A freeze-fracture study of the soma membranes of monoaminergic neurons in the hypothalamic nucleus recessi posterioris of the rainbow trout (Salmo gairdneri Rich.).

Monoaminergic neurons in the hypothalamic nucleus recessi posterioris of the rainbow trout were studied by freeze-fracturing. The size and distribution of intramembrane particles in the nuclear and plasma membranes and the density of nuclear pores in the nuclear envelope were determined. The density of nuclear pores in these cells was significantly greater than in the non-granulated neurons of this nucleus. The density of IMPs in the P face of the inner nuclear membrane was significantly greater than in the P face of the outer nuclear membrane; however in the E faces the density is greater in the outer nuclear membrane but the differences are not statistically significant. In both membranes, the proportion of large particles (greater than 9.6 nm) was greater in the E than in the P faces. The coefficient of partition between the plasma membrane faces was 1.97 +/- 0.24 while in non-granulated neurons was 4.45 +/- 0.51. There are significant differences among these values. Interestingly, the coefficient of partition of the plasma membrane in monoaminergic neurons was lesser than in some other types of neurons. Postsynaptic areas or other membrane specializations were not found on the cell body plasma membrane, which corroborates the results of conventional transmission electron microscopy.