Hypodynamia--hypokinesia induced variations in expression of fos protein in structures related to somatosensory system in the rat.

There have been many reports describing modifications of the sensory and motor cortex following various types of disuse. Hypodynamia--hypokinesia is characterized by the absence of weight-bearing and by a decrease in motor activity. We have shown a reorganization of the cortical cartography after hypodynamia--hypokinesia. In order to give an anatomical account for this cortical plasticity, we set out to determine whether cerebral and spinal structures exhibited variations of their neuronal activation. For this purpose, immunocytochemical detection of Fos protein was performed in the rat brain and spinal cord. Following stimulation of the sciatic nerve, Fos protein was detected in the primary and secondary somatosensory cortex in control rats and in rats submitted to an episode of 14 days of hypodynamia--hypokinesia. Results showed that the stimulation of the sciatic nerve induced an increase in the number of Fos-immunoreactive neurons in all these structures. Moreover, after hypodynamia--hypokinesia, the number of Fos-immunoreactive neurons was increased in the primary and secondary somatosensory cortex and in the spinal cord. These results provide evidence for a higher activation of cortical cells after hypodynamia--hypokinesia in comparison to controls. These data support the hypothesis that hypodynamia--hypokinesia contributes to the development of functional plasticity.

Activation of ventrolateral medullary neurons projecting to spinal autonomic areas after chemical stimulation of the central nucleus of amygdala: a neuroanatomical study in the rat.

Several studies have shown that the central nucleus of amygdala is involved in cardiovascular regulation. The control of this function may be mediated by activation of the ventrolateral medulla neurons that project to preganglionic neurons located in the intermediolateral nucleus of the spinal cord. The aim of the present study was to examine whether stimulation of the central nucleus of amygdala activated ventrolateral medulla neurons projecting to the intermediolateral nucleus. For this purpose, the injection of a retrograde tracer, the cholera toxin b subunit (CTb), into the intermediolateral nucleus of the T2 segment was combined with immunohistochemical detection of Fos protein following chemical stimulation of the central nucleus of amygdala. Results showed that retrogradely labeled neurons were found throughout the ventrolateral medulla. Moreover, chemical stimulation of the central nucleus of amygdala induced: (1) a decrease of arterial blood pressure; (2) an expression of Fos protein mainly in sub-populations of neurons located in the intermediate and caudal parts of the ventrolateral medulla; (3) a significantly higher number of double labeled neurons (CTb-immunoreactive/Fos-immunoreactive) in the rostral part of the ventrolateral medulla than in the other parts of this region. These results show that the central nucleus of amygdala influences the activity of brainstem neurons projecting to the intermediolateral nucleus. Data were discussed in terms of descending amygdalofugal pathways involved in the hypotension.

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.

Double immunocytochemistry for the detection of Fos protein in retrogradely identified neurons using cholera toxin B subunit.

The focus of this paper was to describe a method combining the neuroanatomical technique of retrograde transport of cholera toxin B subunit (CTB) with the technique of Fos functional labeling. This method allowed us to evaluate whether neurons identified by retrograde tracing were activated following chemical stimulation of another brain area. We have used this method at the light microscopic level to determine whether the stimulation of the rostral ventrolateral medulla activated retrogradely labeled adrenal sympathetic preganglionic neurons in the spinal cord. CTB-containing neurons, Fos immunoreactive neurons and double labeled neurons were observed in spinal autonomic areas. These results suggest that the rostral ventrolateral medulla exerts a descending activation upon identified adrenal preganglionic neurons. The method described in this protocol can be applied for other brain areas in order to establish if a given structure can activate an identified population of neurons linked with a particular target of central or peripheral nervous system.

Expression of Fos protein in adrenal preganglionic neurons following chemical stimulation of the rostral ventrolateral medulla of the rat.

The ventrolateral medulla is known to be involved in the regulation of arterial blood pressure, especially via its connections with sympathetic preganglionic neurons (SPNs) mainly located in the intermediolateral nucleus of the spinal cord. It has been shown that stimulation of the rostral part of the ventrolateral medulla (RVLM) elicits a release of catecholamines from the adrenal medulla. The aim of the present study was to demonstrate the existence of a functional pathway between the RVLM and adrenal SPNs using the combination of a retrograde tract tracing technique (cholera toxin B subunit) with the immunohistochemical detection of Fos protein following the chemical stimulation of RVLM. The data obtained showed that: (1) chemical stimulation of the RVLM induced Fos immunoreactivity in the intermediolateral nucleus and particularly in SPNs projecting to the adrenal medulla; (2) along the thoracic segments T2-T12, 26.1% of retrogradely identified adrenal SPNs were Fos-immunoreactive with the greatest percentage (30.9%) in the T8 segment. These results favored a functional control of the RVLM on adrenal SPNs which may contribute to a substantial activation of the cardiovascular system via the release of adrenal catecholamines.

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.

Induction of c-Fos-like protein in bulbar catecholaminergic neurones by electrical stimulation of the sensorimotor cortex in the rat.

The sensorimotor cortex (SMC) establishes a functional connectivity with the nucleus tractus solitarius (NTS) and the rostral ventrolateral medulla (RVLM). These bulbar nuclei are known to contain catecholaminergic neurones involved in the cardiovascular control. The aim of the present study was to establish the proportion of catecholaminergic neurones activated by electrical stimulation of SMC. For this purpose, double immunocytochemical procedures were used to reveal the distribution of Fos protein and tyrosine hydroxylase (TH). The results showed that, in the NTS, 7% of the neurones immunoreactive for TH expressed Fos-protein, versus 34% in the RVLM. These data provide evidence that the SMC activated preferentially catecholaminergic neurones of the RVLM which are known to be involved in cardiovascular control via spinal preganglionic neurones.

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.

Expression of c-fos in bulbar nuclei involved in cardiovascular control following the electrical stimulation of sensorimotor cortex in the rat.

Previous studies have shown that electrical stimulation of the sensorimotor cortex (SMC) induces responses of the autonomic nervous system such as variations in heart rate and arterial pressure. Neuroanatomical studies have shown the existence of monosynaptic projections from the SMC to the nucleus tractus solitarius (NTS), the rostral ventrolateral medulla (RVLM) and the dorsal nucleus of the vagus nerve (DNV), which are bulbar nuclei involved in cardiovascular control. The aim of the present study was to establish whether there exists a functional connectivity between the SMC and these nuclei. Electrical stimulation applied to the SMC of 7 rats for 1 h induced the expression of c-fos-protein-like immunoreactivity in the nucleus of some neurons in NTS, RVLM and DNV. These data support the view that the SMC has functional connections with bulbar neurons involved in cardiovascular control.