In the present study some experimental parameters for in situ hybridization histochemistry (ISHH) have been analysed using 35S-labelled and alkaline phosphatase-conjugated probes, in order to develop a reproducible double-labelling procedure. We have compared the total exclusion of tissue fixation with tissue sections fixed by immersion in formalin. In addition, the effect of dithiothreitol was assessed both when combining radiolabelled and non-radioactive probes on a single tissue section and when the probes were used separately. Hybridization of unfixed tissue resulted in stronger specific labelling and lower background both for radiolabelled and alkaline phosphatase-conjugated probes. No loss in tissue preservation was seen at the light microscopic level after hybridization of unfixed tissue. High concentrations (200 mM) of dithiothreitol strongly suppressed background when using 35S-labelled probes, whereas in the non-radioactive procedure, alkaline phosphatase labelling could only be achieved with very low dithiothreitol concentrations (less than 1 mM). This incompatibility led to a protocol using unfixed tissue sections and a sequential hybridization procedure, with the radiolabelled probe and high concentrations of dithiothreitol in the first step and the alkaline phosphatase-conjugated probe without dithiothreitol in the second step.

The distribution of neurons in the rat CNS that synthesize mRNA for the alpha 1A/D and alpha 1B adrenoceptors was revealed by the in situ hybridization method. Forty-eight-mer DNA probes were synthesized to two different and unique regions of both the alpha 1A/D and alpha 1B mRNAs. Tissue sections from all levels of the CNS and some peripheral ganglia were incubated in a hybridization cocktail containing one of these four probes. The two mRNAs were expressed in a discrete and often complementary manner to each other, and identical hybridization patterns were seen for the probes directed against the same mRNA. The alpha 1A/D probes hybridized heavily with neurons in the internal granular and internal plexiform layers of the olfactory bulb, in layers II-V of most areas of the cerebral cortex, and in the lateral aspect of the lateral amygdaloid nucleus, with pyramidal neurons of CA1-CA4 regions, hilar and granular neurons of the dentate gyrus, and neurons in the reticular thalamic nucleus, cranial and spinal motor nuclei, and the inferior olivary nucleus. Light labeling was seen in a variety of other regions in the brain and spinal cord. The alpha 1B probes hybridized heavily with neurons in the mid layers of cerebral cortex and with virtually all neurons in the thalamus, except the reticular and habenular nuclei. In addition, labeling was seen in the lateral and central amygdaloid nuclei, in brainstem and spinal motor nuclei, over most neurons of the dorsal and medullary raphe nuclei and neurons of the intermediolateral cell column in the spinal cord. Light labeling was seen in the septal nucleus, the horizontal limb of the diagonal band, the paraventricular and lateral hypothalamic nuclei, the pontine and medullary reticular formation, and in most laminae in the spinal cord. The patterns of labeling obtained with the alpha 1B probes resemble the labeling seen in previous autoradiographic ligand binding studies utilizing "general" alpha 1 ligands, while the labeling patterns seen with the alpha 1A/D probes do not correspond to any published alpha 1 receptor distribution pattern, indicating that this mRNA likely encodes for a novel adrenoceptor. The present findings further expand the heterogeneity of adrenoceptor mRNAs presented in two accompanying studies (Nicholas et al., 1993a,b). This differential distribution of adrenoceptors subtypes provides a framework for the functional diversity to the apparently widespread, diffuse, and rather homogeneous noradrenergic innervation of the CNS.

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The potential role of certain important immunoregulatory and effector cytokines in autoimmune neuroinflammation have been studied. We have examined the expression of mRNA, with in situ hybridization, of interferon gamma (IFN-gamma), interleukin 4 (IL-4) and transforming growth factor beta (TGF-beta) both in sections of spinal cords and the antigen-induced expression of these cytokines by lymphoid cells after stimulation with a dominant encephalitogenic peptide of MBP (MBP 63-88) during the course of actively induced experimental autoimmune encephalomyelitis (EAE) in Lewis rats. In spinal cords, the target organ in EAE, cells expressing mRNA for IFN-gamma, first appeared at the onset of clinical signs, i.e., day 10 postimmunization (p.i.), peaked at the height of disease (day 13 p.i.) and then gradually decreased concomitant with recovery. Very few IL-4 mRNA-expressing cells appeared in the spinal cord with no clear relation to clinical signs or histopathology. In contrast, expression of mRNA for TGF-beta did not increase until day 13 p.i., at height of the disease, shortly preceding recovery. These data are consistent with a disease upregulating role of IFN-gamma, while TGF-beta may act to limit central nervous system (CNS) inflammation. In lymphoid organs, primed MBP 63-88 reactive T cells showed an interesting time-dependent evolution of their cytokine production in vitro. Thus, early after immunization there was a conspicuous MBP 63-88-induced production of both IFN-gamma and IL-4. Such cells may act in the initiation and promotion of the disease. Later, in the recovery phase, MBP 63-88 induced lymphoid cells to TGF-beta production. Thus, an autoantigen-specific production of TGF-beta occurred during EAE and hypothetically such a mechanism may serve to downregulate aggressive autoimmunity systemically.