The frequency distributions of silver grain counts from autoradiographs

Steroid regulation of calcitonin gene-related peptide mRNA expression in motoneurons of the spinal nucleus of the bulbocavernosus

Motoneurons express calcitonin gene-related peptide (CGRP). Previous studies have shown that CGRP immunoreactivity is regulated by testosterone in the androgen-sensitive motoneurons of the spinal nucleus of the bulbocavernosus (SNB). In this research the effect of plasma levels of testosterone on the expression of alpha CGRP mRNA in the SNB motoneurons of adult male rats was studied with in situ hybridization. The number of motoneurons expressing alpha CGRP mRNA and the level of alpha CGRP mRNA expression was significantly higher in the SNB of castrated male rats than in the SNB of gonadally intact rats. Using a 5x background labeling criterion in castrated rats 88.1 +/- 4.5% while in intact rats 75.3 +/- 6.4% of SNB motoneurons expressed alpha CGRP mRNA. Testosterone replacement at the time of castration prevented the effect of castration on the expression of alpha CGRP mRNA in SNB motoneurons. In castrated rats, the increase in the number of SNB cells expressing CGRP was the result of increased steady state levels of alpha CGRP mRNA in all SNB neurons.

Graphical and statistical approaches to data analysis for in situ hybridization

Quantification of gene expression in a morphological context is an invaluable tool for neurobiological investigation. The ability to measure the quantity of specific mRNA molecules at the level of the single neuron permits one to monitor the modulation of complex cell synthetic activity of intact neuron populations. The cells of interest can be contiguous or dispersed in functionally significant patterns throughout a broad anatomical region of the brain. The application of quantitative in situ hybridization is technically difficult and labor intensive. Nevertheless, it has great utility for investigating gene expression from a structural perspective. (1) In situ hybridization permits one to ask questions concerning the anatomical pattern of neuronal gene expression. (2) It permits analyses concerning the initiation of expression, cell location, cell type, and alterations of level of expression within a spatial and temporal context. (3) In cases where blotting methods suggest a message exists at low copy, in situ hybridization permits queries at the single-cell level. For example, in situ hybridization can determine if very few cells are expressing the gene product or if many neurons dispersed throughout a brain region exhibit low mRNA copy number/cell. Quantitative analyses also allow detailed investigation of cell response to physiologically meaningful stimulation. Our application of statistical and numerical methods is a demonstration of the utility of probabilistic models; the mixture distribution accounted for data from both labeled and unlabeled sources. In agreement with many previous investigations, grain density over an unlabeled uniform source (oxytocinergic cells) was suitably described by the Poisson distribution. The population of labeled vasopressinergic cells, however, was best described by the negative binomial distribution. Previous investigations from different fields of biology show that the negative binomial can be used to describe many biological phenomena, and this distribution was considered in at least two previous investigations to evaluate autoradiographic data which did not fit the Poisson function. From a theoretical perspective, the probabilistic relationship between beta-particle decay (a Poisson function) and the distribution of message levels among individual neurons in a cell group (gamma distribution) prompts consideration of the negative binomial. For both data sets the observed variances were larger than the mean, and the labeled portion of the data sets exhibited positive skewness.(ABSTRACT TRUNCATED AT 400 WORDS)