Morphometry of Dorsal Raphe Nucleus Serotonergic Neurons in Alcoholism

Alcoholism: Clinical and Experimental Research (OnlineEarly Articles).
22 March 2007

• Mark D. Underwood^1,2
• ¹Department of Neuroscience, New York State Psychiatric Institute, New York, New York; and
• ²Department of Psychiatry, College of Physicians & Surgeons of Columbia University, New York, New York,
• J. John Mann^1,2
• ¹Department of Neuroscience, New York State Psychiatric Institute, New York, New York; and
• ²Department of Psychiatry, College of Physicians & Surgeons of Columbia University, New York, New York, and
• Victoria Arango^1,2
• ¹Department of Neuroscience, New York State Psychiatric Institute, New York, New York; and
• ²Department of Psychiatry, College of Physicians & Surgeons of Columbia University, New York, New York

• ¹Department of Neuroscience, New York State Psychiatric Institute, New York, New York; and ²Department of Psychiatry, College of Physicians & Surgeons of Columbia University, New York, New York.

This work was supported by AA11293, AA09004, MH40210, MH46745, and MH47097.

Reprint requests: Mark Underwood, PhD, Department of Neuroscience, New York State Psychiatric Institute, 1051 Riverside Drive Box 42, New York, NY 10032; Fax: 212-543-5998; E-mail: undie@neuron.cpmc.columbia.edu

Abstract

Background:

Reduced serotonergic function is hypothesized in alcohol abuse and dependence. Serotonergic innervation of the cortex arises predominantly from the dorsal raphe nucleus (DRN). We sought to determine the number and morphometric characteristics of DRN serotonergic neurons postmortem in alcoholic individuals (n=9; age: 16–66years; 8M:1F) compared with psychiatrically normal, nonalcoholic controls (n=6; age: 17–74 years; 4M:2F).

Methods:

Brainstems were collected at autopsy, fixed and cryoprotected. Alcohol dependence or abuse was determined by psychological autopsy (DSM-IV), the presence of liver fatty changes or cirrhosis and/or high blood alcohol level. Tissue was sectioned at 50 μm (−25°C). A series of 1:10 sections was immunoreacted with antiserum to tryptophan hydroxylase (TPH), the rate-limiting enzyme in the biosynthesis of serotonin. The total number of TPH-immunoreactive (IR) DRN neurons was determined by stereology. Neuron morphometry indices were determined using a video-based imaging system attached to a microscope. We identified TPH-IR neurons every 1,000 μm in each brainstem and measured neuron area, total cross sectional neuron area, and the total area and density of immunolabeled processes.

Results:

Dorsal raphe nucleus neuron number (controls: 80,386±10,238; alcoholic individuals: 85,884±12,478) was not different between groups but TPH-IR was greater in alcoholic individuals throughout the rostrocaudal extent of the DRN. The volume of the DRN was 66±9 mm³ in controls and 55±5 mm³ in alcoholic individuals (p>0.05). The average size of DRN neurons did not differ between groups (353±12 μm² for controls vs 360±15 μm² for alcoholic subjects). However, the area occupied by neuron processes (area of processes/DRN area) was 2.2-fold greater in alcoholic individuals compared with controls (p<0.05).>

Conclusions:

The increased area occupied by neuron processes in alcoholic individuals may represent sprouting and, together with greater TPH-IR, be a compensatory response to impaired serotonergic transmission or cumulative effects of alcohol on the serotonin system.