Table 1 Forced exposure studies specifying delivery methods, concentration or flow rate used, strain and sex, whether the study contained baseline and well-defined behavioral categories, and a summary of results.

From: Understanding rat emotional responses to CO₂

Strain	Delivery method	Concentration/flow rate	Sex	Baseline or control	Defined behaviors	Results	Reference
W	Gf	~17%	M	✓	✓	↑ line crossing (locomotor activity), ↑ rearing, ↑ nose to lid, ↑ escape behaviors, and ↑ ultrasonic vocalizations (mean range 22 ± 19 kHz)	⁶
W	Gf	17%	M	✓	✓	↑ line crossing (locomotor activity; 50% of the rats), ↑ rearing, ↑ nose to lid, ↑ escape behaviors (60% of the rats)	⁷
W	Pf	10%	✗	✓	✓	↔ in freezing/immobility, ↔ rearing	³²
W	Pf	>97%	M/F	✗	Vague	↓ wall touching, ↑ wall climbing (rearing), ↔ vocalizations^a	⁹
W	Pf	100%	M	✗	✗	↓ normal behavior, ↑ behavioral agitation and excitation, ↓ immobility/freezing, ↑ signs of asphyxia	³
SD	Gf	10%	M	✓	✓	↔ line crossing (locomotor activity), ↔ rearing, ↔ escape behaviors	²⁹
SD	GF	~18%	F	✓	✓	↑ line crossing (locomotor activity), ↑ rearing, ↔ escape behaviors, ↔ freezing/immobility	²⁷
SD	Gf_a	20%	M	✓	Telemetric recordings	↑ locomotor activity, ↔ freezing/immobility	²⁴
SD	Gf_a	20%	M	✓	✗	↑ freezing /immobility	³⁰
SD	Gf	23%	M	✓	✓	↑ line crossing, ↑ rearing	²⁸
SD	Gf	30%	F	✓	✓	↑ ultrasonic vocalizations (median range 51 kHz)	²
SD	Gf	High but undefined	M	✓	✓	↑ wall climbing (rearing), ↑ activity, ↑ shaking (undefined), ↔ ultrasonic vocalizations	²⁶
SD	Gf	30%	M/F	✗	✓	↑ rearing, ↔ jumping, ↔ digging^b	³³
SD	Pf	10%	✗	✓	✓	↔ freezing/immobility and ↓ rearing	³²
SD	Pf	~75%	M	✗	Vague	↔ signs of distress, ↔ vocalization, ↔ escape behaviors, ↔ tail lashing	³¹
LE	Gf	High but undefined	M	✓	✓	↔ wall climbing (rearing), ↓ activity, ↑ shaking (undefined), ↔ ultrasonic vocalizations	²⁶
LE	Pf	10%	✗	✓	✓	↑ freezing/immobility and ↓ rearing	³²
F	Gf	35%^c	M	✗	✗	↑ interest and curiosity, ↔ vocalizations, ↔ signs of pain	¹⁰
WK	Pf	10%	✗	✓	✓	↑ freezing/immobility, ↔ rearing	³²
P-rat	Gf		M/F	✗	✓		³⁵
		10%				↔ rearing, ↔ rearing (5 in), ↔ rearing (7 in), ↔rearing (5 in/rear)^d
		30%				↑ rearing, ↔ rearing (5 in), ↔ rearing (7 in), ↔rearing (5 in/rear)^d
		70%				↔ rearing, ↔ rearing (5 in), ↔ rearing (7 in), ↑rearing (5 in/rear)^d

Strain: W Wistar, SD Sprague Dawley, LE Long Evans, WK Wistar Kyoto, F Fisher, BN Brown Norway, P-rat alcohol preferring rats; delivery method: Pf pre-fill, Gl gradual fill, GF_a 20% CO₂ challenge; concentration or flow rate: static concentration (%) or flow rate (% CO₂ chamber vol. min⁻¹); sex: M male, F female, ✗ unspecified; baseline: ✓ present, ✗ absent; defined behaviors: ✓ if a clear ethogram, vague if an unclear ethogram, ✗ absent; results: ↑ increase, ↓ decrease, ↔ no change in behavior or absent.
^aWithin the same study, two different results were found depending upon age: for young rats no change in activity but increase in stationary episodes, while old rats decreased both activity and stationary episodes. These authors concluded arrived to the same conclusion for both young and old rats.
^bBehavior when exposed to CO₂ in an induction chamber in comparison to exposure in the rat home cage.
^cFlow rate was given as 6 l/min⁻¹ and cage size unspecified, calculations were made based on the brand and type of the cage (Makrolon type III = ~17.2).
^dComparison between flow rates.

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Table 1 Forced exposure studies specifying delivery methods, concentration or flow rate used, strain and sex, whether the study contained baseline and well-defined behavioral categories, and a summary of results.

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