Background

Alzheimer’s disease (AD) is the most common cause of senile dementia. One to five percent of AD cases are familial and all the other cases are late-onset also known as sporadic AD. The understanding of sporadic AD has progressed substantially from studies using an AD animal model created by intracerebroventricular (icv) injection of streptozotocin (STZ) (Mayer et al., 1990; Lannert and Hoyer, 1998).

STZ is a glucosamine-nitrosourea derived from soil microbe Streptomyces achromogenes. The icv injection of STZ impairs cerebral glucose and energy metabolism, which may be a central event for triggering neurodegeneration in AD (Nitsch and Hoyer, 1991; Plaschke and Hoyer, 1993; Duelli et al., 1994). The mechanisms of icv STZ-induced AD-like pathology were recently reviewed by Grieb (2016) and Kamat et al. (2016). The pathological alterations induced by icv injection of STZ are analogous to the features of sporadic AD, which include increase in β-amyloid protein and hyperphosphorylation of tau protein in several brain structures, intensive neuronal death, increase of the brain ventricles, cerebral inflammation, cognitive deficit, anxiety- and depression-like behaviors, decrease in social interaction, increase of core body temperature and cold-avoidance behavior (Kraska et al., 2012; Santos et al., 2012; Chen et al., 2013; Mehla et al., 2013; Knezovic et al., 2015; Dehghan-Shasaltaneh et al., 2016; Crunfli et al., 2018; Moreira-Silva et al., 2018; Motzko-Soares et al., 2018; Vicente et al., 2018; Amani et al., 2019; Crunfli et al., 2019). STZ is usually diluted in saline, citrate buffer, or artificial cerebrospinal fluid, and administrated in a single or multiple injections in a range of 1-3 mg/kg, unilaterally or bilaterally in the lateral ventricles of the brain (Grunblatt et al., 2007; Kraska et al., 2012; Mehla et al., 2013; Dehghan-Shasaltaneh et al., 2016; Adeli et al., 2017). The pathological alteration induced by STZ are progressive and time- and dose-dependent. Thus, icv-STZ injection is characterized by an acute-fast impairment in the memory, followed by partial recovery, and then, a chronic-slow memory impairment (Knezovic et al., 2015). Also, higher doses of STZ promote more severe and fast neurodegeneration and more evident cognitive deficit (Kraska et al., 2012; Knezovic et al., 2015, Dehghan-Shasaltaneh et al., 2016).

Here, we describe a step-by-step protocol used in our laboratory, as summarized in Figure 1. Approximately 30 days from the icv-STZ injection at a dose of 2 mg/kg, clear cognitive impairment and neurodegeneration were observed (Moreira-Silva et al., 2018; Motzko-Soares et al., 2018; Vicente et al., 2018). The protocol used in our laboratory was standardized based on evidences that show: (1) STZ at high doses (≥ 3 mg/kg) promotes alteration on locomotor activity (Dehghan-Shasaltaneh et al., 2016), and also induce acute neurotoxic effect with fast severe neurodegeneration that differs from the slow neurodegenerative progress observed in sporadic AD (Kraska et al., 2012); (2) STZ at lower doses (≤ 1 mg/kg) promotes a very slow neurodegenerative progress and is more appropriate to study neuroprotective drugs (Kraska et al., 2012); (3) an intermediate dose of STZ (around 2 mg/kg) was previously reported as the most efficient dose to modeling a sporadic AD-like pathology (Dehghan-Shasaltaneh et al., 2016); (4) multiple injections of STZ increases animal mortality (Mehla et al., 2013); and (5) STZ shows better stability in solution at pH 4.5 than at neutral pH (Junod et al., 1967).


Figure 1. Protocol scheme. STZ (2 mg/kg, 2 µl/ventricle) or vehicle (2 µl/ventricle) is injected in both lateral ventricles of the rat’s brain. In the first week post-surgery, animal recovery should be evaluated. After 30 days of icv-STZ injection, animal behavior and the neurodegenerative alterations induced by icv-STZ can be evaluated.