.

Fronto-parietal control of electrodermal activity in the cat.

The aim of this work was to investigate the direct involvement of the fronto-parietal cortex in the control of spinal autonomic centers eliciting electrodermal activity (EDA). This autonomic response, linked with the activity of sweat glands, was recorded as skin potential responses (SPRs) from forepaws in the cat. Animals were paralyzed by gallamine and SPRs were obtained under halothane anaesthesia. For each animal, a transection of the medulla sparing only pyramidal tracts was carried out. SPRs were elicited by direct electrical stimulation of pericruciate and posterior parietal cortical areas before and after such a transection. Results showed that in intact preparations, stimulation of the pericruciate cortex evoked SPRs at lower thresholds than the posterior parietal cortex. After the bulbar transection, only the stimulation of pericruciate areas still elicited SPRs at low intensities. Results are interpreted as indicating that fronto-parietal control of EDA is probably mediated by a double descending system: one involving corticoreticulospinal pathways and a direct corticospinal one. We hypothesized that the somatic motor cortex initiates descending programs to autonomic centers at bulbar and spinal levels, and that these centers are involved in autonomic adjustments to somatomotor movements.

Influence of skin temperature on latency and amplitude of skin potential responses in the cat.

The effect of skin temperature changes on skin potential response (SPR) amplitude and latency was examined in the cat. SPRs were elicited either by stimulating the reticular formation or the distal end of the median nerve. At room temperature, the latency due to the neuroglandular transmission and to the peripheral effector accounts for about half of the total latency of SPR evoked by reticular stimulation. This latency increases to several seconds at low skin temperatures (approximately 10 degrees C), decreases with temperature, and is minimal (300 msec) at high temperatures (over 40 degrees C). SPR amplitude increases with skin temperature, reaches a maximal value (usually around 30 degrees C) and then decreases at higher temperatures. The decrease of latency at higher temperatures confirms results previously obtained in humans. However, the mechanisms of amplitude decrease for high temperatures remain unclear.