Parkinson’s-like Brain Changes Reversed in Mice Over a Year

WHO:

ScienceAlert - The researchers were neuroscientist Xuelin Lou of the Medical College of Wisconsin, cell biologist Prince Joshi, and physiologist Fan Fan.

Yahoo - The researchers were neuroscientist Xuelin Lou of the Medical College of Wisconsin, cell biologist Prince Joshi, and physiologist Fan Fan.

ScienceAlert - The experiment used young adult male mice; control mice received the same injection mixture without rotenone.

Yahoo - The experiment used young adult male mice; control mice received the same injection mixture without rotenone.

ScienceAlert - Lou said the resolution of the mice’s Parkinson’s-like deficits was “totally unexpected.”

Yahoo - Lou said the resolution of the mice’s Parkinson’s-like deficits was “totally unexpected.”

WHAT:

ScienceAlert - After rotenone exposure, mice initially traveled shorter distances, moved more slowly, struggled to balance on a rotating rod, and spent less time exploring the open arms of an elevated maze.

Yahoo - After rotenone exposure, mice initially traveled shorter distances, moved more slowly, struggled to balance on a rotating rod, and spent less time exploring the open arms of an elevated maze.

ScienceAlert - Without treatment, the mice gradually improved: open-field movement reached control levels within about four months; rotating-rod performance was no longer significantly different from controls by seven months; and anxiety-related test results were similar at 12 months.

Yahoo - Without treatment, the mice gradually improved: open-field movement reached control levels within about four months; rotating-rod performance was no longer significantly different from controls by seven months; and anxiety-related test results were similar at 12 months.

ScienceAlert - Early after exposure, cells detectable using tyrosine hydroxylase (TH), an enzyme needed to make dopamine, were about 40 percent lower in number and density in the substantia nigra pars compacta. A broader neuronal marker showed total neuronal density was preserved.

Yahoo - Early after exposure, cells detectable using tyrosine hydroxylase (TH), an enzyme needed to make dopamine, were about 40 percent lower in number and density in the substantia nigra pars compacta. A broader neuronal marker showed total neuronal density was preserved.

ScienceAlert - At 12 months, TH-positive cell counts and density were comparable between groups, although the enzyme signal remained weaker in exposed mice. Control mice’s TH-positive cell density was about 45 percent lower at 12 months than in early examinations; exposed mice showed little change.

Yahoo - At 12 months, TH-positive cell counts and density were comparable between groups, although the enzyme signal remained weaker in exposed mice. Control mice’s TH-positive cell density was about 45 percent lower at 12 months than in early examinations; exposed mice showed little change.

ScienceAlert - Lou said, “Our findings suggest that they just lose their identity”; lower TH detection did not prove that the cells had died.

Yahoo - Lou said, “Our findings suggest that they just lose their identity”; lower TH detection did not prove that the cells had died.

ScienceAlert - The study was published in iScience. The 12-month analyses included three to eight animals per group, depending on the measurement.

Yahoo - The study was published in iScience. The 12-month analyses included three to eight animals per group, depending on the measurement.

WHERE:

ScienceAlert - Researchers examined the substantia nigra pars compacta, a movement-related midbrain region.

Yahoo - Researchers examined the substantia nigra pars compacta, a movement-related midbrain region.

ScienceAlert - Lou was affiliated with the Medical College of Wisconsin.

Yahoo - Lou was affiliated with the Medical College of Wisconsin.

WHEN:

ScienceAlert - Mice received daily rotenone injections for 21 days; movement problems appeared within four weeks of the experiment’s start, followed by behavioral assessments over 12 months.

Yahoo - Mice received daily rotenone injections for 21 days; movement problems appeared within four weeks of the experiment’s start, followed by behavioral assessments over 12 months.

WHY:

ScienceAlert - Rotenone was used to model some Parkinson’s-related movement problems by interfering with mitochondria, the energy-producing structures in cells. Parkinson’s damages dopamine-producing cells.

Yahoo - Rotenone was used to model some Parkinson’s-related movement problems by interfering with mitochondria, the energy-producing structures in cells. Parkinson’s damages dopamine-producing cells.

ScienceAlert - Rotenone and certain other pesticides have been associated with increased Parkinson’s risk in people, but the association does not establish causation.

Yahoo - Rotenone and certain other pesticides have been associated with increased Parkinson’s risk in people, but the association does not establish causation.

ScienceAlert - Lou said the findings do not mean pesticide exposure is harmless or disprove its association with Parkinson’s risk, and should not be directly extrapolated to patients or workers at risk.

Yahoo - Lou said the findings do not mean pesticide exposure is harmless or disprove its association with Parkinson’s risk, and should not be directly extrapolated to patients or workers at risk.

HOW:

ScienceAlert - Researchers administered daily rotenone injections to exposed mice and compared them with controls, using open-field, rotating-rod, and elevated-maze tests. Brain tissue measurements were taken from different animals at each time point.

Yahoo - Researchers administered daily rotenone injections to exposed mice and compared them with controls, using open-field, rotating-rod, and elevated-maze tests. Brain tissue measurements were taken from different animals at each time point.

ScienceAlert - Possible explanations for recovery include improved function in surviving dopamine-producing neurons, resistance to age-related cell loss, new neuronal branches, changes in neuronal connections, and links between cellular metabolism and gene activity; the mechanism remains unclear.

Yahoo - Possible explanations for recovery include improved function in surviving dopamine-producing neurons, resistance to age-related cell loss, new neuronal branches, changes in neuronal connections, and links between cellular metabolism and gene activity; the mechanism remains unclear.

ScienceAlert - The mouse models lacked several features of human Parkinson’s, including significant accumulation of abnormally modified alpha-synuclein. Rotenone can also cause muscle weakness and general illness that affect movement tests.

Yahoo - The mouse models lacked several features of human Parkinson’s, including significant accumulation of abnormally modified alpha-synuclein. Rotenone can also cause muscle weakness and general illness that affect movement tests.

(UPDATED October 28, 2026 19:07 UTC)

Mice given daily injections of the pesticide rotenone developed Parkinson’s-like movement problems, but gradually recovered on behavioral tests over the following year, a surprising result for researchers led by neuroscientist Xuelin Lou of the Medical College of Wisconsin. In the brain’s movement-related region, dopamine-related cell markers initially fell by about 40 percent even though overall neuron density was preserved; by 12 months, marker counts were comparable between exposed and control mice, though the signal remained weaker in exposed animals. The study, published in iScience, does not show that pesticide exposure is harmless or establish how recovery occurred, and its findings in mice should not be directly applied to people.