Total number of neurons in the habenular nuclei of the rat epithalamus: a stereological study

Abstract

The total number of neurons in the medial and lateral habenular nuclei of the rat epithalamus was estimated using modern stereological counting methods and systematic random sampling techniques. Six to eight young adult male rats, and a complete set of serial 40-microm glycolmethacrylate sections for each rat, were used to quantify neuronal numbers. After a random start, a systematic subset (e.g. every third) of the serial sections was used to estimate the total volume of each nucleus using Cavalieri's method. The same set of sampled sections was used to estimate the number of neurons in a known subvolume (i.e. the numerical density N(v)) by the optical disector method. Multiplication of the total volume by N(v) yielded the total number of neurons. It was found that the right medial habenular nucleus consisted, on average, of 18,000 neurons (with a coefficient of variation of 0.18), while the right lateral habenular nucleus had 13,000 neurons on average (0.14). These total neuronal numbers provide important data for the transfer of information through these nuclei and for species comparisons.

Fig. 1

Photographs of coronal sections (left column) showing the boundaries of the right habenular complex. Line diagrams (right column) illustrate the boundaries used to delineate the MHb and the LHb. Every fifth section from the beginning to end of the MHb has been photographed and illustrated (i.e. sections 140–180; A–I). The LHb is also illustrated in this series (i.e. sections 150–175; C–H). Note that the LHb ends relatively abruptly – it was present in section 179, but was not present in section 180 (i.e. I). Note also that section 145 was replaced with section 146 because there were air bubbles in section 145. There is neither MHb nor LHb in section 185 (i.e. J). D3V, dorsal third ventricle; Hi, hippocampus; LHb, lateral habenular nucleus; LV, lateral ventricle; MHb, medial habenular nucleus; sm, stria medullaris. Scale bar = 0.2 mm.

Fig. 1

Photographs of coronal sections (left column) showing the boundaries of the right habenular complex. Line diagrams (right column) illustrate the boundaries used to delineate the MHb and the LHb. Every fifth section from the beginning to end of the MHb has been photographed and illustrated (i.e. sections 140–180; A–I). The LHb is also illustrated in this series (i.e. sections 150–175; C–H). Note that the LHb ends relatively abruptly – it was present in section 179, but was not present in section 180 (i.e. I). Note also that section 145 was replaced with section 146 because there were air bubbles in section 145. There is neither MHb nor LHb in section 185 (i.e. J). D3V, dorsal third ventricle; Hi, hippocampus; LHb, lateral habenular nucleus; LV, lateral ventricle; MHb, medial habenular nucleus; sm, stria medullaris. Scale bar = 0.2 mm.