Modulation of serotonin 5-HT3 receptor expression in injured adult rat spinal cord motoneurons

Novel localization of low affinity NGF receptor (p75) in the stroma of prostate cancer and possible implication in neoplastic invasion: an immunohistochemical and ultracytochemical study

BACKGROUND

The localization of low affinity nerve growth factor receptor (p75) in prostate carcinogenesis is still unclear. Our aim was to reinvestigate the localization of p75 in normal and pathological prostate and to check a possible correlation to neoplastic grading.

METHODS

Specimens from 33 prostate cancers and from normal prostatic tissue were analyzed for p75 expression at light and ultrastructural levels.

RESULTS

In normal tissue p75-immunoreactivity was restricted to basal cells in the epithelial compartment and to nerves and blood vessel in stroma. During carcinogenesis, p75-immunoreactivity progressively decreased at the periphery of the foci according to the increase in malignancy. No p75-immunoreactivity was detected inside of the foci. On the contrary, in stroma we found a dramatic increase in p75-immunoreactivity correlated to an increase in malignancy. In this compartment, for the first time ultrastructural analysis identified p75-immunoreactivity in smooth muscle cells (SMC) that are p75-negative in normal conditions.

CONCLUSION

The present study confirms at ultrastructural level a malignant-dependent p75 decrease in basal cells of neoplastic foci. Furthermore, we show a novel, malignant-dependent localization of p75 in SMC in the stroma around the neoplastic foci. Since p75 expression is present in muscle cells only during the earliest stages of differentiation and mature muscle cells lose this expression, we hypothesize that p75 re-expression in stromal SMC is a further mechanism related to the general de-differentiation of the stroma connected to the neoplastic invasion. According to this hypothesis, our results suggest that p75 analysis could be a novel prognostic marker for prostate cancer.

Neural plasticity after peripheral nerve injury and regeneration

Injuries to the peripheral nerves result in partial or total loss of motor, sensory and autonomic functions conveyed by the lesioned nerves to the denervated segments of the body, due to the interruption of axons continuity, degeneration of nerve fibers distal to the lesion and eventual death of axotomized neurons. Injuries to the peripheral nervous system may thus result in considerable disability. After axotomy, neuronal phenotype switches from a transmitter to a regenerative state, inducing the down- and up-regulation of numerous cellular components as well as the synthesis de novo of some molecules normally not expressed in adult neurons. These changes in gene expression activate and regulate the pathways responsible for neuronal survival and axonal regeneration. Functional deficits caused by nerve injuries can be compensated by three neural mechanisms: the reinnervation of denervated targets by regeneration of injured axons, the reinnervation by collateral branching of undamaged axons, and the remodeling of nervous system circuitry related to the lost functions. Plasticity of central connections may compensate functionally for the lack of specificity in target reinnervation; plasticity in human has, however, limited effects on disturbed sensory localization or fine motor control after injuries, and may even result in maladaptive changes, such as neuropathic pain, hyperreflexia and dystonia. Recent research has uncovered that peripheral nerve injuries induce a concurrent cascade of events, at the systemic, cellular and molecular levels, initiated by the nerve injury and progressing throughout plastic changes at the spinal cord, brainstem relay nuclei, thalamus and brain cortex. Mechanisms for these changes are ubiquitous in central substrates and include neurochemical changes, functional alterations of excitatory and inhibitory connections, atrophy and degeneration of normal substrates, sprouting of new connections, and reorganization of somatosensory and motor maps. An important direction for ongoing research is the development of therapeutic strategies that enhance axonal regeneration, promote selective target reinnervation, but are also able to modulate central nervous system reorganization, amplifying those positive adaptive changes that help to improve functional recovery but also diminishing undesirable consequences.

Differential subcellular localization of the 5-HT3-As receptor subunit in the rat central nervous system

Following the cloning and sequencing of the A subunit of the 5-HT3 receptor, two alternatively spliced isoforms, 5-HT3-AS and 5-HT3-AL, have been identified. In order to analyse the distribution of the receptor, a polyclonal antibody has been produced against the short form which is the most abundant in the central nervous system [Doucet et al. (2000) Neuroscience 95, 881-892]. As expected from the recognition of functional 5-HT3 receptors, immunostaining by this anti-5-HT3-R-AS antibody matched the distribution of the high-affinity 5-HT3 binding sites in the rat brain and spinal cord. 5-HT3-AS-like immunoreactivity was detected at low levels in the limbic system, particularly in the amygdala and the hippocampus, and in the frontal, piriform and entorhinal cortices. High levels of immunoreactivity were found in the brainstem, mainly in the nucleus tractus solitarius and the nucleus of the spinal tract of the trigeminal nerve, and in the dorsal horn of the spinal cord. At the ultrastructural level, immunostaining was generally found associated with axons and nerve terminals (70-80%) except in the hippocampus, where labelled dendrites were more abundant (56%). This preferential localization on nerve endings is consistent with the well-documented physiological role of 5-HT3 receptors in the control of neurotransmitter release. However, the different distribution in the hippocampus raises the question of whether differential addressing mechanisms exist for preferentially targeting 5-HT3 receptors to postsynaptic dendritic sites as compared to presynaptic nerve endings, depending on the nature of the neurons bearing these receptors.